Section C - Student Note

Definitions:
- Species: Groups of organisms capable of interbreeding to produce fertile offspring.
- Habitat: The environment where a species lives.
- Population: A group of organisms of the same species in a specific area.
- Community: Different populations interacting in a particular area.
- Ecosystem: A community interacting with its abiotic environment.
- Ecology: The study of interactions among organisms and their environment.

Autotrophs: Organisms that produce their own food using light (photosynthesis) or chemical processes (chemosynthesis).
Heterotrophs: Organisms that obtain organic materials from other living or dead organisms.
Consumers: Heterotrophs that ingest living organisms.
Detritivores: Organisms that consume non-living organic matter.
Saprotrophs: Decomposers that absorb organic nutrients from dead organisms through external digestion.

Food Chain: A linear sequence of energy transfer from producers to various levels of consumers.
Food Web: A complex network of interlinked food chains demonstrating feeding relationships in an ecosystem.
Trophic Levels: Classifications in a food chain, including:
- Producers (1st level)
- Primary Consumers (2nd level)
- Secondary Consumers (3rd level)

Light Energy Source: Nearly all ecosystems receive initial energy from sunlight.
Energy Losses:
- Materials not consumed or assimilated.
- Heat loss during cellular respiration.

Pyramid of Numbers: Represents the number of organisms per trophic level.
Pyramid of Biomass: Displays the total mass of living organisms at each trophic level.
Pyramid of Energy: Measures energy flow through an ecosystem, usually expressed in kJ/m²/yr.

Biotic Factors: Living elements affecting ecosystems (e.g., feeding relationships).
Abiotic Factors: Non-living elements affecting ecosystems (e.g., temperature, light, water).
Nutrient Recycling: Nutrients must be recycled within ecosystems while energy is lost as heat.