Free Forms and Functions of Plants MCQs with Answers

71. The given diagram shows three plant cells arranged side by side.The movement of water molecules from cell 1 to cell 3 would discontinue in case of:

• A. Apoplast pathway
• B. Symplast pathway
• C. Vacuolar pathway
• D. Trans-membrane pathway

Explanation: The symplast pathway involves the movement of water through the cytoplasm of cells, connected by plasmodesmata which is shown in figure. So any disruption in this pathway will result in impaired water transport.

72. The least soluble pigment is identified as:

• A. Carotene
• B. Xanthophyll
• C. Chlorophyll a
• D. Chlorophyll b

Explanation: In paper chromatography, pigments separate based on their differing solubilities in the chosen solvent and their affinity to the chromatography paper. More soluble pigments will travel further up the paper with the solvent, while less soluble pigments will travel shorter distances or remain near the origin. Chlorophyll b has travelled least distance so it is least soluble.

73. During photorespiration, ribulose biphosphate carboxylase combines with oxygen gas whichresults in lowering the overall rate of:

• A. ADP synthesis
• B. NAD formation
• C. Nitrogen fixation
• D. Carbon dioxide fixation

Explanation: During photorespiration, ribulose biphosphate carboxylase (RuBisCO) combines with oxygen instead of carbon dioxide, leading to a process that releases carbon dioxide and consumes energy, ultimately reducing the efficiency of carbon dioxide fixation. This process competes with the Calvin cycle, which is responsible for carbon fixation in photosynthesis. Thus, the presence of oxygen decreases the overall rate of carbon dioxide fixation.

74. In light dependent reactions of photosynthesis, the cyclic electron transport yields only:

• A. ATP
• B. Water
• C. Oxygen
• D. NADPH

Explanation: The cyclic electron transport in the light-dependent reactions of photosynthesis specifically produces ATP. This is because the electrons are cycled back to the photosystem, allowing for the generation of ATP without the production of NADPH or oxygen. Water is consumed, not produced, in these reactions, as it is split to provide electrons. Oxygen is released as a by-product of the water-splitting process but only in non-cyclic electron transport. NADPH is also a product of non-cyclic electron transport, not cyclic.

75. The set of factors which causes the slowest rate of transpiration in terrestrial plants is:

• A. Humidity: high, Temperature: low, Wind Speed: high
• B. Humidity: low, Temperature: high, Wind Speed: high
• C. Humidity: high, Temperature: low, Wind Speed: low
• D. Humidity: low, Temperature: high, Wind Speed: low

Explanation: The correct answer is Option C:Humidity: high, Temperature: low, Wind Speed: lowTranspiration is the process of water movement through a plant and its evaporation from aerial parts. High humidity reduces the gradient for water vapor diffusion, low temperatures slow down evaporation, and low wind speed means less removal of water vapor from the leaf surface, all contributing to the slowest rate of transpiration.

76. The biological process which uses the property of latent heat of vapourisation of water is

• A. Transpiration
• B. Translocation
• C. Excretion
• D. Egestion

Explanation: The correct answer is transpiration. Transpiration is the process by which water is absorbed by plant roots and then evaporated from the leaves into the atmosphere. This process utilizes the latent heat of vaporization, as water changes from liquid to vapor, helping in cooling the plant and also in nutrient uptake. In contrast, translocation involves the movement of nutrients and food within the plant and does not require the latent heat of vaporization. Excretion and egestion involve the removal of waste substances from the body, which do not directly involve the vaporization of water.

77. In photosynthesis, oxygen molecules are formed as a by-product during:

• A. Photolysis
• B. Chemiosmosis
• C. Carbon fixation
• D. Cyclic phosphorylation

Explanation: In photosynthesis, oxygen is released during the photolysis of water, which occurs in the light-dependent reactions. Photolysis uses light energy to split water molecules into hydrogen ions, electrons, and oxygen. This process is essential for providing electrons for the electron transport chain and contributes to the formation of NADPH and ATP.

78. The given diagram represents guard cells of stomata in two different conditions.Which of the following options is TRUE about conditions I and II in guard cells?

• A. Condition I shows guard cells in a turgid state, leading to a closed stomatal pore
• B. Condition II represents flaccid guard cells, resulting in an open stomatal pore
• C. Condition I indicates turgid guard cells with an open stomatal pore, while Condition II shows flaccid guard cells with a closed stomatal pore
• D. Both conditions show guard cells in the same state, impacting stomatal opening similarly

Explanation: The correct answer is Option C.In Condition I, the guard cells are turgid, meaning they are swollen due to water intake, which causes the stomatal pore to open. This condition is typical during the day when photosynthesis is active.In Condition II, the guard cells are flaccid, indicating water loss, causing the stomatal pore to close. This usually occurs at night or during water stress conditions to conserve water.

79. In the chloroplasts of plant cells, a large number of antenna pigment molecules in the photosystems, embedded in the thylakoid membrane, allow the:

• A. Reaction centre to gain the greatest possible amount of energy
• B. Light energy to be harvested in the molecule of electron acceptor
• C. Accessory pigment molecules to get closely associated with each other
• D. Chlorophyll-b molecule in the reaction centre to become highly energised

Explanation: The correct answer is Option A. Antennae pigment molecules in the photosystem are responsible for capturing light energy and funneling it to the reaction center. This process maximizes the amount of energy that the reaction center can gain, which is crucial for efficient photosynthesis.

80. In the light dependent reactions of photosynthesis, both cyclic and non-cyclic flow of electrons take place. The cyclic flow of electrons is called 'cyclic' because, after the production of:

• A. ATP molecules, the electrons are cycled back into the photosystem I
• B. ATP molecules, the electrons are cycled back into the photosystem II
• C. NADPH molecules, the electrons are cycled back into the photosystem I
• D. NADPH molecules, the electrons are cycled back into the photosystem II

Explanation: The correct understanding involves recognizing that in the cyclic flow of electrons during the light-dependent reactions of photosynthesis, electrons are cycled back to photosystem I, not photosystem II, after ATP production. This process does not produce NADPH, as it is focused solely on ATP generation.