what are the end product of photosynthesis class 10

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What Are the Products of Photosynthesis?

Photosynthesis is a set of chemical reactions that plants and other organisms use to make chemical energy in the form of sugar. Like any chemical reaction, photosynthesis has reactants and products . Overall, the reactants of photosynthesis are carbon dioxide and water, while the products of photosynthesis are oxygen and glucose (a sugar).

Here’s a closer look at the products of photosynthesis and the balanced equation for the reaction.

The reactants for photosynthesis are carbon dioxide and water, while the products are the sugar glucose and oxygen.

Balanced Chemical Equation for Photosynthesis

Photosynthesis actually involves many chemical reactions, but the net balanced equation is that six moles of carbon dioxide react with six moles of water to produce one mole of glucose and six moles of oxygen. Light from the Sun provides the activation energy for the reaction. Sometimes light is listed in the balanced equation as a reactant, but it’s usually omitted.

6 CO 2  + 6 H 2 O → C 6 H 12 O 6  + 6 O 2

Carbon Dioxide + Water + Light → Glucose + Oxygen

Closer Look at the Products of Photosynthesis

Photosynthesis occurs in a series of steps that are classified as light-dependent reactions and light-independent reactions. Adding up the reactants and products of these reactions gives the overall equation for photosynthesis, but it’s good to know the inputs and outputs for each stage.

Light-Dependent Reactions

The light-dependent reactions or light reactions absorb certain wavelengths of light to make adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). The light reactions occur in the chloroplast thylakoid membrane. The overall balanced equation for the light-dependent reactions is:

2 H 2 O + 2 NADP +  + 3 ADP + 3 P i  + light → 2 NADPH + 2 H +  + 3 ATP + O 2

Light-Independent Reactions

While the light reactions use water, the light-independent reactions use carbon dioxide. The light-independent reactions are also called the dark reactions. These reactions do not require darkness, but they don’t depend on light to proceed. In plants, algae, and cyanobacteria, the dark reactions are called the Calvin cycle. Bacteria use different reactions, including the reverse Krebs cycle.

The overall balanced equation for the light-independent reactions (Calvin cycle) in plants is:

3 CO 2  + 9 ATP + 6 NADPH + 6 H +  → C 3 H 6 O 3 -phosphate + 9 ADP + 8 P i  + 6 NADP +  + 3 H 2 O

Finally, the three-carbon product from the Calvin cycle becomes glucose during the process of carbon fixation.

Other Products of Photosynthesis

Glucose is the direct product of photosynthesis, but plants turn most of the sugar into other compounds. These are indirect products. Linking glucose units forms starch and cellulose. Cellulose is a structural material. Plants store starch or link it to fructose (another sugar) to form sucrose (table sugar).

What Is Not a Product of Photosynthesis?

On an exam, you may need to identify which chemical is not a product of photosynthesis. For the overall process, choose any answer except “glucose” or “oxygen.” It’s good to know the overall reactants and products of the light reactions and dark reactions, in case you’re asked about them. The products of the light reactions are ATP , NADPH, protons, and oxygen. The products of the dark reactions are C 3 H 6 O 3 -phosphate, ADP, inorganic phosphate, NADP + , and water.

Where Does Photosynthesis Occur?

In addition to knowing the reactants and products of photosynthesis, you may need to know where photosynthesis occurs in different organisms.

• In plants, photosynthesis occurs in organelles called chloroplasts. Photosynthetic protists also contain chloroplasts. Leaves contain the highest concentration of chloroplasts in plants. Plants obtain carbon dioxide via diffusion through leaf stomata. Water comes from the roots and travels to the leaves via the xylem . Chlorophyll in chloroplasts absorbs solar energy. Oxygen from photosynthesis exits the plant via leaf stomata.
• Photosynthesis occurs in photosynthetic bacteria in the plasma membrane. Chlorophyll or related pigments are embedded in this membrane.
• Bidlack, J.E.; Stern, K.R.; Jansky, S. (2003).  Introductory Plant Biology . New York: McGraw-Hill. ISBN 978-0-07-290941-8.
• Blankenship, R.E. (2014).  Molecular Mechanisms of Photosynthesis  (2nd ed.). John Wiley & Sons. ISBN 978-1-4051-8975-0.
• Reece J.B., et al. (2013).  Campbell Biology . Benjamin Cummings. ISBN 978-0-321-77565-8.

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What Is the End Product of Photosynthesis?

Describe What a Photosystem Does for Photosynthesis

Humans and most other animals need certain things to survive. Oxygen is one of them, and the carbohydrate glucose is another. Fortunately for them, plants (and certain bacteria and algae) produce both of these as the result of a complex process known as photosynthesis.

The Formula

The formula associated with the process of photosynthesis is

6H 2 O + 6CO 2 = C 6 H 12 O 6 + 6O 2 .

This formula tells you is that six molecules of water plus six molecules of carbon dioxide will produce one molecule of glucose plus six molecules of oxygen. This entire process goes through two distinct stages before it is completed. The first stage is a light-dependent process and the second stage is a light-independent process.

Light Dependent

In the light-dependent process, the electrons of the chloroplasts (special organelles used to carry out photosynthesis) are excited into a higher energy state when they are bombarded with light. These excited electrons cause a series of reactions that produce adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). ATP and NADPH are then used to make carbon bonds in the light-independent process. Water molecules present in the light-dependent process are split. Their oxygen molecules are released into the atmosphere.

Light Independent

Recall the splitting of the water molecules in the light-dependent process that released oxygen molecules into the atmosphere. Since water is H 2 0, there is still a hydrogen atom remaining. This hydrogen atom is used in the light-independent process when plants take carbon dioxide from the atmosphere. The carbon dioxide and hydrogen become bound together through a process called carbon fixation, which forms a non-specific carbohydrate.

Photophosphorylation

Photophosphorylation is the process by which light energy produces NADPH. Special pigments found in the plant’s cells known as chlorophyll make this process possible. The two main types of chlorophyll are chlorophyll A and chlorophyll B. In simple terms, the electrons of water molecules present in chlorophyll B become excited by the presence of light. Chlorophyll B takes one of these excited electrons splitting the H 2 O molecule into H + and O -2 . O -2 is converted into O 2 and released into the atmosphere. The excited electron is attached to a primary electron receptor, and through a series of complex reactions forms NADPH. NADPH is the energy carrier used in carbon fixation.

The Calvin Cycle

Plants produce glucose in a process known as the Calvin cycle. The carbon dioxide captured in the light-independent process is processed in this cycle. For every six molecules of carbon dioxide captured and put into the cycle, one molecule of glucose is produced. The chemical that captures the carbon dioxide for use in the Calvin cycle is ribulose biphosphate.

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Photosynthesis

Reviewed by: BD Editors

Photosynthesis Definition

Photosynthesis is the biochemical pathway which converts the energy of light into the bonds of glucose molecules. The process of photosynthesis occurs in two steps. In the first step, energy from light is stored in the bonds of adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). These two energy-storing cofactors are then used in the second step of photosynthesis to produce organic molecules by combining carbon molecules derived from carbon dioxide (CO 2 ). The second step of photosynthesis is known as the Calvin Cycle. These organic molecules can then be used by mitochondria to produce ATP, or they can be combined to form glucose, sucrose, and other carbohydrates. The chemical equation for the entire process can be seen below.

Photosynthesis Equation

Above is the overall reaction for photosynthesis. Using the energy from light and the hydrogens and electrons from water, the plant combines the carbons found in carbon dioxide into more complex molecules. While a 3-carbon molecule is the direct result of photosynthesis, glucose is simply two of these molecules combined and is often represented as the direct result of photosynthesis due to glucose being a foundational molecule in many cellular systems. You will also notice that 6 gaseous oxygen molecules are produced, as a by-produce. The plant can use this oxygen in its mitochondria during oxidative phosphorylation . While some of the oxygen is used for this purpose, a large portion is expelled into the atmosphere and allows us to breathe and undergo our own oxidative phosphorylation, on sugar molecules derived from plants. You will also notice that this equation shows water on both sides. That is because 12 water molecules are split during the light reactions, while 6 new molecules are produced during and after the Calvin cycle. While this is the general equation for the entire process, there are many individual reactions which contribute to this pathway.

Stages of Photosynthesis

The light reactions.

The light reactions happen in the thylakoid membranes of the chloroplasts of plant cells. The thylakoids have densely packed protein and enzyme clusters known as photosystems . There are two of these systems, which work in conjunction with each other to remove electrons and hydrogens from water and transfer them to the cofactors ADP and NADP + . These photosystems were named in the order of which they were discovered, which is opposite of how electrons flow through them. As seen in the image below, electrons excited by light energy flow first through photosystem II (PSII), and then through photosystem I (PSI) as they create NADPH. ATP is created by the protein ATP synthase , which uses the build-up of hydrogen atoms to drive the addition of phosphate groups to ADP.

The entire system works as follows. A photosystem is comprised of various proteins that surround and connect a series of pigment molecules . Pigments are molecules that absorb various photons, allowing their electrons to become excited. Chlorophyll a is the main pigment used in these systems, and collects the final energy transfer before releasing an electron. Photosystem II starts this process of electrons by using the light energy to split a water molecule, which releases the hydrogen while siphoning off the electrons. The electrons are then passed through plastoquinone, an enzyme complex that releases more hydrogens into the thylakoid space . The electrons then flow through a cytochrome complex and plastocyanin to reach photosystem I. These three complexes form an electron transport chain , much like the one seen in mitochondria. Photosystem I then uses these electrons to drive the reduction of NADP + to NADPH. The additional ATP made during the light reactions comes from ATP synthase, which uses the large gradient of hydrogen molecules to drive the formation of ATP.

The Calvin Cycle

With its electron carriers NADPH and ATP all loaded up with electrons, the plant is now ready to create storable energy. This happens during the Calvin Cycle , which is very similar to the citric acid cycle seen in mitochondria. However, the citric acid cycle creates ATP other electron carriers from 3-carbon molecules, while the Calvin cycle produces these products with the use of NADPH and ATP. The cycle has 3 phases, as seen in the graphic below.

During the first phase, a carbon is added to a 5-carbon sugar, creating an unstable 6-carbon sugar. In phase two, this sugar is reduced into two stable 3-carbon sugar molecules. Some of these molecules can be used in other metabolic pathways, and are exported. The rest remain to continue cycling through the Calvin cycle. During the third phase, the five-carbon sugar is regenerated to start the process over again. The Calvin cycle occurs in the stroma of a chloroplast. While not considered part of the Calvin cycle, these products can be used to create a variety of sugars and structural molecules.

Products of Photosynthesis

The direct products of the light reactions and the Calvin cycle are 3-phosphoglycerate and G3P, two different forms of a 3-carbon sugar molecule. Two of these molecules combined equals one glucose molecule, the product seen in the photosynthesis equation. While this is the main food source for plants and animals, these 3-carbon skeletons can be combined into many different forms. A structural form worth note is cellulose , and extremely strong fibrous material made essentially of strings of glucose. Besides sugars and sugar-based molecules, oxygen is the other main product of photosynthesis. Oxygen created from photosynthesis fuels every respiring organism on the planet.

Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology 6th. ed . New York: W.H. Freeman and Company. Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry . New York: W.H. Freeman and Company.

