NCERT Class 11-Biology: Chapter – 13 Photosynthesis in Higher Plants Part 7 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Question 2:

The entire process of photosynthesis consists of a number of reactions. Where in the cell do each of these take place?

a. Synthesis of ATP & NADPH ________

b. Photolysis of water ________

c. Fixation of ________

d. Synthesis of sugar molecule ________

e. Synthesis of starch ________


(a) Outer side of thylakoid membrane

(b) Inner side of thylakoid membrane

(c) Stroma of chloroplast

(d) Chloroplast

(e) Chloroplast

Question 3:

Which property of the pigment is responsible for its ability to initiate the process of photosynthesis? Why is the rate of photosynthesis higher in the red and blue regions of the spectrum of light?


Pigments are substances capable of absorbing light at certain wavelengths. This means that various pigments can absorb light of various colours. So, if pigment A can become excited by colour X, colour Y will stimulate pigment B. Once the pigment gets excited after light is absorbed, it provides energy for the future photosynthesis so that light energy can be used.

The most abundant pigment in plants is chlorophyll a. This pigment demonstrates the optimal efficiency between blue and red-light wavelengths

Other pigments also show optimal efficiency between blue and red light, as shown in these charts. In this chart, it is clear that the photosynthesis is on the best level between the blue and rot wavelengths (displaying a rate of photosynthesis) . This is mainly due to chlorophyll a. This is also due to the action of accessory pigments, however. This means that in the range of red and blue light the rate of photosynthesis is higher.

Question 4:

What can we conclude from the statement that the action and absorption spectrum of photosynthesis overlap? At which wavelength do they show peaks?


The first chart shows the photosynthesis rate; by oxygen release. The second diagram shows the absorption by chlorophyll in a of various light wavelengths; the rate of photosynthesis is superimposed. In the peaks and troughs of both the graphs appear to imitate each other. The diagrams peak at a wavelength of over , which is equal to blue. The two diagrams then appear dry. Then it peaks again between and , which is the same as red. This therefore shows that the spectrum of action and absorption overlaps. The black line shows the photosynthesis action spectrum, while the blue line displays the spectrum of absorption. Four nm, are the peak wavelength.

Question 5:

Under what conditions are plants superior to ?


Under the following conditions, plants are superior to plants: Even at low CO2 levels, plants can carry out photosynthesis. At approximately , plants show saturation whereas plants show only after saturation. The availability of CO2 is therefore a limited factor for plants; not plants.

Plants have a higher optimum temperature, but plants have a lower optimum temperature. Therefore, even at high temperatures, plants can perform photosynthesis; this is not the case with plants.

Because of Kranz anatomy, plant is not affected by high levels of oxygen in the atmosphere. Kranz anatomy ensures that photorespiration in plants is not carried out. But with plants, this is not the case.

Question 6:

In the figure given below, the black line (upper) indicates action spectrum for photosynthesis and the lighter line (lower) indicates the absorption spectrum of chlorophyll a, answer the followings:

Chapter 13 - Question 6- TheLight Absorbed

a. What does the action spectrum indicate? How can we plot an action spectrum? Explain with an example.

b. How can we derive an absorption spectrum for any substance?

c. If chlorophyll a is responsible for light reaction of photosynthesis, why do the action spectrum and absorption spectrum not overlap?


(a) The rates of photosynthesis indicate the action spectrum. The measurement is oxygen release the oxygen releases on y-axis and the wavelength on x-axis can be compared to the action spectrum. The absorption by pigments of different wavelengths, such as chlorophyll a as shown on this graph, can be demonstrated.

(b) The absorption of various wavelengths for a particular pigment can be done by the processing, such as chlorophyll a, or chlorophyll b, or any other pigment.