Understanding Bioenergetics: Photosynthesis, Respiration and Metabolism

Bioenergetics in Plants and Animals

Photosynthesis

Photosynthesis is the process by which plants convert carbon dioxide and water into glucose and oxygen, using light energy. The equation for photosynthesis is:

6CO2 + 6H2O → C6H12O6 + 6O2

Several factors affect the rate of photosynthesis:

• Light intensity: Higher light levels increase the rate of photosynthesis up to a certain point.
• Carbon dioxide concentration: Higher CO2 levels increase the rate of photosynthesis.
• Temperature: Photosynthesis occurs most efficiently within a specific temperature range.
• Chlorophyll: This green pigment absorbs light energy, enabling photosynthesis.

The glucose produced during photosynthesis is used by plants for energy, growth, and the production of other organic molecules.

Respiration

Respiration is the process by which glucose is broken down to release energy for various life processes.

Aerobic respiration occurs in the presence of oxygen and follows the equation:

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

Aerobic respiration takes place in the mitochondria of cells and releases a large amount of energy.

Anaerobic respiration occurs in the absence of oxygen and follows the equation:

C6H12O6 → 2C3H6O3 + Energy

Anaerobic respiration takes place in the cytoplasm of cells and releases a smaller amount of energy.

Effects of Exercise

During exercise, the body's demand for energy increases, leading to an increased rate of respiration. This can result in an oxygen debt, where the body's oxygen supply is insufficient to meet the demand. The body compensates by increasing breathing rate and switching to anaerobic respiration, which produces lactic acid.

Metabolic Rate

Metabolic rate is the rate at which the body uses energy for various life processes. Factors that influence metabolic rate include:

• Body size: Larger organisms generally have higher metabolic rates.
• Age: Metabolic rate tends to decrease with age.
• Physical activity: More active individuals have higher metabolic rates.
• Temperature: Metabolic rate increases at higher temperatures.

Worked Example

Problem: Explain the difference between aerobic and anaerobic respiration.

Solution:

• Aerobic respiration requires oxygen and occurs in the mitochondria, releasing a large amount of energy.
• Anaerobic respiration does not require oxygen and occurs in the cytoplasm, releasing a smaller amount of energy.
• The equations for aerobic and anaerobic respiration are different, with aerobic respiration producing carbon dioxide and water as waste products, while anaerobic respiration produces lactic acid.