NCERT Solutions for Class 11 Biology Chapter 13 Photosynthesis in Higher Plants

Updated on Feb 6, 2020 - 11:31 a.m. IST by Neha Gupta

NCERT solutions for class 11 biology chapter 13 photosynthesis in higher plants: You may have heard that green plants make their own food by photosynthesis. During this process, carbon dioxide from the atmosphere is taken in by leaves through stomata and is used for making carbohydrates, glucose and starch. In the solutions of NCERT class 11 biology chapter 13 photosynthesis in higher plants, you will get those questions along with their answers which will be related to the photosynthesis in higher plants. You know that photosynthesis takes place only in the green parts of the plants, mainly in the leaves. In this chapter, you will learn that within the leaves, the mesophyll cells have a large number of chloroplasts that are responsible for $CO_2$ fixation and within the chloroplasts, the membranes are sites for the light reaction, while the chemosynthetic pathway occurs in the stroma. Also, make sure that you will go through each concept of this chapter very carefully because it's important and you can get answers of all the questions in NCERT solutions for class 11 biology chapter 13 photosynthesis in higher plants. Like photosynthesis has two stages: the light reaction and the carbon fixing reactions. If you are looking for an answer from any other chapter even from any other class then go with NCERT Solutions , there you will get all the answers of NCERT easily.

Here are the important topics of NCERT solutions for class 11 biology chapter 13 photosynthesis in higher plants mentioned below:

13.1 What do we Know?

13.2 Early Experiments

13.3 Where does Photosynthesis take place?

13.4 How many Pigments are involved in Photosynthesis?

13.5 What is Light Reaction?

13.6 The Electron Transport

13.6.1 Splitting of Water

13.6.2 Cyclic and Non-cyclic Photo-phosphorylation

13.6.3 Chemiosmotic Hypothesis

13.7 Where are the ATP and NADPH Used?

13.7.1 The Primary Acceptor of CO_2

13.7.2 The Calvin Cycle

13.8 The C_4 Pathway

13.9 Photorespiration

13.10 Factors affecting Photosynthesis

13.10.1 Light

13.10.2 Carbon dioxide Concentration

13.10.3 Temperature

13.10.4 Water

In Chapter 13 - Photosynthesis in Higher Plants you will also study about the carbon fixation cycle, CO 2 is added by the enzyme, RuBisCo, to a 5-carbon compound RuBP that is converted to 2 molecules of 3-carbon PGA. This is then converted to sugar by the Calvin cycle, and the RuBP is regenerated. During this process, ATP and NADPH synthesized in the light reaction are utilized. RuBisCO also catalyzes a wasteful oxygenation reaction in C_3 plants: photorespiration.

After going through NCERT solutions for class 11 biology chapter 13 photosynthesis in higher plants, you must be able to answer the questions which are given below:

NCERT solutions for class 11 biology chapter 13 photosynthesis in higher plants- Solved Exercise Questions:

Q1. By looking at a plant externally can you tell whether a plant is C ₃ or C ₄ ? Why and how?

Answer:

External morphology does not necessarily differentiates $C_{3}$ plants from $C_{4}$ plants. The $C_{4}$ leaves are isobilateral but all isobilateral leaves are not $C_{4}$ in nature. Anatomically, $C_{3}$ plants can be differentiated from $C_{4}$ plants as $C_{4}$ plants possess leaves with Kranz anatomy.

Q2. By looking at which internal structure of a plant can you tell whether a plant is C ₃ or C ₄ ? Explain.

Answer:

By looking at the internal structure of the leaf, it can be revealed whether the plant is C3 or C4. In C4 plants, a leaf has Kranz anatomy wherein the undifferentiated mesophyll occurs in concentric layers around vascular bundles. Each vascular bundle is surrounded by a bundle sheath of large sized chloroplast containing cells. The chloroplasts of the bundle sheath cells are devoid of grana but contain starch grains. The chloroplasts of the mesophyll cells are granal and starch grains do not occur in them. In C3 plants, bundle sheath cells are neither very large, nor they contain chloroplasts. The mesophyll is differentiated into palisade and spongy parenchyma. All chloroplasts are granal and possess starch grains.

Q3. Even though a very few cells in a C ₄ plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss why?

Answer:

The productivity of a plant is directly proportional to the rate of photosynthesis which in turn is dependent on the amount of carbon dioxide present in a plant. In C4 plants a mechanism for increasing the concentration of carbon dioxide is present. Here, the Calvin cycle occurs in the bundle-sheath cells. The C4 compound malic acid from the mesophyll cells is broken down inside the bundle- sheath cells. This causes the release of carbon dioxide gas. The increase in Carbon dioxide gas ensures that the enzyme RuBisCo does not act as an oxygenase, but as a carboxylase. This prevents losses by photorespiration thus increasing the rate of photosynthesis. Hence, it can be concluded that even though a very few cells in a $C_{4}$ plant carry out the biosynthetic – Calvin pathway, yet they are highly productive.

Q4. RuBisCo is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCo carries out more carboxylation in C ₄ plants?

