NIOS Class 12 Biology Chapter 11 Photosynthesis

NIOS Class 12 Biology Chapter 11 Photosynthesis Solutions to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Biology Chapter 11 Photosynthesis Notes and select need one. NIOS Class 12 Biology Chapter 11 Photosynthesis Question Answers Download PDF. NIOS Study Material of Class 12 Biology Notes Paper 314.

NIOS Class 12 Biology Chapter 11 Photosynthesis

Join Telegram channel

Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 12 Biology Chapter 11 Photosynthesis Solutions, NIOS Senior Secondary Course Biology Solutions for All Chapter, You can practice these here.


Chapter: 11




1. (i) Define photosynthesis.

Ans: The process by which green plants prepare their own food (carbohydrates) from simple substances such as CO₂ and water (H₂O) in presence of sunlight and chlorophyll is termed as photosynthesis.

(ii) Give the overall general chemical equation of photosynthesis.


2. (i) List the two categories of photosynthetic pigments.

Ans: Chlorophyll and carotenoids.

(ii) Which pigments are known as accessory pigments?

Ans: Carotenoids and chlorophyll ‘b’.

3. (i) What does chlorophyll do to the light falling on it?

Ans: Chlorophyll absorbs light and convert it into electrical and chemical energy.

(ii) Which pigment system absorbs the red wavelength of light?

Ans: Chlorophyll ‘a’ and Chlorophyll ‘b’.

4. Answer the following:

(i) In which colour of light, rate of photo- synthesis is minimum and in which colour of light it is maximum?

Ans: Minimum in green light and yellow light; but maximum in blue and red light.

(ii) Name the type of energy that is used in the process of photosynthesis. In which form does this energy get stored in plant body?

Ans: Light energy and chemical energy.

5. Which molecule is the source of evolution of oxygen in photosynthesis: CO₂ or H₂O?

Ans. From the photolysis of (H₂O) in PS II.


1. What is the role of NADP?

Ans: NADP. It acts as electron acceptor andis then reduced to NADPH2.

2. Why is dark reaction called so?

Ans: It is called reaction since it is independent of light.

3. What is the role of the enzymes:

(i) rubisco.

Ans: Rubisco. It is a part of C₃ cycle. It combines with CO₂ to produce a C₃ compound named PGA (phosphoglyceric acid).

(ii) PEPCO and where are they present?

Ans: PEPCo. It is a part of C₄ pathway. It combines with CO₂ to form a C₄ compound known as OAA (oxaloacetic acid).

The Rubisco is found in mesophyll cells of C₃ plants. Rubisco is found in the bundle sheath cells of C₄ plants. PEPCO only occurs in mesophyll cells of C₄ .

4. Explain Kranz anatomy.

Ans: Kranz Anatomy: In it, the vein in the leaf is enclosed by bundle sheath having many chloroplasts, having bulliform cells in upper epidermis called Kranz anatomy. Several chloroplasts occur in mesophyll cells as well as bundle sheath cells.

5. Differentiate between the chloro-plasts present in the mesophyll cells and in the bundle sheath cells of the leaf of a C₄ plant.

Ans: Difference between chloroplasts found in bundle sheath cells and mesophyll cells of leaf of a C₄ plant.

Chloroplasts in bundle sheath cells in leaf of a C₄ plantChloroplasts in mesophyll cells of a leaf in a C₄ plant
1. The chloroplasts are agranal that is they do not have grana.The chloroplasts are granal, i.e. have thyla-koids.
2. Grana absent in the thylakoids. The chlo-roplasts are longer.The chloroplasts are smaller but have well developed grana.

6. Why are C₄ plants more efficient than C₃ plant?

Ans: Because there is no photorespiration in C₄ plants and hence there is no loss of carbon dioxide (CO₂).

7. Name the two sets of reactions in photosynthesis in which light energy is required.

Ans: It is called “photolysis of water.”


1. List the internal factors that influence the role of photosynthesis?

Ans: Chlorophyll content, leaf age, leaf anatomy like size, the internal structure as well as distribution of stomata, etc.

2. State the principle of limiting factor.

Ans. The law of limiting factors is called law of minimum as shown by Blackmann (1905) and is defined “as when a process is conditioned as to its rapidity by a number of separate factors, rate of process is limited by pace of slowest factor”

3. Give an example of chemosynthetic bacteria.

Ans: Nitrosomonas is a chemosynthetic bacterium.

4. Why are prokaryotes not able to produce ATP by chemiosmosis?

Ans: Since prokaryotes are not able to maintain H+ gradient across a membrane in absence of membrane bound organelles in their cytoplasm.


