Question

The rate of biomass production by living beings in an ecosystem is called what?

• A. Production
• B. Productivity
• C. Biomass Accumulation
• D. Energy Transfer Rate

Answer 1

Answer:

B. Productivity

Productivity in Ecosystems

• Productivity in an ecosystem refers to the rate at which biomass (organic matter) is produced by living organisms, primarily producers, over a given period and area. It is a fundamental concept in ecology, indicating the health and energy flow within an ecosystem.

• Types of Productivity

  • Gross Primary Productivity (GPP): This is the total rate at which solar energy is converted into organic matter (biomass) by primary producers (plants, algae, cyanobacteria) through photosynthesis. It represents the total amount of energy captured by producers before any respiration.
  • Net Primary Productivity (NPP): This is the rate at which primary producers accumulate biomass after accounting for the energy they use for their own respiration (R). It is calculated as NPP = GPP - R. NPP is the energy available to the next trophic levels (herbivores).
  • Secondary Productivity: This refers to the rate of biomass production by consumers (heterotrophs) through the assimilation of food. It is generally much lower than primary productivity because of energy loss at each trophic level.

• Measurement and Units

  • Productivity is typically measured in terms of weight per unit area per unit time (e.g., grams per square meter per year - g/m²/year) or energy per unit area per unit time (e.g., kilocalories per square meter per year - kcal/m²/year).

• Factors Affecting Productivity

  • Sunlight: The primary energy source for photosynthesis. More light generally means higher GPP.
  • Temperature: Optimal temperatures are crucial for enzyme activity in metabolic processes.
  • Water Availability: Essential for photosynthesis and nutrient transport.
  • Nutrient Availability: Key nutrients like nitrogen, phosphorus, and potassium are vital for plant growth. Limiting nutrients can restrict productivity.
  • Species Composition: The types of plants and organisms present influence overall productivity.

• Ecological Significance and Competitive Exam Facts

  • Energy Flow: NPP is the available energy that supports all other trophic levels in an ecosystem. The 10% Law of Energy Transfer states that only about 10% of the energy from one trophic level is transferred to the next.
  • Highest Productivity Ecosystems: Tropical rainforests, coral reefs, and estuaries are among the most productive ecosystems on Earth due to abundant sunlight, water, and nutrients.
  • Lowest Productivity Ecosystems: Deserts and open oceans (especially the deep ocean) typically have very low productivity due to limiting factors like water, nutrients, or light.
  • Biogeochemical Cycles: Productivity plays a crucial role in carbon cycling, as CO2 is fixed during photosynthesis.
  • Ecosystem Services: High productivity ecosystems provide essential services like oxygen production, carbon sequestration, and habitat provision.