A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle. The Milky Way's disk spans at least 100,000 light-years and probably contains several hundred billion stars, which makes our home galaxy a giant. The smallest known galaxies in the Universe are actually tiny satellites of the Milky Way: objects like Segue 1 and Segue 3. They contain only a few hundred stars, orbiting their combined center of mass at less than the speed that Earth orbits the Sun: just 15 km/s.

We live on the Earth. On the Earth indicates on the surface of the Earth. the outer surface of Earth known as crust is the place where we live along with other species. in the Earth means in the interior of Earth which can be mantle, core or even deep inside crust. Much of Earth's water is thought to have come from asteroids impacting the planet early in its history. Image via NASA/Don Davis. The surface of the very young Earth was initially an ocean of magma. Hydrogen and noble gases from the solar nebula were drawn to the planetary embryo, forming the first atmosphere. The sun, at 4.6 billion years old, predates all the other bodies in our solar system. But it turns out that much of the water we swim in and drink here on Earth is even older.

Sirius is the brightest star in the night sky. Its name is derived from the Greek word Σείριος Seirios "glowing" or "scorching".Sirius, also called Alpha Canis Majoris or the Dog Star, brightest star in the night sky, with apparent visual magnitude −1.46. It is a binary star in the constellation Canis Major. Although white to blue-white in color, Sirius might be called a rainbow star, as it often flickers with many colors. 

Metamorphosis is a biological process in which a larva transforms into an adult. It involves sudden and abrupt changes in the body structure of the animal by cell growth and differentiation. It is generally observed in amphibians (e.g., frogs) and insects (e.g., butterflies), etc.
The life cycle of a frog has three life stages.

• Eggs Eggs are the result of external fertilisation which transform into fish like tadpoles.
• TadpoleTadpole has gills, small mouth and fish like tail to swim inside lakes and ponds.
• Frog: Tadpole grows and transforms into a small frog which is an amphibian by nature.

• Fresh water is the most precious substance on earth. It can neither be added nor subtracted from the earth.
• Water is used for agriculture, industries, generating electricity through reservoirs of dams, etc.
• The major causes of water shortage are increasing population, resign demands for food and cash crops, increasing urbanization and rising standards of living.
• Water is available through the water cycle, which is a constant movement from oceans to atmosphere and back to ocean through precipitation.

Indiscriminate use of resources and pollution caused by man is leading to degradation of land. Industries dump their waste openly and non degradable polythene bags are disposed off in landfills. Indiscrimate use of chemical fertilisers is one of the biggest contributing factors to land degradation. Deforestation results in loosening of the top soil and leads to easy erosion. Therefore man's activities are leading to land degradation.

To conserve land resources, sustainable development will have to be practiced. It is rightly said, nature has enough for man's need not man's greed. Therefore using timber but planting new trees in place of the ones cut will and segregation of waste and stopping dumping of plastic with other degradable waste will go a long way in helping restore land to its previous healthy state. enforcing strict laws against industries openly dumping their waste will have a prohibitive effect on such industries and make them treat their waste and find better ways of disposing their waste.  

Following are the four ways to prevent water pollution:
1.Chemical industries which pollutes the water most should be set up away from rivers and water reservoirs.
2.Waste water of industries should not be directly disposed off in the rivers.
3.Water of industries should not only be purified but also used for irrigation.
4. People should not bathe in rivers and should not wash their clothes in rivers. 

Friction can be increased by the following methods:

1. Grooves are made in the soles of shoes to increase friction and prevent slipping.
2. Treads are made in the tyres of vehicles to increase friction and prevent skidding of vehicles on wet roads.
3. Spikes are provided in the shoes of players and athletes to increase friction and prevent slipping.
4. Gymnasts apply some coarse substance on their hands to increase friction for better grip.
5. Machine belts are made of special materials to increase friction and drive machine wheels properly.

(i) Buckets made of iron get rusted but those made of plastic are not rusted.
(ii) Food can be stored in plastic containers, as they are resistant to chemicals in the food
(iii) Teflon coated pans are used instead of metallic as it does not react with chemicals in the food.

All the crops need water for their growth which they absorb from the soil. The process of supplying water to the crop plants in the fields is called irrigation. The time and frequency of irrigation varies from crop to crop and season to season. Irrigation is necessary to provide moisture for the germination of seeds. It is also necessary for the absorption of nutrient elements by the plants from the soil. Crops are supplied water for irrigation from different sources like rivers, canals, wells, dams, ponds and lakes.

Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Deposition is the phase transition in which gas transforms into solid without passing through the liquid phase. Deposition is a thermodynamic process. The reverse of deposition is sublimation and hence sometimes deposition is called desublimation. This causes the water vapor to change directly into a solid.

Natural resources are materials from the Earth that are used to support life and meet people's needs. Any natural substance that humans use can be considered a natural resource. Oil, coal, natural gas, metals, stone and sand are natural resources. Other natural resources are air, sunlight, soil and water. Each person on the planet uses on average over 8 tonnes of natural resour- ces per year, or 22 kg per day. If we include the unused extraction of materials (overburden), each inhabitant of the planet uses almost 40 kg per day.

1/4 and 1/2we will take lcm of 4 and 2 ...so that their denomenator would became sametheir lcm is 4 now we have to find 5 rational numbers b/w 1/4 and 2/4now we will multiply both the equations by 61/4 x 6 =6/242/4 x 6 = 12/24
therefore .....7/24 , 8/24 , 9/24 , 10/24 , 11/24

Bacteria are unicellular organisms belonging to the prokaryotic group where the organisms lack a few organelles and a true nucleus.

examples:  Streptococcus and Bacillus, Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria