Earth can be divided into three main layers: the core, the mantle and the crust. Each of these layers can be further divided into two parts: the inner and outer core, the upper and lower mantle and the continental and oceanic crust. Both the inner and outer core are made up of mostly iron and a little bit of nickel. the Earth has four layers: the solid crust on the outside, the mantle and the core -- split between the outer core and the inner core. Broadly speaking, the Earth has four layers: the solid crust on the outside, the mantle and the core — split between the outer core and the inner core.

A numeral system (or system of numeration) is a writing system for expressing numbers; that is, a mathematical notation for representing numbers of a given set, using digits or other symbols in a consistent manner. ... The number the numeral represents is called its value. A writing method for expressing numbers is called a "numeral system". In the most common numeral system, we write numbers with combinations of 10 symbols {0,1,2,3,4,5,6,7,8,9}. These symbols are called digits, and numbers that are expressed using 10 digits are called "decimal" or "base-10" numbers.

Leguminous plants replenish the soil by the presence of Rhizobium. These plants contain legumes and nodules which reside in the bacteria called rhizobium. These bacteria convert the atmospheric nitrogen into a soluble form that can be absorbed by roots.

The Earth has different compositional and mechanical layers. Compositional layers are determined by their components, while mechanical layers are determined by their physical properties. The outermost solid layer of a rocky planet or natural satellite. Chemically distinct from the underlying mantle. Earth can be divided into three main layers: the core, the mantle and the crust. Each of these layers can be further divided into two parts: the inner and outer core, the upper and lower mantle and the continental and oceanic crust. Both the inner and outer core are made up of mostly iron and a little bit of nickel.

A group of drummers who arose in southern India called the Parayan were considered untouchable because their drumheads were made of cowhide. Even people who had no choice in the matter (those born to parents who were both Dalits) were not allowed to be touched by those of higher classes nor ascend the ranks of society. A monarchy is a country that is ruled by a monarch, and monarchy is this system or form of government. A monarch, such as a king or queen, rules a kingdom or empire. In a constitutional monarchy, the monarch's power is limited by a constitution. But in an absolute monarchy, the monarch has unlimited power. A dictatorship is a government or a social situation where one person makes all the rules and decisions without input from anyone else. Dictatorship implies absolute power — one person who takes control — of a political situation, a family, a classroom or even a camping expedition.

Reversible: Things or processes which can be reversed are called reversible. For example, a folded sheet of paper can be unfolded and hence folding a sheet of paper is reversible.

Irreversible: Things or processes which cannot be reversed are called irreversible. For example, when milk turns into curd; it cannot be changed back to milk and hence is an irreversible change.

Dalits are also discriminated against in hiring and in the payment of wages by private employers. Dalits' attempts to enforce their rights are met with retaliatory violence and social and economic boycotts. It involves massive violations of civil, political, economic, social and cultural rights. Caste systems divide people into unequal and hierarchical social groups. ... They have also – through IDSN and by other means – managed to place caste discrimination firmly on the international human rights agenda.

Photosynthesis

• The process by which plants make their own food in the presence of sunlight, carbon-dioxide present in air, water, minerals and chlorophyll present in leaves is termed as photosynthesis.

The reaction that takes place in the process of photosynthesis can be written as:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

The photosynthesis equation is as follows: 6CO2 + 6H20 + (energy) → C6H12O6 + 6O2 Carbon dioxide + water + energy from light produces glucose and oxygen. ... In most plants, water is supplied from the roots, with the leaves collecting carbon dioxide via the stomata and sunlight captured by the chloroplasts in the leaves. During this process, organisms such as plants go through the light-dependent and light-independent reactions to convert carbon dioxide and water into sugars and oxygen.

In order to obtain silk, mulberry trees are cultivated, silkworms are reared and their cocoons are collected to get silk fibres. The various steps involved are:

(i) Rearing of silkworms: A female silk moth lays hundreds of eggs at a time. The eggs are stored by the farmers at suitable temperature and humidity under hygienic conditions. When the eggs hatch, silkworms come out of the eggs. The silkworms are fed mulberry leaves. After 25-30 days, the silkworms stop eating and get ready to spin cocoons. The silkworms enclose themselves completely inside the silken cocoons in two or three days.

(ii) Processing of cocoons to obtain silk fibres: The pile of cocoons is placed in hot water. Hot water makes the silk fibres of cocoons to separate out. The long fibres are obtained by unwinding the threads from cocoons. This process is called reeling.

(iii) Converting silk fibres into silk cloth: Silk fibres obtained from cocoons are spun (twisted) to form silk threads called silk yarn. The silk yarn is then woven on looms into silk cloth by the weavers

The Harappan culture grew and developed in India at the same time as other civilisations in the other parts of Asia and Africa mainly in the valleys of the rivers Nile, Euphrates, Tigris and Hwang-Ho. The Harappan culture became important about 4,500 years ago or in about 2,500 B.C.

A change which occurs without a change in the composition and chemical nature of the substance is called a physical change. It means that there is a change only in the physical properties of the substance. Properties like colour, hardness, rigidity, fluidity, density, melting point and boiling point are known as physical properties. Melting of ice or boiling of water is a physical change because ice, water and water vapours are chemically the same substance that is H₂O.

It is the mode of nutrition where two organisms live together for mutual benefit. For example, lichens. The association of algae and fungi is called lichen. Alga survives in water. Its need for water is fulfilled by the fungus which in turn consumes the food made by alga. The fungus in turn gives to the alga, water and minerals it obtains from the substratum on which it lives. This association of algae and fungi makes them look as if they are one single organism

Grass eating animals are called ruminant animals. Example – cow. They have special stomach to digest cellulose present in the grass. Their stomach is large and is divided into four compartments.

1. Rumen:
2. Omasum 
3. Abomasum
4. Reticulum

   Rumen is the first and the biggest compartment of a cow’s stomach. It contains cellulose digesting bacteria. When a cow eats grass as food, it does not chew it completely but swallow it and gets stored in the rumen. The bacteria present in the rumen start to digest cellulose and gets partially digested. The partially digested food/grass in the rumen of a cow is called cud. After some time, the cud is brought back into the mouth and is chewed thoroughly. That is why, a cow moves its jaws from side to side and chew continuously even when it is not eating grass.

   The process by which the cud is brought back from the stomach to the mouth of the animal and chewed again is called rumination. The animals which chew the cud are called ruminants. When the cud is thoroughly chewed in the mouth of the cow, it is swallowed and goes into the other compartments of the cow’s stomach and then into the small intestine for complete digestion and absorption.