What is symbiosis?

Symbiosis is a phenomenon in which two living organisms live together in such a way that they are mutually beneficial to each other. For example, the colourful clownfish live symbiotic relationship with the sea anemones. The clownfish enjoy the protection of the poisonous nettle fibres of the sea anemone and the sea anemone survives on the left-over food of the fish. 

The lichens that live in association with a fungus and an alga are also good examples of symbiotic relationships. Through the close interaction between its symbiotic partners, the lichens are able to grow in places, where they could never have existed alone.

 How do plants reproduce?

Plants reproduce in a variety of ways. Many species build side shoots, from which new plants grow. PIants like mosses and ferns reproduce with the help of spores, which are distributed by the wind and grow to become new plants. 'Higher plants' or the seed plants with male and female sexual organs have stamens with pollen and the stigma. 

The male pollen sticks to the stigma and is passed on to the egg cell in the ovary. A fertilized egg ripens to become a fruit, which contains the seeds. The seeds can be dispersed widely through wind or through animals who eat the fruits and discard the seeds.

 Why do deciduous trees shed their leaves in autumn, but conifers do not shed their needles?

Deciduous trees lose a lot of water through evaporation from their large and thin leaves. In summer, this does not pose a problem, since the roots soak in enough water from the soil, but in winter this is not possible because the soil is frozen. If the leaves are not shed before winter, the water will continue to evaporate and the plant will dry up. 

Moreover, the leaves can become brittle with frost and crack. Therefore, the deciduous trees shed their leaves as a precautionary measure. In contrast, the needles of the conifers are leathery and small, and there is very little evaporation through them. The needles are also frost-proof and stop their growth in winter.

 What are algae?

Algae are plant-like living organisms. They live in the seas, freshwater, or damp land areas. They range from tiny single-celled organisms, which can be seen only under a microscope, to larger plant-like planktons, used as food by blue whales or flamingoes. 

Large, leaf-like algae, known as 'seaweed, grow extensively in shallow waters to form dense underwater forests.

 Why should lichens be protected?

Many lichens grow in hospitable terrain; for instance, in the rocky highlands and cold Arctic. They also grow on the walls of the houses in big cities. The growth rate of lichens is very slow-apes species grow less than one
millimeter in a year. If you step on them, you may destroy in seconds a plant that took hundreds of years to grow. Since lichens are very sensitive to air pollution, they are often used as pollution indicators. The cleaner the air the more lichen will grow.

 What is photosynthesis?

The chloroplast inside the green leaves of plants is the 'workshop' where photosynthesis takes place. Water (H,O) is supplied to the leaves by the roots, and carbon dioxide (CO,) is absorbed from the air through tiny pores on the lower side of the leaf. Both these are broken down into the elements hydrogen (H), carbon (C), and oxygen (0) with the help of chlorophyll and sunlight. Plants build 'glucose' (grape sugar) from these elements and oxygen is released in the atmosphere as a by-product. Photosynthesis has been the source of oxygen in the air since the origin of life on the Earth. 

During photosynthesis, carbon dioxide and water are broken down with the help of the sun's energy. The end products of this process react together to form glucose (grape sugar) and oxygen. Glucose is stored in the plant and oxygen is released in the atmosphere, through tiny openings in the leaf.

 What is a star?

Stars are heavenly bodies, which shine like our sun. Many shine brightly, the others have a dim glow. Some are red while others are blue. Stars are giant balls of gas made of hydrogen, bound together by their own force of gravity. The energy that makes them shine comes from a kind of power plant in their interior, where atomic nuclei of hydrogen atoms are fused together to form helium atoms. 

The stars do not live forever and 'die' at some point. Many simply get extinguished, while very heavy stars expand and explode. Their remains become either a neutron star or a 'black hole'

 What is the difference between asteroids, comets, and meteors?

Asteroids are small heavenly bodies, which move around the sun like the planets. Thus, they are also called planetoids. Most of them go around the sun in the aste roid belt. Even comets, like Halley's comet, which has been sighted many times in the sky, are small heavenly bodies. They are characterized by a different orbit and a bright glowing tail. 

Meteorites are cosmic chunks of rock. When they enter the atmosphere, impact pressure causes the body to heat up and emit light, thus forming a fireball, also known as a meteor or shooting/falling star. They may occur very frequently.

 Why are some planets so big?

The largest planets of the solar system are the planets Jupiter and Saturn. Both planets have distinct bands around them with stripes. Saturn can be recognized easily by its rings. Uranus, uniquely tilted sideways, and the blue Neptune, the coldest of the outer planets, are also much larger than the inner planets. 

The outer planets are so big because they are comprised mainly of gases such as helium and hydrogen. These planets have a solid core, which is surrounded by liquid or frozen gas. This reason why they are also known as 'gas giants'.

 Why does the sun shine?

To a large extent, the sun is made up of hydrogen, which is converted into the element helium inside the sun's atmosphere. In the resultant fusion of two hydrogen atoms with helium, a lot of energy is released. As a result, the core of the sun heats up to an unimaginable
temperature: about 8 million °C! On the surface of the sun, the temperature is 'only' around 550o °C. 

The sun releases this heat energy in the form of radiation, which gives it its fiery glow. About every 11 years, the
surface of the sun changes and what we know as sunspots occur. The surface is somewhat cooler and darker around the spots. Thus, they radiate less energy. A few researchers believe that an increase in the occurrence of these spots causes ice ages on the Earth.

 Why does the moon change its shape?

