2.5 - Compensation Point

Light Intensity and Attainment of Compensation Point

Compensation point is the level of light intensity when the rate of respiration is equal to the rate of photosynthesis. Glucose produced from photosynthesis is used in cell respiration.

Figure 15 - When the light intensity increases, the uptake of carbon dioxide also increases. However, the usage of glucose during respiration is faster compared to the production of glucose during photosynthesis (net loss). When light intensity increases beyond the compensation point, the rate of photosynthesis is now higher than the rate of respiration. More carbon dioxide is absorbed through the stoma to sustain the high rate of photosynthesis. As a result, more oxygen is produced into the atmosphere. At this stage, the production of glucose exceeds the rate of glucose consumption during respiration (net gain). Excess glucose is stored in the form of starch in plants. The higher rate of photosynthesis than the rate of respiration is important to ensure growth and production of flowers, seeds and fruits of the plants. Oxygen produced can also support the life of other living organisms.

Comparison between Photosynthesis and Respiration in Plants

• Similarities

  • Both processes happen in living organisms
  • Both involve the uptake and release of gases

• Differences

  • Photosynthesis

    • Organism involved:
      • Green plants
      • Photosynthetic bacteria
    • Types of cell involved: Cells that contain chlorophyll
    • Types of metabolism: Anabolism, synthesize glucose by using carbon dioxide and water
    • Site of reaction: Chloroplast
    • Reaction substances: Carbon dioxide and water
    • Reaction products: Glucose
    • By products: Oxygen and water
    • Changes of energy: Light energy to chemical energy
    • Require light: Yes

  • Respiration

    • Organism involved: All living organisms
    • Types of cell involved: All cells
    • Types of metabolism: Catabolism, break down of glucose to generate energy
    • Site of reaction: Mitochondrion
    • Reaction substances: Oxygen and glucose
    • Reaction products: Energy
    • By products: Carbon dioxide and water
    • Changes of energy: Chemical energy to ATP and heat energy
    • Require light: No