Photosynthesis in Higher Plants Test - 19

Correct option: C

Chlorophyll is a critical component in the photosynthetic process as it helps  plants and algae absorb energy from the sunlight for the process. However, chlorophyll absorbs most from the blue portion and then the red portion of the electromagnetic spectrum. It reflects green color. So when it is seen in the red light it would appear black.

• Photorespiration occurs when the $$CO_2$$ levels inside a leaf become low.
• This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss. 
• If the plant continues to attempt to fix $$CO_2$$, when its stomata are closed, the $$CO_2$$ will get used up and the $$O_2$$ ratio in the leaf will increase relative to $$CO_2$$ concentrations. 
• Photorespiration is absent in $$C_4$$ plants and CAM plants. Thus they are more efficient than $$C_3$$ plants.

So, the correct answer is option B.

Manganese is the essential element for photolysis of water. This reaction is catalyzed by a reactive center in photosystem II containing four manganese ions. Manganese basically uses its electrons to split the water and thus the evolution of oxygen also.

P-700 is the reaction centre of chlorophyll a molecule in association with photosystem I. Its absorption spectrum peak at 700 nm. When photosystem I absorb light, an electron is excited to a higher energy level in the P-700 chlorophyll.

Correct option: D

Chlorophyll a is widely distributed in green plants and it is also called primary photosynthetic pigment and universal photosynthetic pigment. Chlorophyll absorbs most from the blue portion and then the red portion of the electromagnetic spectrum. It reflects green colour. It is the primary electron donor in electron transport chain. 

• Photorespiration is a process in plant metabolism, which attempts to reduce the consequences of a wasteful oxygenation reaction by the enzyme RuBisCO. 
• The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, however approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), producing a product that cannot be used within the Calvin–Benson cycle. This process reduces the efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in $$C_3$$ plants. 
• Photorespiration involves a complex network of enzyme reactions, that exchange metabolites between chloroplasts, leaf peroxisomes, and mitochondria.