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What is the by product of photosynthesis, name the tissue which transport soluble products of photosynthesis in a plant., read the extract given below and answer the questions that follows:there are many activities that are undertaken by directly using natural resources. when we produce a good by exploiting natural resources, it is an activity of the primary sector. since most of the natural products we get are from agriculture, dairy, fishing, forestry, this sector is also called agriculture and related sector. the secondary sector covers activities in which natural products are changed into other forms through ways of manufacturing that we associate with industrial activity. it is the next step after primary. the product is not produced by nature but has to be made and therefore some process of manufacturing is essential. after primary and secondary, there is a third category of activities that falls under tertiary sector and is different from the above two. these are activities that help in the development of the primary and secondary sectors. these activities, by themselves, do not produce a good but they are an aid or a support for the production process. the various production activities in the primary, secondary and tertiary sectors produce a very large number of goods and services. also, the three sectors have a large number of people working in them to produce these goods and services. the value of final goods and services produced in each sector during a particular year provides the total production of the sector for that year. and the sum of production in the three sectors gives what is called the gross domestic product (gdp) of a country. it is the value of all final goods and services produced within a country during a particular year. gdp shows how big the economy is.q. which of the following statement is not true, photosynthetic end products, it is said that peepal tree release oxygen during night but during night in absence of sunlight plant can't perform photosynthesis. and we know that without photosynthesis plant can't produce oxygen so how that plant is able to release oxygen comment it., top courses for class 10 view all.

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Related content, name the tissue which transport soluble products of photosynthesis in a pla ... more nt., read the extract given below and answer the questions that follows:there ar ... more e many activities that are undertaken by directly using natural resources. when we produce a good by exploiting natural resources, it is an activity of the primary sector. since most of the natural products we get are from agriculture, dairy, fishing, forestry, this sector is also called agriculture and related sector. the secondary sector covers activities in which natural products are changed into other forms through ways of manufacturing that we associate with industrial activity. it is the next step after primary. the product is not produced by nature but has to be made and therefore some process of manufacturing is essential. after primary and secondary, there is a third category of activities that falls under tertiary sector and is different from the above two. these are activities that help in the development of the primary and secondary sectors. these activities, by themselves, do not produce a good but they are an aid or a support for the production process. the various production activities in the primary, secondary and tertiary sectors produce a very large number of goods and services. also, the three sectors have a large number of people working in them to produce these goods and services. the value of final goods and services produced in each sector during a particular year provides the total production of the sector for that year. and the sum of production in the three sectors gives what is called the gross domestic product (gdp) of a country. it is the value of all final goods and services produced within a country during a particular year. gdp shows how big the economy is.q. which of the following statement is not true, it is said that peepal tree release oxygen during night but during night in ... more absence of sunlight plant can't perform photosynthesis. and we know that without photosynthesis plant can't produce oxygen so how that plant is able to release oxygen comment it..

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Photosynthesis

Class 10 - selina concise biology solutions, progress check 1.

Answer the following in "Yes" or "No"

(i) All parts of a green plant carry out photosynthesis.

(ii) All green parts of a plant carry out photosynthesis.

(iii) Photosynthesis is the only biological process that releases oxygen into the air.

(iv) Out of nine types of chlorophylls, chlorophyll a and b are the most abundant.

(v) Too much light destroys chlorophyll.

(vi) No transpiration occurs during photosynthesis.

(vii) During sunlight, the guard cells turn flaccid to open the stomata.

(i) No Corrected Statement — A few parts of a green plant like roots and flowers does not carry out photosynthesis as they lack chloroplasts and chlorophyll.

(vi) No Corrected Statement — Photosynthesis and transpiration go on side by side.

(vii) No Corrected Statement — During sunlight, the guard cells turn turgid to open the stomata.

Progress Check 2

Write the overall summary of the chemical equation of photosynthesis.

6 CO 2 + 12 H 2 O → chlorophyll light energy C 6 H 12 O 6 + 6 H 2 O + 6 O 2 ↑ 6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{chlorophyll}]{\text{light energy}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{H}_2\text{O} + 6\text{O}_2 \uparrow 6 CO 2 ​ + 12 H 2 ​ O light energy chlorophyll ​ C 6 ​ H 12 ​ O 6 ​ + 6 H 2 ​ O + 6 O 2 ​ ↑

Which single substance in the above equation is repeated in raw material as well as reproduced as an end product?

What is the source of oxygen released in photosynthesis — CO 2 or H 2 O ?

What happens in photolysis?

The energy of Sun absorbed is used in splitting the water molecule into its two components (Hydrogen and Oxygen) and releasing electrons. This process is termed as photolysis.

Dark reaction involves utilisation of CO 2 in producing C 6 H 12 O 6 (glucose). Why is this phase called dark reaction ?

The given reaction does not require light. It can occur during day as well as night. Therefore, it is known as Dark reaction.

Glucose produced during photosynthesis is soon polymerised into starch. What does polymerisation mean?

The process of conversion of many simpler molecules into a complex, bigger molecule is termed as polymerisation. Several molecules of glucose join together to form a starch molecule.

Why is it better to call the dark phase of photosynthesis as "light-independent phase"?

The old term 'dark-phase' did not mean that it occurs when it is dark i.e. night. It only means that the reactions are not dependent on light. That is why, it is now better called as "light-independent phase".

Progress Check 3

How do the following favour increased photosynthesis?

(i) Large surface area of the leaf.

(ii) Thinness of the leaf.

(iii) More numerous stomata.

(i) Large surface area of the leaf enables maximum light absorption by plant. Increased absorption of solar energy increases the Photosynthesis.

(ii) Thinness of the leaf reduces the distance between cells facilitating rapid transport of raw materials and translocation of food.

(iii) More numerous stomata allow rapid gaseous exchange and speed up the process of photosynthesis.

Name the three end-products of photosynthesis and mention the fate of each of them in the plant.

The three end products of photosynthesis are:

• immediately consumed by the plant cells
• stored in the form of insoluble starch
• converted into sucrose
• used in synthesizing fats, proteins,etc.
• Water — can be reutilized in continuance of photosynthesis.
• Oxygen — It is used in respiration in the leaf cells. Extra oxygen is released and diffused out in atmosphere.

If we keep on increasing CO 2 concentration in the air, will the rate of photosynthesis also keep on increasing in direct proportion? Yes/No. Explain.

Increasing carbon dioxide concentration increases rate of photosynthesis but it is stabilised at a particular point (upto 0.02% of CO 2 ) if there is no change in light intensity. If the light intensity is increased then increase in carbon dioxide concentration further increases the rate of photosynthesis and is again stabilised at 0.05% of CO 2 .

Progress Check 4

Why is it necessary to destarch the leaves of a plant before performing an experiment on photosynthesis?

In any experiment on photosynthesis, the presence of starch shows that the process of photosynthesis occurred. Therefore it is necessary to remove any pre-existing starch from the leaves. For destarching, the plant is kept for 24-48 hours in dark. It stops the synthesis of starch and the pre-existing starch, by then, is removed from leaves and is stored in storage organs.

Why do we perform the iodine test ?

We perform the iodine test to test the presence of starch.

What chemical do you use to remove CO 2 from inside a flask in certain experiments on photosynthesis ?

• Potassium hydroxide

All food chains start with a plant. Why is this so?

The plants are called producers. They are the only organism with ability to convert the solar energy into chemical energy of the food. Therefore, all food chains start with a plant.

The honey bee produces honey. In terms of the food chain, is the honey bee a producer or a consumer?

In terms of food chain, the honey bee is a consumer as it consumes plant nectar and derive its energy from nectar to carry out all the physiological processes. Honey produced by it is derived indirectly from plants. Therefore, Honey bee cannot be called as a producer.

Multiple Choice Type

Chlorophyll is located in :

Reason — Chlorophyll is located in the walls of thylakoid.

Which of the following is not applicable to the process of photosynthesis ?

• Oxygen is evolved
• Carbon dioxide is absorbed

Carbon dioxide is evolved

• Water is utilized

Reason — In the process of photosynthesis, carbon dioxide is absorbed and oxygen is evolved as a by-product.

The colour of VIBGYOR spectrum which is reflected by chlorophyll is:

Reason — The colour of any object is the light that is reflected by it. The chlorophyll reflects green colour and therefore it is green to our eyes.

The basic functional unit of solar energy which is absorbed by the pigment chlorophyll is:

• Phytochrome

Reason — The basic functional unit of solar energy is photon that is absorbed by the chlorophyll molecules and this leads to start of chain of reactions of photosynthesis.

The molecules of water split during:

• Photorespiration
• Phosphorylation
• Photophosphorylation

Reason — The chlorophyll molecule absorbs solar energy and this energy is used to split the water molecule. This process ia called photolysis. (photo means light, lysis means disintegration)

The granum is a pile of many :

Reason — Stacked thylakoids are known as granum.

Which of the following is used to remove chlorophyll from the leaves:

• Iodine solution

Methylated spirit

Reason — The leaf is boiled in Methylated spirit to remove chlorophyll.

The raw material which is reduced during photosynthesis is :

Carbon dioxide

Reason — Carbon dioxide loses its oxygen or is reduced to form glucose. (loss of oxygen is reduction)

The optimum temperature for the process of photosynthesis is :

Reason — The rate of photosynthesis is maximum at 35°C and falls beyond it.

Question 10

Conversion of several glucose molecules into starch is termed as :

Polymerisation

Reason — Polymerisation is the process by which simple monomers (glucose) join to form complex polymers (starch).

Very Short Answer Type

Name the following:

(a) The category of organisms that prepare their own food from basic raw materials.

(b) The kind of plastids found in the mesophyll cells of the leaf.

(c) The compound which stores energy in the cells.

(d) The first form of food substance produced during photosynthesis.

(e) The source of CO 2 for aquatic plants.

(f) The part of chloroplast where the dark reaction of photosynthesis takes place.

(a) Autotrophs.

(b) Chloroplasts.

(c) ATP (Adenosine triphosphate).

(d) Glucose.

(e) The carbon dioxide dissolved in water.

(f) Stroma.

Given below are groups of terms. In each group, the first pair indicates the relationship between the two terms. Complete the second pair accordingly.

(a) Chlorophyll : Magnesium :: Haemoglobin : ............... .

(b) Light reaction : Granum :: Dark reaction : ............... .

(c) Producers : Autotrophs :: Consumers : ............... .

(d) Respiration : Carbon dioxide :: Photosynthesis : ............... .

(e) Water and minerals : Xylem :: Prepared food : ............... .

(a) Chlorophyll : Magnesium :: Haemoglobin : Iron

(b) Light reaction : Granum :: Dark reaction : Stroma

(c) Producers : Autotrophs :: Consumers : Heterotrophs

(d) Respiration : Carbon dioxide :: Photosynthesis : Oxygen

(e) Water and minerals : Xylem :: Prepared food : Phloem

Short Answer Type

Identify the false statements and rewrite them correctly by changing the first or last word only.

(a) Dark reaction of photosynthesis occurs during night time.

(b) Photosynthesis requires enzymes.

(c) Green plants are consumers.

(d) Photosynthesis results in loss of dry weight of the plants.

(e) Photosynthesis stops at a temperature of about 35°C.

(f) Photosynthesis occurs only in cells containing chloroplasts.

(g) Green plants perform photosynthesis.

(h) Algae are autotrophs.

(a) False Corrected statement — Dark reaction of photosynthesis occurs simultaneously with light reaction.

(c) False Corrected statement — Green plants are producers.

(d) False Corrected statement — Respiration results in loss of dry weight of the plants.

(e) False Corrected statement — Photosynthesis stops at a temperature of about 40°C.

Fill in the blanks with the appropriate answer from the choices given in the brackets.

(a) The site of light reaction in the cells of a leaf is ............... (cytoplasm, stroma, grana).

(b) The chemical substance used to test the presence of starch in the cell of a leaf is ............... (CaCl 2 , iodine solution, Benedict solution).

(c) Stroma is the ground substance in ............... (cytoplasm, chloroplast, ribosomes).

(d) The dark reaction of photosynthesis is known as ............... (Hill reaction, cyclic phosphorylation, Calvin cycle).

(e) In the flowering plants, food is transported in the form of ............... (sucrose, glucose, starch).

(a) The site of light reaction in the cells of a leaf is grana .

(b) The chemical substance used to test the presence of starch in the cell of a leaf is iodine solution .

(c) Stroma is the ground substance in chloroplast .

(d) The dark reaction of photosynthesis is known as Calvin cycle .

(e) In the flowering plants, food is transported in the form of Sucrose .

