Ecosystems, Year 11: communities, competition and adaptations

Organism, population, community, ecosystem

HintStart with one living thing, then all of its kind, then every kind together, then add the surroundings.

The whyA single living thing belongs to a group of its own species in the same place. All the groups of different species living there together form the next level, and adding the non-living surroundings they interact with gives the largest level.

An ecosystem

HintA pond, a rock pool and a woodland are each an example.

The whyThe living part is called biotic and the non-living part, such as the light, water and soil, is called abiotic. Both are included because the organisms depend on their surroundings as well as on one another.

A stable community

HintThe missing adjective also describes a ladder that will not wobble.

The whyIn an old woodland or a coral reef, the numbers of each species go up and down a little from year to year but do not change much overall, because births, deaths, food supply and conditions balance out.

mineral ions

HintThey are dissolved in the water that roots take in, and include nitrates.

The whyPlants make their own food, so they do not compete for it. What limits them is what photosynthesis and growth need: light, room to grow, and the two things their roots absorb, one of which supplies elements such as nitrogen and magnesium.

food; mates; territory

HintOne keeps the animal alive, one lets it breed, and one is the area it defends.

The whyAn animal needs enough to eat, a partner to reproduce with and an area in which to feed and raise young. Where any of these is in short supply, the individuals best able to win it are the most likely to survive and breed.

An abiotic factor

HintThe prefix 'a-' means 'not', as in 'atypical'.

The whyThe GCSE course lists seven: light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, carbon dioxide levels for plants, and oxygen levels for animals living in water.

oxygen

HintIt is the gas that animals need for aerobic respiration.

The whyWater holds far less of this gas than air does, and the amount varies with temperature and with pollution. If the level falls, fish and many invertebrates cannot respire fast enough and die or move away.

Light intensity has increased, so the plants can photosynthesise faster and grow

HintThink about what the leaves overhead were keeping from the ground.

The whyUnder a closed canopy little light reaches the woodland floor, so photosynthesis there is slow. When a gap opens, more light arrives, plants on the ground make more glucose and seedlings that were barely surviving can grow.

pH

HintIt is written with two letters, one small and one capital.

The whySome plants, such as heathers, grow only in acidic soil, while others need neutral or alkaline soil. Together with the minerals available, this decides which plant species can live in a place, and so which animals can live there too.

Wind (its intensity and direction)

HintIt is a factor you can feel but cannot see.

The whyStrong winds dry out and damage shoots on the side they blow from, so growth is stunted and lopsided. Because the strongest winds usually come from one direction, the trees end up leaning away from it.

A biotic factor

HintThe word shares its root with 'biology'.

The whyThe GCSE course lists four: the availability of food, new predators arriving, new pathogens, and one species out-competing another so that its numbers fall too low for it to breed.

A new pathogen

HintIt is the general word for a microorganism that causes disease.

The whyThe trees had not met this fungus before and most have little resistance to it. As ash trees die, the many insects, lichens and birds that depend on them lose their food and shelter as well.

There are too few individuals left to breed successfully

HintA population survives only if enough new young are produced.

The whyA species does not have to be killed directly to disappear from a community. If a competitor takes most of the food or space, fewer individuals survive, and once they are too scarce to find mates and raise young, the population cannot replace its losses.

37.5

HintFind the size of the drop first, then compare it with the number you started with.

The whyThe decrease is 400 − 250 = 150 pairs. As a fraction of the starting number this is 150 ÷ 400 = 0.375, which is 37.5%. A percentage change is always worked out from the original value.

It falls, because with less food fewer mice survive the winter and breed

HintAcorns are an important part of what these animals eat in the colder months.

The whyThe availability of food is a biotic factor, because the food is itself a living thing or comes from one. When the supply drops, more animals starve and fewer young are raised, so the population falls; in a good year it rises.

An extremophile

HintThe ending '-phile' means 'lover of', as in 'bibliophile'.

The whyMost living things would be killed by such conditions, because their enzymes and cells would stop working. These organisms have adaptations, such as enzymes that keep their shape when very hot, that let them thrive where almost nothing else can.

structural; behavioural; functional

HintOne is about the body's shape, one is about what the organism does, and one is about how its body works inside.

The whyA feature of the body, such as thick fur, is the first type. Something the organism does, such as migrating, is the second. A process inside the body, such as making very little urine, is the third.

functional

HintIt is not a shape and not an action; it is about how an organ works.

The whyThis type of adaptation is a process inside the body, to do with reproduction or metabolism. Here the kidneys reabsorb most of the water, which lets the camel go for days without drinking in the desert.

Each bird loses less heat, so it uses less energy keeping warm

HintCompare how much of one penguin's surface faces the cold air when it stands alone and when it is surrounded.

The whyHuddling is a behavioural adaptation. A penguin in the middle of the group is sheltered from the wind and surrounded by warm bodies, so its stored fat lasts longer during the months when it cannot feed.

vents

HintThey are openings in the sea floor through which heated water escapes.

The whyThis is the example the GCSE course names. Far below the reach of sunlight, hot water rich in minerals pours out of the sea bed, and bacteria there survive temperatures and pressures that would destroy most cells.