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SUMMARY IV

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How Organisms Communicate

The Effect of Stimuli on the Behaviour of an Organism

♥ Both animals and plants react to stimuli

♥ The four main stimuli are light, sound, chemicals and touch.

♥ The chemical stimuli may act on the sense of smell, the sense of taste or on both of these senses.

 

Emitters and Receptors

♥ An emitter organ is responsible for producing a stimulus e.g. a light emitter organ.

♥ A receptor is a group of scattered cells or an organ which receives a stimulus e.g. the ear of mammals.

♥ Some organisms have a more sensitive receptor organ for a particular stimulus than for other types of stimuli. This is because they specialize in one particular sense e.g. smell in dogs.

♥ The efficiency of one type of receptor organ varies between different organisms.

 

Communication Inside the Organism

♥ Sensory cells are linked to muscle cells and other tissues by nerve cells.

♥ In animals with a complicated body structure there is a control centre which links the sensory cells to the muscle cells.

♥ As the bodies of different animals become more complex, so does the control centre - the brain.

♥ The brain co-ordinates the body's response to stimuli.

♥ The human central nervous system is composed of the brain and the spinal cord.

♥ Reflex actions are not co-ordinated by the brain although, in most cases, the brain is immediately aware that the reflex action has taken place.

 

Interdependence of Living Things

Social Behaviour

♥ Some large groups of animals are only temporary.

♥ Some permanent groups of animals do not show any social behaviour.

♥ Being a member of a group is an advantage to an individual because it can feed in greater safety, it is less likely to be attacked and it is able to find a mate more easily.

♥ A group of animals which shows social behaviour will be organized enough to show division of labour and co-operation between its members.

♥ Members of these groups are direct relations of one another.

 

Special Relationships

♥ Mutualism is an association between two organisms which benefits both of the organisms in the relationship.

♥ Parasitism is an association between two organisms, one of which harms the other one in some way.

 

The Ecosystem

♥ The producer organisms in an ecosystem are the green plants. They convert the sun's energy into chemical energy.

♥ The herbivores are the primary consumers. They take into their bodies the energy which has been stored by the producers.

♥ The secondary consumers are carnivores. They take into their bodies the energy which has been stored by the herbivores.

♥ Green plants are autotrophs. They use the energy of the sunlight to make their food.

♥ Animals are heterotrophs. They gain their energy by eating other organisms.

♥ Energy flows from the sun to the autotrophs and then from the autotrophs to the heterotrophs.

♥ A food chain ends with the top carnivore. A food chain is never very long because the amount of energy available for the consumers decreases along the food chain.

♥ Since most animals have a varied diet, a food web will show more clearly how many different things an animal eats.

♥ All green plants compete with each other for sunlight, water and minerals. All animals which eat the same thing are also in competition with each other.

♥ Decomposer organisms and scavengers help to re-cycle essential chemicals through the food web.

 

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