Ecosystems, Year 11: sampling, pollution and biodiversity

A transect

HintIn fieldwork it is usually a long tape measure or a marked rope.

The whyA quadrat is placed at set distances along the line, for example every two metres, and the organisms in it are counted. Because the positions are in order along the line, the results show how a species changes from one end of the habitat to the other.

To find out how the distribution of a species changes across a habitat

HintThink of a seashore, where conditions change steadily from the top of the beach down to the sea.

The whyRandom quadrats are used to estimate how many of a species live in an area that is much the same all over. A line of samples is used where a factor such as light, moisture or trampling changes gradually, to see where the species is found and where it is not.

4800

HintFind the mean for one quadrat, then work out how many quadrats would cover the whole lawn.

The whyThe mean is 60 ÷ 10 = 6 daisies per quadrat. One quadrat covers 0.25 m², so that is 6 ÷ 0.25 = 24 daisies per m². For the whole lawn, 24 × 200 = 4800 daisies.

A larger sample is more representative, so unusual patches affect the mean less

HintImagine one of the three had landed, by chance, on the only bare patch.

The whyPlants are never spread perfectly evenly, so any single quadrat may hold many more or many fewer than is typical. With only a few quadrats one odd result shifts the mean a long way; with many, the odd results tend to cancel out.

The light intensity, using a light meter

HintThey need a reading of the factor itself, taken at the same places as the counts.

The whyThe investigation asks whether the distribution of the plant follows a factor. That needs two sets of readings from the same positions: the abundance of the plant and the size of the factor. Other factors, such as soil moisture, also change along the line and may explain part of the pattern.

6

HintPut the seven counts in order of size before you choose.

The whyIn order the counts are 1, 4, 4, 6, 9, 10, 15. The median is the middle value, which is the fourth of the seven. For the same data the mode is 4 and the mean is 49 ÷ 7 = 7.

growing; rising

HintOne reason is about how many people there are; the other is about how each of them lives.

The whyMore people need more food, water, energy and goods. On top of that, as people become better off each one tends to use more and throw more away. Unless the waste is handled properly, more pollution follows.

sewage; fertiliser

HintOne is carried away by toilets and drains; the other supplies plants with mineral ions.

The whyPollution can occur in water, in air and on land. In rivers and lakes the three main sources are waste from homes, chemicals that are meant to feed crops but drain off the fields, and poisonous substances from industry.

acidic

HintThink about what kind of substance has a pH below 7.

The whyBurning fuels releases tiny solid particles and gases such as sulfur dioxide. The gases dissolve in moisture in the air and fall as acid rain, which damages trees and can make lakes unable to support fish. Chemistry covers how the gases form.

Landfill; toxic chemicals can leak out of the waste into the soil

HintThe name joins a word for ground with a word for packing a hole.

The whyBurying waste takes up land that other species could use, and the waste itself can contain poisonous substances, for example from batteries and paints. If these escape they contaminate the soil and can be washed into streams.

It kills plants and animals, so fewer species survive in the polluted area

HintBiodiversity is the variety of living things found in a place.

The whySome species are more sensitive to a pollutant than others and disappear first. When they go, the species that fed on them or sheltered in them may follow, so the variety of life falls further than the pollutant alone would cause.

building; quarrying; farming; waste

HintThink of houses and roads, digging out stone, growing food, and getting rid of rubbish.

The whyEach of these takes over land that was a habitat. As the human population grows, more land is used in all four ways, and the species that lived there are left with less space, or none.

compost

HintGardeners buy it in bags to grow seedlings and pot plants in.

The whyPeat is partly decayed plant material that has built up over thousands of years in waterlogged ground. It holds water well, which made it popular with gardeners and growers, but it forms far more slowly than it is dug out.

The habitat becomes smaller, so fewer of the species that live only there can survive

HintMany bog plants and animals are found nowhere else.

The whyPeat bogs are home to particular plants, animals and microorganisms that are adapted to wet, acidic conditions. When the peat is removed or the bog is drained, that habitat shrinks and the variety of species it supported falls.

carbon dioxide

HintIt is the gas you breathe out, and the main product when a fuel burns.

The whyPeat is a store of carbon, taken in from the air by plants over thousands of years. Burning it, or draining a bog so that microorganisms can decay the peat, turns that carbon back into a gas that adds to global warming.

It is cheap and easily available, and it helps to increase food production

HintThink about what growers and shoppers want from the things they buy.

The whyThis is a conflict between two needs. Growers want an affordable compost that produces good crops; conserving peatlands protects a rare habitat and keeps carbon locked in the ground. Decisions about peat have to weigh one against the other.

Benefit: wild plants, insects, birds and mammals can live there. Cost: less land for the crop, so less income

HintAsk what gains a home, and what the strip would otherwise have been used for.

The whyA field of one crop offers food and shelter to very few species. Hedgerows and field margins bring back a variety of plants and the animals that depend on them. The strip cannot be harvested, so the gain for wildlife comes at a price to the farmer.

Animals are bred in captivity to increase their numbers, and some can later be released into the wild

HintZoos and wildlife parks often run them.

The whyWhen very few individuals of a species remain, keeping and breeding them in safety stops the species dying out while the threats in the wild are dealt with. The young can then be used to rebuild wild populations.

Less waste goes to landfill, so less land is taken or polluted

HintThink about where the rubbish would otherwise end up.

The whyLandfill sites cover habitats and can leak toxic chemicals. Recycling reduces the amount buried, and it also means fewer new raw materials have to be quarried or harvested, which leaves more habitat undisturbed.

The habitat stays intact, so the many species living in the forest keep their food and shelter

HintA wood is home to far more than its trees.

The whyTropical forests hold a very large share of the world's species. Clearing them removes the habitat of all of those species at once. Leaving the trees standing also keeps carbon out of the atmosphere, which is why the same programmes aim to cut carbon dioxide emissions.

regeneration

HintThe habitat had already been lost and is being brought back.

The whyProtecting a habitat means preventing damage to one that still exists. Here the damage had already been done, so the work is to restore the conditions the bog species need. Both approaches are used to maintain biodiversity.