Community level systems flashcards

B4.1 Ecosystems

Population, community and ecosystem

Population: every individual of a single species in one area. Community: the populations of every species living together in one area. Ecosystem: the community plus the non-living parts of the area.

Abiotic vs biotic factors: examples

Abiotic (non-living): temperature, light intensity, moisture, soil pH. Biotic (caused by living organisms): predators, food supply, competition.

Predation, mutualism and parasitism

Predation: predator gains, prey killed (ladybirds and aphids). Mutualism: both gain (nitrogen-fixing bacteria in clover root nodules). Parasitism: parasite gains, host harmed (tapeworm, flea).

What do plants and animals compete for?

Plants: light, water, mineral ions, space. Animals: food, water, shelter, territory, mates. Competition within a species is often stronger, because individuals need identical resources.

Why does a pyramid of biomass narrow at each level?

Biomass is lost at each transfer: egestion (undigested material in faeces), excretion (urea, CO₂) and respiration (glucose broken down, carbon lost as CO₂).

Producers make 450 kg of biomass; primary consumers gain 36 kg. Efficiency of transfer?

36 ÷ 450 × 100 = 8%. The lower level is always the denominator. 92% is lost.

Why are food chains usually only four or five levels long?

So much biomass is lost at each step that too little remains to support another level.

How do decomposers break down dead material?

Bacteria and fungi secrete enzymes onto it; the enzymes break large insoluble molecules into small soluble ones; decomposers absorb them for growth and respiration, releasing CO₂ to the air and mineral ions to the soil.

Processes that move carbon in the carbon cycle

Photosynthesis takes CO₂ into producers; feeding passes carbon along food chains; respiration, decomposition and combustion return CO₂ to the air.

The water cycle, in order

Evaporation (and transpiration) → condensation → precipitation → run-off and drainage → uptake by roots or drinking, then it repeats.

Conditions for fastest decay, and why waterlogged soil slows it

Warm (up to the enzymes' optimum), moist and plenty of oxygen. Waterlogged soil fills the air spaces, so oxygen is short; decay is slow and anaerobic microorganisms can produce methane (as in peat bogs).

A 90 g sample of leaves falls to 54 g in 9 days. Percentage loss and rate of decay?

Mass lost = 36 g. Percentage loss = 36 ÷ 90 × 100 = 40%. Rate = 36 ÷ 9 = 4.0 g per day.