Science: Grade 5
Life and Living: Senses in Animals and Humans
SENSES IN ANIMALS AND HUMANS
What are the Senses?
The senses are organs in the body that both humans
and animals use to take in information from the
environment.
Humans use their senses to see where they are going,
to hear a conversation or music, to feel if something
is hot or cold, to taste whether food is sour or sweet
and to warn us of danger, such as smelling smoke.
We Communicate Using Our Senses
As humans, we do not have to rely on our senses as much as animals do in order to survive,
there are many things that we would not be able to do without them. Our senses help us to
enjoy the world around us.
Sense of Smell
The 5 senses are:
The Five Senses
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Taste – we taste with our tongue
Touch – we feel with our skin
Hearing – we hear with our ears
Smell – we smell with our nose
Sight – we see with our eyes
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Science: Grade 5
Life and Living: Senses in Animals and Humans
Our sense organs respond to certain stimuli in our environment. For example, our eyes
respond to light, our ears respond to sound, our tongue and nose responds to chemicals and
our skin responds to pressure and heat. Our senses have receptors which can detect light,
smell, touch, taste and sound and transmit messages to our brains through our nervous
system.
Animals have the same senses as we do, but use them in different ways. They rely on their
senses to:




find food
find a mate
look after their young
avoid danger and protect themselves
Mouse Finding Food
Finding a Mate
Animals Use Senses to Care for their Young
Sight
Eyes are the organs used to see. Vision or sight is the body’s most dominant sense. Sight
provides both humans and animals with a huge amount of information about their
surroundings.
Sight is our Most Dominant Sense
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Life and Living: Senses in Animals and Humans
Our eyes contain millions of light detecting cells which convert light into electrical signals
that travel to our brains. In our brains, these signals are changed into coloured, 3D images.
The eyelids protect the eye from bright light, dirt and injury.
The eyebrows stop sweat from getting into the eyes.
The eyelashes keep dirt and dust out of the eye and protect the eye from glare.
The pupil lets lights into the eye.
A tear duct in the corner of the eye drain tears away from the eye.
The iris is the coloured part of the eye.
The cornea is the transparent layer that covers the surface of the eye.
When we see, what we are actually seeing is beams of light which bounce off an object and
into our eyes. The light enters through the cornea of the eye and then passes through the
pupil into the lens. The image is then focused through a jelly- like substance called the
vitreous humor, onto the back surface of the eyeball called the retina.
An Eye
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Life and Living: Senses in Animals and Humans
The retina is filled with 150 million light sensitive cells which send the information to the
brain through the optic nerve. This image is sent to the brain upside down and the brain has
to then turn the image so that it appears the right way up!
Spectacles (glasses) are used by people to correct poor vision. Binoculars and telescopes
make far away objects seem closer, while microscopes magnify tiny objects to make them
appear bigger.
Spectacles
Using a Telescope
Using a Microscope
to Magnify Objects
Many animals have a much better sense of sight than humans. For example, a falcon can see
a 10 cm object from a distance of 1,5 km.
Some fish can see the infra-red wavelength of the electromagnetic spectrum.
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Science: Grade 5
Life and Living: Senses in Animals and Humans
Smell
Our nose is the organ that we use for smell.
Nose
The senses of smell and taste are closely linked because both work by detecting chemicals.
However our sense of smell is 10 000 times more sensitive than our sense of taste, so when
you have a cold, often you will not be able to taste your food.
Receptors in our Nose Send
Messages to our Brain
The organ used to smell is the nose. When we smell something the chemicals in the substance
that we smell dissolves in the mucous of our nose. Receptors here send messages to our
brain. Our sense of smell is connected to our memory, so a certain smell can remind us of
certain events and places.
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Science: Grade 5
Life and Living: Senses in Animals and Humans
There are 7 main odours that humans can detect as shown in the table below:
Odour
Camphoric
Example
Mothballs
Musky
Aftershave or
perfume
Rose
Floral
Ethereal
Dry cleaning fluid
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Picture
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Life and Living: Senses in Animals and Humans
Odour
Pungent
Example
Vinegar
Putrid
Rotten eggs
Peppermint
Chewing gum
Picture
Although humans can detect between 4 000 and 10 000 different smells, a human’s sense of
smell is much weaker than an animal’s sense of smell.
