Plant Physiology: I. Photosynthesis

Total Questions: 37

11. Which one of the following gases is essential for photosynthesis process? [43ʳᵈ B.P.S.C. (Pre) 1999, U.P.P.C.S (Pre) 2011]

Correct Answer: (b) CO₂
Solution:Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. In this process, carbon dioxide (CO₂) is taken in from the atmosphere and oxygen (O₂) is released out during the formation of glucose (C₆H₁₂O₆).

Photosynthesis is the physicochemical process by which green plants, algae, and some bacteria synthesise organic compounds in the presence of sunlight using components such as carbon dioxide and water. In this process, light energy is converted to chemical energy in the form of sugars and Oxygen as a byproduct. Photosynthesis by green plants and other photoautotrophs is the basis of life as it is the primary source of all food on Earth.

Photosynthesis takes place in the chloroplast organelle of plant cells. It is a double-membrane organelle having its own DNA, mitochondria, and ribosomes. It also contains a third inner membrane, called thylakoid.

Thylakoid membranes: They look like stacks of coins. It contains chlorophyll.
The membrane system is responsible for trapping the light energy for the synthesis of ATP and NADPH.

Stroma: The space between the thylakoid and the chloroplast membranes is called the stroma. Within the stroma, enzymatic reactions occur to synthesize sugar, subsequently leading to the formation of starch.

12. Which one of the following is not required for photosynthesis process? [U.P. R.O./A.R.O. (Pre) 2017]

Correct Answer: (b) Oxygen
Solution:Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. In this process, carbon dioxide (CO₂) is taken in from the atmosphere and oxygen (O₂) is released out during the formation of glucose (C₆H₁₂O₆).

Photosynthesis is the physicochemical process by which green plants, algae, and some bacteria synthesise organic compounds in the presence of sunlight using components such as carbon dioxide and water. In this process, light energy is converted to chemical energy in the form of sugars and Oxygen as a byproduct. Photosynthesis by green plants and other photoautotrophs is the basis of life as it is the primary source of all food on Earth.

Photosynthesis takes place in the chloroplast organelle of plant cells. It is a double-membrane organelle having its own DNA, mitochondria, and ribosomes. It also contains a third inner membrane, called thylakoid.

Thylakoid membranes: They look like stacks of coins. It contains chlorophyll.
The membrane system is responsible for trapping the light energy for the synthesis of ATP and NADPH.

Stroma: The space between the thylakoid and the chloroplast membranes is called the stroma. Within the stroma, enzymatic reactions occur to synthesize sugar, subsequently leading to the formation of starch.

13. The radiant energy absorbed by the plants results in— [R.A.S./R.T.S. (Pre) 1999]

Correct Answer: (a) Photolysis of water
Solution:When sunlight reaches a plant, the chlorophyll pigment in the chloroplasts absorbs the light energy.

This absorbed energy excites the chlorophyll molecule, raising its electrons to a higher energy level.

The excited chlorophyll molecule then initiates the process of photolysis, where water molecules are split into oxygen and hydrogen ions, releasing electrons.

The electrons released from photolysis are then transported through a series of electron transport chains within the chloroplast, generating ATP (adenosine triphosphate) and NADPH (reduced nicotinamide adenine dinucleotide phosphate).

The ATP and NADPH produced are used as chemical energy to drive the Calvin cycle, where carbon dioxide is fixed into organic compounds like glucose.

14. Most of the oxygen on Earth is produced by : [U.P. Lower Sub. (Pre) 2015]

Correct Answer: (b) Algae
Solution:Approximately 90% of the photosynthesis on Earth is done by aquatic plants and algae. Among these, 85% is in the sea (mainly by algae) and remaining 5% is in river, ponds etc. In the process of photosynthesis, CO₂ (carbon dioxide) is absorbed and carbohydrate and oxygen are produced.

15. Photosynthesis occurs in : [43ʳᵈ B.P.S.C. (Pre) 1999]

Correct Answer: (c) Day or night
Solution:Through the process of photosynthesis, green plants have a capacity of manufacturing their food from simple substances as CO₂ and H₂O in presence of light. Normally, plants utilize sunlight (day) but marine algae also use moonlight. Photosynthesis even occurs in electric light.

16. The process by which plants produce food is called : [44ᵗʰ B.P.S.C. (Pre) 2000]

Correct Answer: (d) Photosynthesis
Solution:Through the process of photosynthesis, green plants have a capacity of manufacturing their food from simple substances as CO₂ and H₂O in presence of light. Normally, plants utilize sunlight (day) but marine algae also use moonlight. Photosynthesis even occurs in electric light.

17. The process by which plants synthesize their food is called: [U.P.R.O./A.R.O. (Mains) 2013]

Correct Answer: (c) Photosynthesis
Solution:Through the process of photosynthesis, green plants have a capacity of manufacturing their food from simple substances as CO₂ and H₂O in presence of light. Normally, plants utilize sunlight (day) but marine algae also use moonlight. Photosynthesis even occurs in electric light.

18. Photosynthesis occurs in : [53ʳᵈ to 55ᵗʰ B.P.S.C. (Pre) 2011]

Correct Answer: (c) Chloroplast
Solution:Photosynthesis takes place primarily in leaves and partially in stems. It takes place within specialized cell structures called chloroplasts. A leaf has a petiole or the stalk and a lamina, the flat portion of the leaf. As its area is broad, the lamina helps in the absorption of sunlight and carbon dioxide during photosynthesis. Photosynthesis takes place in the chloroplasts that have chlorophyll present in them. It is the chlorophyll that absorbs light energy from the sun. There are tiny pores called stomata that function as roadways for carbon dioxide to enter and oxygen to leave the plant.

19. Which of the following types of light are strongly absorbed by plants? [I.A.S. (Pre) 2007]

Correct Answer: (b) Blue and red
Solution:Plants use only certain colours from light for the process of photosynthesis. The chlorophyll absorbs blue, red and violet light rays. Photosynthesis occurs more in blue and red light rays and less or not at all in green light rays.

Since chlorophyll absorbs red and blue light, the green light is reflected back, making plants appear green to our eyes.

20. Chlorophyll absorbs ________ wavelengths of the sunlight. [68ᵗʰ B.P.S.C. (Pre) 2022]

Correct Answer: (a) red and blue
Solution:Chlorophyll is a chemical photoreceptor that traps light for photosynthesis in plants. It absorbs light in the red (long wavelength) and the blue (short wavelength) regions of the visible light spectrum. Green light is not absorbed but mainly reflected, making the plant appear green.