C4.2 Energy Transfer (SL)

Vocabulary flashcards summarising key terms and definitions related to nutrition and energy transfer in ecosystems (Unit C4.2).

Open System

A system that exchanges both energy and matter with its surroundings; ecosystems operate as open systems.

Closed System

A system that exchanges energy but not matter with its surroundings.

Ecosystem

All interactions between a community of organisms and their physical environment, functioning as an open system.

Sunlight (in ecosystems)

Principal external energy source that sustains almost all ecosystems by driving photosynthesis.

Photoautotroph

Organism that uses light energy to convert inorganic molecules into organic compounds via photosynthesis.

Photosynthesis

Process by which photoautotrophs convert light, CO₂ and H₂O into glucose and O₂, storing chemical energy in carbon compounds.

Chemoautotroph

Organism that derives energy from oxidation of inorganic molecules (e.g., H₂S, NH₃) to build organic compounds.

Chemosynthesis

Conversion of inorganic molecules into organic compounds using energy released from oxidation reactions, performed by chemoautotrophs.

Oxidation Reaction (in metabolism)

Chemical reaction releasing high-energy electrons; powers chemosynthesis and cell respiration.

Cell Respiration

Oxidative breakdown of organic compounds to release energy transferred to ATP, producing CO₂ and H₂O.

Adenosine Triphosphate (ATP)

Energy-carrying coenzyme hydrolysed to ADP + Pi to power cellular activities.

Autotroph

Organism that synthesises its own organic compounds from inorganic substances using external energy; called a producer.

Producer

Autotrophic organism that forms the first trophic level, supplying organic matter and energy to a community.

Heterotroph

Organism that obtains organic compounds from other organisms; includes consumers and decomposers.

Consumer

Heterotroph that ingests and internally digests organic matter from other organisms.

Herbivore

Consumer that feeds primarily on plant material.

Carnivore

Consumer that feeds primarily on animal tissue.

Omnivore

Consumer that feeds on both plant and animal matter.

Saprotroph (Decomposer)

Heterotroph that lives on or in non-living organic matter, secretes enzymes for external digestion, and absorbs the products.

External Digestion

Breakdown of organic material outside an organism’s body, characteristic of saprotrophs.

Internal Digestion

Breakdown of ingested food within the body, characteristic of consumers.

Trophic Level

An organism’s position in a feeding sequence (e.g., producer, primary consumer).

Food Chain

Linear diagram showing transfer of energy and matter between organisms through feeding.

Food Web

Network of interrelated food chains depicting multiple feeding pathways within a community.

Pyramid of Energy

Graphical representation of energy content (J·m⁻²·yr⁻¹) at each trophic level; always upright with ~10% transfer between levels.

Energy Loss Between Trophic Levels

Reduction of available energy due to respiration, heat production, unconsumed or undigested matter.

Energy Efficiency (10 % Rule)

Only about 5–20 % (≈10 %) of chemical energy is passed to the next trophic level; the rest is lost mainly as heat.

Feeding Restrictions

Limits on ecosystem trophic levels because cumulative energy losses make higher levels energetically unviable.