The circulation of nitrogen element through living things and non-living environment is called nitrogen cycle in nature. The main steps involved in nitrogen cycle are:

1. The nitrogen fixing bacteria present in the soil and in the root nodules of leguminous plants, blue-green algae and lightning in the sky fix atmospheric nitrogen and convert it into compounds of nitrogen which go into the soil.
2. The roots of the plants absorb compounds of nitrogen from the soil for their growth and convert them into plant proteins and other organic compounds which make up the body of the plants.
3. The plants are eaten up by animals as food. Animals convert plant proteins into animal proteins and other organic compounds which make up their body.
4. When plants and animals die the complex nitrogen compounds present in their dead bodies are decomposed and converted into simple compounds of nitrogen by certain bacteria and fungi present in the soil.
5. Certain bacteria convert some part of nitrogen compounds into atmospheric nitrogen which goes back into the atmosphere and thus the amount of nitrogen content remains more or less constant.

Seed Drill: It is an implement used for sowing seeds with the help of tractors. By using a seed drill, the seeds are sown at correct depth and correct intervals. The seeds sown with a seed drill are in regular rows and get covered by soil. This prevents the seeds to be picked up and eaten by birds. Advantages of using a seed drill:

1. By using a seed drill for sowing, the seeds are sown at correct depth and correct intervals.
2. The seeds sown with a seed drill are in regular rows.
3. When the seeds are sown in furrows by a seed drill, the seeds get covered by soil and hence cannot be picked up and eaten by birds.
4. Since it is tractor driven, it saves time and labour.

• Preparation of Soil:

The upper layer of earth is called soil in which crop plants are grown. Soil provides minerals, water, air, humus and anchorage to the plants. Preparation of soil is the first step in cultivating a crop for food production. The soil is prepared by ploughing, levelling and manuring.

The process of loosening and turning the soil is called ploughing (tilling). It is done by using an implement called plough. Ploughs are made of wood or iron having an iron tip for easy penetration into the soil. The ploughs are pulled by a pair of bullocks or by a tractor.

Advantages of ploughing:

1. The loose soil allows the plant roots to penetrate freely and deeper into the soil so that plants are held more firmly to the ground.
2. The loose soil allows the roots of the plants to breathe easily.
3. The loose soil helps in the growth of worms and microbes present in the soil as they help in turning and loosening of soil.
4. Ploughing also uproots and buries the weeds standing in the field and thereby suffocates them to death.
5. The loosening and turning of soil during ploughing brings the nutrient rich soil to the top so that the plants can use these nutrients.

Galvanisation is the process of zinc-plating other metals to protect them from corrosion. Metal sculptures are shown being cleaned in an acid bath then dipped in a bath of molten zinc. This forms a zinc coating which will protect the metal inside for hundreds of years. Galvanization is a metal coating process in which a ferrous part is coated with a thin layer of zinc. The zinc coating seals the surface of the part from the environment, preventing oxidation and weathering from occurring. ... Crystalline surface of a hot-dip galvanized handrail.

1. Change in Body Shape – When puberty sets in, a time of rapid changes in body shape and appearance starts in boys and girls which makes them look different from one another.

Changes in body shape and appearance in boys and girls brought about by the onset of puberty of puberty are as follows:

1. Boys develop broader shoulders and wider chests than girls.
2. Girls develop broader hips than boys.
3. Boys develop more muscles than girls.
4. Girls develop breasts.
5. Boys develop Adam’s Apple which makes them look different from girls.
6. Boys develop facial hair but the girls do not have facial hair.

1. Voice Change - At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice box in boys can be seen as a protruding part of the throat called Adam’s apple. In girls, the larynx is hardly visible from the outside because of its small size. Generally, girls have a high pitched voice, whereas boys have a deep voice.
2. Increased Activity of Sweat and Sebaceous Glands - During puberty the secretion of sweat glands and sebaceous glands (oil glands) increases. Many young people get acne and pimples on the face at this time because of the increased activity of these glands in the skin. The accumulation of oil, sweat and dead skin cells blocks the tiny pores in the skin of the face where bacteria grows causing swelling and redness and thus leads to pimples.
3. Development of *** Organs - The onset of puberty brings about complete growth and development of *** organs in boys and girls due to which their reproductive system starts functioning. The male *** organs like the testes and ***** develop completely. The testes begin to produce sperms. In girls, the ovaries enlarge and start releasing mature eggs.
4. Reaching Mental, Intellectual and Emotional Maturity – When a person reaches puberty, he or she becomes an adolescent. Adolescence continues up to the age of 18 or 19 years. During adolescence, a boy or a girl reaches mental, intellectual and emotional maturity. Adolescence is a period of change in a person's way of thinking. Adolescents are more independent than before and are also self conscious. Intellectual development takes place and they tend to spend considerable time thinking. In fact, it is often the time in one's life when the brain has the greatest capacity for learning. Sometimes, an adolescent may feel insecure while trying to adjust to the changes in the body and mind. The changes which occur in the body of boys and girls may cause emotional swings which show intense feelings like joy, anger, boredom, worries or sadness which are not based on reasoning or knowledge. These changes are a natural part of growing up process.

A satellite is an object that moves around a larger object. Earth is a satellite because it moves around the sun. The moon is a satellite because it moves around Earth. Earth and the moon are called "natural" satellites. But usually when someone says "satellite," they are talking about a "man-made" satellite. The word "satellite" refers to a machine that is launched into space and moves around Earth or another body in space. Earth and the moon are examples of natural satellites. Thousands of artificial, or man-made, satellites orbit Earth.

Plastics are non-corrosive in nature, they do not react even if they come in contact with strong chemicals. For example, the cleaning chemicals that we use at home are stored in plastic bottles, instead of metal containers. Plastics are non-corrosive in nature as: (i) they do not react with any substances. (ii) plastics do not react with air and water which are essential for corrosion. ... All the above mentioned properties make plastic useful for storage of various kinds of materials, including chemicals. Plastic is a non reactive substance as handles of pans are made of plastic so it is clear that it has no thermal conductivity and electricians wear plastic gloves to save them from electric shock and thus it does not show electrical conductivity.

Bovine means ruminant, which is to have a chambered stomach. Cows, as well as deer, goats, bison and giraffes fall into this category. If you want to be cow/cattle specific, the adjective is vaccine. The adjective for members of the swine family is suine (relating to Suina) also suilline. Bovine comes from the Latin word for "cow", though the biological family called the Bovidae actually includes not only cows and oxen but also goats, sheep, bison, and buffalo. So bovine is often used technically, when discussing "bovine diseases", "bovine anatomy", and so on.