Question

In what form does energy flow through an ecosystem when organisms consume each other?

• A. A) As heat directly
• B. B) In the form of carbon-carbon bonds
• C. C) As light photons
• D. D) Through water currents

Answer 1

Answer:

B. B) In the form of carbon-carbon bonds

Energy Flow in Ecosystems: The Role of Chemical Bonds

• Energy in an ecosystem originates primarily from the sun, captured by producers (autotrophs) through photosynthesis. This light energy is converted into chemical energy.
• This chemical energy is stored within the organic molecules produced by organisms, specifically in the carbon-carbon (C-C) bonds that form the backbone of these molecules (e.g., glucose, starches, proteins, fats).
• When one organism consumes another, these organic molecules are ingested. The digestive processes break down these complex molecules, releasing the energy stored in their chemical bonds.
• This released energy is then used by the consumer for various metabolic activities such as growth, reproduction, movement, and maintenance of body temperature.

• Key Concepts and Facts for Competitive Exams:

  1. Unidirectional Energy Flow: Energy flow in an ecosystem is always unidirectional, from the sun to producers, then to consumers, and finally to decomposers. It does not cycle back.
  2. Trophic Levels: Organisms are categorized into different feeding levels called trophic levels:
     • Producers (First Trophic Level): Autotrophs (e.g., plants, algae) that convert light energy into chemical energy.
     • Primary Consumers (Second Trophic Level): Herbivores that feed on producers.
     • Secondary Consumers (Third Trophic Level): Carnivores or omnivores that feed on primary consumers.
     • Tertiary Consumers (Fourth Trophic Level): Carnivores that feed on secondary consumers.
  3. Lindeman's 10% Rule: Only about 10% of the energy from one trophic level is transferred to the next higher trophic level. The remaining 90% is lost, primarily as heat during metabolic processes (respiration) or is unavailable (e.g., indigestible parts). This rule explains why food chains are typically short (3-5 links).
  4. Thermodynamics in Ecosystems:
     • First Law of Thermodynamics (Law of Conservation of Energy): Energy cannot be created or destroyed, only transformed. In ecosystems, light energy is transformed into chemical energy.
     • Second Law of Thermodynamics (Law of Entropy): During every energy transformation, some energy is lost as heat to the environment, increasing entropy. This explains the inefficiency of energy transfer between trophic levels.
  5. Food Chains and Food Webs: A food chain illustrates a single pathway of energy transfer, while a food web represents multiple interconnected food chains, showing the complex feeding relationships within an ecosystem.
  6. Difference between Energy Flow and Nutrient Cycling: While energy flows unidirectionally and is largely dissipated as heat, matter (nutrients like carbon, nitrogen, phosphorus) cycles through an ecosystem, being reused by different organisms.
  7. Gross Primary Productivity (GPP) vs. Net Primary Productivity (NPP): GPP is the total rate at which producers convert light energy into chemical energy. NPP is the energy remaining after producers account for their own respiration (NPP = GPP - Respiration). NPP represents the energy available to higher trophic levels.