Look at your surroundings. There may be walls, windows, chairs, tables and similar objects around you. Perhaps there are also machines, cars and gadgets. There may be other people too, and pets and plants. Which ones are alive? You can probably tell at a single glance if an object is living or not. For example, a dog is alive but a book is not.
But exactly how did you decide which things are alive and which are non-living? Perhaps you watch them to see if they move. A person or animal moves. Even a sleeping cat breathes softly. But a toy electric car moves and it is not alive, while a plant does not seem to move yet it is a living thing. Perhaps you look for signs of breathing. But the snails and plants in an aquarium do not seem to breathe, and they are alive. The giant panda is just a picture, but you know from looking at it that a real panda would be alive. How?
Living things are called organisms. We know if something is a living organism, rather than non-living, from several features. First, an organism grows and develops at some stage, usually changing its shape and getting bigger. Second, life processes happen inside the organism that change chemical substances from one form to another and which use up energy. Third, an organism must take in raw materials for its growth and also take in energy to power its life processes. Fourth, an organism reproduces—it produces more of its own kind.
ORIGINS OF LIFE
How did life begin? Scientific studies show that planet Earth formed about 4600 million years ago, from a massive ball of cloud, dust and gases whirling through space. At first, the rocks of Earth were far too hot for life. But gradually they cooled and massive rainstorms lasting many thousands of years filled the lakes, seas and oceans with water.
These seas contained all kinds of salts, minerals and other chemical substances. By chance, some of them joined to each other—perhaps helped by the energy of lightning flashes from the storms that raged across the globe. A few simple chemicals gathered as blobs. Other chemicals joined around them. These others then broke off to form blobs of their own. The first very simple living things had reproduced. This may have happened as long as 3000 million years ago. Life stayed as simple microscopic organisms for another 2000 million years.
GROUPS OF LIVING THINGS
To understand how living things have changed or evolved in the past, and how they work and survive today, it helps to know which ones are similar to each other. So organisms are classified or put into groups. There were once only two main groups or kingdoms, plants and animals.
Picture Credit : Google