Characteristics of life
It is not easy to give a precise definition of the term ‘life’. However, by observation and experimentation, we can record the activities that are the characteristics of organisms. Observe the living things around you. Compare them with non-living things. Try to write down a list of 10 characteristics of life that living things have in common. Some characteristics of living things are:
- Growth and Development
Now we learn in detail about these main characteristics of life.
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If you observe the animals around you, you will notice that they all have to feed. They must feed in order to survive, to grow and to carry out their daily activities. Do plants need food? If so, what do plants feed on?
Though plants have no organs of ingestion such as the mouth, they do take in water and mineral salts from the soil. Their leaves absorb carbon dioxide from the air. You can take away certain necessary minerals or nutrients from the soil and you will notice that the plants do not grow as well and would eventually die. Green plants take in the raw materials to make their own food. Non-green plants take in organic food substances.
This is release of energy by the breakdown of food substances like glucose in all living cells.
Every organism require energy to perform its vital activities such as growth and movement. Green plants derive their energy from sunlight by means of photosynthesis. Animals obtain theirs from the complex organic food they feed on. In both plants and animals, the organic food substances, especially carbohydrates and fats, store up energy. This energy is set free when they are broken down by oxidation into simpler substances such as carbon dioxide and water. This process is called Respiration.
Reaction of Respiration ……………….
Excretion is the removal of metabolic waste products that have been produced as a result of processes occurring inside the cells of an organism. Carbon dioxide, for example, is a waste product of respiration. It is excreted from your body through your lungs.
There are numerous chemical reactions occurring in the cells of an organism. These are metabolic reactions. Some of these reactions produce substances which are unless to the organism or may even be harmful. Hence they must be eliminated. The process by which the organism removes such metabolic waste substances are called excretion.
Most animals have special organs for removing their excretory substances such as carbon dioxide, water, mineral salts and nitrogenous waste products. Plants also excrete their waste products, but lack specialized excretory organs.
Living organism are open systems continually receiving and disposing both energy and materials. This process is basic to their continued existence. If it stops or break down, the organism dies.
This refers to all the chemical reactions that occur inside the tissue cells of an organism. Since these chemicals reactions take place in living organism, they are called biochemical reactions.
The growth of an organism involves the addition of more body substance. For example, you started off life as a single cell less than 1mm in diameter. Now, you are a large organism made up of billions of different types of cell.
Growth is a permanent increase in the mass and volume of an organism as a result of converting absorbed food into living protoplasm. Some of the new living materials formed are used to repair worn-out parts of the cells, the rest is added to the original living matter to bring about an increase in size. This may make the organism more complex or even change its form, e.g. a seed germinates into a seedling and grows into a mature plant. The egg of a butterfly hatches into a caterpillar, grows and changes into a pupa and finally emerges as an adult insect. The body form of an organism can change and get bigger, becoming more complex. This kind of growth is characteristic of most living organisms. We say most because some parasites actually become simpler in structure during the later phase of growth.
Non-lining matter such as a bicycle does not grow. However, a crystal immersed is a saturated solution may increase in size.
Movement is a characteristic of organisms. It is more easily detected in most animals than in plants. The movement of organism is independent of external agents such as the wind or water currents. Most animals are able to move from one place to another. Such a movement is called locomotion.
The movement of organisms from one point to another in a directed and controlled way is called locomotion.
Some animals do not have the power of locomotion, for example, corals and sponges. They are fixed to one place, but they can still move parts of their bodies. Most plants are unable to carry out locomotion but slow movements of their body parts are always taking place, e.g. the flowers of plants slowly open and shoots bend towards light as they grow. Some microscopic water organisms, e.g. Euglena, are able to move freely from place to place, resembling animals in this respect.
Living organisms are able to detect and respond to changes in their environment. This is called sensitivity. The organism detects a stimulus from the environment and produces a response to that stimulus.
Animals and plants are sensitive to any changes in the immediate surroundings. They often react to these changes in a way beneficial to themselves. For instance, cockroaches forage in a dark room but will find cover immediately when the light is turned on.
If you smell something unpleasant or touch something very hot, you immediately move from it. When the sensitive plant Mimosa pudica (touch-me-not) is touched, its leaves automatically fold up.
When a potted green plant is placed in a closed box the shoot grow vertically upwards. However, when light is allowed to enter through a hole made on one side of the shoots grow towards the light.
In all these examples, a change in the environment or an external influence cause the organisms to react in a predictable way. Such a change or external influence is called stimulus (stimuli: plural). This reaction of an organism to a stimulus is known as a response.
This property of living organisms that result in an appropriate response to a stimulus is termed sensitivity or irritability.
All living organisms are able to reproduce their own kind. In this way, the species lives on though individuals die. Individuals are never immortal. They die of disease or old age, in accidents or are eaten by other organisms. Thus, reproduction is necessary for the species to survive.
The production of new offspring is a process by which genetic information is passed from one generation to the next. For example, your mother and father passed their genetic information on to you. Thus, reproduction ensure the continuation of the species.
Living organisms are able to adjust and adapt themselves to changes in their environment. This adaptability increases their chances of survival and the perpetuation of their own species.
For instance, a change of seasons or a shortage of food may cause certain birds to migrate to another place where the conditions are more favorable. To get enough sunlight, a plant may grow very straight and tall to be above the plants around it. Non-living things do not show this adaptive response.
An adaptation is any characteristic of an organism that, in the environment in which they are living, improves their chances of survival and so enables them to leave behind offspring. For example, fish that are more streamlined are better adapted to life in livers than fish which are not.
Distinguishing a living organism from non-living matter
Some of the characteristics of living organisms given above can be found in certain non-living things.
For example, a motorcar can move and give off wastes products when its fuel is burnt. It is also a well-organized and complex structure. Indeed men have often used machines as models to help them understand how living organisms work. But machines do not produce themselves and do not grow. Thus all these characteristics must be considered in distinguishing a living organism from non-living matter.