Ecosystems, Year 11: communities, competition and adaptations

Organism, population, community, ecosystem

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

为什么A 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

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

为什么The 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

提示The missing adjective also describes a ladder that will not wobble.

为什么In 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

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

为什么Plants 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

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

为什么An 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

提示The prefix 'a-' means 'not', as in 'atypical'.

为什么The 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

提示It is the gas that animals need for aerobic respiration.

为什么Water 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

提示Think about what the leaves overhead were keeping from the ground.

为什么Under 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

提示It is written with two letters, one small and one capital.

为什么Some 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)

提示It is a factor you can feel but cannot see.

为什么Strong 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

提示The word shares its root with 'biology'.

为什么The 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

提示It is the general word for a microorganism that causes disease.

为什么The 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

提示A population survives only if enough new young are produced.

为什么A 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

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

为什么The 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

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

为什么The 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

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

为什么Most 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

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

为什么A 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

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

为什么This 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

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

为什么Huddling 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

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

为什么This 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.