Characteristics of Living Organisms

Characteristics of Living Organisms:

Biology is the study of life. If an organism is to be considered as living, it must possess certain basic life characteristics; for instance, a stone cannot move and this makes it non-living.

The point in the above instance is; every living organism must be able to move. As a result, movement is regarded as one of the basic characteristics of life.

Please read on an introduction to biology and the concept of viruses here.

Below are the basic characteristics of living organisms:

1. Movement: All living organisms move. Movement should not be confused with locomotion.

Locomotion requires a change of position while movement does not necessarily require a change of position. For instance, plants undergo bending movements while remaining on the same point (or position). Animals on the other hand can move from one point to another (locomotion).

When a plant is put in a dark room, it will attempt to move or bend towards light. This is known as positive phototaxis.

You can read on the concepts of force and motion here.

2. Respiration: Respiration is quite different from breathing. For respiration to occur, the process of breathing must first take place.

Breathing implies the exchange of gases. For instance, organisms breathe in oxygen (inhalation) and breathe out carbon(IV)oxide (exhalation). Conversely, respiration focuses on the use of the inhaled oxygen.

Inhaled oxygen is used for oxidizing or breaking down digested food (usually glucose) to produce energy (ATP); and this is what aerobic respiration entails.

Glucose is a simple sugar derived from the breakdown of carbohydrates (or complex sugars).

Please read on carbohydrates and sugars here.

Carbon(IV)oxide and water are waste products from aerobic respiration, thus organisms breathe them out.

Note: Respiration can also be anaerobic if food is broken down in the absence of oxygen.

Aerobic respiration occurs in an organelle of the cell called mitochondria and ATP is generated through the process. For this reason, the mitochondria is often regarded as the power house of the cell.

ATP is an acronym for Adenosine Tri Phosphate.

Please read on global acronyms and their meanings here.

3. Nutrition: All living organisms must feed to stay alive. Without food, organisms will neither grow, reproduce nor excrete.

Plants are organisms that manufacture their own food and are thus referred to as autotrophs. Animals on the other hand depend on ready made food, thus are referred to as heterotrophs.

• Please read more on autotrophic nutrition, photosynthesis and chemosynthesis here.
• You can read on food chain here.

4. Irritability: All organisms must be able to respond to stimuli if they are to survive in their environment. As an instance, a desert plant will have its root penetrating deep into the soil in order to get water.

Based on survival instincts, all animals will attempt to fight or run for survival whenever they sense danger.

Please read on the uniqueness of man here.

Note: A stimulus is anything that can elicit a physiological response in an organism. Stimulus can be either external or internal.

The sense organs (eyes, nose, ear, tongue and skin) acts as sensory receptors to external stimuli; that is, they receive stimuli from our environment. Examples of stimuli include touch, pressure, heat, cold, light, pain, water, sound, chemicals and so on.

Another name for irritability is sensitivity

Please read more on homeostasis here.

5. Growth: All living organisms must grow in size and mass. The food we eat (preferably protein) provides the basis for our growth through cell division. In addition to enhancing growth, protein also repair worn out tissues.

6. Excretion: All living organisms must remove metabolic waste product form their body. Metabolic waste products include water, urea, carbon(IV)oxide, sweat and so on.

Feces is not a metabolic waste product. This is so because it isn't produced via the body cells. Rather, they are undigested materials eaten via the mouth but didn’t even enter the body cells in the first instance. Inshort, they are not absorbed by the intestines into the body cells.

In larger animals, The removal of solid undigested materials from the anus is termed as egestion.

7. Reproduction: All living organisms have the ability to reproduce; that is, give birth to their young or offspring. Reproduction ensures the continuity of life for the various species of organism.

Living organisms reproduce in two ways:

• Sexually: These require the sex cells of the male and female organisms. The male sex cell is the sperm while that of the female are the eggs or ova.

When both sex cells meet (usually inside the female, but could also take place externally); fertilization occurs and a zygote is formed.

The reproduction involving sperm and egg is termed sexual reproduction.

Please read on the male reproductive system here.



• Asexually: This form of reproduction requires only one parent organism. No sex cells (sperm and egg) are involved.

The parent organism reproduces by dividing itself (cell division or binary fission), budding, spore formation or some other means.

Reproduction in this manner is termed asexual reproduction.

Please read on asexual reproduction in plants (plant propagation).

8. Death: All living organism must die. After death occurs, an organism will be considered as non-living because it cannot carry out other life characteristics.

Normally, living organisms are expected to grow and mature before they die.

Death is said to occur when an organism cannot carry out the other basic characteristics of life.

9. Adaptation: All living organisms must adapt to their environment if they are to survive. For instance, a fish is able to live in water because it has gills and fins.

Also, a camel is able to survive in the desert because it has large feet to aid walking on sand without sinking. It also has long eyelashes to help protect it from the blowing sand and wind.

Please read on desert biome, types and characteristics of desert here.

The point is:

All organisms have various features on them that enables them adapt within their habitat.

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Note: Plants are also able to live in different habitats because they have the required adaptive features towards that habitat. For instance:

• Plants that live in/on water are termed hydrophytes.
• Plants that live on land with moderate amount of water are termed mesophytes.
• Plants that live on deserts or arid lands are termed xerophytes.

10. Competition: Due to the limitation of resources, all living organisms must be able to compete for the necessary available resources if they are to stay alive.

The limited resources include food, water, light, mates, space and so on.

You may have observed that male lizards (with red necks) map out their territories in order to enjoy all the resources within it. To this end they will usually undergo fierce competition from their male counterparts before such territories can become theirs.

Please read on the characteristics of reptiles here.

The above form of behavior in male lizards is termed territorial behavior or territoriality.

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