Nehru Bal Pustakalaya

Rohini Muthuswami
Illustrations
Atul Srivastava Vardhan

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 is an autonomous body established

illustrated books for various age groups in 30 Indian languages and

the series Nehru Bal Pustakalaya.

ISBN 978-81-237-9074-9
First Edition 2020 (Saka 1941)
© Rohini Muthuswami
The Fascinating World of Biology (English Original)
` 85.00
Published by the Director, National Book Trust, India
Nehru Bhawan, 5 Institutional Area, Phase-II
Vasant Kunj, New Delhi-110 070
www.nbtindia.gov.in

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 CONTENTS
Nature’s Incredible Phenomena and Science 5
1. The Beetle by the Moonlight 7

2. The Courtship of Peacock 12

3. A House on its Back 18

4. The Glow-Worms 23

5. The Flight of the Birds 28

6. The Cat’s Tongue 33

7. The Power of Sugars 38

8. The Colourful Chameleon 43

9. Echolocating your way in Dark 48

10. The Thirsty Crow 53

References 58

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Facinating-Eng NEW 04-02-2020.indd 4 20/02/2020 11:15:14
 Nature’s Incredible
Phenomena and Science
Have you ever looked at a sunflower? Surrounded by the yellow
petals are hundreds of tiny brown dots. From afar they look as
if they have been arranged randomly in the middle. But if you
look carefully, you will see that there is an order to the apparent
randomness. They are arranged in a format known as ‘Fibonacci
numbers.’
I learnt Fibonacci numbers in school, but it never made much
sense to me. Why do we need it? What is its use?
Now, when I look at the sunflower in my garden, I understand a
bit. The Nature uses mathematics in her own fashion.
The world of biology uses mathematics, chemistry and physics. In
the ten essays presented in this book, we will explore the ‘Fascinating
World of Biology’ to see how some of the phenomena we observe
can be explained by principles of mathematics, chemistry, physics,
and of course biology.

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 THE BEETLE By
THE MOONLIGHT

The divine dung beetle, Khepri,

rolls the Sun through the the sky.
-Ancient Egypt

The beetle was industriously rolling the dung ball. I

stopped by to watch it.
The dung beetle is found across the world wherever
there is dung as dung is its primary source of food. Some
of the dung beetles are choosy; they prefer dung of only
one species of animal. Other dung beetle species are less
choosy; they feed on dung of many different species of
animals.
But the question that persisted in my mind was: How
do these beetles, especially the ones that are active in the
night, navigate the dung ball, rolling it in a neat straight
line when the light from the Moon is barely sufficient for
us to see beyond our noses?

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 The answer is surprising: Studies done on the African
dung beetle show that they use the polarization pattern
of the light to navigate the dung ball.
Light, as we all have learnt, is described as an
electromagnetic radiation, composed of massless particles
called ‘photons’ that travel like a sea-wave with the
speed of light. The photons, though they have no mass,
possess energy. And depending upon how much energy

