Temperature and Water as Factors Affecting Photosynthesis Quiz

Temperature and Water as Factors Affecting Photosynthesis

Photosynthesis in a living leaf rarely reaches its theoretical maximum, and two environmental variables largely explain the gap: temperature and water. This quiz tests your grasp of how each factor reshapes the photosynthetic response you have already mapped.

Temperature: the enzymatic dark reactions are temperature controlled, while the light reactions are temperature sensitive but affected to a much lesser extent.
C₃ versus C₄: C₄ plants respond to higher temperatures with higher rates, whereas C₃ plants have a much lower temperature optimum.
Habitat: tropical plants carry a higher temperature optimum than plants adapted to temperate climates.
Water: although a reactant in the light reaction, water acts mainly through its effect on the plant — closing stomata, reducing CO₂ availability, and wilting leaves.

Work through the fifteen questions carefully and read each explanation, since the reasoning matters as much as the answer.

Q1. Why are the dark reactions of photosynthesis described as temperature controlled?

Because they are enzymatic reactions

Because they require photons of light

Because they occur only at night

Because they take place in the stroma without enzymes

The dark reactions are catalysed by enzymes, and enzyme activity depends strongly on temperature, so the dark reactions are temperature controlled.

Q2. Compared with the dark reactions, how are the light reactions affected by temperature?

They are affected to a much lesser extent

They are affected to a much greater extent

They are completely unaffected by temperature

They are affected in exactly the same way

The light reactions are also temperature sensitive, but the material states clearly that they are affected to a much lesser extent than the enzymatic dark reactions.

Q3. Which group of plants responds to higher temperatures and shows a higher rate of photosynthesis?

C4 plants

C3 plants

Plants grown in deep shade

Temperate climate plants

According to the lesson, C4 plants respond to higher temperatures and show higher rates of photosynthesis, while C3 plants have a much lower temperature optimum.

Q4. What is stated about the temperature optimum of C3 plants?

They have a much lower temperature optimum

They have a much higher temperature optimum than C4 plants

They have no temperature optimum at all

Their optimum is identical to that of C4 plants

The material states that C3 plants have a much lower temperature optimum, in contrast with C4 plants which respond to higher temperatures.

Q5. On what does the temperature optimum for photosynthesis of different plants depend?

On the habitat to which they are adapted

On the colour of their flowers

On the number of seeds they produce

On the age of the individual leaf only

The temperature optimum for photosynthesis of different plants depends on the habitat that they are adapted to.

Q6. How does the temperature optimum of tropical plants compare with that of plants adapted to temperate climates?

Tropical plants have a higher temperature optimum

Tropical plants have a lower temperature optimum

Both groups have exactly the same optimum

Tropical plants have no temperature optimum

The lesson states that tropical plants have a higher temperature optimum than plants adapted to temperate climates.

Q7. Water is one of the reactants in the light reaction. How is the effect of water as a factor on photosynthesis best described?

It acts more through its effect on the plant than directly on photosynthesis

It acts only directly on the light reaction chemistry

It has no effect on photosynthesis whatsoever

It acts only by changing the colour of chlorophyll

Although water is a reactant in the light reaction, its effect as a factor is more through its effect on the plant rather than directly on photosynthesis.

Q8. What happens to stomata when a plant experiences water stress?

The stomata close

The stomata open wider

The stomata disappear entirely

The stomata become permanently fixed open

Water stress causes the stomata to close, and this closure reduces the availability of ##\ce{CO2}## to the leaf.

Q9. Why does stomatal closure during water stress reduce the rate of photosynthesis?

It reduces the availability of ##\ce{CO2}##

It increases the availability of ##\ce{CO2}##

It stops light from reaching chlorophyll

It raises the temperature of the leaf to the optimum

When stomata close, ##\ce{CO2}## entry into the leaf is restricted, so ##\ce{CO2}## availability is reduced and photosynthesis is limited.

Q10. Besides closing stomata, what does water stress do to leaves?

It makes them wilt

It makes them grow larger

It increases their surface area

It turns them permanently dark green

Water stress also makes leaves wilt, which reduces the surface area of the leaves and their metabolic activity as well.

Q11. How does wilting reduce photosynthesis in a leaf?

It reduces the surface area of the leaves and their metabolic activity

It increases the chlorophyll content of the leaf

It raises the ##\ce{CO2}## concentration inside the leaf

It speeds up the enzymatic dark reactions

Wilting reduces the surface area of the leaves and their metabolic activity, both of which lower the photosynthetic performance of the plant.

Q12. Which statement correctly contrasts the temperature responses of C3 and C4 plants?

C4 plants respond to higher temperatures while C3 plants have a much lower temperature optimum

C3 plants respond to higher temperatures while C4 plants have a much lower temperature optimum

Both groups have identical temperature optima

Neither group responds to temperature at all

The lesson states that C4 plants respond to higher temperatures and show higher rates of photosynthesis, while C3 plants have a much lower temperature optimum.

Q13. Which pair of factors is treated in this lesson as external factors affecting photosynthesis?

Temperature and water

Chlorophyll and stomata

Glucose and oxygen

Enzymes and pigments

The lesson examines temperature and water as external environmental factors that modulate how efficiently ##\ce{CO2}## is captured and processed.

Q14. A plant adapted to a temperate climate is compared with a tropical plant. Which statement is correct?

The temperate plant has a lower temperature optimum than the tropical plant

The temperate plant has a higher temperature optimum than the tropical plant

Both plants have the same temperature optimum

The temperate plant has no temperature optimum

The temperature optimum depends on the habitat of adaptation, and tropical plants have a higher temperature optimum than plants adapted to temperate climates.

Q15. Which sequence correctly describes the indirect effect of water stress on photosynthesis?

Water stress → stomata close → ##\ce{CO2}## availability reduced → photosynthesis falls

Water stress → stomata open → ##\ce{CO2}## availability rises → photosynthesis rises

Water stress → chlorophyll breaks down → light absorption stops → photosynthesis falls

Water stress → leaves expand → surface area increases → photosynthesis rises

Water stress closes the stomata, which reduces ##\ce{CO2}## availability; this is why water's effect as a factor is described as indirect, acting through the plant rather than directly on photosynthesis.