The process of centrifugation is used in dairies to separate cream from milk . 
Centrifugation is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated at a high speed in a centrifuge machine.
The milk is put in a closed  container in big centrifuge machine .
when the centrifuge machine is switched ON,  the milk is rotated at very high speed in a container. 
Due to this process, milk separates into cream and skimmed milk. 
The cream being lighter floats over the skimmed milk.
 

Newton’s Third Law of Motion states: ‘To every action there is an equal and opposite reaction’. 

Examples

1.A gun recoils when a bullet is fired from it:

2.A man walking on the ground

 3.Rowing a boat 

Newton’s second law of motion states that the time rate of change of momentum is directly proportional to the resultant of external force and change in momentum is in the direction of the resultant external force.

Mathematically, it states that the external force acting on a body is equal to the product of mass and acceleration of the body.

Apical meristem is a region of growth found in the plant’s shoots tips and root tips as well as the tips of new leaves and shoots. Apical meristem belongs to one of the four types of meristems. The other three are categorized as lateral meristems, namely: cork cambium, vascular cambium, and the intercalary meristem.

Aquatic organisms are used to a certain range of temperature in the water-body where they live. A sudden marked change in this temperature can be dangerous for them. It affects breeding of aquatic animals. The eggs and larvae of various animals are particularly susceptible to temperature changes.

Organic matter and nutrients cause an increase in aerobic algae and deplete oxygen from the water column. This causes the suffocation of fish and other aquatic organisms. Sulfate particles from acid rain can cause harm to the health of marine life in the rivers and lakes it contaminates and can result in mortality. A lack of sufficient oxygen kills off aquatic life and plants, resulting in dead zones and threatening the survival of the ecosystem. Land animals, birds, and humans can also be harmed by the contaminated water, or by consuming fish or shellfish that lived in contaminated water.

Almost all types of water pollutants affect the life forms living in the water. The pollutants encourage the growth of some life forms and can harm the growth of other life forms. This affects the balance between various organisms that persists in that system (ecosystem). With the increase in the amount of organic wastes in water, bacteria multiply very rapidly thus using up the available oxygen. The lack of oxygen hence caused kills the fish and other aquatic animals.
Aquatic organisms are used to a certain range of temperature in the water body where they live, a sudden marked change in this temperature can be very dangerous for them (they are cold blooded animals), e.g., it affects breeding of aquatic animals. The eggs and larvae of various animals are particularly susceptible to temperature changes.

Although the mass water level is fairly constant on earth, the amount of freshwater available to us is a minor part of the whole. Only 3% of all the water on earth is freshwater and not even all that is considered clean water that is safe for humans. Only 1% of all the water on Earth is acceptable drinking water.

A small shift in the amount of freshwater on Earth can have a profound effect on what is available for human consumption. Climate change, drought, degraded groundwater, other pollution, and overuse are a constant threat to the water supply.

The bodies of terrestrial organisms cannot tolerate the high amounts of dissolved salts present in saline water. So, they need fresh water for life processes like cellular reactions, transportation and excretion processes etc.

Ozone layer, comprising high concentration of ozone about 18-50 km above in the atmosphere, is commonly called ozone blanket. It is being depleted by air pollutants. Chlorofluorocarbons (CFCs) are synthetic harmful chemicals which are widely used in refrigerators and air conditioners as propellants. These chlorofluorocarbons are air pollutants and are mainly responsible for the depletion ofozone layer in the atmosphere. When these are released in the air, these harmful chemicals produce active chlorine' (Cl and CIO radicals) and fluroine in the presence of UV radiation. These radicals, through chain reaction, then destroy the ozone by converting it into oxygen. Due to this, the ozone layer in the upper atmosphere (i.e, stratosphere) becomes thinner. A single chlorine atom can destroy one lakh ozone molecules. Cholorofluorocarbons are, therefore, termed major ozone depleting substances (ODS). Other ozone depleting substances are nitrogen oxides and hydrocarbons. The thinning of ozone layer allows more ultra violet (UV) radiations to pass through it which then strike the earth. These cause following harmful effects on man, animals and plants:
(i) Skin cancer.
(ii) Damage to eyes, also increase incidence of cataract disease in eyes.
(iii) Damage to immune system.
(iv) Increased embryonic mortality in animals and humans.
(v) In plants too, there will be increased death rate of seedlings, increased incidence of harmful mutations and reduction in yields.

The ozone layer is a region in the earth’s stratosphere that contains high concentrations of ozone and protects the earth from the harmful ultraviolet radiations of the sun.

The ozone layer is found in the lower portion of the earth’s atmosphere. It has the potential to absorb around 97-99% of the harmful ultraviolet radiations coming from the sun that can damage life on earth. If the ozone layer was absent, millions of people would develop skin diseases and may have weakened immune systems.

The SI unit of work is joule (J). Joule is defined as the work done by a force of one newton causing a displacement of one meter.
It is named after the 19th-century English physicist James Prescott Joule, which is defined as the work required to exert a force of one newton through a displacement of one metre.

Lining of blood vessels are made up of squamous eithelium.

Carbon Cycle

It is one of the biogeochemical cycles in which carbon is exchanged among the biosphere, geosphere, hydrosphere, atmosphere and pedosphere.

All green plants use carbon dioxide and sunlight for photosynthesis. Carbon is thus stored in the plant. The green plants, when dead, are buried into the soil that gets converted into fossil fuels made from carbon. These fossil fuels when burnt, release carbon dioxide into the atmosphere.

