1.1 Agricultural Practices
When plants of the same kind are cultivated at one place on a large scale, it is called a crop.
If we talking about the India, then India is a vast country. The climatic conditions like temperature, humidity and rainfall vary from one region to another. Accordingly, there is a rich variety of crops grown in different parts of the country. Despite this diversity, two broad cropping patterns can be identified. There are:
Kharif Crops : The crops which are sown in the rainy season are called kharif crops. The rainy season in India is generally from June to September. Paddy, maize, soyabean, groundnut and cotton are kharif crops. Continue Learning
2.1 Microorganisms
We have seen and learn several kinds of plants and animals. However, there are other living organisms around us which we normally cannot see. These are called microorganisms or microbes.
Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope. That is why these are called microorganisms or microbes. Continue Learning
3.1 What are Synthetic Fibres?
The synthetic fibres, on the other hand, are made by human beings. That is why these are called synthetic or man-made fibres.
A synthetic fibre is also a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer. The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit. So, a polymer is made of many repeating units. Continue Learning
4.1 Physical Properties of Metals and Non-metals
The property of metals by which they can be beaten into thin sheets is called malleability. This is a characteristic property of metals. The property of metal by which it can be drawn into wires is called ductility.
The things made of metals produce a ringing sound when struck hard. Since metals produce ringing sounds, they are said to be sonorous. The materials other than metals are not sonorous. Continue Learning
5.1 Coal
There are some exhaustible natural resources like coal, petroleum and natural gas. These were formed from the dead remains of living organisms (fossils). So, these are all known as fossil fuels.
- Inexhaustible Natural Resources: These resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Examples are: sunlight, air.
- Exhaustible Natural Resources: The amount of these resources in nature is limited. Continue Learning
6.1 What is Combustion?
A chemical process in which a substance reacts with oxygen to give off heat is called combustion. The substance that undergoes combustion is said to be combustible. It is also called a fuel. The fuel may be solid, liquid or gas. Sometimes, light is also given off during combustion, either as a flame or as a glow.
The lowest temperature at which a substance catches fire is called its ignition temperature. Continue Learning
7.1 Deforestation and Its Causes
There are a great variety of plants and animals exist surrounding us. They are essential for the well-being and survival of mankind. A major threat to survival of these organisms is deforestation.
Deforestation means clearing of forests and using that land for other purposes. Trees in the forest are cut for some of the purposes mentioned below: Continue Learning
8.1 Discovery of the Cell
The basic structural unit of an organ, which is the cell.
Robert Hooke in 1665 observed slices of cork under a simple magnifying device. Hooke observed as boxes or cells in the cork were actually dead cells.
Cells of living organisms could be observed only after the discovery of improved microscopes. Very little was known about the cell for the next 150 years after Robert Hooke's observations. Continue Learning
9.1 Modes of Reproduction
Reproduction is essential for the continuation of a species. Imagine what would have happened if organisms had not reproduced.
In plants, there are two modes by which animals reproduce. These are:
- Sexual reproduction, and Continue Learning
10.1 Adolescence and Puberty
Growing up is a natural process. The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence.
Adolescence begins around the age of 11 and lasts upto 18 or 19 years of age. Since this period covers the ‘teens’ (13 to 18 or 19 years of age), adolescents are also called ‘teenagers’. Continue Learning
11.1 Force − A Push or a Pull
In our daily life there has many actions like picking, opening, shutting, kicking, hitting, lifting, flicking, pushing, pulling are often used to describe certain tasks. Each of these actions usually results in some kind of change in the state of motion of an object.
So, a push or a pull on an object is called a force. Continue Learning
12.1 Force of Friction
The force of friction always opposes the applied force. Like the force of friction acts between the surface of the book and the surface of the table.
12.2 Factors affecting Friction
Friction is caused by the irregularities on the two surfaces in contact. Even those surfaces which appear very smooth have a large number of minute irregularities on them. Irregularities on the two surfaces lock into one another. When we attempt to move any surface, Continue Learning
13.1 Sound is Produced by a Vibrating Body
When a tightly stretched band is plucked, it vibrates and produces sound. When it stops vibrating, it does not produce any sound.
We see that a vibrating object produces sound. In some cases, the vibrations are easily visible to us. But in most cases, their amplitude is so small that we cannot see them. However, we can feel them. Continue Learning
14.1 Do Liquids Conduct Electricity?
To test whether a liquid allows electric current to pass through it or not, we can use the same tester.
When the liquid between the two ends of the tester allows the electric current to pass, the circuit of the tester becomes complete. The current flows in the circuit and the bulb glows. Continue Learning
15.1 Lightning
Lightning is also an electric spark, but on a huge scale.
15.2 Charging by Rubbing
When a plastic refill is rubbed with polythene, it acquires a small electric charge. Similarly, when a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects. the process of charging the refill and the plastic comb, polythene and hair also get charged. Continue Learning
16.1 What makes Things Visible
The sense of sight is one of the most important senses. Through it we see mountains, rivers, trees, plants, chairs, people and so many other things around us.
The eyes alone cannot see any object. It is only when light from an object enters our eyes that we see the object. The light may have been emitted by the object, or may have been reflected by it. Continue Learning
17.1 The Moon
The moon is the brightest object in the night sky. The stars, the planets, the moon and many other objects in the sky are called celestial objects. The study of celestial objects and associated phenomena is called astronomy.
The day on which the whole disc of the moon is visible is known as the full moon day. Thereafter, every night the size of the bright part of the moon appears to become thinner and thinner. Continue Learning
18.1 Air Pollution
As we know that air consists of a mixture of gases. By volume, about 78% of this mixture is nitrogen and about 21% is oxygen. Carbon dioxide, argon, methane, ozone and water vapour are also present in very small quantities.
When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution. Continue Learning