Botany MCQs for NEET — Practice Questions with Answers

If the intensity of light increases 20 times, the rate of photosynthesis will increase until feedback inhibition occurs. Photosynthesis rates do not increase indefinitely with light intensity; they eventually reach a plateau due to limitations such as enzyme saturation and other regulatory mechanisms within the plant cells.

Sugarcane is known to be one of the most efficient converters of sunlight into chemical energy through the process of photosynthesis. This is largely due to its C4 photosynthetic pathway, which is more efficient than the C3 pathway found in many other plants. C4 plants like sugarcane can fix carbon dioxide more effectively under high temperature and light conditions, leading to higher rates of photosynthesis and biomass production.

Cyclic photophosphorylation is confined to Photosystem I. In this process, the electrons are cycled back to the Photosystem I reaction center rather than being passed on to NADP+. This cycle generates ATP without the production of NADPH or oxygen. It is an essential process to maintain the right balance of ATP and NADPH in the chloroplasts.

For the synthesis of one glucose molecule, 18 ATP molecules are required in the C3 cycle (Calvin cycle) and 30 ATP molecules are required in the C4 cycle. In the C3 cycle, 6 turns of the cycle are needed to fix enough carbon for one glucose molecule, consuming 18 ATP and 12 NADPH. In the C4 cycle, additional ATP is used in the process of carbon fixation and transport, leading to a higher overall ATP requirement.

For chlorophyll formation, Fe⁺⁺ (iron) and Mg⁺⁺ (magnesium) are essential. Iron is necessary for the synthesis of chlorophyll, while magnesium is a central atom in the chlorophyll molecule. Therefore, the correct answer is Fe⁺⁺ and Mg⁺⁺.

In angiosperms, the translocation of sugar primarily occurs in the form of sucrose. Sucrose is efficiently transported through the phloem to various parts of the plant where it can be utilized or stored.

Quinones are mobile electron carriers. They play a crucial role in the electron transport chain, a series of reactions that occur in the mitochondria during cellular respiration, helping in the transfer of electrons between different complexes.

During the dark reaction (Calvin cycle), carbon fixation occurs when carbon dioxide (CO₂) is attached to a five-carbon sugar named ribulose bisphosphate (RuBP). This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase (RuBisCO). The product of this reaction is an unstable six-carbon intermediate, which immediately splits into two molecules of 3-phosphoglyceric acid (PGA). Therefore, the three carbon atoms of each molecule of 3-phosphoglyceric acid (PGA) are derived from both RuBP and CO₂.