Plant Physiology: I. Photosynthesis

Total Questions: 37

31. Which one of the following is the process involved in photosynthesis? [I.A.S. (Pre) 2014]

(a) Potential energy is released to form free energy
(b) Free energy is converted into potential energy and stored
(c) Food is oxidized to release carbon dioxide and water
(d) Oxygen is taken, and carbon dioxide and water vapour are given out

Correct Answer: (b) Free energy is converted into potential energy and stored

Solution:On earth, the main source of energy is sunlight which is transformed by photosynthesis into a form of chemical energy that can be used by photosynthetic and non-photosynthetic organisms alike. By converting the energy of sunlight to a usable form of potential chemical energy, photosynthesis is the ultimate source of metabolic energy for all biological systems.

32. Which of the following has the maximum efficiency to convert solar energy into chemical energy? [U.P.P.S.C. (R.I.) 2014]

(a) Chlorella
(b) Tiger
(c) Earthworm
(d) Cuscuta

Correct Answer: (a) Chlorella

Solution:In the process of photosynthesis, solar energy changes into chemical energy. Chlorella is a single-celled green algae belonging to the class of Chlorophyceae. Chlorella is believed to be capable in serving as a potential food and energy source. Among the given options, Chlorella has the maximum efficiency to convert solar energy into chemical energy through photosynthesis.

33. Which of the following is not the work of roots? [Uttarakhand P.C.S. (Mains) 2006]

(a) Photosynthesis
(b) Water absorption
(c) Absorption nutrients
(d) To help the plants

Correct Answer: (a) Photosynthesis

Solution:Photosynthesis takes place in leaves which prepare food for the plants by absorbing light, CO₂ and water. Generally, root cells do not contain chloroplasts; so there is no chance of photosynthesis.

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.

34. Which one of the following does not increase the amount of carbon dioxide in carbon cycle on earth? [U.P.P.C.S. (Mains) 2012]

(a) Respiration
(b) Photosynthesis
(c) Decay of organic matter
(d) Volcanic action

Correct Answer: (b) Photosynthesis

Solution:Carbon dioxide is an atmospheric constituent that plays several vital roles in the environment. It is a greenhouse gas that traps infrared radiation heat in the atmosphere. It plays a crucial role in the weathering of rocks. It is the carbon source for plants. It is stored in biomass, organic matter in sediments and in carbonate rocks like limestone. The primary source of carbon/CO₂ is outgassing from the earth’s interior at mid-ocean ridges, the decay of organic matter, hotspot volcanoes and subduction-related volcanic arcs. Photosynthesis and respiration are essentially the opposite of one another. Photosynthesis takes CO₂ from the atmosphere and replaces it with O₂. Respiration takes O₂ from the atmosphere and replaces it with CO₂.

35. In the nighttime, it is advised not to sleep under trees because : [67ᵗʰ B.P.S.C. (Pre) 2022]

(a) they liberate less amount of oxygen
(b) they liberate harmful gases at night
(c) they liberate carbon dioxide
(d) they liberate carbon monoxide
(e) None of the above/More than one of the above

Correct Answer: (c) they liberate carbon dioxide

Solution:Since photosynthesis does not occur at night, oxygen is not being produced by the trees. In addition to this, the trees continue respiring and releasing carbon dioxide, thereby causing the amount of carbon dioxide to be increased and the amount of oxygen to be reduced in the surrounding area. So at night if we sleep under big trees we do not have sufficient amount of oxygen.

36. It is harmful to sleep under a tree at night because the tree releases : [M.P.P.C.S. (Pre) 2000]

(a) Oxygen
(b) Carbon dioxide
(c) Carbon monoxide
(d) Sulphur dioxide

Correct Answer: (b) Carbon dioxide

37. Photosynthesis using the invisible part of the sunlight is done by some — [U.P.P.C.S. (Pre) 2013]

(a) Trees
(b) Algae
(c) Bacteria
(d) Fungi

Correct Answer: (c) Bacteria

Solution:The bacteria which are found in the deep sea, for example green sulphur bacteria, uses infrared radiations for photosynthesis to produce energy.

Photosynthesis relies on wavelength-specific light called Photosynthetically Active Radiation (PAR), which ranges from 400 to 700 nm (visible light).

The wavelengths shorter than 400 nm or longer than 700 nm give a low CO₂ assimilation yield.

At the lower intensity, there is a linear relationship between incident light and CO₂ fixation rates (Biomass conversion).

An increase in incident light beyond a point can cause the breakdown of chlorophyll and a decrease in photosynthesis.

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