The property of metals by which they can be drawn into wires is called ductility. Gold is most ductile element.

The term polymer id derived from two greek words POLY meaning many and MER meaning units. Therefore polymer refers to combination of repeating units. Cotton is a natural polymer known as cellulose which is composed of large number of glucose units. Other examples of natural polymers includes silk, wool, cellulose, DNA and proteins. Some of the synthetic polymers are nylon, Teflon polyester, polyethylene etc..

Microorganisms cannot be seen with naked eyes. They can be seen with the help of a microscope.

The food materials like milk, fruits, vegetables, meat, fish, cooked food, etc. get spoiled easily as they contain a lot of water due to which microorganisms can grow on them easily. We can prevent such food items by the proper methods of food preservation. The process in which the food materials are given a suitable physical or chemical treatment to prevent their spoilage is called food preservation. The various methods of food preservation are:

1. Sun drying – Drying (dehydration) means removal of water from food materials which are to be preserved. In the absence of moisture, the food does not get spoiled because the microorganisms which spoil the food do not grow in dry conditions. The vegetables like spinach, methi leaves, peas and cauliflower are preserved by sun drying method.
2. Heat and Cold Treatments – Heat kills many microorganisms and prevents the food from spoilage. Example – boiling of milk to prevent its spoilage. Pasteurised milk can be consumed without boiling as it is free from harmful microbes. During pasteurisation, milk is heated to about 70^oC for 15 to 30 seconds and then suddenly chilled and stored.
3. Storage and Packing – Now-a-days, dry fruits and even vegetables are sold in sealed, air-tight packets to prevent the attack of microorganisms on them.

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.

There are following four major groups of microorganisms:
(i)   Bacteria
(ii)   Fungi
(iii)   Protozoa
(iv) Algae.
In addition viruses are also considered as fifth group of microorganisms.

• Winnowing is the process of separating grains from chaff.
• Threshing is the process of loosening edible part of grain from husk and straw to which it is attached.

Phosphorus is a very reactive non-metal which catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.

The major gas that contributes to absorption of heat is carbon dioxide. Other greenhouse gases are methane, nitrous oxides, CFCs, and ozone.

Harmful effects of microorganisms:

1. Bacteria: Causes various diseases such as typhoid, diarrhea, and cholera.
2. Fungi: Causes a large number of diseases in plants and in animals such as rust diseases in plants, fruit rot in apple, red rot in sugar cane and ring worm disease in human beings.
3. Algae: Algal boom in water (rapid growth of algae) causes poisonous effect after they die, which in turn results in the death of aquatic organisms.
4. Protozoa: Causes Amoebic dysentery, pyorrhoea and sleeping sickness etc.
5. Virus: Cause small fox, common cold, influenza, herpes, hepatitis, polio and rabies.

Mitosis

• Mitosis is a continuum of changes but biologists like break down the stages of mitosis into four main stages, prophase, metaphase, anaphase and telophase.
• The focus in this class is on an understanding of the process and not a memorization of phases.
• The only phase name you will need to remember is metaphase.
• In mitosis the nuclear membrane is broken down, spindle fibers (microtubules) attach to the chromatids at the centromere and pull apart the chromatids.
• When the chromatids reach separate ends of the cells the spindle fibers disintegrate and a nuclear membrane rebuilds around the chromosomes making two nuclei.
• Each nucleus is identical to the original nucleus as it was in G1.

Meiosis

• Meiosis is the form of nuclear cell division that results in daughter cells that have one half the chromosome numbers as the original cell.
• In organisms that are diploid, the end result is cells that are haploid. Each daughter cell gets one complete set of chromosomes, i.e., one of each homologous pair of chromosomes.
• In humans this means the chromosome number is reduced from 46 to 23.
• The only cells that undergo meiosis will become sperm or eggs.
• The joining together of a sperm and egg during fertilization returns the chromosomes number to 46.
• Cells that undergo meiosis go through the cell cycle including the S phase so begin the process with chromosomes that consist of two chromatids just as in mitosis.
• Meiosis consists of meiosis I and meiosis II. In meiosis I homologous chromosomes are separated into different nuclei.

Substances are classified into two types. They are,

Pure Substance:  A substance which is made of one kind of particle.
Examples - iron, aluminium, silver and gold.

Mixtures:  A substance which contains two or more different particles is known as mixtures.
Example: Salt solution is made up of two components, salt and water. Therefore,salt solution is a mixture.

Jute fiber

• Jute fiber is used  for making carpets,gunny bags,ropes and bags.
• Source of earning money.
• Used as a packing material.

Cotton

• Apparel - Wide range of wearing apparel: blouses, shirts, dresses, childrenswear, active wear, separates, swimwear, suits, jackets, skirts, pants, sweaters, hosiery, neckwear.
• Home Fashion - curtains, draperies, bedspreads, comforters, throws, sheets, towels, table cloths, table mats, napkins

A main pipeline is laid in the field.Perpendicular pipes having rotating nozzles at the top are joined to the main pipelines at regular intervals.When water from a tube-well is allowed to flow through the main pipelines under pressure with the help of a pump,it escapes from the rotating nozzles.This water gets sprinkled on the crop plants as if it is raining.
Advantages
1) It is more useful for the uneven land where sufficient water is not available.
2) It is very useful for sandy soil.

<i>There is a disadvantage with synthetic fibers that synthetic fibers melt on heating. If the cloth catches fire it can be very disastrous. The fabric melts and sticks to the body of the person wearing it. It is therefore advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen.</i>

The process of conversion of atmospheric nitrogen into nitrogenous compounds and making it available for plants is called as nitrogen fixation. The organisms which fix nitrogen to plants are called as nitrogen fixers. Microorganisms in the soil convert atmospheric nitrogen into ammonium compounds, thereby enabling the survival of plants and animals.