The sudden and extreme changes taking place during the development of a animal is called metamorphosis,

we get paper from trees. By recycling paper we can reduce the number of trees cut down a year. the ways by which we can conserve paper are :

1. One should make the most use of these paper products without being wasteful and then recycle them.
2. Be selective about what you print. At home, at school, and at work, you can save paper by cutting down on the amount of material you print off.

By the filtering of sewage water waste by proper system.

O₂=O+O       (by UV rays)

O₂+O=O_{3 (ozone)}

Lesser will be the pressure 

Not jouce is juice

Yes because i they connected by zinc and copper plate because of their jouce

LEDs have many advantages over incandescent light sources, including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, camera flashes, and lighted wallpaper. They are also significantly more energy efficient and, arguably, have fewer environmental concerns linked to their disposal.

Generally, this period is referred as teenage. During this period, the younger boy/ girl emerges from childhood and merges into adulthood.  In fact it is  an age of great changes. Like physical growth, changes in emotions, etc.

Upto 14-15

Smoke+fog

The gases like cfcs pollute atmospere

FOR AIR POLLUTION

- to use ecofriendly means of transportation preferably bicycles or walking till possible

- to stop people smoking which releases smokes and thus causes various health diseases

FOR WATER POLLUTION

-not to throw waste in rivers etc

-  Self hygiene must be maintained and drinking water must not be polluted.

{for more ways google it}

the distance between far point and near point of an eye is called range of vision

for a normal adult eye range of vision is 25cm-infinity

When speaking of human development, the term embryo refers to the first eight weeks of pregnancy, while foetus refers to the later stages of pregnancy after eight weeks. 

The embryonic period is all about the formation of important systems of the body. 

The foetal period, on the other hand, is more about growth and development so the baby can survive in the outside world.

1. Comets are substance made up of ice and dust and planets are spherical bodies that revolve around the sun.
2. Ex of comets is Hiliary  comet and Ex of planet is Earth

Ans. Calorific value of a fuel can be determined using Bomb Calorimeter. The procedure is explained below.

The crucible of the calorimeter is filled with the known mass of fuel, and then it is ignited. This heats the surrounding water, and the initial and final temperatures are recorded using a thermometer. The calorific value can be determined using the heat balance. 
Heat given by the fuel is equal to the heat gained by the water.

Nutrient needs are greater during adolescence than any other time in the lifecycle. Between the ages of 12 and 18, older children will experience several growing spurts, which are associated with hormonal, intellectual, and emotional changes that can make adolescence a challenging part of life. Failure to consume an adequate diet at this time can result in delayed physical development and growth. Nutrition is also important during this time to help prevent adult diet-related chronic diseases, such as cardiovascular disease, cancer, diabetes, and osteoporosis.

changes during the age of  puberty are regulated by the testosterone in male and by estrogen and progesterone in female.

Beside bad odour and dirt many germs and chemicals are present in water that must be removed before using it.

The difference between Sound waves and Light Waves are: Sound Waves require a medium where Light Waves do not require a medium

Sound Waves

1. Require a medium.

2. Travel with a speed of 332 m/s at 0 C.

3. Are longitudinal waves consisting of compressions and rarefactions.

4. Are of different frequencies, giving notes of different pitches.

5. Do not travel far as their energy is dissipated easily.

Light Waves

1. Do not require a medium

2. Travel with a speed of 3 *10⁸ m/s.

3. Are electromagnetic waves consisting of varying electric and magnetic fields.

4. Are of different frequencies, resulting in different colors.

5. Can travel through a much greater distance.

Question 1:

What are the different ways in which water gets contaminated?

Answer :

Water gets contaminated by the addition of:
(i) Agricultural chemicals: Farmers use excessive amounts of pesticides and fertilizers to increase crop production. These chemicals get carried away to the water bodies due to rains and floods which lead to water pollution.
(ii) Industrial wastes: Industries release harmful chemical wastes into water sources, thereby polluting them.
(iii) Sewage wastes: Waste materials from kitchens, toilets, and laundry sources are also responsible for contaminating water.

Question 2:

At an individual level, how can you help reduce air pollution?