Animals have a Strong Sense of Smell
Animals use their sense of smell to find food, find each other and to explore their
environment.
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Life and Living: Senses in Animals and Humans
Dogs have a very good sense of smell, which is why they are used to find drugs, bombs and
missing people. Sharks also have a very good sense of smell and can smell blood from over
4 km away.
Sniffer Dog
Sharks can Smell
Blood from a Distance
Taste
Taste helps us to detect and enjoy the flavours of food and drinks. It is the weakest of the 5
senses.
The Tongue is Used to Taste
Our tongue is the organ that we use for taste. It is covered with around 10 000 taste buds
which can detect substances in food and drink. These taste buds have receptors which send
the messages to our brain and tell us if the food or drink tastes nice or not.
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Life and Living: Senses in Animals and Humans
The four main tastes that we can detect are:

sweet
Sweet Taste – Cupcakes
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sour
Sour Taste - Lemons and Limes

salty
Salty Taste – Fish

bitter
Bitter Taste - Black Coffee
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Life and Living: Senses in Animals and Humans
The salty and sweet taste buds are at the front of your mouth, the sour taste buds are at the
sides and the bitter taste buds are at the back of the tongue.
When we are very young, we have taste buds on the sides and roof of our mouth as well as
our tongue, so we are very sensitive to taste. These disappear as we get older and our taste
buds become less sensitive, which is why our taste for certain foods can change.
Insects have the most highly developed sense of taste.
Insects have a Highly Developed
Sense of Taste
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Life and Living: Senses in Animals and Humans
Many animals use their tongues to taste. Snakes, some lizards and cats use their tongues to
smell. They have a Jacobson’s organ on the roof of their mouth, so when they pull back their
tongue, the food touches the Jacobson’s organ and they taste the food.
Snakes Use their Tongues to Smell
Fish can taste with their fins and tail, as well as with their mouth.
Fish Taste with Mouth, Fins and Tail
Some invertebrates, such as butterflies, have sense organs for tasting on their feet and
antennae.
Butterflies Taste with their
Feet and Antennae
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Life and Living: Senses in Animals and Humans
The earthworm’s body is covered with taste receptors.
Earthworms have Taste
Receptors over their Body
Touch
The sense organs for the other 4 senses are found in a specific place on our bodies, but the
sense organ for touch, i.e. the skin, is found all over our bodies.
Touching Hands
The skin consists of 2 main layers – the epidermis on the outside and the dermis inside. The
dermis contains sensory receptors and nerves which help us to detect if something is hot or
cold, for example.
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Life and Living: Senses in Animals and Humans
There are around 20 different touch receptors which send messages to our brain through the
spinal cord. The most common receptors are heat, cold, pain and pressure.
Pain receptors are important for safety because they warn your brain if you are getting hurt.
We have more pain receptors than any other touch receptors in our bodies.
The fingertips, lips, neck, feet and tongue have the most receptors and are therefore the most
sensitive to touch. Each fingertip has around 100 touch receptors in it. This is why it hurts a
lot when you burn your tongue, as well as why blind people use Braille to read. Braille works
by feeling raised patterns of dots.
Using Braille to Read
Animals use touch in the same way that we do, however, they have special features, like
whiskers, which helps them to feel things from further away.
Whiskers Help Cats to Feel
Some lizards can detect temperature of sand within 1° C, which helps them to know when to
lay their eggs.
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Life and Living: Senses in Animals and Humans
Hearing
After sight, hearing is the sense that provides humans with the most information. The ears are
the organs used for hearing. Hearing allows us to know what is going on around us.
Hearing
The 25 000 sensory receptors in our ears are stimulated by the vibration of sound waves
coming from a vibrating sound source.
