Why do people have different coloured eyes?
The shape of the eye is round, except for the little bulge in
the front part. This curve in front is called the cornea. The cornea is
transparent and it helps the light rays enter the eye.
Around this entrance
is the coloured part of the eye called the iris. To regulate the light that enters
the eye, we have the iris and the pupil. The little black dot in the centre is
the pupil.
The size of the pupil is controlled by the iris according to
the brightness of the light available. If the eye has to see something in a
very bright light the opening becomes very small, if the light is dim, the opening
becomes large.
The iris has pigment in it to protect itself against light.
Everyone has pigment at the rear part of the iris. But only a few people have it
at the front, when the front part has no pigment at the front, it remains
almost transparent.
It absorbs the red and yellow light waves as the rays of
light pass through it. The remaining light that bounces off the pigment at the
rear of the eye is mostly blue. And this is why we see that some eyes are blue.
If the front part of the iris also develops pigment, it
absorbs different kinds of light rays and the colour of the eyes depends on the
light bouncing back from the rear of the iris.
Sometimes a person has blue eyes when young, but brown eyes
later in life because it takes some time to develop pigment at the front of the
iris.
How do we see different
colours?
Newton, the great scientist, was the first one to show that
what we call white light is actually a mixture of all the colours we see in
the rainbow.
When a beam of light passes through a glass prism, it
separates all the colours, and the outcoming light shows us all the colours of
the rainbow – red, orange, yellow, green, blue, and violet. Each colour blends
gradually into its neighbouring one smoothly. This coloured band is called a
spectrum.
Different colours are determined by different wavelengths. The
shortest visible light waves are violet, and the longest is red. The shorter and
longer wavelengths than these cannot be seen by human eyes.
When white light falls on an object, only some of the
wavelengths are reflected back to reach our eyes, the rest are absorbed by the
object. A piece of green paper, for example, absorbs all other wavelengths
except a certain range of those producing green colour.
Only these reach our
eyes and we see green colour. If an object reflects back almost all the wavelengths we see it as a white object. If an object absorbs almost all
wavelengths we see it as a black object. Normally most of the colors we see
around us are not a single wavelength but a mixture of many wavelengths which
give us mixed shades of colors.
What colours do colour-blind
people see?
The human eye is a sensitive camera that normally produces coloured
pictures for us. But sometimes this camera is unable to distinguish between
certain colours. People who cannot see all the colours of the visual spectrum
are called colour-blind.
About one in every 12 males and one in every 200 females
suffer from this defect. Colour blindness is a great handicap. It is
particularly so for those who drive vehicles on the road.
Driving can be dangerous
for them because they cannot distinguish between red and green signals. Colourblind
people are not given jobs as pilots or engine drivers for the same reason.
There are different kinds of colourblindness. In the most
common form, a person cannot tell the difference between yellow and pale green.
In another common one, a person cannot distinguish red from green. To him both
the colors appear a kind of gray. Some people are totally colourblind. To them,
all colours appear as shades of black and white.
Colorblindness is considered a hereditary disease. Until now
no cure has been found for this.
What does the pulse
tell the doctor?
The human heart beats almost non-stop day and night. Each
time the heart beats, it sends a pulsation through the arteries carrying blood.
The alternate expansion and contraction of the heart produce a throbbing in
the arteries of the body.
A doctor counts the pulse of a patient by pressing a blood vessel or artery in the wrist. The number of beats he feels in one minute is the pulse rate. The pulse rate can be counted by feeling the beats in many other parts of the body too.
The pulse indicates how often the heart is beating and this can show how strong your heart is and many other things about your body in general. An irregular pulse rate indicates some abnormality in the functioning of the body and heart.
The pulse rate of a normal healthy person is about 75 beats
per minute. The pulse rate in children is much higher than that of adults. The
normal pulse rate of a seven-year-old child is about 90 beats per minute. A newborn baby can have a pulse rate of 140. For old people, it can be about 60 per
minute.
Small animals or birds need a higher pulse rate. A small bird
may have a pulse rate of almost 200 beats per minute while for an elephant it
will be only about 25!
Why are vitamins vital
to us?