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 it possesses we can differentiate them into X-rays, UV-
rays, or visible light.
The visible light that is emitted from any source like
the Sun or a light bulb is unpolarized because it can travel
in all directions.
If you take a piece of a rope and move it up and down,
it will travel up and down but only in one direction. If you
made the light move like that, up and down, only in one
direction, that light is now known as ‘polarized.’ How can
an unpolarized light be converted into a polarized light?
The unpolarized light can be converted into polarized
light by putting it in a filter such that the waves that
emerge after passing through the filter can move only
in one direction. What kind of filter? Crystals like calcite
can function like filter (polarizer). So can plastic films
that are coated with organic molecules in one direction.
These plastic films are called ‘polaroids’ and are used in
polaroid cameras.
Interestingly, the sky too is a polarizer. Our eyes cannot
discern the polarized light but the eye of the beetle, can.
Why? This is because of special structures that are present
in the eye of the beetle.
The beetle possesses compound eyes. Each eye is
composed of microvilli, which are small hair like cells
that function as light absorbing particle. Each microvillus
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 contains many light receiving pigments called ‘rhodopsin’.
And in each microvillus, these rhodopsins are aligned
in one particular direction. Thus, all the microvilli face
one direction and are maximally attuned to receive light
polarized in a direction parallel to the direction in which
the microvilli are arranged. These microvilli cannot receive
any other light.
Does this mean that the beetle can receive only
polarized light?
No. The microvilli are arranged in only one direction
in the dorsal rim of the eye. In the rest of the region of
the eye, the microvilli are placed in no particular pattern.
So, in the rest of the region they can receive unpolarized
light but in the dorsal rim they can perceive only the
polarized light.
But what happens on moonless nights? How do beetles
forage food on those nights? Well, the scientists have
observed that the beetles tend to wander directionless
on such nights. Many of them cease their activities 45-50
minutes after sunset as the amount of light available for
navigation drops dramatically.
So, is this property unique to the dung beetles?
No.
Bees and ants and other insects as well as fish can
perceive the polarization pattern of the sunlight. They too
use polarized light for navigation, just like the dung beetle.

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 The difference is that they use the polarization pattern
of the sunlight. As the Sun changes its position, the
polarization pattern also changes.
Can we do it? No, we cannot, because the light
receiving pigment, rhodopsin, is oriented randomly in
our eyes and therefore, we are not able to detect the
polarization pattern of the light.
The polarization pattern is simplest during twilight and
the light of the whole sky is polarized in one direction.
However, of all the animals known, only the dung beetle
has figured out how to use this light for navigation when
it forages for food!

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 THE COURTSHIP
OF THE PEACOCK

He approaches her, trailing his whole fortune,

Perfectly cocksure, and suddenly spreads
The huge fan of his tail for her amazement.
-David Wagoner

The peacocks enliven the early months of summer when

they perform an inspired courtship dance. Through the
months of March and April, the peacock performs, displays
its magnificent tail, in the hope of attracting the peahen.
The peacock’s plumage, despite its magnificence, is
cumbersome. It hinders its movements. The peacock has
to carry it everywhere. If he sees a predator, he cannot
run away as fast as he would have been able to if he had
no tail. Even flight is difficult. Then, why is the peacock
endowed with an elaborate plumage?
The answer to this question lies in a theory known as
‘Signalling Games.’
Signalling is a form of communication. There is a sender
and a receiver. The sender possesses certain information,

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 which he/she needs to communicate. And the receiver
needs to interpret this information upon receiving. The
most important point to remember in the signalling
games is that the sender knows what information he/she
possesses. However, the receiver does not know what
information the sender possesses. So, the sender must
decide how to communicate this information and the
receiver has to decide how to respond to this information.
Sounds completely confusing, doesn’t it?
Let us see if we can use the signalling games to
understand the courtship of the peacock. In this example,
the peacock is the sender and the peahen is the receiver.
What information does the peacock communicate? Well,
he communicates his fitness to mate. He is telling the
peahen that he has more resistance to diseases, that he
has sufficient fat reserves per unit body weight, and that
their offspring have a good chance to survive. How does
this peacock communicate this information? Why, by his
plumage, of course!
If you look closely at the peacock’s plumage, you will
notice that each feather has, what is known as, an eyespot.
Marion Petrie at Whipsnade Zoo, United Kingdom, has
studied the courtship behaviour of the peafowl extensively
and has documented that the number of eyespots directly
correlates with the fitness of a peacock. That is to say,
a physically-fit peacock will have a greater number of

