VMBO Year 2 · HAVO/VWO Years 2–3 · Ecology and sustainability · Section 6.1

Organisms and their environment

Environment and ecology

Organisms are influenced by their environment, but also change it. Plants release oxygen during photosynthesis, and animals may alter the soil.

Ecology studies these interactions between organisms and their surroundings.

• Biotic factors: Influences involving living organisms, such as members of the same species, predators and competitors.
• Abiotic factors: Non-living influences, such as temperature, light, water and soil conditions.

Levels in ecology

Ecologists study relationships at different levels:

• Individual: One organism, such as an elephant.
• Population: Members of the same species living in an area and potentially reproducing with one another.
• Community: All the populations living together in an area.
• Biotope: The physical environment and abiotic conditions associated with a community.
• Ecosystem: A community and its non-living environment, including their interactions.
• Biosphere: The parts of Earth where life occurs.

Feeding relationships

Organisms are connected through feeding. A simple chain often begins with plants, followed by herbivores and then carnivores.

• Food chain: A sequence in which one organism or group is eaten by the next.
• Link: One step or feeding group in the chain.
• Food web: A network of interconnected food chains in an ecosystem.

Biomass

Organisms contain organic substances such as fats and proteins. Biomass is the mass of biological material, often measured as dry mass for comparisons.

Only part of the material and energy at one feeding level becomes biomass at the next. Biomass therefore usually decreases towards higher feeding levels in simple terrestrial food-chain models, although some ecosystems show different standing-biomass patterns.

Accumulating substances

Some persistent pollutants, such as certain pesticides or forms of heavy metals, enter organisms and are passed on through feeding relationships.

Bioaccumulation is build-up within an organism over time. Some pollutants also become more concentrated at higher feeding levels, called biomagnification.

Predators near the top of a food chain may then receive harmful concentrations. This does not happen equally with every substance.