1. Describe briefly the process of photosynthesis.

Ans: Photosynthesis: It is the “synthesis of food by green plants in presence of sunlight.” These plants are capable of synthesising carbo-hydrates from CO₂ and H₂O in the sunlight.

It occur in two steps:

(A) Light reaction.

(B) Dark reaction.

(A) Light Reaction: It occurs in grana of chloroplast in the presence of light. Essential steps are excitation of chlorophyll, photolysis of water molecule, photophosphorylation and reduction of NADP to NADPH2.

H₂O → H⁺ + OH⁻

2OH → H₂O + O + e⁻

ADP + Pi → ATP


(B) Dark Reaction: It occurs in stroma in absence of light. It has three parts-carboxylation, glycolytic reversal and regeneration of RuBP. 6 mols of CO₂ react with RuBP to form short lived six carbon intermediate in presence of RuBP enzyme. Unstable compound breaks into 12 mols of 3 phosphoglyceric acid. Six mols of PGA form 6 mols of phosphoglyceraldehyde. ATP and NADPH2 are used in this process. Six mols of these are used in formation of carbohydrates and rest are used in the regeneration of RuBP to run the cycle again.

2. Write short notes on:

(i) Ultrastructure of chloroplast.

Ans: Ultrastructure of chloroplast: Chloroplasts are cell organelles found in cell cytoplasm. They have double membrane. They perform photosynthesis in plants. Thylakoids lie in the matrix of chloroplast. They may be oval or elliptical. They have DNA also.

Fig. 11.8. Ultra structure of chloroplast.

(ii) Pigments involved in photosynthesis.

Ans: Pigments Involved in Photosyn-thesis: They are chlorophyll, phytochrome and carotenoids. They absorb light. Carote-noids and phycobilins are accessory pigments. They convert sun’s energy into the chemical energy. They are found in the chloroplasts. Chlorophyll ‘α’ is the main pigment that traps solar energy. It is known as reaction centre.

3. What are accessory pigments? Why they are called so?

Ans: Carotenoids and chlorophyll ‘b’ are known as accessory pigments because they absorb light in the range of wavelength not absorbed by chlorophyll and then transfer it to chlorophyll. They pass on absorbed energy to chlorophyll ‘α’ molecule. These pigments called reaction centres and accessory pigments are called harvesting centres. Both are packed into the functional clusters known as photosystems.

4. Mention path of electrons in the light reaction of photosynthesis.

Ans: Path of Electron in Light Reaction of Photosynthesis: It occurs through cyclic and non-cyclic photophosphorylation.

In the light reaction, the chlorophyll molecules absorbs a photon of light resulting in its excitation. This excited chlorophyll has an electron at the energy state.

The non-cyclic photophosphorylation: It is a biochemical process in which the elec-tron emitted by P860 is accepted by by P₇₀₀. The oxidised P₆₈₀ regains its electron by photolysis of water 2H⁺, 2e and oxygen. The proteins (H⁺) accumulate inside the thylakoid membrane into the stroma along the H⁺ concentration gradient is used to produce ATP. This is similar to the production of ATP by F₀ – F₁ articles in micro-chondria. The electron emitted from the P₇₀₀ ultimately is passed in NADP along with the protons glucerated by splitting of H₂O as a result of which NADPH is formed. It is called non-cyclic photophos-phorylation. It needs constant supply of water molecule to be oxidised and NADP to be reduced.

In cyclic photophosphorylation only PSI is functional. The photolysis of water and libera-tion of O₂ do not take place. Only APT is synthe sized. This system PS I is functional only in the bacteria.

5. What do you understand by photophosphorylation.

Ans: Photophosphorylation: Formation of ATP from ADP and Pi in the presence of light is known as the photophosphorylation.

It may be cyclic or non-cyclic.

6. Discuss photolysis of water and its significance.

Ans: Photolysis of Water: It is the break. ing down of water molecules.

Significance of Photolysis of Water:

(i) It is the use of water as a source of elect-ronic for CO₂ fixation.

(ii) It is used for release of O₂ as by-product of photosynthesis.

7. Describe the reactions occurring during dark reaction of photosynthesis.

Ans: Dark Reactions: They occur in three


(a) Carboxylation.

(b) Glycolytic rever-sal.

(c) Regeneration of RuBP.

(a) Carboxylation: During this phase, three molecules of RuBP joins with three mole-cules of CO2 and form 6-C unstable compound in the presence of enzyme RuBP Carboxylase. This six carbon unstable compound at once breaks into six molecules of 3-phosphoglyceric acid (PGA), a three carbon compound.

(b) Reduction: The six molecules of ATP and NADPH, obtained from light reac-tions convert the 6 molecules of glyceraldehyde phosphate through the intermediate 1, 3-dis-phosphoglyceric acid.

