The Characteristics of Living Things
A living thing pertains to any organism or a life form that possesses or shows the characteristics of life or being alive.
All living things share life processes such as growth and reproduction.
Most scientists use seven life processes or characteristics to determine whether something is living or non-living.
The Characteristics of Living Things
All living organisms are capable of movement. Movement is the change of position of the whole organism or just part of an organism.
For animals and unicellular organisms the movement is of the whole body. This is known as locomotion. Most animals move about using legs, wings or fins.
Unicellular organisms such as amoeba, paramecium and euglena use the locomotory structures pseudopodia, cilia and flagella respectively.
In plants only part of it may move towards different factors such as light, water, gravity etc. They move by growing. Their roots grow down in the soil and their shoots grow up into the air or towards a source of light.
2. Irritability (sensitivity)
Irritability is the ability of an organism to respond to a stimulus. Stimulus (plural; stimuli) is anything that causes a response in an organism.
Examples of stimuli include: an alarm clock, a smell of breakfast cooking and a fly landing on your skin.
All living things are sensitive to certain changes in their surroundings, that is, they are aware of what is happening around them. This is possible because they have special organs known as sense organs by which they detect these changes.
Examples of sense organs include: eyes for vision (sight); skin for temperature, touch, pressure detection; tongue for tasting; nose for smelling; and ears for hearing and body balance.
Plants do not have sense organs but are still able to detect and respond to things like gravity, water and light.
3. Feeding (Nutrition)
All living things need food to provide energy for such activities such as growth, repair and health.
Animals get their food by eating other living things or food materials that were once living things. Herbivores (e.g. rabbits) eat plants, carnivores (e.g. lions) eat other animals, and omnivores (e.g. humans) eat animals and plants. Plants make their own food through the process called photosynthesis.
The process of taking in food, synthesizing it, digesting and oxidizing it to release energy or build the body is called nutrition.
Respiration is the breaking down of food materials within cells to release energy.
Respiration usually involves the use of oxygen. All living things need energy for movement, growth and development, and functioning of body organs.
Excretion is the process of removing metabolic waste products from the body of living organisms
All living things produce wastes such as carbon dioxide, water, urea, ammonia etc.. Some of these chemicals if left to accumulate in the cells would seriously poison the living organism hence they need to be removed.
Waste products are removed from the body by excretory organs such skin, kidneys, lungs and liver.
Reproduction is the process by which living things produce new individuals of their kind. All living things reproduce, to replace organisms lost by death.
If a group of organisms does not reproduce fast enough to replace those which die, the group becomes extinct. Reproduction ensures continuation of life when parent generation dies.
Human beings bear babies; birds hatch chicks; and plants produce seedlings as new organisms, which eventually grow to mature organisms to replace those lost by deaths.
Growth is defined as an irreversible (permanent) increase in size and dry weight of an organism involving differentiation. All living things need food in order to grow and build up their bodies.
Animals grow until they reach certain adult size, but most plants can grow continuously throughout their lives.
A table of differences between living things and non-living things
|They respire||Do not respire|
|They grow||Do not grow|
|They respond to stimuli||Do not respond to stimuli|
|They reproduce||Do not reproduce|
|They excrete||Do not excrete|
|They feed||Do not feed|
|They move||Do not move|
Most scientists classify living things into one of the following six kingdoms.
Bacteria are single-celled microorganisms that don’t have a nuclear membrane.
Protozoans are single-celled organisms that are generally much larger than bacteria. They may be autotrophic or heterotrophic.
Chromists are a diverse group of plant-like organisms and range from very small to very large. They are found in almost all environments.
Fungi are multicellular and rely on breaking down organic material as they are not able to make their own food.
Plants are multicellular and autotrophic – they use photosynthesis to produce food using sunlight.
Animals are multicellular. They are heterotrophic and rely on other organisms for food.
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