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Part XX: How Organisms Communicate

The Effect of Stimuli on the Behaviour of an organism
The Effect of Chemical Stimuli
The Effect of Sound Stimuli
The Effect of Light Stimuli
The Effect of the Touch on Stimulus
The Effect of Stimuli on Behaviour Summary
(useful for revision)

The Effect of Stimuli on Behaviour : Questions

Emitters and Receptors
Sound Emitters and Receptors
Light Emitters and Receptors
Touch Receptors
Emitters and Receptors Summary (useful for revision)
Emitters and Receptors : Questions

Communication inside the Organism
The Vertebrate Central Nervous System

Topic Chapters Index

 

Lobster, Plymouth Marine Aquarium, UK © Shirley Burchill

Lobsters have chemical receptors on their mouthparts,
tail and antennae, as well as on their legs

 

Fact File No.51

There are 250 species of insect known to produce sex odours. 60 of these are butterflies and moths. The other 190 are beetles.

Of the 250 species of insect that produce sex odours, in 200 cases it is the female which attracts the male. In the other 50 cases it is the male which attracts the female.

 

Dung beetle © Paul Billiet

Insects detect chemicals in the air using their
antennae and palps on their mouthparts

 

Fact File No.53

Male silkmoths (Bombyx) have 40000 sex odour receptor cells on each antenna. The honey bee has 500000 receptor cells on each of its antennae.

CHEMICAL EMITTER AND RECEPTOR ORGANS

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Large animals which use chemical stimuli have special glands which are open to the surface of the animal's body. In insects these glands are usually found in the abdomen, although ant trails are made by secretions from a gland in an ant's mouth. In vertebrates the gland is either located somewhere on the head or near the openings of the sex organs at the rear of the animal.

 

Chemical Receptor organs

Small aquatic animals and small land animals with wet body surfaces have chemical receptors all over their bodies. Larger invertebrates have chemical receptors in various parts of their bodies. Spiders have chemical receptors at the tips of their legs while most crustacea have them on their mouthparts, tail and antennae, as well as on their legs.

Insects detect chemicals in the air using their antennae and palps on their mouthparts. Snails and slugs are able to detect chemicals with all parts of their bodies but they are both more sensitive around the mouth, on the tentacles and at the front of the foot. It is the tentacles which detect the odours from foods.

Most vertebrates have developed a special structure, the nose, which samples the air as they breathe.

 

Model showing nasal cavities © Shirley Burchill

 

It is no accident that the nose is found at the front of the head. It is in a good position to detect chemical stimuli as soon as possible. Some reptiles, such as snakes, use their tongues to pick up chemicals in the air. This is why they constantly flick their tongues in and out. The tongue of a snake is forked at its end and, when the tongue is in the mouth, the two tips are placed in small sensory pits in the roof of its mouth. This is how the snake 'smells' its environment. The taste organs of fish are not only found near the mouth but also on the fins and, in some cases, on the tail!

Mosquitoes find their human victims by sensing the presence of lactic acid, carbon dioxide and moisture on the skin. The mosquitoes are also attracted by body heat and movement.

 

Fact File No.52

Man has 40000 sensory cells per mm2 in his nose. The rabbit has 120000 per mm2, the fish has up to 95000 per mm2 and an eel possesses 800000 sensory cells per mm2.

The smelling area in a human nose is 3m2. In a dog the smelling area in the nose is 130m2. Only 40 receptors in the human nose have to be stimulated by as few as 9 molecules of skunk odour for the human nose to detect it!

 

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