Answer :

An individual can reduce air pollution by:
(i) Avoiding the use of cars as much as possible and by using public transport whenever possible.
(ii) By not using vehicles for short distances. 
(iii) By using clean fuels such as LPG and CNG instead of diesel and petrol.
(iv) Always disposing the garbage properly and not burning it.
(v) Controlling the emissions from vehicles and household chimneys.

Question 3:

Clear, transparent water is always fit for drinking. Comment.

Answer :

No. Clear and transparent water is not always fit for drinking. Water might appear clean, but it may contain some disease causing micro-organisms and other dissolved impurities. Hence, it is advised to purify water before drinking. Purification can be done by water purifying systems or by boiling the water.

Question 4:

You are a member of the municipal body of your town.
Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

Answer :

To ensure the supply of clean water to all residents the following steps must be taken:
(i) The main water source must be built in clean surroundings and should be maintained properly.
(ii) Chemical methods such as chlorination must be used for purifying water.
(iii) The area around water pipes must also be clean.

 

Question 5:

Explain the differences between pure air and polluted air.

Answer :

Pure air contains around 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide. Other gases such as argon, methane, ozone, and water vapours are also present in small quantities. When this composition of air is altered by the addition of harmful substances or gases such as nitrogen dioxide, sulphur dioxide, carbon monoxide, and particulate matter, then the air is said to be polluted.

Question 6:

Explain circumstances leading to acid rain. How does acid rain affect us?

Answer :

Burning of fossil fuels such as coal and diesel releases a variety of pollutants such as sulphur dioxide and nitrogen dioxide into the atmosphere. These pollutants react with water vapours present in the atmosphere to form sulphuric acid and nitric acid respectively. These acids come down with the rain, thereby resulting in acid rain.
Effects of acid rain: 
(i) Acid rains damage crops. 
(ii) Acid rains corrode buildings and structures especially those made of marble such as Taj Mahal.

Question 7:

Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

Answer :

(d) Nitrogen

 

Question 8:

Describe the ‘Greenhouse Effect’ in your own words.

Answer :

Greenhouse effect may lead to global warming, i.e., an overall increase in the average temperature of the Earth. Greenhouse effect is caused by greenhouse gases. Examples of greenhouse gases include carbon dioxide, methane, and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed by earth and then released back to the atmosphere. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus, helps in human survival. However, an indiscriminate increase in the amount of greenhouse gases can lead to excessive increase in the Earth’s temperature leading to global warming.

Question 9:

Prepare a brief speech on global warming. You have to deliver the speech in your class.

Answer :

Global warming is an increase in the average temperature of the Earth’s surface. It occurs as a result of an increased concentration of greenhouse gases in the atmosphere. The greenhouse gases include carbon dioxide, methane, and water vapour. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth’s temperature leading to global warming.
 

Question 10:

Describe the threat to the beauty of the Taj Mahal.

Answer :

Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on the monument (that is completely made of marble), they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble. 
 

Question 11:

Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

On Mercury temperatures can get as hot as 430 degrees Celsius during the day and as cold as -180 degrees Celsius at night.
Mercury is the planet in our solar system that sits closest to the sun. The distance between Mercury and the sun ranges from 46 million kilometers to 69.8 million kilometers. The earth sits at a comfy 150 million kilometers. This is one reason why it gets so hot on Mercury during the day.

The other reason is that Mercury has a very thin and unstable atmosphere. At a size about a third of the earth and with a mass (what we on earth see as ‘weight’) that is 0.05 times as much as the earth, Mercury just doesn’t have the gravity to keep gases trapped around it, creating an atmosphere. Due to the high temperature, solar winds, and the low gravity (about a third of earth’s gravity), gases keep escaping the planet, quite literally just blowing away.
Atmospheres can trap heat, that’s why it can still be nice and warm at night here on earth.
Mercury’s atmosphere is too thin, unstable and close to the sun to make any notable difference in the temperature.

