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Life On Earth
(i)Beginning of life
The formation of chemicals in Ocean, in shallow pools, around volcanoes triggered the beginning of life i.e. to say, the beginning of first living cells. Chemicals possess the characteristic feature of copying themselves and hold the bubbles of oil together. And these tiny blot of chemicals were the beginning of the first living cells.
Chemical formation and reactions commenced owing to the lightnings, storms,fumes of volcanic eruptions, meteorites hitting the earth, intense heat etc.
(2)Development of life
The living cells were microscopic and one celled creatures similar to the bacteria of today. These one-celled creatures eventually began to use Sun light to make food, giving off oxygen in the process. As the oxygen built up in the atmosphere, it shielded the earth from Sun's harmful radiations. The extra oxygen helped the development of larger, more complex cells with a nucleus and special structures for carrying out different tasks. Around 600 million years ago, life really took off. There was a huge explosion of animal life in the ocean and the ancestors of probably all the modern animal groups came into being.
Around 100 millions of years, some simple animals without backbones like Jellyfish or Worms deveoped into animals with backbones including the first fish. Plants were the first to move into the land, followed by insects,small animals and walking fish called amiphibians.From amphibians developed the first large sand animals, reptiles such as the dinosaurs and later birds and mammals including humans.
Evolution
Evolution is development of life from earlier simple forms and is not each the result of special creation. In the middle of 19th century, Charles Darwin and Alfred Russell suggested that evolution happens because nature selects variations, which will survive. As the environment changes overtime, those individuals with variations best suited to the environment are more likely to survive and reproduce, while other individuals die out. So, as the environment changes, the individuals change too.
New life for Old
Since life first appeared on earth, millions of living things have died out.i.e.they have become extinct. They have been killed off by competition from other life forms, by rapid changes in climate or by changes caused by the drifting continents about the globe. So, the millions of different things on earth today are only a tiny fraction of all the living things that have ever existed.
Reproduction of Life
Life on earth would grind to a halt if there is no reproduction of living things. The living things change or evolve overtime through reproduction. Reproductiion causes living things to replace themselves and increase their numbers.
There are two types of reproduction- (i) Asexual and (ii) Sexual. In asexual reproduction, the parent first splits into two or more pieces or grow an extra part that becomes a new individual. Female eggs grow into babies without any input from a male, as happens in aphids. Hence, the off springs are identitical to their parents. Sexual reproduction involves the joining together of two special sex cells one from each parent. In animals, the male parent produces sperm cells and the female parent produces egg cells. In plants, the male sex cells are called pollen and the female ones are called egg cells. To produce a new individual, a sperm cell or pollen cell must join with an egg cell. This joining together is called Fertilisation.Here; the offspring is not identitical to their parents.
In Flowering plants, the egg cells stay put but the pollen may also fertilize on the same plant but very often travels from one flower to another with the help of wind, water, birds and animals. In most animals that live in the water, fertilisation takes place outside the animal's bodies. The egg and sperms are shed into the water and fertilization happens there. Animals that live on land fertilize the eggs inside the female's body because eggs and sperms quickly dry out and die in the open air.
Genes
Genes are found in the Nucleus or Control Center of a cell. Everytime a new cell is made; the DNA is copied so that each new cell has its own identitical copy of the genes. The final appearance and behaviour of an individual is determined both by its genes and by outside influences. These influences include things such as how much food it eats, what climate it lives in and whether it has suffered disease or injury during its development. But only the characteristics controlled by its genes can be inherited.
Sexual reproduction mixes up the genes twice-once when the sex cells are made and once again when fertilization happens. So, each individual off spring is different from its parents and from its brothers and sisters.
Senses
Most animals have eyes, which give them a picture of their surroundings. Most animals pick up sounds with ear in their head. The sense of taste is closely linked with the sense of smell. These two senses allow animals to find food, to send messages to one another and to avoid things that are harmful. Mammals use their nose for smelling things, snakes smell with their tongue and moths with their antennae. Octopuses taste with their tentacles and flies taste with their feet. Some animals can detect electricity, magnetism, water vibrations and heat. Birds use their magnetic sense to help them find their way when they migrate. Most fish have special lateral lines along the sides of their bodies that help them to pick up vibrations in the water. Sharks can pick up electrical signals from the Nucleus of fish to help them zoom in on their prey with deadly accuracy. Thus all the animals, birds possess 5 senses namely seeing, hearing.tasting, smelling and touching. Only the human beings are blessed with the 6th sense-Rational Mind-the senses enabling a man differentiate good and bad, mother and wife, etc.
Forms of living Things
Scientists once classified living things mainly by their shape and appearance and the way they develop. Now they can also compare the DNA (the molecule that makes up the genes) that parents pass on to their off spring. Living things, which look similar, may have different DNA.
The animal kingdom contains millions of different kinds or species of living things. Gorrillas, Chimpanzees and orangutans are closely related to humans and human blood is similar to the blood of these animals. A man can get a transfusion from a Chimpanzee. the brain cases of humans and gorillas are same in size at birth. Humans,chimpanzees and gorillas are prone to the same type of diseases.
Plants were the first living things to move out of the Ocean into land. They live on the earth for longer. And without plants, all animals including humans would die. scientists have identified more than 2,70,000 different kinds or species of plants.
Fungi are neither plants nor animals. Fungi cannot absorb Sun's energy to make food. They absorb their food from other living things. Fungi breakdown dead and decaying materials.
The most abundant life forms on earth are bacteria. Bacteria can only be seen with a very powerful microscope. A typical bacterial cell is about 1,000 times smaller than an animal cell. viruses are even smaller. These tiny packages of genetic material are not true living things because they cannot grow and reproduce on their own. They come to life inside living cells and invade other cells in order to make copies of themselves. A human body is carrying more than 100 trillion hitch hikers, the bacteria's which are just a tiny fraction of the millions of different kinds of bacteria that exist.
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