Photosynthesis in Green Plants: 18 MCQs with answers

C · $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

The balanced equation is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$ in the presence of light and chlorophyll. The other options either reverse the reaction or have incorrect atom counts.

B · Plants make food in leaves; soil provides water and minerals.

Plants make their own food (glucose) in the leaves using light, water, and carbon dioxide. The soil supplies water and minerals, not food.

D · Stomata

Stomata are tiny pores on the leaf surface that allow gas exchange: $CO_2$ enters and $O_2$ leaves.

C · No photosynthesis occurs because chlorophyll is absent.

White patches lack chlorophyll, so they cannot absorb light energy and cannot photosynthesise.

B · It becomes pale and weak because it cannot make new glucose.

Without light, photosynthesis stops, so the plant uses stored food without replacing it, becoming pale and weak.

A · True

The oxygen released during photosynthesis comes from the splitting of water molecules, not from carbon dioxide.

A · Light provides energy but is not a raw material.

Light supplies the energy to drive the reaction, but the atoms of glucose come from $CO_2$ and water. Light is not a raw material.

B · It absorbs blue and red light and captures that energy.

Chlorophyll absorbs mainly blue and red light and traps that energy to drive photosynthesis.

B · Another factor, such as light intensity, has become limiting.

When one factor is increased but the rate does not rise, another factor (like light intensity or temperature) has become the limiting factor.

A · Photosynthesis stores energy; respiration releases energy.

Photosynthesis converts light energy into chemical energy stored in glucose; respiration releases that energy from glucose.

C · It stops because carbon dioxide is a raw material.

Carbon dioxide is a raw material for photosynthesis. Without it, the reaction cannot proceed, even if water and light are present.

A · Roots → xylem → leaf mesophyll cells → chloroplasts

Water is absorbed by roots and carried through xylem to the leaves, where it reaches the mesophyll cells and chloroplasts.

B · The oxygen comes from the splitting of water molecules.

The oxygen atoms in the released $O_2$ come from water ($H_2O$), not from carbon dioxide.

A · It captures light energy and stores it as chemical energy in glucose.

Photosynthesis converts light energy into chemical energy stored in glucose, which then passes through food chains. Oxygen release is a by-product, not the energy source.

B · The rate is low because temperature is the limiting factor.

Temperature affects the enzymes controlling photosynthesis. Near freezing, the rate is low even if light and $CO_2$ are plentiful, making temperature the limiting factor.

A · Respiration occurs all the time in plant cells, using oxygen.

Plants respire continuously, day and night, using oxygen to release energy from glucose. Photosynthesis only occurs in light.

D · The rate of photosynthesis will plateau and not increase further.

The correct option is true because, after a certain light intensity, the rate of photosynthesis reaches a maximum level (saturation point) and cannot increase further, regardless of additional light.

D · Photosynthesis will stop, leading to a decline in glucose production and eventual weakening of the plant.

The correct option is true because without carbon dioxide, the plant cannot perform photosynthesis, leading to no glucose production, which is essential for its energy and health.