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 eyespots than a peacock that is not physically fit. A
physically-fit peacock might have more than 150 eyespots
in his plumage.
When the peahen sees the plumage, she cannot sit
and count the number of eyespots to determine which
of her suitors possess more eyespots, and therefore, are
more fit. So how does she figure out which peacock to
mate with? Although we do not have any experimental
proof, it appears that the peahen looks at the symmetry
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 of appearance. A plumage will be most symmetrical if
the number of eyespots in the right side is equal to
the number of eyespots in the left. Therefore, instead
of counting the eyespots, the peahen makes a quick
assessment. How does the plumage look to her visually?
Is it attractive? Is it symmetrical? If yes, then she would
consider mating with that particular peacock.
Now, here is the dilemma. The peacock wants to pass
the information that he is, indeed, a fit mate. But what if
he truly is not? What if he communicates false information?
How should the peahen assess this information?
This involves something known as ‘Honest Signalling.’
The question that a peacock has to ask himself is what he
will get if he lies. In other words, what are the incentives
of speaking the truth? What benefits will he get if he tells
the truth and what happens if he tells a lie?
Suppose there is a peacock that is physically weak. If
he has to grow a beautiful plumage, he will have to spend
a considerable amount of energy to grow a tail.
Being physically weak, it is too costly an investment.
Why should he do it? He might as well save that energy
and use it to become physically stronger. Then there is
also an additional problem. If he grows the tail, it will be
difficult for him to flee from predators. When he thinks
about these aspects, he decides that it is not worth it
to grow a beautiful plumage. So, these factors act as a

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 deterrent and a physically weak peacock will have very
little incentive to tell a lie. Therefore, peacocks are believed
to be honest signallers. This implies that a peahen does
not have to worry that the peacock dancing in front of
her is telling a lie. All she has to observe is which peacock
has more symmetrical plumage and therefore, with whom
she should mate.
The peacock’s job is over once the mating is done.
The plumage moults and the peacock, a bird shorn of
all his magnificence, moves about from July to March
searching for food. In March, the plumage reappears, and
the courtship cycle starts all over again.

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 A HOUSE
ON ITS BACK
And seeing the snail, which everywhere doth roam,
Carrying his own house still, still is at home,
Follow (for he is easy paced) this snail,
Be thine own palace, or the world’s thy goal.
-John Donne

The snail slowly made its way across the pavement, slime
oozing out. It was brown in colour and the shell glistened
in the Sun. When I squatted down to get a better look of
the shell, I could see the tiny spirals.
A spiral is just a curve in space, which runs around
a centre. Spirals can be of different types: Archimedean
spiral, logarithmic spiral, three-dimensional spiral, Fibonacci
spiral, etc. This last one is what we are concerned with
when we want to understand how a snail’s shell grows.
We learn about Fibonacci numbers in school. Leonardo
Fibonacci was an Italian mathematician and was born in
1170, long before the Renaissance period. As he travelled
along with his father, who had a trading post in the port

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 of Algeria, he became acquainted with the Hindu-Arabic
numerals and brought them into the European continent.
I remember that my mathematics textbook had a figure
of rabbits. It was indeed with rabbits that Fibonacci began
his observations as he was interested in understanding how
fast the rabbits would breed under ideal circumstances. He
started with an assumption that rabbits never die because
they are neither killed nor starved. He then made a second
assumption that the female rabbit always produces a pair

month. With these two assumptions, he said that if in

the beginning there was one pair, then at the end of one
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 month, there would still be only one pair. At the end of two
months, the female rabbit produces one pair of rabbits so
that the total is two pairs. At the end of the third month,
the original female produces another pair making a total
of three pairs. At the end of the fourth month, there will
be five pairs. And at the end of the fifth month, there will
be eight pairs and so on, producing a number series 1, 1,
2, 3, 5, 8, 13, 21, 34..., which is called as Fibonacci number.
The rabbit problem is not very realistic, but the Fibonacci
number has numerous uses. We can use these numbers
to create a series of rectangles. First, we draw a rectangle
of unit 1. Adjacent to it, we draw another rectangle of

