An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs produce their own food, they are sometimes called producers. Plants is autotroph because they create there own food.

Ways to conserve water are as follows:

1. Turn off the tap immediately after use. Get the leaking taps repaired immediately.
2. Take bath by filling water in a bucket and not directly under the flowing tap.
3. Wash the utensils by filling water in basin and not under the running water.
4. Use the water from washing rice, vegetables or fruits for watering the plants at home.
5. Do not use a full flush from the cistern in the toilet when a half flush is sufficient.

In a compass, the tiny magnet is free to rotate on a pivot or pin and always comes to rest along the North-South direction. The compass has a circular dial with various directions marked on it. The magnetic needle in a compass is enclosed in a small brass box having a glass top. The north pole of compass needle is painted with a different colour to distinguish it from the South Pole.

The magnetic compass is used by soldiers and sailors to find directions. A freely suspended magnet always points in the north-south direction because the earth behaves as if a giant bar magnet is buried at its centre and it is the force exerted by the earth’s imaginary magnet which acts on the freely suspended magnet.

• The increase in size of an object on heating is called expansion.
• The decrease in size of an object on cooling is called contraction.

  Expansion on heating is a reversible change:

  When an object is heated, it increases in size thus expansion takes place on heating. When the hot object is cooled, it decreases in size and comes back to the original size by contraction.

A device for making fabrics by weaving yarn or threads is called a loom.

It is used for weaving of yarn to make fabrics. The loom which is worked by hand is called ‘handloom’ whereas the loom which works with electric power is called ‘powerloom’.

A volcano is an opening in the earth's crust through which lava, volcanic ash, and gases escape. Beneath a volcano, liquid magma containing dissolved gases rises through cracks in the Earth's crust. As the magma rises, pressure decreases, allowing the gases to form bubbles.

The cyclic movement of water from the atmosphere to the Earth and back to the atmosphere through various processes is called as water cycle.
Different steps of water cycle include evaporation, transpiration, condensation, precipitation and surface run-off.
a) Evaporation - The water present on the surface of oceans evaporates by the sun’s heat. This process of conversion of water from liquid state to vapour state is called evaporation. Evaporation also takes place from wet clothes, fields, ponds, lakes and rivers.
b)Transpiration - Plants take in water from the soil to prepare their own food and also for other life processes. They release excess water into air in the form of water vapour by the process of transpiration.
c) Condensation - The evaporated water is carried away by warm air. As the warm air moves higher from the surface of the Earth, it starts to cool down. This water vapour condenses to form tiny water droplets which float in air to form clouds or fog.
d) Precipitation - All these droplets collect to form bigger drops of water. Bigger water drops come down ads rain by the process of precipitation. If the air is too cold, the water drops can become snow or hail and may settle on the top of a mountain. When these snow or hail melts, they can become part of a river or a stream.
e) Surface run-off – Some amount of rain water is absorbed by the soil and settles down as ground water. Most of the rain water flows down the hills and mountains to collect into rivers, lakes or streams. Rain also washes away the topmost layer of the soil into water bodies.

Centrifugation:

Principle: This method is based on the principle of settling down under mechanical rotation, where insoluble heavier solid particles are present in an insoluble solid-liquid mixture.

Technique: The mixture is placed in a test-tube and kept in a centrifugation machine. On centrifugation, the solid particles settle down under the influence of an outward centrifugal force and the liquid component of the mixture floats above it.

Coal tar is a thick, black liquid having an unpleasant smell which is obtained by heating coal in the absence of air. It is a mixture of 200 carbon compounds which includes benzene, toluene, phenol, aniline, anthracene and naphthalene.

Uses:

1. Coal tar is used to make synthetic fibres, drugs, plastics, synthetic dyes, paints, pesticides, etc.
2. It has been traditionally used for metalling the roads. These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads.
3. Naphthalene balls used to repel moths and other insects are also obtained from coal tar.

An adaptation is an evolutionary process of a living species to live in its habitat or habitats and capable to reproduce. As the environment is not a permanent existence, the organisms have to keep adapting to the changing environment. Adaptation is a process which runs parallel to evolution. Today, if we see species like dinosaurs extinct, it is because they could not adapt to the changing environment. As we study evolution, we also notice the various stages man has been through before becoming the modern man. It is all a part of ecological adaptations.