Exam practice

Energy is obtained from the environment.

Suitable weather is needed for farming. (“Favorable” is also right.)

In bad weather, animals move from their homes to favorable places. (“Suitable” is also right.)

Plants turn yellow when they get no sunlight.

Chlorophyll is found only in green plants. (“Cold” and “green” are not needed.)

Heat: the Sun, a fire, an electric heater (also a gas stove, a candle).

Light: the Sun, an electric bulb, a torch (also a candle, a kerosene lamp).

• Plants need sunlight to make their food. Without it, they can’t make food, so they can’t grow.
• Without sunlight, they stop making green chlorophyll. Their leaves turn yellow.
• They grow thin and weak, and in the end they die.
• Places with no sunlight are also cooler, and plants need warmth to grow and flower.

Winter is too cold for many vegetables. Frost and cold winds can kill them. In a plastic tunnel, sunlight passes through the clear plastic and warms the soil and the air inside. The warm air can’t blow away, and frost can’t settle on the plants. So it stays warmer inside than outside. The plants also still get light. That is why vegetables like tomatoes grow well in a tunnel even in winter.

Plants need heat to grow, to flower, to make fruit, to ripen their seeds, and to give out extra water from their leaves.
Animals need heat to grow, to keep their bodies warm, to have young ones, and to hatch their eggs.

Coal is a source of energy that will finish if we keep using it.

Excessive use of energy makes the natural sources of energy run out.

Using solar energy doesn’t cause pollution in the environment.

The Sun is the main source of energy. (“Electricity” and “less” are not needed.)

Firewood, charcoal, dung cakes, biogas, cooking gas (LPG), kerosene, petrol, diesel, coal, electricity, batteries, sunlight (solar panels, solar water heaters, drying clothes) and flowing water (a water mill).

Any two, for example:

• switching off lights, fans and TV when nobody is using them;
• cooking with a pressure cooker, and on an improved stove;
• using LED bulbs, which give the same light with much less electricity;
• drying clothes in the sun instead of with a heater;
• walking or cycling for short trips;
• using a solar water heater.

Any two:

• Biogas burns with no smoke, so the kitchen stays clean and our eyes and lungs stay healthy. Firewood fills the kitchen with smoke.
• Biogas is made from dung, so no trees are cut. Using firewood destroys forests.
• Biogas is renewable: cows make fresh dung every day.
• The waste left after making biogas is good manure for the fields.

An electric vehicle is better.

• It burns no fuel, so it gives out no smoke. A diesel vehicle’s smoke dirties the air and harms our health.
• Diesel is a fossil fuel that will run out, and Nepal has to buy it from other countries. Nepal makes its own electricity from its rivers, and rivers don’t run out.

Some sources make smoke and use up forests. Others don’t. If we choose the clean ones, the air stays clean and forests are saved.
Example: a family cooks on an open wood fire. Smoke fills the kitchen, and trees are cut for firewood. Then they build a biogas plant and cook with biogas. Now there is no smoke, no trees are cut, and the waste from the plant becomes manure. By choosing the right source of energy, they keep their home and the environment clean.

• Switch off lights, fans, TV and computers when they are not in use.
• Use LED bulbs instead of old bulbs.
• Cook with a pressure cooker, on an improved stove. Cover the pot with a lid.
• Use the Sun’s energy: dry clothes and grain in the sun; use a solar water heater.
• Use renewable sources such as biogas, solar power and hydroelectricity, instead of kerosene and diesel.
• Walk, cycle or take a bus instead of a car or motorbike.
• Take only dry, fallen firewood, and plant new trees.