Are the following statements true or false ? Give reason in support of your answer.

(a) The rate of photosynthesis continues to rise as long as the intensity of light rises.

(b) The outside atmospheric temperature has no effect on the rate of photosynthesis.

(c) If you immerse a leaf intact on the plant in ice cold water, it will continue to photosynthesise in bright sunshine.

(d) Destarching of the leaves of a potted plant can occur only at night.

(e) If a plant is kept in bright light all the 24 hours for a few days, the dark reaction (biosynthetic phase) will fail to occur.

(f) Photosynthesis is considered as a process supporting all life on earth.

(a) False Corrected statement — Photosynthesis increases with the light intensity up to a certain limit only, and then it gets stabilised at the point S'(0.02% CO 2 ).

(b) False Corrected statement — The atmospheric temperature is an important external factor affecting photosynthesis. With the rise in temperature, the rate of photosynthesis rises. This rise occurs up to the optimum temperature of 35°C (maximum suitable temperature when the photosynthesis occurs best) after which the rate falls and stops above 40°C.

(c) False Corrected statement — Ice cold water will hamper the process of photosynthesis in the immersed leaf, even if there is sufficient sunshine because the temperature is an important factor for the rate of photosynthesis.

(d) False Corrected statement — For destarching, the potted plant can be kept in a dark room for 24-48 hours. During this period, all the starch will be removed from the leaves and stored in the storage organs.

(e) False Corrected statement — If a plant is kept in bright light all the 24 hours for a few days, the dark reaction (biosynthetic phase) will continue to occur because the dark reaction is independent of light and it occurs simultaneously with the light dependent reaction.

Given below are five terms. Rewrite the terms in the correct order so as to be in logical sequence with regard to photosynthesis: (i) water molecules, (ii) oxygen, (iii) grana, (iv) hydrogen and hydroxyl ions, (v) photons.

Photons, grana, water molecules, hydrogen and hydroxyl ions, oxygen.

State any four differences between photosynthesis and respiration.

Complete the following food chains by writing the names of appropriate organisms in the blanks:

(i) Grass → ............... → Snake → ...............

(ii) ............... → Mouse ............... → Peacock

(i) Grass → Grasshopper → Snake → Hawk

(ii) Corn → Mouse → Snake → Peacock

Name these :

(a) Two aquatic plants which can be used for the experiment of photosynthesis.

(b) Two plants having variegated leaves.

(c) Two raw materials for photosynthesis.

(d) Four essentials for photosynthesis.

(e) Two main phases of photosynthesis.

(a) Hydrilla, Elodea

(b) Geranium, Croton

(c) Carbon dioxide, water

(d) Light, Chlorophyll, Carbon dioxide and water

(e) Photo-chemical phase, Biosynthetic phase

Match the terms given in column A with column B:

Complete the following by filling the blanks 1 to 5 with appropriate words/ terms/ phrases:

To test the leaf for starch, the leaf is boiled in water to (1) ............... . It is next boiled in methylated spirit to (2) ............... . The leaf is placed in warm water to soften it. It is then placed in a dish and (3) ............... solution is added. The region, which contains starch, turns (4) ............... and the region, which does not contain starch, turns (5) ............... .

To test the leaf for starch, the leaf is boiled in water to (1) kill the cells. It is next boiled in methylated spirit to (2) remove chlorophyll. The leaf is placed in warm water to soften it. It is then placed in a dish and (3) iodine solution is added. The region, which contains starch, turns (4) blue-black and the region, which does not contain starch, turns (5) brown. .

Write the exact location of each :

(a) Chlorophyll

(b) Chloroplast in the parts of a plant

(d) Guard cells

(e) Palisade cells

(a) Wall of thylakoid.

(b) Mesophyll cells of upper and lower epidermis of leaves.

(c) Chloroplast.

(d) Stomata.

(e) Beneath epidermis.

Descriptive Type

Define the following terms:

(a) Photosynthesis

(b) Thylakoids

(c) Chloroplast

(d) Photolysis of water

(e) Polymerisation

(a) Photosynthesis — Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch), from carbon dioxide and water, by using light energy and release oxygen as a by-product.

(b) Thylakoids — Closely packed flattened sacs arranged in piles in the interior of chloroplasts are called Thylakoids.

(c) Chloroplast — Chloroplasts are minute oval bodies bounded by a double membrane which contains Thylakoids arranged in piles called Grana lying in a colourless ground substance called Stroma.

(d) Photolysis of water — Photolysis of water is defined as the splitting of H 2 O molecules into hydrogen ions and oxygen in the presence of light.

(e) Polymerisation — Polymerisation is the process in which several glucose molecules are transformed to produce one molecule of starch.

Given below is the figure of an experimental set-up, showing a physiological act of the plants. Study and answer the following questions.

(a) What is the objective of this experiment ?

(b) Name and define the process shown here.

(c) Why do we destarch the leaves before performing the experiment ?

(d) How do we destarch the leaves ?

(e) What will be the observation when we pour iodine solution over the bleached experimental leaf.

(f) Write a well-balanced equation of the above process.

(a) The objective of given experiment is to show that sunlight is necessary for photosynthesis.

(b) The process shown here is photosynthesis.

Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch), from carbon dioxide and water, by using light energy and release oxygen as a by-product.

(c) We destarch the leaves before experiment in order to remove the starch from leaves so that occurence of photosynthesis can be detected.

(d) To destarch the leaves the plant is kept in dark for 24-48 hours. This stops photosynthesis in the plant. During this time the starch already present in the leaves is translocated to storage organ of the plant fom the leaves.

(e) When we pour iodine solution over the bleached experimental leaf the area where starch is present turns blue.

(f) The equation for photosynthesis is given below:

Give reasons/explain:

(a) It is necessary to place a plant in the dark before starting an experiment on photosynthesis.

(b) It is not possible to demonstrate respiration in a green plant kept in sunlight.

(c) Most leaves have the upper surface more green and shiny than the lower surface.

(d) During the starch test, the leaf is -

• boiled in water.
• boiled in methylated spirit.

(a) A plant used for experiments on photosynthesis should initially be placed in the dark for 24 to 48 hours to destarch the leaves. During this period, all the starch will be removed from the leaves and stored in the storage organs. The leaves will not show the presence of starch. So the various experiments on photosynthesis can be carried out effectively.

(b) If a green plant is kept in bright light, it tends to use up all the CO 2 produced during respiration, for photosynthesis. Thus, the release of CO 2 cannot be demonstrated. Hence, it is difficult to demonstrate respiration as these two processes occur simultaneously.

(c) Due to more amount of chlorophyll on the upper surface more light is trapped. The chloroplasts are concentrated in the upper layers of the leaf which helps cells to trap the sunlight quickly. The upper surface is more green and shiny because it has a waxy coating to prevent loss of water due to evaporation.

(d) During the starch test,

• The leaf is boiled in water to kill the cells.
• The leaf is boiled in methylated spirit till it becomes pale-white due to the removal of chlorophyll. The leaf now becomes hard and brittle.

Distinguish between the following pairs on the basis of words indicated in the brackets ( )

(a) Light reaction and Dark reaction (end products)

(b) Producers and Consumers (organisms)

(c) Grass and Grasshopper (mode of nutrition)

(d) Stoma and Stroma (structure)

(a) Differences between light reaction and dark reaction (end products) —

(b) Differences between producers and consumers (organisms) —

(c) Differences between grass and grasshopper (mode of nutrition) —

(d) Differences between stoma and stroma (structure) —

How would you demonstrate that green plants release oxygen when exposed to light?

• Place some water plants (Elodea or Hydrilla) in a beaker containing pond water and cover them by a short-stemmed funnel.
• Invert a test-tube full of water over the stem of the funnel. (Ensure that the level of water in the beaker is above the level of stem of the inverted funnel).
• Place the apparatus in the sun for a few hours. Bubbles of the gas will collect in the test-tube.
• Test the gas in the test-tube. A glowing splinter bursts into flame which shows the presence of oxygen.

Describe the main chemical changes which occur during photosynthesis in

Light reaction

Dark reaction

The light reaction occurs in two main steps:

Step 1 — Activation of chlorophyll The chlorophyll on exposure to light energy becomes activated by absorbing photons.

Step 2 — Splitting of Water The absorbed energy is used in splitting the water molecule (H 2 O) into its two components (Hydrogen and Oxygen) and releasing electrons.

2 H 2 O ⟶ energy of 4 photons 4 H + + 4 e − + O 2 2 H_2O \overset{\text{energy of 4 photons}}{\longrightarrow} 4H^+ + 4e^- + O_2 2 H 2 ​ O ⟶ energy of 4 photons ​ 4 H + + 4 e − + O 2 ​

This reaction is known as photolysis of water.

End result of the products of photolysis The hydrogen ions (H + ) are picked up by a compound NADP (Nicotinamide adenine dinucleotide phosphate) to form NADPH.

N A D P + + e − + H + ⟶ enzyme N A D P H NADP^+ + e^- + H ^+ \overset{\text{enzyme}}{\longrightarrow} NADPH N A D P + + e − + H + ⟶ enzyme ​ N A D P H

The oxygen (O) component is given out as molecular oxygen (O 2 ).

2 O ⟶ O 2 2O \longrightarrow O_2 2 O ⟶ O 2 ​

The electrons (e - ) are used in converting ADP (adenosine diphosphate) into energy rich compound ATP (adenosine triphosphate) by adding one phosphate group P i (inorganic phosphate).

A D P + P i  (inorganic phosphate) ⟶ A T P ADP + P_i \text{ (inorganic phosphate)} \longrightarrow ATP A D P + P i ​  (inorganic phosphate) ⟶ A TP

This process is called photophosphorylation.

The reactions in this phase do not require light energy and occur simultaneously with the light reaction. The time gap between the light and dark reaction is less than one thousandth of a second. In the dark reaction, ATP and NADPH molecules (produced during light reaction) are used to produce glucose (C 6 H 12 O 6 ) from carbon dioxide. Fixation and reduction of carbon dioxide occurs in the stroma of the chloroplast through a series of reactions. The glucose produced is either immediately used up by the cells or stored in the form of starch.

Below is the summary of events in Light reaction and Light independent reactions of photosynthesis:

Structured / Application / Skill Type

Given below is a schematic diagram to illustrate some aspects of photosynthesis.

(a) Fill up the gaps, in blank spaces (1-4), by writing the names of the correct items.

(b) What phenomenon do the thick arrows A and B indicate?

(a) Blank spaces (1-4) are labelled below:

• 1 → Sunlight
• 3 → Glucose

(b) Phenomena represented by thick arrows A and B are:

• A → Transpiration
• B → Translocation

Given below is the representation of a certain phenomenon in nature with four organisms 1-4.

(a) Name the phenomenon represented.

(b) Name any one organism that could be shown at No .5

(c) Name the biological process which was the starting point of the whole chain.

(d) Name one natural element which all the organisms 2-4 and even 5 are getting from No. 1 for their survival.

(a) Food chain

(b) Hawk, Eagle

(c) Photosynthesis

A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours and then placed in bright sunlight for a few hours. Observe the diagram and answer the questions:

(a) What aspect of photosynthesis is being tested in the above diagram?

(b) Why was the plant placed in the dark before beginning the experiment?

(c) Write a balanced chemical equation to represent the process of photosynthesis.

(d) What will be the result of starch test when performed on leaf A shown in the diagram?

(e) Draw a neat and labelled diagram of a chloroplast.

(a) The above experiment is conducted to show that chlorophyll is necessary for photosynthesis.

(b) The plant was placed in the dark before beginning the experiment to destarch the leaves.

(c) Balanced chemical equation representing the process of photosynthesis is given below:

(d) After the starch test on leaf A, only the green parts of the leaf turn bluish, showing the presence of starch.

