UNIT 3 The interaction function Natural Science 2. Secondary Education EXAMPLES OF SENSE ORGANS
Jan 01, 2016
UNIT
3Examples of sense organs
SENSEORGANS
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CHEMORECEPTORORGANS
PHOTORECEPTORORGANS
MECHANORECEPTORORGANS
Natural Science 2. Secondary Education
• 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.
UNIT
3Examples of sense organs
Natural Science 2. Secondary Education
• The photoreceptor organs of animals are the eyes.
• They capture light and permit sight.
• They are normally on the head.
Photoreceptor organs
UNIT
3Examples of sense organs
Natural Science 2. Secondary Education
• 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
UNIT
3Examples of sense organs
Natural Science 2. Secondary Education
• 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
UNIT
3Examples of sense organs
Natural Science 2. Secondary Education
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.
UNIT
3Examples of sense organs
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
UNIT
3Examples of sense organs
Natural Science 2. Secondary Education
• 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
UNIT
3Examples of sense organs
Go back to the Start menuNatural Science 2. Secondary Education
• These capture substances which are in the air, water and foods.
• They provide two closely related senses: smell and taste.
Chemoreceptor organs
UNIT
3Examples of sense organs
Natural Science 2. Secondary Education
• 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
UNIT
3Examples of sense organs
Go back to the Start menuNatural Science 2. Secondary Education