Question 1

During photosynthesis in green plants, which of the following is the primary function of chlorophyll?

Accepted Answer

Chlorophyll is the green pigment present in chloroplasts that absorbs light energy from the sun. According to NCERT Class 10 Biology, chlorophyll's primary role is to capture light energy (photons) during the light-dependent reactions of photosynthesis. This absorbed light energy is then converted into chemical energy in the form of ATP and NADPH, which are used in the light-independent reactions (Calvin cycle) to synthesize glucose. While chlorophyll does not directly synthesize glucose or release oxygen, it is essential for capturing the light energy that drives the entire photosynthetic process.

Question 2

During photosynthesis in green plants, the light-dependent reactions occur in the thylakoid membranes of chloroplasts and produce two essential products. Which of the following correctly identifies both products of the light-dependent reactions?

Accepted Answer

The light-dependent reactions of photosynthesis occur in the thylakoid membranes and produce ATP (adenosine triphosphate) and NADPH (reduced nicotinamide adenine dinucleotide phosphate). These two products are then used in the light-independent reactions (Calvin cycle) occurring in the stroma to fix CO₂ and synthesize glucose. Water is split during photolysis to release electrons and oxygen gas, but oxygen is a byproduct, not a primary product of the light reactions themselves—it is released as a waste product. The light-dependent reactions do not directly produce glucose; glucose synthesis occurs in the Calvin cycle using ATP and NADPH. Therefore, answer is B.

Question 3

Which part of the human digestive system is responsible for the absorption of most digested nutrients into the bloodstream?

Accepted Answer

The small intestine is the primary site of nutrient absorption. Its inner wall has finger-like projections called villi, which greatly increase the surface area for absorption of digested carbohydrates, proteins, and fats into the blood and lymph. This is a key concept from NCERT Class 10 Life Processes chapter.

Question 4

During photosynthesis in a green plant, if the light intensity is increased from 100 lux to 500 lux while keeping temperature and CO₂ concentration constant, the rate of photosynthesis initially increases but then plateaus. Which of the following best explains why the rate does NOT continue to increase proportionally at higher light intensities?

Accepted Answer

This question tests understanding of limiting factors in photosynthesis — a key NCERT Class 10 concept. At low light intensities, light is the limiting factor, so increasing it increases the photosynthetic rate. However, once light intensity exceeds a certain threshold, other factors (temperature and CO₂ concentration) become limiting. The rate plateaus because the plant cannot process more CO₂ or use more energy at the given temperature, regardless of additional light. This is the principle of limiting factors: the factor in shortest supply controls the overall rate. Option B correctly identifies that CO₂ concentration and temperature become the limiting factors at high light intensity. Option A incorrectly suggests chlorophyll becomes saturated (chlorophyll does not 'saturate' in this context — it is the light reactions that saturate). Option C confuses the concept by suggesting photosynthesis stops, which is false. Option D reverses the logic by claiming light remains limiting even at 500 lux, which contradicts the plateau observation.

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