B4.2 Ecological Niches

Autotrophic

Organisms that make their own food from inorganic sources (e.g., CO₂, sunlight)

Heterotrophic

Organisms that obtain organic compounds by feeding on other organisms

Mixotrophic

Organisms that can switch between autotrophic and heterotrophic nutrition

Producers

Autotrophs that use photosynthesis or chemosynthesis to make organic compounds

Mixotrophs

Organisms that use both autotrophic and heterotrophic strategies depending on conditions

Herbivores

Primary consumers that feed on producers

Carnivores

Secondary or tertiary consumers that feed on animals

Omnivores

Organisms that feed on both plants and animals

Detritivores

Organisms that ingest dead organic matter and digest it internally

Saprotrophs

Organisms that secrete enzymes to externally digest dead matter and absorb the nutrients

Decomposers

A general term including detritivores and saprotrophs - essential for nutrient cycling

Obligate Aerobes

Require a continuous oxygen supply so only live in oxic environments, for example: all animals and plants

Obligate Anaerobes

Inhibited or killed by oxygen so only live in anoxic environments, for example: tetanus bacterium, archaea

Facultative Anaerobes

Use oxygen if available so live in oxic or anoxic environments, for example: E. coli (gut bacterium), yeast

Ingestion

Taking the food into the gut

Digestion

Breaking large food molecules into smaller molecules

Absorption

Transport of digested food across the plasma membrane of epidermis cells and thus into the blood and tissues of the body

Assimilation

Using digested foods to synthesise proteins and other macromolecules and thus making them part of the body's tissues

Egestion

Voiding undigested material from the end of the gut

Holozoic Nutrition

When an organism ingests (eats) solid food, digests it inside the body, and absorbs the nutrients

Phototrophic

Absorption of light energy by pigments: Light → proton gradient → ATP

Chemotrophic

Oxidation of inorganic chemicals, for example Fe2+: Inorganic chemical reactions → energy → ATP