Ecosystems and biodiversity

An ecosystem is the community of organisms in an area together with the non-living (abiotic) factors — temperature, light, water, soil pH. Biodiversity is the variety of species present.

Energy through a food chain

producer → primary consumer → secondary consumer → tertiary consumer.

Only ~10 % of the energy at one trophic level passes to the next. The rest is lost as heat (respiration), in waste (urea, faeces) and in uneaten parts. This is why food chains rarely have more than four or five levels.

Pyramids of biomass

Pyramid of biomass shows the total dry mass at each level. Biomass usually decreases up the chain because of these losses.

Sampling — quadrats and transects

To estimate population in a field, throw quadrats randomly, count the species in each, and use:

mean per quadrat × (total area / quadrat area) = estimated total population.

A transect (line across an environmental gradient, e.g. shore to dune) shows how species distribution changes with abiotic factors.

The carbon cycle

CO₂ → photosynthesis → glucose in plants → eaten / decomposed → respiration / combustion → CO₂. Fossil fuels lock carbon away for millions of years; burning them releases it rapidly.

The water cycle

Evaporation from seas/lakes → transpiration from plants → condensation → precipitation → run-off / infiltration. Plants are a critical step — deforestation reduces transpiration and rainfall.

Human impact

Deforestation, intensive farming and pollution reduce biodiversity. Conservation strategies include legal protection, captive breeding, and replanting.

CCEA tip

For mean-per-quadrat estimates, divide by the number of quadrats used, not the total area; only multiply up to the total area in the final step.