Vitamins are organic compounds present in our usual diet and
are essential for the healthy and normal functioning of our bodies. Vitamins are
present in very minute quantities in the food but this small amount is
sufficient for the body’s requirements.
Vitamins are vital because their absence can cause diseases
and make our bodies weak and incapable of fighting against infections.
Synthetic and natural vitamins usually have the same effect.
Although there are long and complicated names for different vitamins, we know
them by their familiar names represented by simple letters, A, B, C, D, E and so
on. All vitamins can be divided into two groups – the water-soluble group and the fat-soluble group.
Fat-soluble vitamins like A, D, E, and K can be stored by the
body but water-soluble vitamins like C and various vitamins of the B group
cannot be stored by the body and hence must be taken more regularly.
Vitamin A helps produce beautiful skin, bright eyes, and
resistance to infections and diseases and can be obtained by eating yellow and
green leafy vegetables, fruits, eggs, liver and butter.
Vitamin C helps in building resistance to allergies and
infections and is essential for tissues, bones and teeth. This is found in
citrus fruits, raw cabbage & tomatoes. Vitamin D is important for the
healthy growth of the body and can be obtained from fish liver oils.
Vitamins of the B Group consist of about eighteen members.
These are important in preventing fatigue, keeping the nerves relaxed, skin,
eyes and blood in good health. Unrefined flour, cereals, beans, molasses,
yeast, eggs lean meats, and green vegetables are some of the sources of these
vitamins.
Why is protein
essential for our bodies?
The word protein has been derived from a Greek word meaning “first”. And indeed, proteins are the most essential builders of the body. All living cells contain protein. Your skin, muscles, hair, as well as your internal organs like the brain, lungs, heart, liver, kidneys, everything is made from protein.
The proteins are different combinations of substances called
amino acids. There are more than twenty different amino acids containing
nitrogen, hydrogen, oxygen and carbon. Thousands of different kinds of proteins
can be made by different combinations of amino acids.
Since proteins are building bricks of the body, a growing child must get a good amount of these. If foods rich in
protein are under-supplied in the diet of a child, growth and development slow
down. In adults also, if protein supply is not sufficient, the body tissues
fail to repair normally. Insufficient protein in the diet leads to muscles
turning soft and weak resulting in poor posture and sagging muscles.
Protein is also used in making haemoglobin – the iron-containing substance of the red blood corpuscles. The amino acids essential for
survival cannot be made by the human body and must be provided through the
protein in our daily diet.
These amino acids
cannot be stored in the body and must be supplied regularly. All dairy products
(milk, cheese, curd), meats, fish, eggs, nuts, lentils, and bean cereals, contain a good amount of protein.
Because there are many different kinds of proteins present in
different foods which are useful to our bodies it is better to take moderate
amounts of different kinds of foods in different meals.
What is the function of
saliva?
Saliva is a watery, colourless fluid that is produced by some
glands inside our mouth. It contains 98% water and 2% enzymes. The most
important enzyme is ptyalin which helps us digest the food we chew and
eat.
While chewing, the saliva joins the food and helps convert the food into energy. It also helps as a lubricant to help food pass
down the food pipe more easily. Saliva keeps the mouth moist and another enzyme
called lysozyme in it helps in killing the bacteria entering the mouth.
The three pairs of glands that produce saliva are parotid
glands, sublingual glands, and submandibular glands. These are located between
the bones of the ears and the jaws, under the tongue and under the lower jaws
respectively.
These glands are very active and sensitive. Even if you think
of food or imagine yourself eating your favorite dish the saliva from these
glands begins to flow.
These glands can adjust the quantity and nature of
the saliva according to immediate requirements. The three pairs of salivary
glands produce different quantities of saliva for different requirements of the
body.
The largest pair near the ears (parotid) gives larger
quantities of watery saliva to dilute and moisten the food. The glands near the
lower jaw give sticky saliva to make the food ‘slippery’ for easier transfer.
All the salivary
glands have parasympathetic and sympathetic nerves reaching the brain, and
their stimulation produces saliva.
Small children produce more saliva. This happens because the salivary glands are more active for a few years after birth. About 1.5 litres of saliva is secreted in the mouth of an average person every day.