4.1.2 Rate of Photosynthesis

What are the four main factors that affect the rate of photosynthesis?

Temperature, light intensity, carbon dioxide concentration, and amount of chlorophyll.

How does temperature affect the rate of photosynthesis?

As temperature increases, the rate of photosynthesis increases until enzymes begin to denature, causing the rate to decrease.

How does light intensity affect the rate of photosynthesis?

The higher the light intensity, the faster the rate of photosynthesis, until another factor becomes limiting.

How does carbon dioxide concentration affect the rate of photosynthesis?

As carbon dioxide concentration increases, the rate of photosynthesis increases because CO₂ is needed to make glucose.

How does the amount of chlorophyll affect photosynthesis?

Chlorophyll absorbs light energy for photosynthesis. If chlorophyll levels are reduced, e.g. due to magnesium deficiency, the rate of photosynthesis decreases.

What is a limiting factor in photosynthesis?

A limiting factor is an environmental condition in short supply that restricts the rate of photosynthesis, such as low light intensity, low CO₂, or low temperature.

What does a graph showing photosynthesis and light intensity look like?

It shows an increase in rate with higher light intensity until the line levels off, as another factor becomes limiting.

What does a graph showing two limiting factors demonstrate?

It shows two curves under different conditions (e.g. temperatures), demonstrating how one condition can limit photosynthesis compared to another.

What is the inverse square law in photosynthesis?

Light intensity is inversely proportional to the square of the distance from the light source: light intensity ∝ 1/distance².

If a lamp is 2m away from a plant, what happens to the light intensity?

It becomes ¼ of its original value because 1/2² = ¼.

How can farmers use limiting factors to increase yield?

They control conditions in greenhouses (light, CO₂, temperature) to maximise photosynthesis, leading to faster growth and higher profits.

How can oxygen production be used to measure photosynthesis?

By placing pondweed in water, counting oxygen bubbles or measuring oxygen collected in a capillary tube over time.

What variables can be changed in a photosynthesis practical?

Temperature (using a water bath), light intensity (distance of lamp), and time pondweed is left. The independent variable is changed while others are controlled.