(e) Below diagram shows Chloroplast with its different parts labelled:

Given below is the diagram of an experimental set-up:

a. What is the objective of this experiment?

b. Will it work satisfactorily? Given reason.

c. What alteration (s) will you make in it for obtaining expected result?

d. Would you take any step before starting the experiment? Describe this step and explain its necessity.

(a) The objective is to prove that carbon dioxide is necessary for photosynthesis.

(b) No, the experiment will not work satisfactorily because, the beaker contains lime water which does not absorb CO 2

(c) To obtain expected result replace the lime water from potassium hydroxide because it absorbs carbon dioxide.

(d) Before starting the experiment, it is necessary to destarch the leaves of the plant by keeping the plant in complete darkness for 48 hours. This is because if the plant is not destarched, then the experiment will give false results because starch stored previously may be detected in the leaf placed in the beaker even if no starch is produced during the experiment.

Draw a neat diagram of the stomatal apparatus found in the epidermis of leaves and label the Stoma, Guard cells, Chloroplast, Epidermal cells, Cell wall and Nucleus.

Below diagram shows the stomatal apparatus found in the epidermis of leaves with all the different parts labelled:

Given below is the diagram of an experimental set-up (final stage). Study the same and answer the following questions :

(a) What is the main aim of the experiment?

(b) Oxygen gas shown in the experiment is released from which of the raw materials ?

(c) How would you confirm the presence of oxygen gas?

(d) Name the chemical substance which can be added in water to enhance the process/rate of release of oxygen gas.

(e) Draw a neat and labelled diagram of the same experiment for its initial stage.

(a) The main aim of the experiment is to show that oxygen is produced during photosynthesis.

(b) Oxygen is released from Water (H 2 O).

(c) The gas present in the test tube makes a glowing splinter bursts into flames. This shows the presence of oxygen.

(d) Sodium Bicarbonate

ICSE solutions for Class 10 Biology chapter 5 - Photosynthesis [Latest edition]

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Solutions for chapter 5: photosynthesis.

Below listed, you can find solutions for Chapter 5 of CISCE ICSE for Class 10 Biology.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Short Questions

What are the basic requirements of photosynthesis?

Where are the chlorophyll pigments present in a cell?

Name the membrane that connects thylakoid of one granum With the other granum.

Give some adaptations in green leaf photosynthesis.

What is the importance of photosynthesis in the life of the following:

Green plants

Non-green plants

A leaf is a food factory. Explain.

Why green leaves are thin and broad?

State one important function of chloroplasts.

Which tissues and cells are mainly concerned with photosynthesis?

Why Is Photosynthesis Important in Nature?

How do non-green plants such as fungi and bacteria obtain their nourishment?

"Oxygen is a waste product of photosynthesis." Comment.

What is meant by the photolysis of water?

Oxygen given out during photosynthesis comes from water. Explain this statement.

How is the rate of photosynthesis affected when a green plant gets the green light?

Why is it not possible to demonstrate respiration in a green plant kept in sunlight?

Explain, why respiration is said to be a reversed process of photosynthesis?

Name the molecules which are called assimilatory power? Why are they called so?

What is the law of limiting factors?

Complete the following food chain by writing the names of appropriate organisms in the blanks:

Grass → __________ → Snake → __________

 → __________ → __________ → Hen → Man

Complete the following food chain by writing the names of appropriate organisms in the blank:

Grass → __________ → Lion

 __________ → Mouse → _________ → Peaock

On a bright sunny day, water weeds growing in an aquarium were actively giving off bubbles of gas. Use this information to answer questions that follow:

• Name the process occurring in the water weed that has resulted in the evolution of these bubbles.
• Of what gas do these bubbles consist?
• Briefly describe the reactions occurring in the leaves of the water weeds leading to the evolution of these bubbles.
• Give an overall balanced chemical equation to represent the process named in (i) above.

What is meant by a destarched plant? How can it be destarched?

Using the destarched plant describe step by step how would you proceed to prove that in the absence of light the leaf cannot manufacture starch?

A healthy croton plant bearing variegated leaves was kept in a dark cupboard to destarch it after which it was placed in sunlight for a few hours. One of the leaves was then plucked and an outline of the leaf marking the green and the non-green regions was drawn. The leaf was then tested for starch. Using the above information, answer the following questions:

• State the aim of the above experiment.
• Name the chemical used for testing the presence of starch.
• Why is the leaf boiled in water and alcohol before testing for the presence of starch?
• What change is seen on the leaf after the starch test?
• Give the chemical equation to represent the process of starch formation in plants.

A candidate in order to study the importance of certain factors in photosynthesis took a potted plant and kept it in the dark for over 24 hours. Then in the early hours of the morning, she covered one of the leaves with black paper in the center only. She placed the potted plant in the sunlight for a few hours, and then tested the leaf which was covered with black paper for starch.

• What aspect of photosynthesis was being investigated?
• Is there any control in this experiment? If so, state the same.
• Why was the plant kept in the dark before the experiment?
• Describe step by step how the candidate proceeded to test the leaf for the presence of starch.

A potted plant was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours. One of the leaves was covered with black paper in the  centre . The potted plant was then placed in sunlight for a few hours.

What aspect of photosynthesis was being tested?

Why was the plant placed in the dark before beginning the experiment?

During the starch test, why was the leaf

(1) boiled in water

(2) boiled in methylated spirit

Write a balanced chemical equation to represent the process of photosynthesis. 

Write an experiment to demonstrate that CO 2  is necessary for photosynthesis.

List the events taking place in the photo-chemical phase of Photosynthesis.

If you are planning an experiment to show the effect of light on photosynthesis : (1) Will you select white light or green light? Justify your answer. (2) Why would you select a destarched plant?

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Give Reasons

 All life on earth Would come to an end if there were no green plants.

Photosynthesis is considered as a process supporting all life on earth.

Chlorophyll is necessary for photosynthesis.

Chloroplasts are called energy converters.

ATP is needed for the dark reaction.

Respiration is said to be the reversal of photosynthesis.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Differentiate

Differentiate Between:

Light reaction and Dark reaction.

Stroma of chloroplast and Grana of chloroplast

Chloroplast and Chlorophyll

Autotrophs and Heterotrophs.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Diagram Based Questions

The figure below represents the vertical section of a leaf:

(i) Name the parts 1 to 5. (ii) How many veins have been shown? (iii) State the functions of parts 4 and 5.

(i) Identify the above diagram. (ii) Label the guidelines 1-3. (iii) Name the phenomenon which takes place in the above diagram. (iv) Define the phenomenon. (v) What is the importance of the above phenomenon?

The figure given below represents an experiment to demonstrate a particular aspect of photosynthesis. The alphabet ‘A’ represents a certain condition inside the flask.

(i) What is the aim of the experiment? (ii) Identify the special condition inside the flask. (iii) Name an alternative chemical that can be used instead of KOH. (iv) In what manner do the leaves 1 and 2 differ at the end of the starch test?

The figure below represents an experiment performed to demonstrate a particular aspect of photosynthesis. The apparatus was kept in sunlight for almost the whole day. The numeral ‘1’ represents a certain condition inside the flask and the numeral ‘2’ represents a chemical responsible for this condition. (i) What is the object of the experiment? (ii) What is the special condition inside the flask? (iii) What is the chemical substance numbered ‘2’? (iv) In what way will the three leaves (A, B, and C) differ at the end of the experiment, when tested with iodine solution?

The figure below represents an experiment set up to study a physiological process in plants:

(i) Name the physiological process being studied. (ii) Explain the process. (iii) What is the aim of the experiment? (iv) Give a well-balanced equation to represent the process.

The figure given below is for performing an experiment on photosynthesis.

Answer the following: (i) What is the aim of this experiment? (ii) Describe an experiment to show that light is necessary for photosynthesis. (iii) What do you conclude from this experiment? (iv) What is the role of light in photosynthesis?

A well-watered healthy potted plant with variegated leaves was kept in darkness for about 24 hours. It was then set up as shown in the diagram and exposed to light for about 12 hours. At the end of this time, leaf X and leaf Y were tested for starch. Study the diagram and answer the questions that follow: (i) Why was the plant initially kept in darkness for 24 hours? (ii) What is the function of the sodium hydroxide solution in the flask? (iii) Select the correct leaf from the five available choices shown in the diagram as A, B, C, D, and E. Rewrite the correct answer for the filling in the appropriate letter from the questions that follow:

1. After the starch test, leaf X would look like. 2. After the starch test, leaf Y would look like.

The diagram alongside refers to an experiment in which the apparatus was set up with the light source 10 cm away from the plant. After 15 minutes the number of bubbles evolved per minute from the cut stem was recorded. The light source was moved to 20 cm away from the plant, left for 15 minutes and the number of bubbles evolved per minute was again recorded. The experiment was repeated with the light source at distances of 40, 60, 80 and 100 cm away from the plant. Plot a graph for the results obtained and answer the following questions.

(i) From the graph it seems likely that the rate of bubbling per minute at 50 cm would have been (a) 2.0 (b) 2.5 (c) 3.0 (d) 3.5 (ii) The gas produced by the plant during the experiment was (a) air (b) oxygen (c) carbon dioxide (d) nitrogen (e) hydrogen (iii)     The gas collected comes due to the breakdown of (a) glucose (b) starch (c) water (d) air (e) ATP (iv) If ice cubes were added to the water, the rate of bubble formation would (a) Stay the same. (b) Increase because more water is added. (c) Decrease because the temperature drops. (d) Decrease because water freezes. (e) Cannot tell from the information given. (v) If some sodium bicarbonate is added to the water the rate of bubble formation (a) Increases because more respiration occurs. (b) Increases because more photosynthesis occurs. (c) Increases because the gas becomes less soluble. (d) Decreases because carbon dioxide acts as a limiting factor. (e) Decreases because respiration decreases.

 (i) Draw a neat and well-labelled diagram of the Chloroplast. (ii) List the events taking place in the photo-chemical phase of Photosynthesis. (iii) If you are planning an experiment to show the effect of light on photosynthesis : (a) Will you select white light or green light? Justify your answer. (b) Why would you select a destarched plant?

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Sketch and Label the Diagram

Draw a neat and well-labeled diagram of the Chloroplast.

Draw a neat and well-labeled diagram of the apparatus you would set up to show that oxygen is given out during photosynthesis.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Explain the Terms

Explain the Term ATP.

Explain the Term Calvin Cycle.

Explain the Term Free Energy.

Explain the Term NADPH.

Explain the term Plastoquinone.

Explain the term Photosynthesis.

Explain the term Photosynthetic Membrane.

Explain the term Phosphorylation.

Explain the term NADP.

Explain the term Photophosphorylation.

Explain the term Carbon cycle.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Name the Following

Name the following:

The process by which plants produce their food.

The green colouring matter of the plants.

The principal site in a green leaf for photosynthesis.

Source of oxygen given out in photosynthesis.

The site of light reaction in the cell of a leaf.

Light in which the maximum rate of photosynthesis takes place.

A high energy-reduced compound formed in the light reaction and enter into the dark reaction.

The immediate product of photosynthesis.

In-plant cells, carbohydrates are stored in which form.

The chemical substance used to test the presence of starch in the cell of a leaf.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Give Technical Terms

Give technical term:

Name the process which is responsible for the conversion of solar energy to chemical energy that is essential to sustain life on this earth?

Name the structure where photophosphorylation takes place.

The form of energy is converted into chemical energy during photosynthesis.

In photosynthesis radiant energy is converted into which from?

What is the percentage of CO 2 in the air?

Organisms which cannot prepare their own food by photosynthesis.

The main reaction which means the breaking up of water molecules through light.

Which process is the ultimate source of energy for all living organisms?

Name only one plant, you are familiar with which has no chlorophyll.

Name the tissue that transports manufactured starch from the leaves to all parts of the plant.

What does ATP abbreviate for?

What does NADP stand for?

The part of the chloroplast where the dark reaction of photosynthesis takes place.

Name the experiment to demonstrate the importance of light for photosynthesis.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Fill in the Blanks

Complete the following sentence with appropriate word:

A light-induced reaction which leads to the splitting of water is _____ of water.