Space is cold. Space is very cold. So cold in fact, that it can almost reach absolute zero, the point where molecules stop moving (and they always move). In space, the coldest temperature you can get is 2.7 Kelvin, about -270 degrees Celsius.
Sunlight reflected from other planets and moons, gases that move through space, the very thin atmosphere and the surface of Mercury itself are the main reasons that temperatures on Mercury don’t get lower than about -180 °C at night

The water that makes Earth a majestic blue marble was here from the time of our planet's birth, according to a <a href="http://www.sciencemag.org/content/346/6209/623">new study of ancient meteorites</a>, scientists reported Thursday.

Where do the oceans come from? The study headed by <a href="http://www.whoi.edu/profile.do?id=asarafian">Adam Sarafian</a> of the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts, found that our seas may have arrived much earlier on our planet than previously thought.

The study pushes back the clock on the origin of Earth's water by hundreds of millions of years, to around 4.6 billion years ago, when all the worlds of the inner solar system were still forming.

Scientists had suspected that our planet formed dry, with high-energy impacts creating a molten surface on the infant Earth. Water came much later, went the thinking, thanks to collisions with wet comets and asteroids.

"Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space," said study co-author <a href="http://www.whoi.edu/science/GG/people/marschall/">Horst Marschall</a>, a geologist at WHOI.

For that reason, he said, scientists thought that "surface water as it exists on our planet today must have come much, much later—hundreds of millions of years later."

When a rays of light reflected by a plane mirror image formation takes place.

Ans. Bitumen is a mixture of Organic Liquids that are highly Viscous, Black, Sticky, Entirely Soluble in Carbon Disulfide, and composed primarily of highly condensed Polycyclic Aromatic Hydrocarbons.

Naturally occurring or crude bitumen is a sticky, tar-like form of petroleum which is so thick and heavy that it must be heated or diluted before it will flow. At room temperature, it is much like cold molasses.

Ans, Though the moon does rotate around its axis, the speed with which it completes these revolutions match the amount of time it takes to orbit around the Earth, leading the same side to be faced toward Earth at all times. This process takes a about month, meaning the moon's days are as long as an Earth month

If the Moon didn't spin at all, then eventually it would show its far side to the Earthwhile moving around our planet in orbit. However, since the rotational period is exactly the same as the orbital period, the same portion of the Moon's sphere is always facing the Earth

The land is colder than the nearby water due to its lower specific heat. The cold land cools the air above it. ... Winds called landbreezes blow from the high to the low pressure cell. These local winds blow from the cooler land to the warmer ocean.

Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on themonument (that is completely made of marble), they react with marble to form a powderlike substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble.

Taj Mahal is made up of white marble. Marble is composed of calcium carbonate. Calcium carbonate reacts with acids and thus gets corroded. This is the reason; acid rain is damaging the Taj Mahal. This wonderful monument does not look white but is looking pale and dull. If corrective measures are not taken, the future generations may not be able to see the beauty of the Taj.

Water pollution is an appalling problem, powerful enough to lead the world on a path of destruction. Water is an easy solvent, enabling most pollutants to dissolve in it easily and contaminate it. The most basic effect of water pollution is directly suffered by the organisms and vegetation that survive in water, including amphibians. On a human level, several people die each day due to consumption of polluted and infected water.

Water pollutant:

1. Industrial waste
2. Sewage and waste water
3. Mining activities
4. Marine dumping
5. Accidental Oil leakage:
6. Burning of fossil fuels
7. Chemical fertilizers and pesticides
8. Leakage from sewer lines
9. Radioactive waste
10. Animal waste

Though water pollution may occur from a variety of sources, there are two terms used to describe how the water became polluted.

When water is polluted from point sources, this is pollution from a discrete location. This discrete location could be a factory, a sewer pipe or a runoff from a single farm. The BP oil spill in 2010 is an example of point source pollution, because the massive amount of oil leaked from a single point of origin.

Water pollution may also be from non-point source pollution, which is when several points of contamination over a large area contribute to the pollution of a water body. For example, one water body may be contaminated by multiple sources like agricultural runoff, city street runoff, construction sites and residential lawns. The Mississippi River is at great risk for non-point source pollution because it is so large and is exposed to a variety of possible pollution sources.