Exam practice

All the living and non-living things found in a place, taken together, are called the environment.

Living things take in oxygen and give out carbon dioxide when they respire.

The main source of energy on Earth is the Sun.

Using the same thing again and again is called reuse. (The word “atmosphere” is not needed.)

Air is the mixture of gases all around the Earth; this layer of air is the atmosphere. It is mostly nitrogen (about 78 %) and oxygen (about 21 %), with a little carbon dioxide and other gases. Living things need its oxygen to respire, and green plants need its carbon dioxide to make food. Respiration and photosynthesis keep the oxygen and carbon dioxide in the air balanced.

About 71 % of the Earth’s surface is covered with water. Rivers, streams, lakes, ponds, wells, springs and seas are sources of water. Every living thing needs water to live; plants also need it to make their food. Most of the Earth’s water is salty sea water, and very little is fresh water we can use, so we must not waste or pollute it.

Soil covers the land. It is made of tiny pieces of rock, minerals, and the dead, rotting parts of plants and animals. Plants grow in soil and take water and minerals from it. People grow grains, fruits and vegetables in it. It is also the home of earthworms, ants, rats and countless tiny living things. Plant roots hold soil in place; where trees are cut, rain washes it away.

The Sun is the main source of energy on Earth. It gives us heat, which keeps the Earth warm, and light. Plants use sunlight to make their food, and animals eat plants, so all our food gets its energy from the Sun. The Sun’s heat also turns water into vapor, which forms clouds and falls as rain and snow. We use solar energy directly too, with solar panels and solar water heaters.

The parts that make up the environment of a place are its environmental factors: air, water, soil (land), energy (sunlight), plants and animals. They are of two kinds: abiotic (non-living: air, water, soil, light, heat) and biotic (living: plants, animals, microorganisms). They are all linked: plants use sunlight, air, water and soil to make food; animals eat plants and breathe the air; decomposers return dead bodies to the soil.

Using natural resources to meet our needs without harming the environment and without spoiling the quality of the resources is environment friendly behavior. It keeps air, water and soil clean and natural, so that they last for us and for those who come after us. For example: throwing garbage only in its place, sorted into waste that rots and waste that doesn’t; making compost; reusing and recycling things; planting and caring for trees; preventing forest fires; and using less plastic, chemical fertilizer and insecticide.

For example: old notebooks (the blank pages, for rough work); one side of used paper; empty jars and bottles (to store salt, spices, pencils or water); old tins, milk pouches and cut plastic bottles (as flower pots); old newspapers (to wrap things or cover books); cloth bags; old clothes (for younger children, or as dusters); cardboard boxes (to store things).

For example: old newspapers, books and cardboard (made into new paper and cardboard); plastic bottles and buckets (melted into new plastic goods); metal: old iron, tins, broken aluminium pots and copper wire (melted to make new things); glass bottles. In many places, scrap dealers (kabadi) go from house to house to buy them.

All living things, plants and animals alike, respire: they take in oxygen from the air and give out carbon dioxide. Burning wood and fuel also uses oxygen and gives out carbon dioxide. Green plants, in sunlight, make their food by photosynthesis: they take in carbon dioxide and give out oxygen. So respiration uses up oxygen and adds carbon dioxide, while photosynthesis uses up carbon dioxide and adds oxygen. The two together keep the amounts of the two gases in the air balanced (see Figure 4.2). That is why cutting forests upsets this balance.

• Throw garbage only in a bin, and sort it into waste that rots and waste that doesn’t.
• Never burn plastic or rubbish: the smoke is poisonous.
• Carry a cloth bag, and use fewer plastic bags, wrappers and bottles.
• Don’t throw waste into rivers, ponds or wells.
• Walk or cycle for short trips instead of riding a motorbike or car.
• Turn off lights, fans and taps when not needed.
• Plant trees and look after them.
• Tell your family and friends about these habits too.

Plastic doesn’t rot, so it stays in the soil and water for hundreds of years. It blocks drains, harms the soil, and kills animals that swallow it, and burning it gives poisonous smoke. It can be managed in these ways:

• Reduce: use less of it. Carry a cloth or jute bag to the market; refuse plastic bags and straws you don’t need; buy things loose rather than in small packets.
• Reuse: use plastic bottles, jars and buckets again, for example as flower pots or to store things.
• Recycle: keep plastic separate from waste that rots, and give it to the waste collector or a scrap dealer, so it can be made into new things.
• Never burn it or throw it into rivers, fields or forests.
• Rules and awareness: towns can ban thin plastic bags, and schools and families can teach everyone these habits.

Living things that depend on others for their food are called consumers.

Living things that rot and break down the dead bodies of living things are called decomposers.

The main source of light is the Sun.

A frog, which lives by eating insects, is a secondary consumer. (“Producer” and “tertiary” are not needed.)

“Decomposer” is left over.

The non-living parts of an ecosystem are its abiotic factors. Examples: air (oxygen, carbon dioxide, nitrogen), water, soil (with its minerals and rocks), heat and light from the Sun. Living things depend on them: plants need light, water, air and soil to make food, and animals need air and water to live.

Green plants are called producers, because they make (produce) their own food. They use carbon dioxide from the air and water from the soil, in sunlight, with the help of their green chlorophyll. Every other living thing depends on the food they make. Examples: rice, wheat, maize, mustard, grass, mango and banana trees, spinach, and algae in a pond.

Bacteria are decomposers. They break down the dead bodies and wastes of plants and animals with their enzymes, and mix them into the soil as minerals. Plants take up these minerals to make their food again. In this way bacteria:

• clean the ecosystem, so dead bodies and waste don’t pile up;
• return minerals to the soil, so it stays fertile and plants can keep growing;
• complete the cycle that links producers, consumers and decomposers.

Abiotic factors: air, water, soil, rocks, minerals, light, heat and moisture. The slope of the land, its moisture and its soil decide which plants and animals can live there.
Biotic factors:

• Producers: grasses, herbs, shrubs and trees, which make food and give out oxygen.
• Primary consumers: herbivores such as insects, deer, rabbits, elephants and rhinoceroses.
• Secondary consumers: jackals, foxes and wolves, which eat the herbivores.
• Tertiary consumers: leopards and tigers, which eat primary and secondary consumers.
• Decomposers: bacteria and fungi, which rot dead bodies and return minerals to the soil.

They are all linked, so the forest stays in balance.

The balance of the forest will be upset:

• The tigers and leopards that ate the deer will have too little food. Some will starve; others will leave the forest, or come to villages and kill goats and cattle.
• With no deer eating them, the grass and young plants will grow more for a while.
• Other animals that share food with the deer, or that ate the remains of deer killed by tigers (jackals, vultures), will also be affected.

One missing animal changes the whole ecosystem.