A plant that does not perform photosynthesis is _______.

One of the products of ______of water is oxygen.

________ are regarded as complete photosynthetic units of plants.

AIIP stands for ____________.

________molecules of chlorophyll make one quantasome.

Carbon dioxide enters the leaf through _______.

Xanthophyll is ______ coloured pigment.

The conversion of the physical energy of light into chemical energy by the chloroplast is called ____________.

Calvin cycle was proposed by __________.

A dark reaction is a __________ reaction.

A light reaction is a ___________ reaction.

4OH ——> _____ + O 2

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis True & False

Mention, if the following statement is True or False. If false rewrite the wrong statement in its correct form:

 Photosynthesis occurs only in plants.

Too much light destroys chlorophyll.

The unit of light absorbed by the chlorophyll during photosynthesis is the proton.

The process of photosynthesis takes place in the dark.

CO 2 is the life-supporting gas produced due to photosynthesis.

PhotoLysis is the reaction which means the breaking up of water molecules.

Radiant energy is converted into chemical energy by photosynthesis.

Leaves are broad and flat to increase the surface area for photosynthesis.

The raw materials for photosynthesis include water and CO 2 .

Photosynthesis results in loss of dry weight of the plant.

Land plants obtain their CO 2 from the atmosphere.

Photosynthesis occurs in all the cells of a plant.

No transpiration occurs during photosynthesis.

A variegated leaf (one that has green as well as white patches) will only photosynthesize in the green areas.

The dark reaction of Photosynthesis is light-independent.

All the starch produced in a leaf remains stored in it for 2-3 weeks before it is used by other parts of a plant.

Photosynthesis can also occur n artificial light such as that of a 100-watt electric lamp.

KOH absorbs CO 2 .

Out of nine types of chlorophyll, chlorophyll ‘a’ and ‘b’ are most abundant.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis State the Location

State the Location: Thylakoid

State the Location: Stomata

State the location:

Chlorophyll

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis State the Function

Write the functional activity of the following structure: Granum

Write the functional activity of the following structure: Stroma

Write the functional activity of the following structure: Chloroplasts

Write the functional activity of the following structure: Thylakoids

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Choose the Odd One Out

Choose the Odd One Out

Chlorophyll b

Carbon-dioxide

Light intensity

Water content

Temperature

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Multiple Choice Questions

Choose the correct answer: Chlorophyll is present

In the grana of chloroplast

 On the surface of chloroplast

Dispersed throughout the chloroplast

In the stroma of chloroplast

The specific function of light energy in the process of photosynthesis is to

reduce carbon dioxide

synthesise glucose

activate chlorophyll

split water molecule

Choose the Correct Answer: Which one of the following would not be a limiting factor for photosynthesis?

Oxygen 

Carbon dioxide

Choose the correct answer: A cell that lacks chloroplast does not ______________

Evolve CO 2

liberate O 2

Require water

utilize carbohydrates

Choose the Correct Answer: Which would do maximum harm to a tree?

Loss of half of its branches

Loss of half of its flowers

Loss of all of its leaves

Loss of a little bark

Choose the Correct Answer: NADP is expanded as

Nicotinamide, adenosine dinucleotide phosphate

 Nicotinamide, adenine dinucleotide phosphate

Nicotinamide, adenine dinucleous phosphate

Nicotinamide, adenosine dinudeous phosphate

Choose the Correct Answer: A plant is kept in a dark cupboard for about 48 hours before conducting any experiment on photosynthesis to:

Remove starch from the plant

Ensure that starch is not translocated from the leaves

Remove chlorophyll from the leaf of the plant

Remove starch from the experimental leaf

Choose the Correct Answer: The main difference between chlorophyll ‘a’ and ‘b’ is:

Chlorophyll ‘a’ is a linear chain compound and ‘b’ is branched chain

Chlorophyll ‘a’ has no Mg ion in centre of molecule

In chlorophyll ‘a’ there is — CH 3  group whereas in ‘b’ it is — CHO group

All of the above

Choose the Correct Answer: Compensation point means the condition:

When the entire food manufactured in photosynthesis remains unutilised

When the pot is watered just to meet the full requirement of the plant

When rate of photosynthesis is equal to rate of respiration

Where there is neither photosynthesis nor respiration.

ICSE solutions for Class 10 Biology Chapter 5 Photosynthesis Match the Column

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ICSE solutions for Class 10 Biology chapter 5 - Photosynthesis

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Concepts covered in Class 10 Biology chapter 5 Photosynthesis are Photosynthesis: Food-Making Process in Plants, The Carbon Cycle, Chlorophyll: The Vital Plant Pigment, Regulation of Stomatal Opening for Letting in Carbon Dioxide, Experiments on Photosynthesis, Role of Sunlight in Photosynthesis, Light Dependent Reaction (Hill Reaction \ Light Reaction), Photophosphorylation, Adaptations in Leaf to Perform Photosynthesis, Significance of Photosynthesis, Process of Photosynthesis, Factors Affecting Photosynthesis, End Result of the Products of Photosynthesis, Light Independent Reactions (Dark Reaction \ Biosynthetic Phase), Respiration and Photosynthesis, Photosynthesis: Food-Making Process in Plants.

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Development of the idea

Overall reaction of photosynthesis.

• Basic products of photosynthesis
• Evolution of the process
• Light intensity and temperature
• Carbon dioxide
• Internal factors
• Energy efficiency of photosynthesis
• Structural features
• Light absorption and energy transfer
• The pathway of electrons
• Evidence of two light reactions
• Photosystems I and II
• Quantum requirements
• The process of photosynthesis: the conversion of light energy to ATP
• Elucidation of the carbon pathway
• Carboxylation
• Isomerization/condensation/dismutation
• Phosphorylation
• Regulation of the cycle
• Products of carbon reduction
• Photorespiration
• Carbon fixation in C 4 plants
• Carbon fixation via crassulacean acid metabolism (CAM)
• Differences in carbon fixation pathways
• The molecular biology of photosynthesis

Why is photosynthesis important?

What is the basic formula for photosynthesis, which organisms can photosynthesize.

photosynthesis

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• CORE - Photosynthesis in vine leaves as a function of light intensity, temperature, and leaf age
• Khan Academy - Photosynthesis
• Biology LibreTexts - Photosynthesis
• University of Florida - Institute of Food and Agricultural Sciences - Photosynthesis
• Milne Library - Inanimate Life - Photosynthesis
• National Center for Biotechnology Information - Chloroplasts and Photosynthesis
• Roger Williams University Pressbooks - Introduction to Molecular and Cell Biology - Photosynthesis
• BCcampus Open Publishing - Concepts of Biology – 1st Canadian Edition - Overview of Photosynthesis
• photosynthesis - Children's Encyclopedia (Ages 8-11)
• photosynthesis - Student Encyclopedia (Ages 11 and up)
• Table Of Contents

Photosynthesis is critical for the existence of the vast majority of life on Earth. It is the way in which virtually all energy in the biosphere becomes available to living things. As primary producers, photosynthetic organisms form the base of Earth’s food webs and are consumed directly or indirectly by all higher life-forms. Additionally, almost all the oxygen in the atmosphere is due to the process of photosynthesis. If photosynthesis ceased, there would soon be little food or other organic matter on Earth, most organisms would disappear, and Earth’s atmosphere would eventually become nearly devoid of gaseous oxygen.

The process of photosynthesis is commonly written as: 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 . This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products. The sugar is used by the organism, and the oxygen is released as a by-product.

The ability to photosynthesize is found in both eukaryotic and prokaryotic organisms. The most well-known examples are plants, as all but a very few parasitic or mycoheterotrophic species contain chlorophyll and produce their own food. Algae are the other dominant group of eukaryotic photosynthetic organisms. All algae, which include massive kelps and microscopic diatoms , are important primary producers.  Cyanobacteria and certain sulfur bacteria are photosynthetic prokaryotes, in whom photosynthesis evolved. No animals are thought to be independently capable of photosynthesis, though the emerald green sea slug can temporarily incorporate algae chloroplasts in its body for food production.

photosynthesis , the process by which green plants and certain other organisms transform light energy into chemical energy . During photosynthesis in green plants, light energy is captured and used to convert water , carbon dioxide , and minerals into oxygen and energy-rich organic compounds .

It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth . If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time Earth’s atmosphere would become nearly devoid of gaseous oxygen. The only organisms able to exist under such conditions would be the chemosynthetic bacteria , which can utilize the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy.

Energy produced by photosynthesis carried out by plants millions of years ago is responsible for the fossil fuels (i.e., coal , oil , and gas ) that power industrial society . In past ages, green plants and small organisms that fed on plants increased faster than they were consumed, and their remains were deposited in Earth’s crust by sedimentation and other geological processes. There, protected from oxidation , these organic remains were slowly converted to fossil fuels. These fuels not only provide much of the energy used in factories, homes, and transportation but also serve as the raw material for plastics and other synthetic products. Unfortunately, modern civilization is using up in a few centuries the excess of photosynthetic production accumulated over millions of years. Consequently, the carbon dioxide that has been removed from the air to make carbohydrates in photosynthesis over millions of years is being returned at an incredibly rapid rate. The carbon dioxide concentration in Earth’s atmosphere is rising the fastest it ever has in Earth’s history, and this phenomenon is expected to have major implications on Earth’s climate .

Requirements for food, materials, and energy in a world where human population is rapidly growing have created a need to increase both the amount of photosynthesis and the efficiency of converting photosynthetic output into products useful to people. One response to those needs—the so-called Green Revolution , begun in the mid-20th century—achieved enormous improvements in agricultural yield through the use of chemical fertilizers , pest and plant- disease control, plant breeding , and mechanized tilling, harvesting, and crop processing. This effort limited severe famines to a few areas of the world despite rapid population growth , but it did not eliminate widespread malnutrition . Moreover, beginning in the early 1990s, the rate at which yields of major crops increased began to decline. This was especially true for rice in Asia. Rising costs associated with sustaining high rates of agricultural production, which required ever-increasing inputs of fertilizers and pesticides and constant development of new plant varieties, also became problematic for farmers in many countries.

A second agricultural revolution , based on plant genetic engineering , was forecast to lead to increases in plant productivity and thereby partially alleviate malnutrition. Since the 1970s, molecular biologists have possessed the means to alter a plant’s genetic material (deoxyribonucleic acid, or DNA ) with the aim of achieving improvements in disease and drought resistance, product yield and quality, frost hardiness, and other desirable properties. However, such traits are inherently complex, and the process of making changes to crop plants through genetic engineering has turned out to be more complicated than anticipated. In the future such genetic engineering may result in improvements in the process of photosynthesis, but by the first decades of the 21st century, it had yet to demonstrate that it could dramatically increase crop yields.

Another intriguing area in the study of photosynthesis has been the discovery that certain animals are able to convert light energy into chemical energy. The emerald green sea slug ( Elysia chlorotica ), for example, acquires genes and chloroplasts from Vaucheria litorea , an alga it consumes, giving it a limited ability to produce chlorophyll . When enough chloroplasts are assimilated , the slug may forgo the ingestion of food. The pea aphid ( Acyrthosiphon pisum ) can harness light to manufacture the energy-rich compound adenosine triphosphate (ATP); this ability has been linked to the aphid’s manufacture of carotenoid pigments.

General characteristics

The study of photosynthesis began in 1771 with observations made by the English clergyman and scientist Joseph Priestley . Priestley had burned a candle in a closed container until the air within the container could no longer support combustion . He then placed a sprig of mint plant in the container and discovered that after several days the mint had produced some substance (later recognized as oxygen) that enabled the confined air to again support combustion. In 1779 the Dutch physician Jan Ingenhousz expanded upon Priestley’s work, showing that the plant had to be exposed to light if the combustible substance (i.e., oxygen) was to be restored. He also demonstrated that this process required the presence of the green tissues of the plant.