Answer:

RuBisCO functions as oxygenase only when there is a higher concentration of oxygen and a lower concentration of carbon dioxide. Both these conditions are not found in bundle sheath cells of C4 plants. These do not have a photolytic evolution of oxygen. They receive a regular supply of carbon dioxide even when the stomata are closed. Therefore, RuBisCO of C4 plants functions only as a carboxylase and not as oxygenase.

Q5. Suppose there were plants that had a high concentration of Chlorophyll b, but lacked chlorophyll a, would it carry out photosynthesis? Then why do plants have chlorophyll b and other accessory pigments?

Answer:

Chlorophyll-a molecules are essential for the process of photosynthesis as they act as antenna molecules. These molecules get excited by absorbing photons and emit electrons during cyclic and non-cyclic photophosphorylation. Chlorophyll a molecules form the reaction centres for both photosystems I and II. Due to these reasons, photosynthesis is absent in plants lacking chlorophyll a. Chlorophyll b, carotenoids and xanthophylls are accessory pigments. The major functions of these pigments are as follows

1. Absorption of light rays of different wavelengths and transfer of this energy to reaction centres.

2. Carotenoids and xanthophylls also protect the chlorophyll molecule from photo-oxidation.

Thus, it can be concluded that if any plant were to lack chlorophyll-a and contain a high concentration of chlorophyll-b, then this plant would not undergo photosynthesis.

Q6. Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?

Answer:

A leaf kept in dark for long becomes yellow or pale green because of the disintegration of chlorophylls. Light is essential for the production of the chlorophyll pigment. In the absence of light, the production of chlorophyll-a molecules stops and they get broken slowly. It results in the change in colour of the leaf to light green. This causes, the xanthophyll and carotenoid pigments to become predominant, causing the leaf to become yellow. Carotenoids which provide yellow colour to the leaf are more stable.

Q7. Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why?

Answer:

The leaves in shade are much greener than the ones exposed to sunlight because of the following reasons.

The chloroplasts of the mesophyll cells are irregularly arranged, and their orientation is in vertical files along the walls in strong light.
Photooxidation of chloroplasts occurs in bright light and its non-oxidation occurs in shaded areas.

Q8. Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:

(a) At which point/s (A, B or C) in the curve is light a limiting factor?

Answer:

At the A point, light is the limiting factor because the rate of photosynthesis is minimum here.

Q8. Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions: (b)

(b) What could be the limiting factor/s in region A ?

Answer:

IN region A light is a limiting factor. The other limiting factors in this region can be temperature, CO ₂ and H ₂ O.

Q8. Figure 13.10 shows the effect of light on the rate of photosynthesis. Based on the graph, answer the following questions:

Answer:

C represents a stage beyond which light is not a limiting factor and D is the line beyond which the intensity of light does not affect the rate of photosynthesis.

Q9. Give comparison between the following:

(a) C ₃ and C ₄ pathway

Answer:

C3 Pathway	C4 Pathway
There are plants in which the first stable product after the carbon assimilation is a 3-carbon molecule i.e. 3-phosphoglyceric acid. These plants are called C3 plants while the pathway for carbon assimilation in them is called the C3 pathway.	In the plants found in the tropical area, the first stable product after carbon assimilation is a 4 carbon molecule or oxaloacetice acid instead of a 3 carbon compound. These plants are called C4 plants and the pathway of carbon fixation is called as the C4 pathway.
The cells involved are mesophyll cells	The cells involved are mesophyll cells and bundle sheath cells
It is seen in all photosynthetic plants.	It is seen in tropical plants
The enzyme involved is RuBP carboxylase.	The enzyme involved: In mesophyll cells is PEP carboxylase. In bundle sheath cells is RuBP carboxylase.

Q9. Give comparison between the following:

(b) Cyclic and non-cyclic photophosphorylation

Answer:

Cyclic photophosphorylation	Non-cyclic photophosphorylation
Only photosystem I is involved in cyclic photophosphorylation	Both photosystems I and II are involved in non-cyclic photophosphorylation
The active reaction centre is P700	The active reaction centre is P680
Electron transportation occurs in a cyclic manner	Electron transport occurs in a non-cyclic manner
Oxygen evolution does not occur	Oxygen is released as a by product
Only ATP is produced	Both ATP and NADPH are produced

Q9. Give comparison between the following:

Answer:

Anatomy of leaf in C3 plants	Anatomy of leaf in C4 plants
Bundle sheath cells are absent	Bundle sheath cells are present around the vascular bundles
RuBisCO is found in mesophyll cells	RuBisCO is found in bundle sheath cells
Plants do not possess 'Kranz' anatomy of leaves.	Leaves show Kranz anatomy
Chloroplasts are of a single type only	Chloroplasts are dimorphic. The chloroplasts of bundle sheath cells are larger in size and arranged centripetally.
Mesophyll cells have intercellular spaces	Mesophyll cells do not have intercellular spaces

If you have any query in understanding these solutions which are mentioned in the above then again go through the chapter of the NCERT textbook, then try to solve them by yourself and compare them with NCERT solutions for class 11 biology chapter 13 photosynthesis in higher plants. This will help you not only for your school exam as it will also help you in the preparation of other competitive exams like NEET.