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

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UNIT 3
Examples of sense organs
SENSE ORGANS
PHOTORECEPTOR ORGANS
MECHANORECEPTOR ORGANS
CHEMORECEPTOR ORGANS
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Natural Science 2. Secondary Education

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UNIT 3
Examples of sense organs
Sense organs
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.
2: The cat’s ears capture the vibrations of the bird’s chirp.
1: A bird chirps (producing vibrations in air particles) and reflects light.
3: The cat’s eyes capture the light reflected from the bird.
A cat’s sense organs capturing stimuli.
Natural Science 2. Secondary Education
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4. Examples of sense organs
UNIT 3
Examples of sense organs
Photoreceptor organs
The photoreceptor organs of animals are the eyes.
They capture light and permit sight.
They are normally on the head.
Natural Science 2. Secondary Education

5. Examples of sense organs
UNIT 3
Examples of sense organs
Types of eyes (I)
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.
Simple eye
Compound eye
Ommatidium
The compound eye in an insect.
Natural Science 2. Secondary Education

6. Examples of sense organs
UNIT 3
Examples of sense organs
Types of eyes (II)
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.
The camera-type eye of a bird
Natural Science 2. Secondary Education

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Examples of sense organs
Camera-type eyes
Choroid membrane: The middle layer of the eye. It is dark red because it is full of blood capillaries.
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.
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.
Fovea: The part of the retina with the most cones.
Iris: A disc made of muscle. Its function is to open and close the pupil. It gives the eye its colour.
Sclera: The outermost layer. It is white, except for the front part, the cornea, which is transparent.
Optic nerve: This carries the information received by the retina to the brain.
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8. Examples of sense organs
UNIT 3
Examples of sense organs
Mechanoreceptor organs (I)
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.
Ear opening
Structures that detect vibrations
A reptile’s ear
Ear opening
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Examples of sense organs
Mechanoreceptor organs (II)
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.
The lateral line of a fish
Skin
Receptor cell
Channel
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10. Examples of sense organs
UNIT 3
Examples of sense organs
Chemoreceptor organs
These capture substances which are in the air, water and foods.
They provide two closely related senses: smell and taste.
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Examples of sense organs
Chemoreceptor organs
Usually, these receptors are located near the mouth. For example:
Arthropods: on the antennae.
Vertebrates: in the nostrils or on the tongue.
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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