Important methods used for preserving food are :
Chemical Method : Salts and edible are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservations. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
Preservation by Salt : Common salt has been used to preserve meat and fish ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind etc.
Preservation by sugar : Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of food spoiling bacteria.
Preservation by Oil and Vinegar : Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

There are five major groups of microorganisms:

1. Bacteria: They are single celled disease-causing microorganisms. They can be spiral or rod-shaped.
2. Fungi: They are mostly multicellular disease-causing microbes. Bread moulds are common examples of fungi.
3. Protozoa: They mainly include organisms such as Amoeba, Plasmodium, etc. They can be unicellular or multicellular.
4. Virus: Viruses are disease-causing microbes that reproduce only inside |the host organism.
5. Algae: They include multicellular, photosynthetic organisms such as Spirogyra, Chlamydomonas, etc

The process of loosening and turning of soil is called ploughing.
Ploughing of fields is done by using an implement called plough. Plough are made up of wood or iron and they have an iron tip for easy penetration into the soil.The ploughs are pulled by tractor or a pair of bullocks.

The process of loosening & turning the soil is called tilling of the soil. It is important to loosen the soil because:- It allows the roots of the plant to penetrate deep into the soil.

A plastic is synthetic material which can be moulded into desired shape when soft and then hardened to produce a durable article.Plastics are polymers. A number of articles made up of plastics are used in our daily life like water pipes, pens, combs, toothbrushes, toys, shoes, etc.

Salivary glands secrete saliva in the mouth which helps in the digestion of food. Saliva is 98% of water but contains electrolytes, antibacterial compounds, mucus, enzymes etc. It is an exocrine gland which secretes substances outside the body or within a body cavity. Saliva has lubricating properties. It protect the inside cavity of our mouth, teeth and throats as we begin to swallow the food bolus. It also cleanses the mouth after the meal and dissolves it into chemicals that we perceive as taste.

Gaps may form when a person's teeth are too small for the jaw bone.

Classification of Manures and fertilizers

• Natural or organic manures 
• Artificial or chemical fertilizers.

Natural Organic Manures

1. Farm Yard Manure: Well rotten Farm Yard Manure contains O.5.% N., 0.2 % P2 O5 and 0.5 % K2 O.
2. Compost : Well rotted plant and animal residue is called compost.
3. Green Manuring: Shrubs like glyricidia, sesbania, karanj.
4. Biofertilizers :
   1. Rhizobium
   2. Azotobacter
   3. Azospirillum
   4. Blue-green algae
   5. Azolla
   6. Mycorrhizae

Vermi-compost

It is the method of making compost with the use of earthworms, which generally live in soil, eat bio-mass and excrete it in digested form. This compost is generally called vermi-compost or wormi-compost. It is estimated that 1800 worms which is an ideal population for one sq. meter can feed up to 80 tones of humus per day.

• Animals Attack the crops
• Negligence 
• Overuse of chemicals
• Lack of knowledge of New techniques

• He did not use good quality seeds.
• His field was not well irrigated.
• Manures/fertilisers were not properly applied.
• Weeds were not removed.

During summer, we perspire more and the particles at the surface of the liquid gain energy from the surrounding or body surface and change into vapour. Now, cotton being a good absorber of water helps in absorbing the sweat and expose it to the atmosphere for easy evaporation and we feel cool.

Earth attracts every object towards it. We know that force is the product of mass and acceleration due to gravity.

This means, F=m×g  ----(i)

The force by which earth attracts an object towards it is called the weight of the object, which is the product of mass (m) of the object and acceleration due to gravity (g).

Weight is denoted by ‘W’.

Therefore, by substituting in the expression ‘F = mg’ we get,

W=m×g   ----(ii)

The soil considered an important resources because :

•  It provides food through agriculture.
•  It is the source of nutrients for many forms of life.
•  Many valuable minerals are explored from the soil.
•  It is home to various forms of life.
•  It supports vegetation.

Urea reacts with water to form ammonia, which makes the nitrogen within the fertilizer available to plants

The diseases caused by various microorganisms are as follows:

1. Protozoa: Malaria, amoebiosis, dysentery, giardiasis, kala-azar, etc.
2. Virus: AIDS, polio, dengue, rabies, chicken pox, influenza, etc.
3. Bacteria: Pneumonia, diphtheria, tuberculosis, meningitis, leprosy, typhoid, tetanus, syphilis, etc.

The plants need 1 to 2 inches of water per week. If you water too much right after planting and not enough as the potatoes begin to form, the tubers can become misshapen. The last hilling should be done before the potato plants bloom, when the plant is about 6 inches tall.

The fresh grains obtained by harvesting the crops contain higher moisture content which promotes the growth of fungus and moulds on the stored grains and damages them.  So, the food grains obtained by harvesting the crops are dried in the sunshine before storing, to reduce their moisture. The farmers store the dried food grains at home in metal bins and jute bags called gunny bags. Dried neem leaves are used for storing food grains at home. The large scale storage of food grains is stored in either gunny bags or grain silos.

Fertilizers are the inorganic compounds which supply specific nutrients.

For example: NPK (Nitrogen Phosphorous Potassium), ammonium sulphate, ammonium phosphate etc.

Lignite is a soft brown coal that still contains a high amount of water.

ADVANTAGES OF FRICTION
Friction plays a vital role in our daily life. Without friction we are handicap.
1. It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it becomes difficult to walk due to low friction of ice.
2. We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
3. A horse can not pull a cart unless friction furnishes him a secure Foothold.
4. We can write on a paper or on a board.
5. Friction helps in applying the brakes.
6. It helps in walking on floor.
7. Coffee mug stays on the dashboard.
8. Shuffling across a carpet to shock someone.
9. Draging of atmosphire with earth is possible
10. Helps to pevents the life on earth by burning astroids.
DISADVANTAGES OF FRICTION
Despite the fact that the friction is very important in our daily life, it also has some disadvantages like:
1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.
2. Due to friction we have to exert more power in machines.
3. It opposes the motion.
4. Due to friction, noise is also produced in machines.
5. Due to friction, engines of automobiles consume more fuel which is a money loss.
6. Machine efficency is decreased: energy input is lost to heat
7. Getting shocked by doorknobs
8. Rug burn
9. It counteracts movement and so it takes more energy to move, it can cause unwanted heat (e.g. in machine parts), and it wears things out like shoes.
10. Forest fires are caused due to friction between branches of trees

Organic farming is a farming system with minimal or no use of chemicals as fertilizers, herbicides, pesticides etc. and with a maximum input of organic manures, recycled farm-wastes, use of bio-agents such as culture of blue green algae in preparation of biofertilizers, neem leaves or turmeric specifically in grain storage as bio-pesticides, with healthy cropping systems [mixed cropping, inter-cropping and crop rotation. These cropping systems are beneficial in insect, pest and wheat control besides providing nutrients.

• The drinking straw is a very thin pipe which is used to drink Soft drinks.The drinking straw works on the existence of atmospheric pressure.
• A glass tube with a nozzle and Piston for sucking in and ejecting liquid in a thin stream is called syringe. The syringe works on the existence of atmospheric pressure. When the nozzle of a syringe is dipped in a liquid and its piston is withdrawn, the pressure inside the syringe is lower.
• Dropper is a short glass tube with a rubber bulb at one end and a nozzle at the other end.When we press the rubber bulb of the dropper by keeping its nozzle dipped in the liquid , air present in the glass tube and bulb is seen to escape in the form of bubbles. Due to this ,air pressure inside the glass tube and rubber bulb of dropper is very much reduced.