2.5 - Compensation Point

Definition of Compensation Point

• Compensation point is the level of light intensity at which the rate of respiration equals the rate of photosynthesis.
• Glucose produced during photosynthesis is used in plant respiration.

Light Intensity and Attainment of Compensation Point

Below the Compensation Point

• Respiration rate exceeds photosynthesis rate.
• Glucose is used in respiration faster than it is produced: there is a net loss of glucose.
• Carbon dioxide is released overall.

At the Compensation Point

• Photosynthesis rate equals respiration rate.
• Photosynthetic products are completely used for respiration.
• There is no net glucose gain and no excess oxygen is released.
• If both rates remain at the compensation point, no glucose is available for growth, development, or the production of flowers, seeds, and fruits.

Above the Compensation Point

• Photosynthesis rate exceeds respiration rate.
• Carbon dioxide is absorbed through stomata and excess oxygen is released.
• Glucose production exceeds glucose use: excess glucose is stored as starch and supports growth and development.

Comparison Between Photosynthesis and Respiration

Similarities:

• Both occur in living organisms.
• Both involve the uptake and release of gases.

Photosynthesis	Respiration
Organisms: green plants and photosynthetic bacteria	Organisms: all living organisms
Cells: cells containing chlorophyll	Cells: all cells
Metabolism: anabolism; synthesises glucose using carbon dioxide and water	Metabolism: catabolism; breaks down glucose to release energy
Site: chloroplast	Site: mitochondrion
Reactants: carbon dioxide and water	Reactants: oxygen and glucose
Main product: glucose	Main product: energy
By-products: oxygen and water	By-products: carbon dioxide and water
Energy change: light energy is absorbed and converted to chemical energy	Energy change: chemical energy is converted to ATP; heat is released
Light: required	Light: not required