(c) Regeneration of RuBP: The five mole-cules of glyceraldehyde phosphate and three molecules of ATP result in the regeneration of RuBP to maintain the continuity of Calvin cycle. The one molecule of glyceraldehyde phosphate forms the glucose and other sugar.

8. Differentiate between C₃ and C₄ plants.

Ans: Difference Between C₃ and C₄ Plants:

C₃ PlantsC₄ Plants
1. They do not have Kranz anatomy.They have specified ana- tomical features of leaf called Kranz anatomy.
2. RuBP in initial acce- ptor of CO₂.PEP is the initial accep-tor of CO₂.
3. PGA is first stable product of carboxy- lation.Oxaloacetic acid is the first stable product of carboxylation.
4. They undergo photo- respiration.They do not undergo photo- respiration.

9. Differentiate between PSI and PSII.

Ans: Difference Between PSI and PSII:

1. It possesses a reac- tion centre of chloro-phyll ‘a’ molecule with maximum light absorption at 700 nm wavelength; reaction centre P₇₀₀.It possesses a reaction centre of chlorophyll ‘a’ molecule with maxi-mum light absorption at 680 nm; reaction centre P₆₈₀.
2. The set of electron carriers (plastocya-nin, ferredoxin cyto-chrome).The set of electron car-riers (phaeophytin plasto- quinone, cytochromes).
3. Primary electron acceptor an iron protein/Fe-S protein.Primary electron acceptor in a colourless chloro-phyll ‘a’ (lacks magne-sium) and is called phaeophyll ‘a’.

10. What are the products of light reactions? What is the fate of these products?

Ans: The products of light reaction are following:

(a) Oxygen.

(b) ATP. and 

(c) NADPH2.

ATP and NADH2 are used in dark reaction of photosynthesis in stroma to produce carbohy-drates.

11. Why is cyclic photophosphorylation called so?

Ans: During the travel of electrons through the electron acceptors, ATP is formed and hence the process is called cyclic photophosphorylation. This process starts with ejection of electron from P700 which ultimately accepts the same electrons after travelling down hill through series of electron acceptors.

12. What is Kranz anatomy?

Ans: Kranz anatomy: The anatomy in which, the vein of the leaf is surrounded by the bundle sheath containing a number of chloro-plasts, and having bull from cells in upper epidermis is known as “Kranz anatomy”. A large number of chloroplasts are present in the mesophyll cells and the bundle sheath. e.g., C4 plants like maize, jawar and bajra.

Fig. 11.9. T.S. of maize leaf showing arrangement of mesophyll and bundle sheath cells. Maize is a C4 plant.

13. Name the two carboxylase enzymes in C₄ cycle.

Ans: (i) Rubisco in bundle sheath cells.

(ii) RuBP carboxylase.

14. What are chemosynthetic autotrophs?

Ans: Example is Thiobascillus. It uses organic compounds for oxidation and release of energy. There in no need of light and pigments. Chemical energy is used by it. Chemosynthetic bacteria grow in dark.

2S+30₂ + H₂O → 2H₂SO₄ + Energy

15. How does CO₂ concentration affect the rate of photosynthesis?

Ans: CO₂ Concentration: It is app. 0.03%. Its means very low concentration in atmosphere; hence acts as a limiting factor in natural photosynthesis.

It is a raw material for photosynthesis and its concentration influence the rate of photosyn-thesis to a great extent. At optimum tempera-ture and light intensity, if CO₂ is increased, the role of photosynthesis is also increased thereafter.

16. What is the effect of excess of oxyygen on the rate of photosynthesis?

Ans: Photosynthesis:

(i) It is a process used by plants and other organisms to convert light energy into chemical energy.

(ii) In photosynthesis plants take CO2 & water, convert it into glucose & O2 in presence of sunlight.

CO2 + H2O + sunlight C6H12O6 + O2

Effect of excess of oxygen on the rate of photosynthesis:

(i) Oxygen is a product in the process of photosynthesis.

(ii) Rate of photosynthesis is inversely proportional to

(iii) Oxygen concentration.

(iv) Excess of oxygen has inhibitary effect on rate of photosynthesis.

17. Whether light absorbed by green plants, on global basis is limiting factor for photosynthesis or not! Explain.

Ans: Yes. Light absorbed by green plants is limiting factor for photosynthesis.

During photosynthesis, plants convert light energy into chemical energy. It acts as a catalyst for photosynthetic reaction.

CO2 + H2O → C6H12O6 + O2

(i) Absence of sunlight limits the rate of photosynthesis.

(ii) Therefore, Light absorbed by green plants is limiting factor for photosynthesis.

Other limiting factors for photosynthesis:

(a) Temperature.

(b) CO2 concentration.

(c) H2O availability.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top