5.3.1 Primary Producers

Key Points About Primary Producers

1. Role in Ecosystems:

• Primary producers supply energy to all other organisms in the ecosystem (consumers and decomposers).
• They convert sunlight into energy-storing molecules like glucose, which is used by other organisms for respiration.

2. Types of Primary Producers:

• Terrestrial Ecosystems: Mostly plants, such as trees, grasses, and shrubs.
• Aquatic Ecosystems: Include algae, phytoplankton, and some bacteria like cyanobacteria.

3. Energy Transfer Efficiency:

• Only 1-3% of sunlight is captured by plants and converted into chemical energy.
• Energy is lost due to reflection, transmission through leaves, or being in wavelengths unsuitable for photosynthesis.

Measuring Primary Production

1. Gross Primary Production (GPP):

• The total amount of energy converted from light energy into chemical energy by plants in a given area.
• It represents the total energy available to the ecosystem.

2. Net Primary Production (NPP):

• The energy remaining after plants use some for respiration (R).
• NPP = GPP – R
• NPP is the energy available to primary consumers (herbivores) in the ecosystem.

3. Units of Measurement:

• Primary production is measured in $kJ m⁻²\ year⁻¹$ (kilojoules per square metre per year) to standardise energy flow in ecosystems.

Factors Affecting Primary Production

1. Light Availability:

• More light increases photosynthesis, boosting GPP and NPP.

2. Temperature:

• Higher temperatures increase enzyme activity, enhancing photosynthesis. However, extreme heat may damage enzymes.

3. Water Availability:

• A lack of water reduces stomatal opening, limiting carbon dioxide uptake and photosynthesis.

4. Nutrient Availability:

• Nutrients like nitrogen and phosphorus are essential for growth. Low levels reduce primary production.

5. Carbon Dioxide Concentration:

• Higher $CO₂$ concentrations can increase photosynthesis rates.

Key Terminology

• Autotrophs: Organisms that produce their own food (e.g., plants, algae).
• Gross Primary Production (GPP): Total energy converted by plants from sunlight.
• Net Primary Production (NPP): Energy available to the next trophic level after respiration.
• Respiration (R): Energy used by plants for their metabolic processes.