Botany MCQs for NEET — Practice Questions with Answers

The F0 part of ATPase is responsible for the proton channel (transmembrane channel) that allows protons to move back, while the F1 part catalyzes the actual synthesis of ATP from ADP and Pi using the energy released. The text specifically refers to the F0 part's role in movement of protons leading to ATP synthesis.

The chemiosmotic hypothesis, as explained, focuses on how the proton gradient across the thylakoid membrane, built during the light reaction, is utilized by ATP synthase to produce ATP. The context states 'During this process a proton gradient is created across the membrane of the thylakoid. The breakdown of the protons gradient due to movement through the F0 part of the ATPase enzyme releases enough energy for synthesis of ATP.'

The text states: 'After absorbing light, electrons are excited and transferred through PS II and PS I and finally to NAD forming NADH. During this process a proton gradient is created across the membrane of the thylakoid.' The formation of NADH (presumably NADPH in context of photosynthesis) is coupled with the creation of the proton gradient.

The NCERT text states: 'RuBisCO also catalyses a wasteful oxygenation reaction in C3 plants: photorespiration.' This clearly identifies RuBisCO as the enzyme responsible for initiating photorespiration due to its oxygenase activity.

The NCERT text mentions: 'RuBisCO also catalyses a wasteful oxygenation reaction in C3 plants: photorespiration.' This implied that under certain conditions, particularly when $\text{O}_2$ levels are high and $\text{CO}_2$ levels are low, RuBisCO binds with $\text{O}_2$ instead of $\text{CO}_2$, initiating photorespiration.

The NCERT text refers to photorespiration as a 'wasteful oxygenation reaction'. This 'wasteful' nature is due to the consumption of $\text{O}_2$ and the release of $\text{CO}_2$ without the net synthesis of sugars or $\text{ATP}$, effectively undoing some of the work of photosynthesis.

While not explicitly stated as 'high temperature' in the provided excerpt relating to photorespiration, it is a known biological fact that high temperatures contribute to stomatal closure, reducing internal $\text{CO}_2$, and increasing the solubility of $\text{O}_2$ relative to $\text{CO}_2$, thus favoring the oxygenase activity of RuBisCO. The text indirectly mentions factors affecting photosynthesis, and photorespiration is a consequence of environmental conditions impacting RuBisCO's affinity.

The NCERT text states: 'RuBisCO also catalyses a wasteful oxygenation reaction in C3 plants: photorespiration.' This explicitly limits the occurrence of this 'wasteful oxygenation reaction' to C3 plants in this context, distinguishing them from C4 plants mentioned later as having a 'special type of photosynthesis called C4 pathway'.

Photorespiration is a 'wasteful oxygenation reaction' which consumes $\text{ATP}$ and produces $\text{CO}_2$ and other intermediates like phosphoglycolate and glycerate, but it does not produce $\text{ATP}$ as a net gain; rather, it consumes it. The context implies photorespiration as a process that does not lead to efficient energy capture or sugar synthesis.

The NCERT text states: 'Some tropical plants show a special type of photosynthesis called C4 pathway.' It also asks, 'Why do you think RuBisCO carries out more carboxylation in C4 plants?' This implies that C4 plants have adaptations that favor RuBisCO's carboxylation activity, which is indeed the $\text{CO}_2$ concentrating mechanism, minimizing photorespiration.