We went on a journey through different habitats and discussed many plants and animals. In our previous chapter, "Habitat and Adaption", we listed objects, plants and animals found in different surroundings. Suppose we stop a while and think which examples in our list are living? Let us think of examples from a forest. Trees, creepers, small and big animals, birds, snakes, insects, rocks, soil, water, air, dry leaves, dead animals, mushrooms and moss may be only some of the objects that are present in the forest. Which of these are living?
Think of objects that you can see around you at this moment and group them as living and non-living. In some cases, it is easy for us to know. For example, objects like chair or a table in our homes we know that they are not alive. Paheli was reading this rhyme from Complete Nonsense written by Edward Lear: Paheli and Boojho found the poem so very funny, because they knew that a chair or a table is not alive and it cannot talk, walk or suffer from the usual problems that all of us face.
A chair, table, stone or a coin. We know that they are not alive. Similarly, we do know that we are alive and so are all the people of the world. We also see animals around us that are so full of life — dogs, cats, monkeys, squirrels, insects and many others.
How do we know that something is living? Often, it is not so easy to decide. We are told that plants are living things, but they do not appear to move like a dog or a pigeon. On the other hand, a car or a bus can move, still we consider them as non-living. Plants and animals appear to grow in size with time. But then, at times, clouds in the sky also seem to grow in size. Does it mean that clouds are living? No! So, how does one distinguish between living and non- living things? Do living things have some common characteristics that make them very different from the non-living?
You are a wonderful example of a living being. What characteristics do you have which make you different from a non- living thing? List a few of these characteristics in your notebook. Look at your list and mark those characteristics that you have listed, which may also be found in animals or plants.
Some of these characteristics are perhaps common to all living things.
In Chapters 1 and 2, we learnt that all living things need food and how essential it is to animals and to us. We have also learnt that plants make their own food through the process of photosynthesis. Animals depend on plants and other animals for their food.
Food gives organisms the energy needed for them to grow. Organisms also need this energy for other life processes that go on inside them.
Does the dress you had four years back, still fit you? You cannot wear it any more, isn’t it? You must have grown taller during these years. You may not realise it, but you are growing all the time and in few more years you will become an adult.
Young ones of animals also grow into adults. You would surely have noticed pups of a dog grow into adults. A chicken hatched from an egg, grows into a hen or a cock.
Plants also grow. Look around you and see a few plants of a particular type.Some are very small and young, some are grown. They may all be in different stages of growth.Look at the plants after a few days and weeks. You may find that some of them have grown in size. Growth seems to be common to all living things.
Do you think, non-living things cannot show growth?
Can we live without breathing? When we inhale, the air moves from outside to the inside of the body. When we breathe out, the air moves from inside our body to outside. Breathing is part of a process called respiration. In respiration, some of the oxygen of the air we breathe in, is used by the living body. We breathe out the carbon dioxide produced in this process.
The process of breathing in animals like cows, buffaloes, dogs or cats is similar to humans. Observe any one of these animals while they are taking rest, and notice the movement of their abdomen. This slow movement indicates that they are breathing.
Respiration is necessary for all living organisms. It is through respiration that the body finally obtains energy from the food it takes.
Some animals may have different mechanisms for the exchange of gases, which is a part of the respiration process. For example, earthworms breathe through their skin. Fish, we have learnt, have gills for using oxygen dissolved in water. The gills absorb oxygen from the air dissolved in water.
Do plants also respire? Exchange of gases in plants mainly takes place through their leaves. The leaves take in air through tiny pores in them and use the oxygen. They give out carbon dioxide to the air.
We learnt that in sunlight, plants use carbon dioxide of air to produce their own food and give out oxygen. Plants produce their food only during the daytime whereas respiration in them takes place day and night. The amount of oxygen released in the process of food preparation by plants is much more than the oxygen they use in respiration.
How do you respond, if you suddenly step on a sharp object like a thorn, while walking barefoot? How do you feel when you see or think about your favourite food? You suddenly move from a dark place into bright sunlight. What happens? Your eyes shut themselves automatically for a moment till they adjust to the changed bright surroundings. Your favourite food, bright light and a thorn, in the above situations are some examples of changes in your surroundings. All of us respond immediately to such changes. Changes in our surroundings that makes us respond to them, are called stimuli.
Do other animals also respond to stimuli? Observe the behaviour of animals, when the food is served to them. Do you find them suddenly becoming active on seeing the food? When you move towards a bird, what does it do? Wild animals run away when bright light is flashed towards them. Similarly, cockroaches begin to move to their hiding places if the light in the kitchen is switched on at night. Can you give some more examples of responses of animals to stimuli?
Do plants also respond to stimuli? Flowers of some plants bloom only at night. In some plants flowers close after sunset. In some plants like mimosa, commonly known as ‘touch-me-not’, leaves close or fold when someone touches them. These are some examples of responses of plants towards changes in their surroundings.
Place a potted plant in a room a little away from a window through which sunlight enters some time during day time. Continue watering the plant for a few days. Does the plant grow upright, like plants out in the open air? Note the direction in which it bends, if it is not growing upright. Do you think, this may be in response to some stimulus?
All living things respond to changes around them.
All living things take food. Not all the food that is eaten is really used, only a part of it is utilised by the body. What happens to the rest? This has to be removed by the body as wastes. Our body also produces some wastes in other life processes. The process of getting rid of these wastes by the living organisms is known as excretion.
Do plants also excrete? Yes, they do. However, the mechanisms in plants are a little different. Some harmful or poisonous materials do get produced in plants as wastes. Some plants find it possible to store the waste products within their parts in a way that they do not harm the plant as a whole. Some plants remove waste products as secretions.
Excretion is another characteristics common to all living things.
Have you ever seen nests of some birds like pigeons? Many birds lay their eggs in the nest. Some of the eggs may hatch and young birds come out of these eggs.
Animals reproduce their own kind. The mode of reproduction may be different, in different animals. Some animals produce their young ones through eggs. Some animals give birth to the young ones.
Plants also reproduce. Like animals, plants also differ in their mode of reproduction. Many plants reproduce through seeds. Plants produce seeds,which can germinate and grow into new plants.
Some plants also reproduce through parts other than seeds. For example, a part of a potato with a bud, grows into a new plant.
Plants also reproduce through cuttings. Would you like to grow a plant in this way yourself?
Take a cutting from a rose or a menhdi plant. Fix it in the soil and water it regularly. What do you observe, after a few days?
It may not be easy to grow plants from cuttings. Do not be disappointed if your cutting does not grow. Talk to a gardner, if possible, on the care to be given to cuttings to make them grow into plants.
Living things produce more of their own kind through reproduction. It takes place in many different ways, for different organisms.
In chapter, "Gait of Animals", we discussed the various ways in which animals move. They move from one place to another and also show other body movements.
What about plants? Do they also move? Plants are generally anchored in soil so they do not move from one place to another. However, various substances like water, minerals and the food synthesised by them moves from one part of the plant to other. Have you noticed any other kind of movement in plants? Opening or closing of flowers? Do you recall how some plants show movement in response to certain stimuli?
We also have some non-living things moving, of course. A bus, car, a small piece of paper, clouds and so on. Is there something different in these movements from the movements of living beings?
There is such a variety of living organisms, but, all of them show some common characteristics, as we have discussed. Yet another common characteristic is that living beings die. Because organisms die, organism types can survive over thousands of years only if they reproduce their own kind. One single organism may die without ever reproducing, but, the type of organism can exist only if there is reproduction.
We see that, all living things seem to have some common characteristics. They all need food, respire, respond to stimuli, reproduce, show movement, grow and die.
Do we find some non-living things that also show some of these characteristics? Cars, bicycle, clocks and the water in the river move. The moon moves in the sky. A cloud grows in size right in front of our eyes. Can such things be called living? We ask ourselves, do these objects also show all the other characteristics of living things?
In general, something that is living may have all the characteristics that we have discussed, while non-living things may not show all these characteristics at the same time.
To understand this a little better, let us look at a specific example. Consider any seed, say, moong. Is it living? It can stay in a shop for months and not show any growth or some of the other characteristics of life. However, we bring the same seed and plant it in soil, water it and it turns into a whole plant. Did the seed — need food, did it excrete, grow or reproduce when it was in the shop for many months?
We see that there can be cases when we cannot easily say that a thing has all the characteristics that we have discussed, for it to be called living.
Push your hand deep inside a sack of wheat. Do you find it is warm inside? There is some heat being produced inside the sack of wheat. The seeds respire and in that process give out some heat.
We see that respiration is a process that takes place in seeds even when some of the other life processes may not be very active.
It may not be very easy to answer our question — “what then is life”? However, looking at all the diversity of living beings around us, we can conclude that “life is beautiful”!
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