Investigating photosynthesis and limiting factors

≈ 48 min

Investigating photosynthesis and limiting factors

The rate of photosynthesis can be limited by light intensity, carbon dioxide concentration, temperature, chlorophyll content or water availability. A fair investigation changes one independent variable, measures a dependent variable and controls other relevant factors. A graph may level off because another factor becomes limiting; a plateau does not prove that light no longer matters in every situation.

Work it through

A learner measures oxygen bubbles from pondweed at increasing lamp distances. Distance changes light intensity, but the learner must keep plant size, temperature, time and carbon dioxide supply as constant as possible. If the graph flattens near the lamp, carbon dioxide or temperature may now be limiting.

Mastery target

Design a fair test, identify variables and explain a plateau using a possible new limiting factor.

In a fair test of light intensity, which variable should be kept constant?

Temperature

Lamp distance

Measured oxygen output

The conclusion

Name the key biological term from Investigating photosynthesis and limiting factors: enter the term that best fits the explanation and visual model.

Why might a photosynthesis-rate graph flatten as light intensity rises?

Another factor such as carbon dioxide or temperature becomes limiting.

Photosynthesis reverses into respiration.

The plant has no cells.

Light becomes a nutrient.

Which statement corrects a common misunderstanding in Investigating photosynthesis and limiting factors?

Correct: Counting bubbles is an estimate of oxygen production, not a direct count of glucose molecules.

A single observation is enough to prove every biological claim.

Scientific terms are interchangeable whenever they sound similar.

A process always has exactly the same result in every environment.