Also, the animals that consume plants, obtain the carbon stored in the plants. This carbon is returned to the atmosphere when these animals decompose after death. The carbon also returns to the environment through cellular respiration by animals.

Huge carbon content in the form of carbon dioxide is produced that is stored in the form of fossil fuel (coal & oil) and can be extracted for various commercial and non-commercial purposes. When factories use these fuels, the carbon is again released back in the atmosphere during combustion.

Nitrogen Cycle

It is the biogeochemical cycle by which nitrogen is converted into several forms and it gets circulated through the atmosphere and various ecosystems such as terrestrial and marine ecosystems.

Nitrogen is an essential element of life. The nitrogen in the atmosphere is fixed by the nitrogen-fixing bacteria present in the root nodules of the leguminous plants and made available to the soil and plants.

The bacteria present in the roots of the plants convert this nitrogen gas into a usable compound called ammonia. Ammonia is also supplied to plants in the form of fertilizers. This ammonia is converted into nitrites and nitrates. The denitrifying bacteria reduce the nitrates into nitrogen and return it into the atmosphere.

Oxygen Cycle

This biogeochemical cycle moves through the atmosphere, the lithosphere and the biosphere. Oxygen is an abundant element on our Earth. It is found in the elemental form in the atmosphere to the extent of 21%.

Oxygen is released by the plants during photosynthesis. Humans and other animals inhale the oxygen exhale carbon dioxide which is again taken up by the plants.  They utilise this carbon dioxide in photosynthesis to produce oxygen, and the cycle continues.

To determine the percentage of water absorbed by raisins.

Apparatus and materials required:

A bowl, forceps, a common balance, a weight box, blotting paper and a few raisins.

Theory:

When raisins are placed in water (a hypotonic solution), they absorb water by a process called osmosis and swell up. Osmosis is the net movement of solvent molecules from a region of their higher concentration to a region of their lower concentration through a semipermeable membrane. The movement of water into the cells of the raisins through their cell membranes continues until the cells become turgid.

This process is called endosmosis. If these swollen raisins are now kept in a concentrated salt or sugar solution (a hypertonic solution), water from the turgid raisins will come out of the cells and they will shrink. This process is called exosmosis.

The percentage of water absorbed by the raisins due to endosmosis can be measured by knowing the difference of their initial weight and final weight.

Procedure:

1. Take three raisins and weigh them on the common balance. Let this value be W₁.

2. Keep these raisins in a bowl containing water for 2 hours.

3. Take the raisins out of water and gently dry them with the help of blotting paper.

4. Weigh the soaked swollen raisins again on the common balance. Let this value be W₂.

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Observations:

1. Weight of dry raisins = W₁.

2. Weight of swollen raisins =W₂.

3. Weight of the water absorbed by raisins = W₂ – W₁.

4. Percentage (%) of water absorbed by raisins = W₂ – W₁/W₁× 100.

Result:

The soaked swollen raisins weigh more than the dry raisins. This is because the raisins absorbed water by the process of endosmosis.

Precautions:
1. The raisins should be weighed accurately.

2. The raisins should be immersed completely in water.

3. Before weighing the soaked raisins, these should be dried gently with the help of blotting paper.

Aim

To determine the mass percentage of water absorbed by raisins.

Theory
Dry raisins when soaked in water they absorb water and increases their size by the process of osmosis and swell up. Osmosis is the movement of solvent from higher concentration to lower concentration through semi-permeable membrane. The difference in mass between the swollen and dry raisins gives the amount of water absorbed by the raisins.

Materials Required
Raisins, Electronic balance, Blotting Paper, Bowl, Petridish and Forceps

Procedure
Step 1: 10 dry raisins is taken and weigh them on electronic balance. Let it be x.
Step 2: These raisins were put in bowl containing water for 2 hours.

Step 3: These raisins were taken out using forceps and dried gently with the help of blotting paper.
Step 4: Weigh these soaked raisins on electronic balance. Let it be y.

Observation
The weight of dry raisins is x grams and weigh of soaked raisins is y.

Calculation
Weight of water absorbed by raisins = (y - x)
Percentage of water absorbed by raisins = {(y - x)/x} × 100

Result
The weight of the raisins soaked in water is more than the dried raisins because raisins absorbed water by the process of endosmosis.

Precaution
1. Raisins should be dried and weigh accurately.
2. Raisins should be properly soaked.
3. Excess water should be dried gently before weighing.

Water cycle. Water is one of the most important physical components which is essential for survival of life on earth. Ocean is the biggest store house of water which on evaporation forms clouds and which after condensation fall down as rain. After rain it passes through rivers and gets collected again in the ocean. The circulation of water in this manner is known as water cycle. The cycle is also performed through living beings like absorption and transpiration of water by plants and drinking by animals. Animals loose water during respiration and evaporation or perspiration. They loose water through excretion.

1) Without atmosphere life would not be possible as atmosphere protects us from harmful gases. We could not live without air present in atmosphere. In absence of the atmosphere, the earth would get so cold at night that we would not be able to survive. NO CO₂ and N₂ for plants without atmosphere.

We know that the sun is a star and if it explodes it will be known as a supernova. The explosion will be very bright and powerful. The dust released from the explosion will result in make of more stars and planets. That’s how our solar system was made. When the sun explodes, there won’t be light and the planets that are close to the sun will also be destroyed. These planets include Mercury, Venus, and Earth. Once a supernova is formed other existing planets will turn colder as the temperature of the sun reduces.