NCERT Class 11-Biology: Chapter –13 Photosynthesis in Higher Plants Part 4

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Question 2:

Chlorophyll ‘a’ is the primary pigment for light reaction. What are accessory pigments? What is their role in photosynthesis?


Accessory pigments are known to support chlorophyll in the trapping of solar radiation. The accessory pigments are chlorophyll b, xanthophyll’s and carotenoids. They help collect and transfer solar radiation to chlorophyll a. In light harvesting, accessory pigment thus has a supporting role.

Question 3:

Do reactions of photosynthesis called, as ‘Dark Reaction’ need light? Explain.


Dark reactions include the biosynthesis phase in which carbohydrate synthesis occurs. This part of the photosynthesis is not directed on light and is therefore referred to as dark reaction. This does not mean, however, that dark reaction occurs in full darkness but continues even during the day. Dark reaction therefore requires indirectly light but is not dependent on light.

Question 4:

How are photosynthesis and respiration related to each other?


In certain ways, photosynthesis and breathing are related. We know that the breathing of carbohydrates involves the oxidation of energy. Since carbohydrates are prepared for breathing during photosynthesis, breathing can therefore not take place without photosynthesis. In addition, breathing also needs oxygen that is a photosynthesis by-product. Similarly, carbon dioxide is an important raw material for photosynthesis and much of the carbon dioxide comes as a by-product of respiration.

Question 5:

If a green plant is kept in dark with proper ventilation, can this plant carry out photosynthesis? Can anything be given as supplement to maintain its growth or survival?


When a plant is kept in the dark and ventilated correctly, carbon dioxide is still present.

However, it’s sun-free. Therefore, photosynthesis cannot be performed in this plant. The plant can be supplied with adequate amount of water to maintain its survival. However, due to lack of nutrients, the seed would eventually die.

Question 6:

Photosynthetic organisms occur at different depths in the ocean. Do they receive qualitatively and quantitatively the same light? How do they adapt to carry out photosynthesis under these conditions?


Light is seldom photosynthesis limiting factor, because light saturation is 10% of the full sunlight. Light is rarely a limiting factor, with the exception of plants in shade or in dense forest. Photosynthetic organisms are found at different depths on oceans, and they are sufficient to execute photosynthesis by using enough light. In addition, the photosynthetic pigments of these organisms show considerable variations. These pigments help these organisms even in low light conditions to perform photosynthesis.

Question 7:

In tropical rain forests, the canopy is thick and shorter plants growing below it, receive filtered light. How are they able to carry out photosynthesis ?


Light, as only of full sunlight is sufficient in light saturation, is seldom a limiting factor in photosynthesis. Less light may slow the rate of photosynthesis in plants that grow under thick canopy in the woods, but photosynthesis cannot stop at daily times. Therefore, photosynthesis can take place. These plants.

Question 8:

What conditions enable Rubis CO to function as an oxygenise? Explain the ensuing process.


Both carbon dioxide and oxygen are related to RuBisCo. However, RuBisCo is competitive to bind one of them. This means that the enzyme would be used as carboxylase in the event of a higher concentration. However, the enzyme would act as oxygenase in cases of higher concentration of .

Question 9:

Why does the rate of photosynthesis decrease at higher temperatures?


Photosynthesis is an enzyme process through which the process is mediated. We are aware of the optimum temperature range of enzymes. An enzyme could not function if the temperature exceeds this range. This causes a decrease in the rate of photosynthesis at higher temperatures.

Question 10:

Explain how during light reaction of photosynthesis, ATP synthesis is a chemiosmotic phenomenon.


The movement of ions across and down a semi-permeable membrane is called chemical movement. In ATP synthesis, ions move through the thylakoid membrane, which is a semi-permeable diaphragm, during the light photosynthesis reaction.

In addition, proton pumps pump ions with a proton gradient, which is finally synthesized in ATP. Because of these factors, ATP synthesis is called a chemiosmotic phenomenon during light reaction