NCERT Solutions for Class 11 Biology chapter 13 Photosynthesis in Higher Plants PDF – eSaral

# NCERT Solutions for Class 11 Biology chapter 13 Photosynthesis in Higher Plants PDF

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### Download NCERT Solutions for Class 11 Biology chapter 13 Photosynthesis in Higher Plants PDF

Question 1. By looking at a plant externally can you tell whether a plant is $\mathrm{C} 3$ or C4? Why and how?

Solution. C3 plants include sunflower, wheat, spinach, cotton and sugarcane and C4 plants includes pineapple, amaranth, maize etc. Both categories of plants include crop plants, fruits and flowering plants, which makes it very difficult to distinguish between C3 and C4 plants by only looking at the external appearance.

Question 2. By looking at which internal structure of a plant can you tell whether a plant is C3 or C4? Explain.

Solution. -If we will do the microscopic study of the tissues of C3 and C4 plant, then we will be able to classify the plants into $\mathrm{C} 3$ and $\mathrm{C} 4$.

-C3 plants and C4 plants can be distinguished on the basis of Kranz anatomy. C4 plants have Kranz anatomy, which means they have a wreath-like arrangement around the bundle sheath cells. Also, vascular bundles are surrounded by the bundle sheath cells. In leaves, mesophyll cells are not differentiated in the spongy layer and palisade layer. There is a lesser intracellular space and mesophyll have chloroplast. When the leaf tissue of C3 plants is viewed under a microscope. The mesophyll cells of leaves are distinguished into palisade and spongy parenchyma. If we will do the microscopic study of the tissues of $\mathrm{C} 3$ and $\mathrm{C} 4$ plant, then we will be able to classify the plants into $\mathrm{C} 3$ and $\mathrm{C} 4$.

Question 3. Even though a very few cells in a C4 plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?

Solution. – In C4 plants, the dark reaction that is Calvin cycle occurs in bundle sheath cells. Though it has a few numbers of cells being involved in the Calvin cycle, C 4 plants have a high rate of photosynthesis due to the following factors:

-Rapid supply of CO2 from mesophyll cells taking part in initial carbon dioxide fixation.

– Since there is no photolysis of water in the bundle sheath cells hence photorespiration is also absent in them.

-Photosynthates are rapidly withdrawn by the bundle sheath cells as they are present in the bundle sheath cells.

– Photosynthesis continues even when stomata are closed due to fixation of $\operatorname{CO} 2$ released during respiration.

Question 4. RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in C4 plants?

Solution. -RuBisCo is referred to as the Ribulose-1,5-bisphosphate carboxylase oxygenase it is one of the most abundant enzymes present in the biosphere. RuBisCO is comparatively more affinitive for CO2 than for O2. It is the relative concentration of $O 2$ and CO2, which determines whether oxygen will bind or carbon dioxide will bind to the enzyme.That is RuBisCO functions as oxygenase only when there is a higher concentration of oxygen and a lower concentration of carbon dioxide. Also C4 plants, the enzyme RuBisCO is not present in the chloroplast of mesophyll cells. It is present only in bundle sheath chloroplasts which are receiving the supply of CO2 continuously even when the stomata are closed. during the decarboxylation of malic acid into pyruvic acid. Hence, RuBisCO usually acts as carboxylase rather than oxygenase.

Question 5. 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 $\mathrm{b}$ and other accessory pigments?

Solution. If chlorophyll a is absent in the plant then photosynthesis will not occur if chlorophyll a is absent from the system as chlorophyll is the primary pigment which is involved in the absorption of different wavelength of the visible spectrum that is it functions in the trapping of light for photosynthesis further they convert light energy into chemical energy. Plants have accessory pigments such as chlorophyll, xanthophyll and carotenoids these pigments absorb the light energy and pass it on to the chlorophyll molecule. The accessory pigments also prevent the enzymes from photooxidation.

Question 6. Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?

Solution. When leaves are kept in dark, then the photosynthesis stops the green-colored chlorophyll molecule is degraded in the absence of light. The accessory pigments such as xanthophyll and carotenoids become prominent, which are yellow in colour; hence, the colour of leaves changes into yellow from green.

Question 7. 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?

Solution. The chlorophyll content will be more in the shady side of the leaves because the side of the leaf not exposed in sunlight will have more aggregation and concentration of chlorophyll molecule hence it is darker. whereas the leaves exposed in sunlight will lose chlorophyll due to photo-oxidation of the chlorophyll molecule; hence the leaf exposed in sunlight will have a lighter colour.

Question 8. Figure 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?

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

(c) What do $\mathrm{C}$ and $\mathrm{D}$ represent on the curve?

Solution. a) Light is the limiting factor because the rate of photosynthesis is increasing with the intensity of light at the point an and 50 per cent at $\mathrm{B}$.

b) Besides light, other limiting factors will be $\mathrm{CO} 2$ and $\mathrm{H} 2 \mathrm{O}$.

c) 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.

Question 9. Give comparison between the following:

(a) $\mathbf{C}_{ }$and $\mathbf{C}_{4}$ pathways (b) Cyclic and non-cyclic photophosphorylation

(c) Anatomy of leaf in $\mathrm{C}_{3}$ and $\mathrm{C}$. Plants

Solution. (a) $\mathrm{C}$ and $\mathrm{C}$. pathways:

(b) Cyclic and non-cyclic photophosphorylation:

(c) Anatomy of leaf in $\mathrm{C}$ and $\mathrm{C}_{+}$plants: