Other unique characteristics of living things include:
Respiration. Another point in which our two examples are alike is that they both breathe. If we keep either one in an air-tight box it will die. The cat breathes by means of its lungs and it is easy to see the muscular movements involved. The leaves of the plant breathe too, although our eyes cannot detect the way in which this is done. The process of breathing is called respiration in both cases.
Excretion. Both cat and geranium use the food that they assimilate to build up their bodies or to give them energy, and both throw off from their bodies unused and changed food materials by a process called excretion. The animal does this by means of the lungs, skin, intestines and kidneys; the plant by means of the leaves.
Motion. Another way in which all living things are alike is in the power of motion. It is easy to see the cat move, but few observe how the geranium turns its leaves to the light and its roots to the water. Though animals usually have greater freedom of motion, plants do not lack it altogether.
Sensation. In a general way, all plants and animals have the power of responding to touch, heat, light, and other forces outside of themselves. This is sensation, and may vary in its expression, from the mere turning of leaves toward light to the delicate operation of a wonderful sense organ like the human eye.
Reproduction. Both plants and animals reproduce others like themselves. Kittens are born and grow to be cats, and the plant bears seeds which will produce other plants like itself. By this wonderful provision of nature, although all organic things die, others like them are left to take their places. The processes of reproduction and nutrition are the two most important characteristics of all living things.
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