In 1782 it was demonstrated that the combustion-supporting gas (oxygen) was formed at the expense of another gas, or “fixed air,” which had been identified the year before as carbon dioxide. Gas-exchange experiments in 1804 showed that the gain in weight of a plant grown in a carefully weighed pot resulted from the uptake of carbon, which came entirely from absorbed carbon dioxide, and water taken up by plant roots; the balance is oxygen, released back to the atmosphere. Almost half a century passed before the concept of chemical energy had developed sufficiently to permit the discovery (in 1845) that light energy from the sun is stored as chemical energy in products formed during photosynthesis.

This equation is merely a summary statement, for the process of photosynthesis actually involves numerous reactions catalyzed by enzymes (organic catalysts ). These reactions occur in two stages: the “light” stage, consisting of photochemical (i.e., light-capturing) reactions; and the “dark” stage, comprising chemical reactions controlled by enzymes . During the first stage, the energy of light is absorbed and used to drive a series of electron transfers, resulting in the synthesis of ATP and the electron-donor-reduced nicotine adenine dinucleotide phosphate (NADPH). During the dark stage, the ATP and NADPH formed in the light-capturing reactions are used to reduce carbon dioxide to organic carbon compounds. This assimilation of inorganic carbon into organic compounds is called carbon fixation.

Van Niel’s proposal was important because the popular (but incorrect) theory had been that oxygen was removed from carbon dioxide (rather than hydrogen from water, releasing oxygen) and that carbon then combined with water to form carbohydrate (rather than the hydrogen from water combining with CO 2 to form CH 2 O).

By 1940 chemists were using heavy isotopes to follow the reactions of photosynthesis. Water marked with an isotope of oxygen ( 18 O) was used in early experiments. Plants that photosynthesized in the presence of water containing H 2 18 O produced oxygen gas containing 18 O; those that photosynthesized in the presence of normal water produced normal oxygen gas. These results provided definitive support for van Niel’s theory that the oxygen gas produced during photosynthesis is derived from water.

• Light Reaction

We are all aware that the process of photosynthesis requires sunlight . But did you know chloroplast only absorb the blue and red light wavelengths from the sunlight? That is correct. Let us learn about Light Reaction and how it functions.

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Photosynthesis

Photosynthesis is the process by which autotrophic plants make their own food . Co2, water, chlorophyll, and sunlight are four important requirements for this process. Photosynthesis occurs in two steps: Light reaction and Dark Reaction.

• Light Reaction – It is a light dependent reaction
• Dark Reaction – It is a light-independent reaction. Learn about Dark Reaction here in more detail .

Let’s us learn more about the light reaction of photosynthesis.

(Image Source: actforlibraries.com)

The light reaction of light dependent reaction occurs in the chloroplast of the mesophyll cells of the leaves. The chloroplasts are double-membraned cell organelles that are comprised of stacked disc-like structures known as thylakoids. The pigment, chlorophyll, which is required for the process is present on the membrane of these thylakoids and this is where the light reaction occurs.

Browse more Topics under Photosynthesis In Higher Plants

• Dark Reaction and Photorespiration
• Factors Affecting Photosynthesis
• Introduction To Photosynthesis

The Steps Involved in the Light Reaction

The main purpose of the light reaction is to generate organic energy molecules such as ATP and NADPH which are needed for the subsequent dark reaction.

• Chlorophyll absorbs the red and blue segment of the white light and photosynthesis occurs most efficiently at these wavelengths.
• When the light falls on the plant, the chlorophyll pigment absorbs this light and electrons in it gets excited.
• This process occurs in a complex protein system which is collectively called as a photosystem .  There are two closely linked photosystems known as PSI and PSII.
• The chlorophyll pigments which are excited give up their electrons and to compensate for the loss of electrons, water is split to release four H+ ions and four electrons and O2. The electrons that are lost from the PSII enter into an electron transfer chain or ETC.
• The electrons finally reach the reaction centre where they combine with NADP+ and reduce it to NADPH
• While the electrons are taken care of, the built up of H+ ions inside the thylakoid lumen is of equal importance.
• The hydrogen ions building up inside the lumen creates a positive gradient and in the presence of the enzyme ATP synthetase, these H+ ions combine with the ADP in the nearby region to form ATP.
• The oxygen that is a waste product is released by the plant into the atmosphere and some of it is used in photorespiration if the plant needs to.

To summarise the light reaction, we can write it down as the following reaction:

2H 2 O + 2NADP+ + 3ADP + 3Pi → O 2  + 2NADPH + 3ATP

For any plant performing photosynthesis, four factors influence this process. CO2, water, light, and chlorophyll are the raw materials for photosynthesis. But, in case of light dependent reaction or light reaction of photosynthesis, it is most influenced by presence or absence of light. The other three factors do not play a critical role in it.

Solved Example for You

Q: Which colour light are chlorophylls most sensitive to?

Sol: Blue and Red are the colour which chlorophylls are most sensitive to.  Leaves are green and so they reflect the green wavelength of white light. The chlorophyll pigment most efficiently absorbs those wavelengths which lie in the red and blue light regions of white light.

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• Introduction to Photosynthesis

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• Biology Article

Calvin Cycle

Photosynthesis is the biochemical process that occurs in all green plants or autotrophs producing organic molecules from carbon dioxide (CO2). These organic molecules contain many carbon-hydrogen (C–H ) bonds and are highly reduced compared to CO2.

There are two stages of Photosynthesis –

Light-dependent reactions – As the name suggests, it requires light and mainly occurs during the daytime.

Light-independent reactions – It is also called the dark reaction or Calvin cycle or C3 cycle. This reaction occurs both in the presence and absence of sunlight.

Table of Contents

• Explanation
• Carbon Fixation
• Regeneration

Let us have a detailed look at Calvin Cycle or C3 cycle along with its stages.

Calvin Cycle Definition

“Calvin cycle or C3 cycle is defined as a set of chemical reactions performed by the plants to reduce carbon dioxide and other compounds into glucose.”

What is Calvin Cycle?

Calvin cycle is also known as the C3 cycle or light-independent or dark reaction of photosynthesis. However, it is most active during the day when NADPH and ATP are abundant. To build organic molecules, the plant cells use raw materials provided by the light reactions:

1. Energy: ATP provided by cyclic and noncyclic photophosphorylation, which drives the endergonic reactions.

2. Reducing power: NADPH provided by photosystem I is the source of hydrogen and the energetic electrons required to bind them to carbon atoms. Much of the light energy captured during photosynthesis ends up in the energy-rich C—H bonds of sugars.

Plants store light energy in the form of carbohydrates, primarily starch and sucrose. The carbon and oxygen required for this process are obtained from CO2, and the energy for carbon fixation is derived from the ATP and NADPH produced during the photosynthesis process.

The conversion of CO2 to carbohydrate is called Calvin Cycle or C3 cycle and is named after Melvin Calvin who discovered it. The plants that undergo the Calvin cycle for carbon fixation are known as C3 plants.

Calvin Cycle requires the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase commonly called RuBisCO. It generates the triose phosphates, 3-phosphoglycerate (3-PGA), glyceraldehyde-3P (GAP), and dihydroxyacetone phosphate (DHAP), all of which are used to synthesize the hexose phosphates fructose-1,6-bisphosphate and fructose 6-phosphate.

Also read : Photosynthesis

C3 Cycle Diagram

The Calvin cycle diagram below shows the different stages of Calvin Cycle or C3 cycle that include carbon fixation, reduction, and regeneration.

Stages of C3 Cycle

Calvin cycle or C3 cycle can be divided into three main stages:

• Carbon fixation

The key step in the Calvin cycle is the event that reduces CO2.

CO2 binds to RuBP in the key process called carbon fixation, forming two-three carbon molecules of phosphoglycerate. The enzyme that carries out this reaction is ribulose bisphosphate carboxylase/oxygenase, which is very large with a four-subunit and present in the chloroplast stroma. This enzyme works very sluggishly, processing only about three molecules of RuBP per second (a typical enzyme process of about 1000 substrate molecules per second). In a typical leaf, over 50% of all the protein is RuBisCO. It is thought to be the most abundant protein on the earth.

It is the second stage of Calvin cycle. The 3-PGA molecules created through carbon fixation are converted into molecules of simple sugar – glucose.

This stage obtains energy from ATP and NADPH formed during the light-dependent reactions of photosynthesis. In this way, Calvin cycle becomes a pathway in which plants convert sunlight energy into long-term storage molecules, such as sugars. The energy from the ATP and NADPH is transferred to the sugars.

This step is known as reduction since electrons are transferred to 3-PGA molecules to form glyceraldehyde-3 phosphate.

It is the third stage of the Calvin cycle and is a complex process that requires ATP. In this stage, some of the G3P molecules are used to produce glucose, while others are recycled to regenerate the RuBP acceptor.

Also read: Light reaction And Dark reaction

Products of C3 Cycle

• One molecule of carbon is fixed at each turn of the Calvin cycle.
• One molecule of glyceraldehyde-3 phosphate is created in three turns of the Calvin cycle.
• Two molecules of glyceraldehyde-3 phosphate combine together to form one glucose molecule.
• 3 ATP and 2 NADPH molecules are used during the reduction of 3-phosphoglyceric acid to glyceraldehyde-3 phosphate and in the regeneration of RuBP.
• 18 ATP and 12 NADPH are consumed in the production of 1 glucose molecule.

Key Points on C3 Cycle

• C3 cycle refers to the dark reaction of photosynthesis.
• It is indirectly dependent on light and the essential energy carriers are products of light-dependent reactions.
• In the first stage of the Calvin cycle, the light-independent reactions are initiated and carbon dioxide is fixed.
• In the second stage of the C3 cycle, ATP and NADPH reduce 3PGA to G3P. ATP and NADPH are then converted into ATP and NADP+.
• In the last stage, RuBP is regenerated. This helps in more carbon dioxide fixation.

Also Read: C3 and C4 Pathways

Discover more about Calvin cycle or C3 cycle, its stages, and other topics only @ BYJU’S Biology

Frequently Asked Questions

Calvin cycle is also known as the C3 cycle. It is the cycle of chemical reactions where the carbon from the carbon cycle is fixed into sugars. It occurs in the chloroplast of the plant cell.

What are the different steps involved in the Calvin cycle?

The different steps involved in the Calvin cycle include:

What are the end products of C3 cycle?

ADP, NADP, and glucose are the end products of the C3 cycle. ADP and NADP are produced in the first stage of C3 cycle. In the second stage, glucose is produced.

What is carbon fixation in the Calvin cycle?

In the carbon fixation of the Calvin cycle, the carbon dioxide is fixed to stable organic intermediates.

Why is the third step of the Calvin cycle called the regeneration step?

The third step is known as regeneration because Ribulose-bis phosphate that begins the cycle is regenerated from G3P.

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Module 6: Metabolic Pathways

Photosynthesis, identify the basic components and steps of photosynthesis.

The processes in all organisms—from bacteria to humans—require energy. To get this energy, many organisms access stored energy by eating, that is, by ingesting other organisms. But where does the stored energy in food originate? All of this energy can be traced back to photosynthesis.

Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. In brief, the energy of sunlight is captured and used to energize electrons, which are then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis around 300 million years ago.

Figure 1. Photoautotrophs including (a) plants, (b) algae, and (c) cyanobacteria synthesize their organic compounds via photosynthesis using sunlight as an energy source. Cyanobacteria and planktonic algae can grow over enormous areas in water, at times completely covering the surface. In a (d) deep sea vent, chemoautotrophs, such as these (e) thermophilic bacteria, capture energy from inorganic compounds to produce organic compounds. The ecosystem surrounding the vents has a diverse array of animals, such as tubeworms, crustaceans, and octopi that derive energy from the bacteria. (credit a: modification of work by Steve Hillebrand, U.S. Fish and Wildlife Service; credit b: modification of work by “eutrophication&hypoxia”/Flickr; credit c: modification of work by NASA; credit d: University of Washington, NOAA; credit e: modification of work by Mark Amend, West Coast and Polar Regions Undersea Research Center, UAF, NOAA)

Figure 2. The energy stored in carbohydrate molecules from photosynthesis passes through the food chain. The predator that eats these deer receives a portion of the energy that originated in the photosynthetic vegetation that the deer consumed. (credit: modification of work by Steve VanRiper, U.S. Fish and Wildlife Service)

Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis (Figure 1). Because they use light to manufacture their own food, they are called photoautotrophs (literally, “self-feeders using light”). Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”), because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds; hence, they are referred to as chemoautotrophs .

