UNIT 3 The interaction function Natural Science 2. Secondary Education EXAMPLES OF SENSE ORGANS

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3The interaction function

Natural Science 2. Secondary Education

EXAMPLESOF SENSE ORGANS

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3Examples of sense organs

SENSEORGANS

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CHEMORECEPTORORGANS

PHOTORECEPTORORGANS

MECHANORECEPTORORGANS


• Sense organs contain receptor cells that capture a particular type of stimulus and send a signal to the nervous system, which interprets it as a sensation.

Sense organs

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3: The cat’s eyes capture the light reflected from the bird.

2: The cat’s ears capture the vibrations of the bird’s chirp.

A cat’s sense organs capturing stimuli.

1: A bird chirps (producing vibrations in air particles) and reflects light.

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• The photoreceptor organs of animals are the eyes.

• They capture light and permit sight.

• They are normally on the head.

Photoreceptor organs

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• Depending on their complexity, eyes can be classified into different categories:

• Simple eyes. Many invertebrates have these. They only detect the presence or absence of light.

• Compound eyes. Arthropods have these. They are made up of thousands of individual photoreceptor units called ommatidia. Together, these units provide the animals with a mosaic image.

Types of eyes (I)

The compound eye in an insect.

Ommatidium

Compound eye

Simple eye

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• Camera-type eyes. Some invertebrates, such as cephalopods, have these eyes, and almost all vertebrates have them. Their structure is similar to that of a camera and they provide clear images of the animal’s surroundings.

Types of eyes (II)

The camera-type eye of a bird

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Camera-type eyes

Lens: This works just like the lens in a camera, focusing objects.Pupil: This serves the same

purpose as the diaphragm of a camera. It opens and closes to control the amount of light that enters the eye.

Retina: This works like the sensor in a digital camera. It is the innermost layer of the eye. This is where the image received by the eye is formed. This image is formed upside-down, but the brain corrects this and turns it to become an upright image.

Iris: A disc made of muscle. Its function is to open and close the pupil. It gives the eye its colour.

Optic nerve: This carries the information received by the retina to the brain.

Fovea: The part of the retina with the most cones.

Sclera: The outermost layer. It is white, except for the front part, the cornea, which is transparent.

Choroid membrane: The middle layer of the eye. It is dark red because it is full of blood capillaries.

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Go back to the Start menuNatural Science 2. Secondary Education

• There are various types of mechanoreceptor organs which differ depending on the stimulus they capture:

• Hearing organs (ears): These are usually holes that capture vibrations in the air or water.

• Balance organs: Cells that are sensitive to gravity and indicate the position of the animal’s body.

Mechanoreceptor organs (I)

A reptile’s ear

Ear opening

Ear opening

Structures that detect vibrations

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• Lateral line: Found in fish. This line detects vibrations and movements in the water.

• Skin: The skin has receptor cells that respond to pressure. It provides the sense of touch.

Mechanoreceptor organs (II)

The lateral line of a fish

Receptor cellChannel

Skin

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• These capture substances which are in the air, water and foods.

• They provide two closely related senses: smell and taste.

Chemoreceptor organs

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• Usually, these receptors are located near the mouth. For example:

• Arthropods: on the antennae.

• Vertebrates: in the nostrils or on the tongue.

Chemoreceptor organs

Antennae: These contain many receptors that respond to substances in the air, working as olfactory organs.

Tongue: The tongue captures substances from its surroundings and brings them to an olfactory receptor organ

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UNIT 3 The interaction function Natural Science 2. Secondary Education EXAMPLES OF SENSE ORGANS