Sounds are vibrations. These vibrations are transferred to three tiny ear bones which are the
smallest bones in our bodies called ossicles. The sound is then passed into a coiled tube
called the cochlea in the inner part of your ear. From here, nerves send a message to the brain
so that we can hear the sound.
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Life and Living: Senses in Animals and Humans
The eardrum vibrates in a similar way to the original source of the vibration. This allows us
to hear many different sounds.
Humans can hear sounds with a frequency between 20 and 20,000 vibrations per second.
Each vibration is called a Hertz (Hz) and this is the measurement used for sound frequency.
Many ‘hearing-impaired’ (deaf) people use sign language and can lip read, i.e. work out what
other people are saying by the way that their lips move. Hearing aids also help to make
sounds louder for people who have difficulty in hearing.
Sign Language
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Hearing Aid
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Life and Living: Senses in Animals and Humans
A doctor uses an instrument called a stethoscope to listen to your heartbeat and breathing
when he examines you.
Doctor Using a Stethoscope
Animals use hearing to communicate as well as to hunt. A bat makes a shrill call that bounces
off anything solid. They then listen for the echo to help them find their prey. This is
called echolocation.
Bats Use Echolocation to Find Prey
Animals can detect a wider range of sounds than humans. Many animals can hear sounds that
we cannot hear as humans. Animals such as bats, cats, mice, grasshoppers and whales can
hear sounds at frequencies much higher than humans can, i.e. 20 000 Hz. Dogs can hear
sound as high as 40 000 Hz and cats have a range of 100 to 60 000 Hz. Dolphins have the
best hearing of any animal and can hear 14 times better than humans. They can hear up to at
least 100 000 Hz.
Dogs and Cats have Better Hearing than Humans
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Life and Living: Senses in Animals and Humans
Mice communicate by ultrasound. A baby mouse will use a frequency of around 40 000 Hz to
call its mother and an adult mouse uses sound frequencies up to 70 000 Hz.
A Baby Mouse Communicates
by Ultrasound
A whale can transmit sounds up to 200 000 Hz. Dolphins and whales communicate by
making clicks and whistles to each other. Like bats, they also use sound to hunt. The sounds
they make bounce back from solid objects and make an echo.
Dolphins have the Best Hearing
and Use Sound to Hunt
Other animals can make and hear very low frequency sounds that humans cannot hear, i.e.
less than 20 Hz. Animals which are able to do this include the tiger, giraffe, elephant and the
rhino.
Tigers, Giraffes, Elephants and Rhino use Low Frequency Sounds
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Science: Grade 5
Life and Living: Senses in Animals and Humans
Animals use sound not only to sense danger, but also for other things. A male grasshopper,
for example rubs its wings across its legs to make a loud rasping sound in order to attract
females.
A Grasshopper has Ears on its Stomach and uses
Sound to Attract a Mate
Not all animals have ears on their heads. For example, a grasshopper’s ears are on its stomach
and a cricket has ears on its front legs. Frogs' eardrums are found on the outside of its body,
behind its eyes.
A Cricket has Ears on its Stomach
Frogs have External Eardrums
Special Animal Senses
We have seen that animals often have more highly developed senses than humans, especially
their sense of smell, hearing and sight. In addition, they also have unique receptor cells and
can sense stimuli that humans cannot.
Some species also have the ability to sense the world in a way that we cannot. For example,
some fish can sense water pressure and currents. Crabs have hair on their claws and other
parts of their bodies which helps them to detect the water current.
A Crab Claw has Hairs to
Detect Water Current
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Life and Living: Senses in Animals and Humans
Butterflies have hair on their wings to help them detect changes in air pressure.
Butterflies can Detect Changes
in Air Pressure
Bees have a ring of iron oxide on their abdomens which they use to detect magnetic fields.
They may also be able to sense any changes in the Earth’s magnetic field and use this to
navigate.
Bees can Detect Magnetic Fields
Ants and bees can detect polarised light, which they use to help them to navigate.
Several animals, such as fish have the ability to detect very low levels of chemicals.
Fish Can Detect Chemicals
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