The importance of photosynthesis is not just that it can capture sunlight’s energy. A lizard sunning itself on a cold day can use the sun’s energy to warm up. Photosynthesis is vital because it evolved as a way to store the energy in solar radiation (the “photo” part) as high-energy electrons in the carbon-carbon bonds of carbohydrate molecules (the “synthesis” part). Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. When a top predator, such as a wolf, preys on a deer (Figure 2), the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to light, to photosynthesis, to vegetation, to deer, and finally to wolf.

Learning Objectives

• Identify the reactants and products of photosynthesis
• Describe the visible and electromagnetic spectrums of light as they applies to photosynthesis
• Describe the light-dependent reactions that take place during photosynthesis
• Identify the light-independent reactions in photosynthesis

Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates (Figure 3). After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.

Figure 3. Photosynthesis uses solar energy, carbon dioxide, and water to produce energy-storing carbohydrates. Oxygen is generated as a waste product of photosynthesis.

The following is the chemical equation for photosynthesis (Figure 4):

Figure 4. The basic equation for photosynthesis is deceptively simple. In reality, the process takes place in many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3Ps.

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved.

In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the  mesophyll . The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimize water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes.

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a  chloroplast . For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane). Within the chloroplast are stacked, disc-shaped structures called thylakoids . Embedded in the thylakoid membrane is chlorophyll, a pigment (molecule that absorbs light) responsible for the initial interaction between light and plant material, and numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen . As shown in Figure 5, a stack of thylakoids is called a granum , and the liquid-filled space surrounding the granum is called stroma or “bed” (not to be confused with stoma or “mouth,” an opening on the leaf epidermis).

Practice Question

Figure 5. Photosynthesis takes place in chloroplasts, which have an outer membrane and an inner membrane. Stacks of thylakoids called grana form a third membrane layer.

On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

The Two Parts of Photosynthesis

Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light independent-reactions. In the  light-dependent reactions , energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. In the light-independent reactions , the chemical energy harvested during the light-dependent reactions drive the assembly of sugar molecules from carbon dioxide. Therefore, although the light-independent reactions do not use light as a reactant, they require the products of the light-dependent reactions to function. In addition, several enzymes of the light-independent reactions are activated by light. The light-dependent reactions utilize certain molecules to temporarily store the energy: These are referred to as energy carriers. The energy carriers that move energy from light-dependent reactions to light-independent reactions can be thought of as “full” because they are rich in energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. Figure 6 illustrates the components inside the chloroplast where the light-dependent and light-independent reactions take place.

Figure 6. Photosynthesis takes place in two stages: light dependent reactions and the Calvin cycle. Light-dependent reactions, which take place in the thylakoid membrane, use light energy to make ATP and NADPH. The Calvin cycle, which takes place in the stroma, uses energy derived from these compounds to make GA3P from CO 2 .

Photosynthesis at the Grocery Store

Figure 7. Foods that humans consume originate from photosynthesis. (credit: Associação Brasileira de Supermercados)

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle (Figure 7) contains hundreds, if not thousands, of different products for customers to buy and consume.

Although there is a large variety, each item links back to photosynthesis. Meats and dairy link because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from starchy grains, which are the seeds of photosynthesis-dependent plants. What about desserts and drinks? All of these products contain sugar—sucrose is a plant product, a disaccharide, a carbohydrate molecule, which is built directly from photosynthesis. Moreover, many items are less obviously derived from plants: for instance, paper goods are generally plant products, and many plastics (abundant as products and packaging) can be derived from algae or from oil, the fossilized remains of photosynthetic organisms. Virtually every spice and flavoring in the spice aisle was produced by a plant as a leaf, root, bark, flower, fruit, or stem. Ultimately, photosynthesis connects to every meal and every food a person consumes.

Spectrums of Light

How can light be used to make food? When a person turns on a lamp, electrical energy becomes light energy. Like all other forms of kinetic energy, light can travel, change form, and be harnessed to do work. In the case of photosynthesis, light energy is converted into chemical energy, which photoautotrophs use to build carbohydrate molecules. However, autotrophs only use a few specific components of sunlight.

What Is Light Energy?

The sun emits an enormous amount of electromagnetic radiation (solar energy). Humans can see only a fraction of this energy, which portion is therefore referred to as “visible light.” The manner in which solar energy travels is described as waves. Scientists can determine the amount of energy of a wave by measuring its wavelength, the distance between consecutive points of a wave. A single wave is measured from two consecutive points, such as from crest to crest or from trough to trough (Figure 8).

Figure 8. The wavelength of a single wave is the distance between two consecutive points of similar position (two crests or two troughs) along the wave.

Visible light constitutes only one of many types of electromagnetic radiation emitted from the sun and other stars. Scientists differentiate the various types of radiant energy from the sun within the electromagnetic spectrum. The electromagnetic spectrum is the range of all possible frequencies of radiation (Figure 9). The difference between wavelengths relates to the amount of energy carried by them.

Figure 9. The sun emits energy in the form of electromagnetic radiation. This radiation exists at different wavelengths, each of which has its own characteristic energy. All electromagnetic radiation, including visible light, is characterized by its wavelength.

Each type of electromagnetic radiation travels at a particular wavelength. The longer the wavelength (or the more stretched out it appears in the diagram), the less energy is carried. Short, tight waves carry the most energy. This may seem illogical, but think of it in terms of a piece of moving a heavy rope. It takes little effort by a person to move a rope in long, wide waves. To make a rope move in short, tight waves, a person would need to apply significantly more energy.

The electromagnetic spectrum (Figure 9) shows several types of electromagnetic radiation originating from the sun, including X-rays and ultraviolet (UV) rays. The higher-energy waves can penetrate tissues and damage cells and DNA, explaining why both X-rays and UV rays can be harmful to living organisms.

Absorption of Light

Light energy initiates the process of photosynthesis when pigments absorb the light. Organic pigments, whether in the human retina or the chloroplast thylakoid, have a narrow range of energy levels that they can absorb. Energy levels lower than those represented by red light are insufficient to raise an orbital electron to a populatable, excited (quantum) state. Energy levels higher than those in blue light will physically tear the molecules apart, called bleaching. So retinal pigments can only “see” (absorb) 700 nm to 400 nm light, which is therefore called visible light. For the same reasons, plants pigment molecules absorb only light in the wavelength range of 700 nm to 400 nm; plant physiologists refer to this range for plants as photosynthetically active radiation.

The visible light seen by humans as white light actually exists in a rainbow of colors. Certain objects, such as a prism or a drop of water, disperse white light to reveal the colors to the human eye. The visible light portion of the electromagnetic spectrum shows the rainbow of colors, with violet and blue having shorter wavelengths, and therefore higher energy. At the other end of the spectrum toward red, the wavelengths are longer and have lower energy (Figure 10).

Figure 10. The colors of visible light do not carry the same amount of energy. Violet has the shortest wavelength and therefore carries the most energy, whereas red has the longest wavelength and carries the least amount of energy. (credit: modification of work by NASA)

Understanding Pigments

Different kinds of pigments exist, and each has evolved to absorb only certain wavelengths (colors) of visible light. Pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color.

Chlorophylls and carotenoids are the two major classes of photosynthetic pigments found in plants and algae; each class has multiple types of pigment molecules. There are five major chlorophylls:  a , b , c and d and a related molecule found in prokaryotes called bacteriochlorophyll. Chlorophyll a and chlorophyll b are found in higher plant chloroplasts and will be the focus of the following discussion.

With dozens of different forms, carotenoids are a much larger group of pigments. The carotenoids found in fruit—such as the red of tomato (lycopene), the yellow of corn seeds (zeaxanthin), or the orange of an orange peel (β-carotene)—are used as advertisements to attract seed dispersers. In photosynthesis, carotenoids function as photosynthetic pigments that are very efficient molecules for the disposal of excess energy. When a leaf is exposed to full sun, the light-dependent reactions are required to process an enormous amount of energy; if that energy is not handled properly, it can do significant damage. Therefore, many carotenoids reside in the thylakoid membrane, absorb excess energy, and safely dissipate that energy as heat.

Each type of pigment can be identified by the specific pattern of wavelengths it absorbs from visible light, which is the  absorption spectrum . The graph in Figure 11 shows the absorption spectra for chlorophyll  a , chlorophyll b , and a type of carotenoid pigment called β-carotene (which absorbs blue and green light). Notice how each pigment has a distinct set of peaks and troughs, revealing a highly specific pattern of absorption. Chlorophyll a absorbs wavelengths from either end of the visible spectrum (blue and red), but not green. Because green is reflected or transmitted, chlorophyll appears green. Carotenoids absorb in the short-wavelength blue region, and reflect the longer yellow, red, and orange wavelengths.

Figure 11. (a) Chlorophyll a, (b) chlorophyll b, and (c) β-carotene are hydrophobic organic pigments found in the thylakoid membrane. Chlorophyll a and b, which are identical except for the part indicated in the red box, are responsible for the green color of leaves. β-carotene is responsible for the orange color in carrots. Each pigment has (d) a unique absorbance spectrum.

Figure 12. Plants that commonly grow in the shade have adapted to low levels of light by changing the relative concentrations of their chlorophyll pigments. (credit: Jason Hollinger)

Many photosynthetic organisms have a mixture of pigments; using them, the organism can absorb energy from a wider range of wavelengths. Not all photosynthetic organisms have full access to sunlight. Some organisms grow underwater where light intensity and quality decrease and change with depth. Other organisms grow in competition for light. Plants on the rainforest floor must be able to absorb any bit of light that comes through, because the taller trees absorb most of the sunlight and scatter the remaining solar radiation (Figure 12).

When studying a photosynthetic organism, scientists can determine the types of pigments present by generating absorption spectra. An instrument called a  spectrophotometer can differentiate which wavelengths of light a substance can absorb. Spectrophotometers measure transmitted light and compute from it the absorption. By extracting pigments from leaves and placing these samples into a spectrophotometer, scientists can identify which wavelengths of light an organism can absorb. Additional methods for the identification of plant pigments include various types of chromatography that separate the pigments by their relative affinities to solid and mobile phases.

Light-Dependent Reactions

The overall function of light-dependent reactions is to convert solar energy into chemical energy in the form of NADPH and ATP. This chemical energy supports the light-independent reactions and fuels the assembly of sugar molecules. The light-dependent reactions are depicted in Figure 13. Protein complexes and pigment molecules work together to produce NADPH and ATP.

Figure 13. A photosystem consists of a light-harvesting complex and a reaction center. Pigments in the light-harvesting complex pass light energy to two special chlorophyll a molecules in the reaction center. The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor. The excited electron must then be replaced. In (a) photosystem II, the electron comes from the splitting of water, which releases oxygen as a waste product. In (b) photosystem I, the electron comes from the chloroplast electron transport chain discussed below.

The actual step that converts light energy into chemical energy takes place in a multiprotein complex called a  photosystem , two types of which are found embedded in the thylakoid membrane, photosystem II (PSII) and photosystem I (PSI) (Figure 14). The two complexes differ on the basis of what they oxidize (that is, the source of the low-energy electron supply) and what they reduce (the place to which they deliver their energized electrons).