The moon, which causes high and low tides on the Earth, is a sphere. It does not change its shape; only our view of it changes. The reason is that unlike the stars, the moon does not produce light, but only reflects the light of the sun. Since the moon goes around the Earth once in a month, the orientation of the moon, the sun, and the Earth respective to one another changes. 

For this reason, the illuminated part of the moon cannot always be seen clearly from the Earth. Sometimes we see it full, sometimes half, and sometimes not at all. The side of the moon that faces us remains the same. We can see the craters and dark spots on the moon, which are known as 'mares'.

 What is a black hole?

A black hole is a compressed dense mass with an intense gravitational field. The gravitational force of the black hole is so strong that nothing in its surroundings can escape from it, not even light. As a result, the space around a black hole gets distorted. It is similar to a gigantic funnel, which becomes flatter and flatter towards the upper margin. 

Everything near this funnel then slips down and makes the funnel deeper due to its own weight. The
black hole nearest to our solar system is about 8200 light
years away; so there is no real danger of being swallowed
by it.

 What is 'El Niño'?

'El Niño, which means 'the Christ Child' in Spanish, refers to a  disturbance in the Ocean current, which runs off the coast of Peru and which occurs every 3-8 years around Christmas. When distributed, the cold Humboldt current, which flows along the western coast of South America towards the north, is pushed back by warm water masses from southeast Asia. 

No one knows why this happens. The winds blowing over the Pacific also change dramatically during this disturbance; as a result, heavy rainfall and flooding Occurs in places that were earlier dry, while the hot and moist
regions experience such completely dry spells that fertile land dries up, crops wither, and people starve.

 How does a tsunami occur?

The Japanese word 'tsunami' means 'harbour wave'. It is a series of water waves caused by the displacement of a large volume of a body of water, usually an ocean,
though it can occur in large lakes. Tsunamis are caused by undersea landslides or by 'seaquakes', that is an earthquake whose epicentre lies below the ocean. 

If the seabed is displaced up to several metres, the water layer of several kilometres in thickness above it also moves with it. The wave caused by this movement has a lot of energy-much more than a wave of the same height whipped up by the wind. This becomes apparent when the wave moves towards the coast.

 How do we save ourselves from earthquakes?

Living in an earthquake-prone zone is often unavoidable. For instance, almost entire Japan lies in an earthquake-prone zone. For this reason, buildings here are primarily made 'earthquake resistant' so that the loss can be minimized. Buildings are built on foundations made of steel balls or from elastic materials such as bamboo. 

In skyscrapers, a pendulum weighing several tons is installed in the upper floors, which minimizes the vibrations that start in the upper storeys when an earthquake occurs. If an earthquake occurs, we should take refuge, at best, in the open or seek protection under a table.

 How are new seas formed?

Seas arise at places where the Earth's crust cracks open due to expansion. Around 200 million years ago the Atlantic was formed in this way. Today in East Africa, a crack from Malawi to Ethiopia has formed as a result of the eruption of a volcano. If the soil sinks further, water from the oceans will enter the region to give rise to a water body. 

This has already happened in the case
of Red Sea, the continuation of the East African rift system. If the plate continues to
expand, then at some point of time it breaks completely giving rise to a long mid-
ocean volcanic ridge.

 How are volcanoes formed?

Volcanoes are natural phenomenon that occur everywhere, but some places are more prone than the others. The molten rock and gas in the mantle called magma pushes its way upwards and pours to the surface through cracks in the crust. This is a volcano. There are different types of volcanoes; some are explosive others are not, and all erupt as spectacularly as we see on the television. Some eruptions take place unexpectedly, but others can be predicted, which is very important for the people living near a volcano.

 How were mountains formed?

Mountains are formed in two ways. When the tectonic plates move, they collide against each other. When the heavy oceanic part of the plate collides with the continental part, it submerges below it. The Andes, for instance, were formed in this way. The other way is when two continents collide with each other, the plates bend at the point of contact and fold up steeply. The Himalayas or the Alps were formed in this way around 35 million years ago and are counted among the 'young' mountains of the world. Old mountains, such as Black Forest or the Harz mountains, lower ranges because peaks have been wo down by rain, ice, and wind over time.

 What is the atmosphere made up of?

The word 'atmosphere' means a gaseous cover enveloping a planet. Without atmosphere life would not have been possible on the Earth: One-fifth of the atmosphere is oxygen and four-fifths is nitrogen. Like the Earth's interior, the atmosphere too is made up of several layers. All animals and plants live in the lowermost layer of the atmosphere called the 'troposphere'. 

All weather phenomena take place in the troposphere. Even aeroplanes fly in the outer edge of the troposphere. The stratosphere, the mesosphere, the ionosphere, and the exosphere lie above the troposphere.

 

How did we discover that the Earth is round?

About 30oo years ago people believed that the Earth was flat. But people wondered why ships disappeared at the horizon. Sailors too returned from journeys and were proof that ships did not fall off the edge of the Earth. 

The simplest explanation was: the Earth must be round. The final proof came in the year 1522 after the expedition of Ferdinand Magellan, who was the first to sail around the Earth.

What is the internal structure of the Earth?

 What is the internal structure of the Earth?

Like an onion, the Earth has several layers. The outermost layer, the Earth's crust, has an average depth of about 40 km. As compared with the diameter of the Earth, which is around 12,700 km, the Earth's crust is very small. It is primarily made up of solid rocks. 

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Below the crust is the mantle, reaching to a depth of about 2900 km. Due to the heat inside the Earth, the mantle consists of solid and molten rocks. Below the mantle is the core, made up of iron and nickel. The deeper one travels inside the Earth, the hotter it is. The temperature in the core is between 4000 and 5000°C.

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