Both photosystems have the same basic structure; a number of antenna proteins to which the chlorophyll molecules are bound surround the reaction center where the photochemistry takes place. Each photosystem is serviced by the light-harvesting complex, which passes energy from sunlight to the reaction center; it consists of multiple antenna proteins that contain a mixture of 300–400 chlorophyll  a and b molecules as well as other pigments like carotenoids. The absorption of a single photon or distinct quantity or “packet” of light by any of the chlorophylls pushes that molecule into an excited state. In short, the light energy has now been captured by biological molecules but is not stored in any useful form yet. The energy is transferred from chlorophyll to chlorophyll until eventually (after about a millionth of a second), it is delivered to the reaction center. Up to this point, only energy has been transferred between molecules, not electrons.

Figure 14. The photosystem II (PSII) reaction center and the photosystem I (PSI).

In the photosystem II (PSII) reaction center, energy from sunlight is used to extract electrons from water. The electrons travel through the chloroplast electron transport chain to photosystem I (PSI), which reduces NADP + to NADPH. The electron transport chain moves protons across the thylakoid membrane into the lumen. At the same time, splitting of water adds protons to the lumen, and reduction of NADPH removes protons from the stroma. The net result is a low pH in the thylakoid lumen, and a high pH in the stroma. ATP synthase uses this electrochemical gradient to make ATP. What is the initial source of electrons for the chloroplast electron transport chain?

• carbon dioxide

The reaction center contains a pair of chlorophyll  a molecules with a special property. Those two chlorophylls can undergo oxidation upon excitation; they can actually give up an electron in a process called a photoact . It is at this step in the reaction center, that light energy is converted into an excited electron. All of the subsequent steps involve getting that electron onto the energy carrier NADPH for delivery to the Calvin cycle where the electron is deposited onto carbon for long-term storage in the form of a carbohydrate. PSII and PSI are two major components of the photosynthetic electron transport chain , which also includes the cytochrome complex . The cytochrome complex, an enzyme composed of two protein complexes, transfers the electrons from the carrier molecule plastoquinone (Pq) to the protein plastocyanin (Pc), thus enabling both the transfer of protons across the thylakoid membrane and the transfer of electrons from PSII to PSI.

The reaction center of PSII (called  P680 ) delivers its high-energy electrons, one at the time, to the primary electron acceptor , and through the electron transport chain (Pq to cytochrome complex to plastocyanine) to PSI. P680’s missing electron is replaced by extracting a low-energy electron from water; thus, water is split and PSII is re-reduced after every photoact. Splitting one H 2 O molecule releases two electrons, two hydrogen atoms, and one atom of oxygen. Splitting two molecules is required to form one molecule of diatomic O 2 gas. About 10 percent of the oxygen is used by mitochondria in the leaf to support oxidative phosphorylation. The remainder escapes to the atmosphere where it is used by aerobic organisms to support respiration.

As electrons move through the proteins that reside between PSII and PSI, they lose energy. That energy is used to move hydrogen atoms from the stromal side of the membrane to the thylakoid lumen. Those hydrogen atoms, plus the ones produced by splitting water, accumulate in the thylakoid lumen and will be used synthesize ATP in a later step. Because the electrons have lost energy prior to their arrival at PSI, they must be re-energized by PSI, hence, another photon is absorbed by the PSI antenna. That energy is relayed to the PSI reaction center (called  P700 ). P700 is oxidized and sends a high-energy electron to NADP + to form NADPH. Thus, PSII captures the energy to create proton gradients to make ATP, and PSI captures the energy to reduce NADP + into NADPH. The two photosystems work in concert, in part, to guarantee that the production of NADPH will roughly equal the production of ATP. Other mechanisms exist to fine tune that ratio to exactly match the chloroplast’s constantly changing energy needs.

Generating an Energy Carrier: ATP

As in the intermembrane space of the mitochondria during cellular respiration, the buildup of hydrogen ions inside the thylakoid lumen creates a concentration gradient. The passive diffusion of hydrogen ions from high concentration (in the thylakoid lumen) to low concentration (in the stroma) is harnessed to create ATP, just as in the electron transport chain of cellular respiration. The ions build up energy because of diffusion and because they all have the same electrical charge, repelling each other.

To release this energy, hydrogen ions will rush through any opening, similar to water jetting through a hole in a dam. In the thylakoid, that opening is a passage through a specialized protein channel called the ATP synthase. The energy released by the hydrogen ion stream allows ATP synthase to attach a third phosphate group to ADP, which forms a molecule of ATP (Figure 14). The flow of hydrogen ions through ATP synthase is called chemiosmosis because the ions move from an area of high to an area of low concentration through a semi-permeable structure.

Light-Independent Reactions

After the energy from the sun is converted into chemical energy and temporarily stored in ATP and NADPH molecules, the cell has the fuel needed to build carbohydrate molecules for long-term energy storage. The products of the light-dependent reactions, ATP and NADPH, have lifespans in the range of millionths of seconds, whereas the products of the light-independent reactions (carbohydrates and other forms of reduced carbon) can survive for hundreds of millions of years. The carbohydrate molecules made will have a backbone of carbon atoms. Where does the carbon come from? It comes from carbon dioxide, the gas that is a waste product of respiration in microbes, fungi, plants, and animals.

In plants, carbon dioxide (CO 2 ) enters the leaves through stomata, where it diffuses over short distances through intercellular spaces until it reaches the mesophyll cells. Once in the mesophyll cells, CO 2 diffuses into the stroma of the chloroplast—the site of light-independent reactions of photosynthesis. These reactions actually have several names associated with them. Another term, the Calvin cycle , is named for the man who discovered it, and because these reactions function as a cycle. Others call it the Calvin-Benson cycle to include the name of another scientist involved in its discovery. The most outdated name is dark reactions, because light is not directly required (Figure 15). However, the term dark reaction can be misleading because it implies incorrectly that the reaction only occurs at night or is independent of light, which is why most scientists and instructors no longer use it.

Figure 15. Light reactions harness energy from the sun to produce chemical bonds, ATP, and NADPH. These energy-carrying molecules are made in the stroma where carbon fixation takes place.

The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration.

Stage 1: Fixation

In the stroma, in addition to CO 2 , two other components are present to initiate the light-independent reactions: an enzyme called ribulose bisphosphate carboxylase (RuBisCO), and three molecules of ribulose bisphosphate (RuBP), as shown in Figure 16. RuBP has five atoms of carbon, flanked by two phosphates.

Figure 16. The Calvin cycle has three stages.

In stage 1, the enzyme RuBisCO incorporates carbon dioxide into an organic molecule, 3-PGA. In stage 2, the organic molecule is reduced using electrons supplied by NADPH. In stage 3, RuBP, the molecule that starts the cycle, is regenerated so that the cycle can continue. Only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule.

Which of the following statements is true?

• In photosynthesis, oxygen, carbon dioxide, ATP, and NADPH are reactants. GA3P and water are products.
• In photosynthesis, chlorophyll, water, and carbon dioxide are reactants. GA3P and oxygen are products.
• In photosynthesis, water, carbon dioxide, ATP, and NADPH are reactants. RuBP and oxygen are products.
• In photosynthesis, water and carbon dioxide are reactants. GA3P and oxygen are products.

RuBisCO catalyzes a reaction between CO 2 and RuBP. For each CO 2 molecule that reacts with one RuBP, two molecules of another compound (3-PGA) form. PGA has three carbons and one phosphate. Each turn of the cycle involves only one RuBP and one carbon dioxide and forms two molecules of 3-PGA. The number of carbon atoms remains the same, as the atoms move to form new bonds during the reactions (3 atoms from 3CO 2 + 15 atoms from 3RuBP = 18 atoms in 3 atoms of 3-PGA). This process is called  carbon fixation , because CO 2 is “fixed” from an inorganic form into organic molecules.

Stage 2: Reduction

ATP and NADPH are used to convert the six molecules of 3-PGA into six molecules of a chemical called glyceraldehyde 3-phosphate (G3P). That is a reduction reaction because it involves the gain of electrons by 3-PGA. Recall that a  reduction is the gain of an electron by an atom or molecule. Six molecules of both ATP and NADPH are used. For ATP, energy is released with the loss of the terminal phosphate atom, converting it into ADP; for NADPH, both energy and a hydrogen atom are lost, converting it into NADP + . Both of these molecules return to the nearby light-dependent reactions to be reused and reenergized.

Stage 3: Regeneration

Interestingly, at this point, only one of the G3P molecules leaves the Calvin cycle and is sent to the cytoplasm to contribute to the formation of other compounds needed by the plant. Because the G3P exported from the chloroplast has three carbon atoms, it takes three “turns” of the Calvin cycle to fix enough net carbon to export one G3P. But each turn makes two G3Ps, thus three turns make six G3Ps. One is exported while the remaining five G3P molecules remain in the cycle and are used to regenerate RuBP, which enables the system to prepare for more CO 2 to be fixed. Three more molecules of ATP are used in these regeneration reactions.

Evolution of Photosynthesis

Figure 17. The harsh conditions of the desert have led plants like these cacti to evolve variations of the light-independent reactions of photosynthesis. These variations increase the efficiency of water usage, helping to conserve water and energy. (credit: Piotr Wojtkowski)

During the evolution of photosynthesis, a major shift occurred from the bacterial type of photosynthesis that involves only one photosystem and is typically anoxygenic (does not generate oxygen) into modern oxygenic (does generate oxygen) photosynthesis, employing two photosystems. This modern oxygenic photosynthesis is used by many organisms—from giant tropical leaves in the rainforest to tiny cyanobacterial cells—and the process and components of this photosynthesis remain largely the same. Photosystems absorb light and use electron transport chains to convert energy into the chemical energy of ATP and NADH. The subsequent light-independent reactions then assemble carbohydrate molecules with this energy.

Photosynthesis in desert plants has evolved adaptations that conserve water. In the harsh dry heat, every drop of water must be used to survive. Because stomata must open to allow for the uptake of CO 2 , water escapes from the leaf during active photosynthesis. Desert plants have evolved processes to conserve water and deal with harsh conditions. A more efficient use of CO 2 allows plants to adapt to living with less water. Some plants such as cacti (Figure 17) can prepare materials for photosynthesis during the night by a temporary carbon fixation/storage process, because opening the stomata at this time conserves water due to cooler temperatures. In addition, cacti have evolved the ability to carry out low levels of photosynthesis without opening stomata at all, a mechanism to face extremely dry periods.

Now that we’ve learned about the different pieces of photosynthesis, let’s put it all together. This video walks you through the process of photosynthesis as a whole:

In Summary: An Overview of Photosynthesis

The process of photosynthesis transformed life on Earth. By harnessing energy from the sun, photosynthesis evolved to allow living things access to enormous amounts of energy. Because of photosynthesis, living things gained access to sufficient energy that allowed them to build new structures and achieve the biodiversity evident today.

Only certain organisms, called photoautotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that absorbs certain portions of the visible spectrum and can capture energy from sunlight. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules and release oxygen as a waste product into the atmosphere. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place, and starch accumulates. In prokaryotes, such as cyanobacteria, the process is less localized and occurs within folded membranes, extensions of the plasma membrane, and in the cytoplasm.

The pigments of the first part of photosynthesis, the light-dependent reactions, absorb energy from sunlight. A photon strikes the antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll  a to the electron transport chain, which pumps hydrogen ions into the thylakoid interior. This action builds up a high concentration of ions. The ions flow through ATP synthase via chemiosmosis to form molecules of ATP, which are used for the formation of sugar molecules in the second stage of photosynthesis. Photosystem I absorbs a second photon, which results in the formation of an NADPH molecule, another energy and reducing power carrier for the light-independent reactions.

Check Your Understanding

Answer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does  not  count toward your grade in the class, and you can retake it an unlimited number of times.

Use this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.

• Authored by : Shelli Carter and Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution
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• Photosynthesis: Crash Course Biology #8. Authored by : CrashCourse. Located at : https://youtu.be/sQK3Yr4Sc_k . License : All Rights Reserved . License Terms : Standard YouTube License