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 unit 1. Then we top them with a rectangle of unit 2. Now,
we draw a rectangle of unit 3 keeping in mind that the
longest side touches both the rectangle of unit 1 and 2
such that the sum of the longest side is 3. Once the unit
3 rectangle is ready, we can create a rectangle of unit 5.
The trick is to remember that the size of the longest side
is equal to the Fibonacci number.
Once we have the Fibonacci rectangle, we can create a
Fibonacci spiral. To do so, take a pencil and draw a quarter
of circle in each square. What you will get is a spiral, the
kind you will see on a snail’s shell.
Why did Nature choose Fibonacci spiral? Why not any
other type of spiral?
A snail has to worry about two aspects. The first aspect
is that the size of the body must be relative to the size of
the shell. The two must grow at a similar rate because if
the shell becomes too heavy, it will not be able to drag it
along. In addition, the center of gravity would be altered
and the poor snail would topple over. The second aspect
is, of course, that the shell cannot be too small. It is not
a decorative piece. The shell is a protective cover against
threatening elements. The shell has to be big enough so
that the snail can withdraw into it when the need arises.
The shell of the snail is made of calcium carbonate
or lime. The shell is extended as the snail grows by
depositing lime at the shell opening. Each new addition

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 of lime, because of the above-mentioned constraints, tries
to maintain more or less a constant relationship with the
previous shell. The net result is a ‘Fibonacci spiral.’
The snail shell provides a valuable lesson, not only in
mathematics, but also for designing armours. For example,
the scaly foot snail lives at the bottom of the Indian Ocean
near vents that spew hot waters. In addition, this snail is
preyed by crabs as well as by other snail species.
The scaly foot snail has evolved to combat both the
hot water as well as predators by creating a shell that is
composed of three layers. The outermost layer is made
of iron-sulfide, the innermost layer of calcium carbonate.
In between these two layers is present a thick organic
layer. The iron-sulfide layer is the first line of defence
against predators. It is brittle and can crack easily under
pressure, but the jagged ends could possibly grind down
the attacker’s claws. The middle layer is soft and flexible,
able to fill the cracks up and protect the inner layer from
feeling pressure. The outer and the middle layer together
protect the snail against the acidic nature of the hot
springs. Finally, the inner layer is rigid providing structural
support.
And this is what intrigues the defence specialists.
Can they copy the snail while designing armours for the
soldiers?

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 THE GLOW-WORMS

Among the crooked lanes, on every hedge,

The glow-worm lights his gem; and through the dark,
A moving radiance twinkle.
-James Thomson

Have you ever seen tiny speckles of light gleaming on

the hedges on a dark night? They appear and disappear,
lasting for just a few seconds. These are the fireflies. They
are also known as ‘glow-worms.’ Quirkily enough, these
are not flies but are beetles.
How do fireflies produce light?
The production of light in fireflies occurs through a
process called ‘bioluminescence.’ Light is produced from an
energy source. In fireflies, the energy source is a chemical
reaction that takes place in their abdomen in a special
organ known as lantern. The chemical reaction involves
Adenosine Triphosphate (ATP) which is the energy source
in all the living organisms. It involves an enzyme known

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 as luciferase and a compound known as luciferin. The
reaction requires oxygen. The reaction can be given as:
Luciferin + ATP + O2 oxyluciferin + AMP + light.
Luciferase catalyses this reaction. AMP stands for
Adenosine monophosphate.
This light is emitted in the form of blue-green colour
and in pulses. This is known as ‘bioluminescence.’ In this
reaction heat is not produced. Have you ever touched a
light bulb after it has been switched on for some time?
It will be hot because the reaction produces heat. On

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 the other hand, the light that is produced by fireflies is
called as ‘cold light’ because there is no heat generation.
As there is no heat production, the light generated by
these organisms is one of the most efficient methods of
light production.
Why do fireflies produce this light? The adult fireflies
produce this light to attract potential mates. However, the
young or the larve of the fireflies do not emit light.
Are fireflies the only organisms that can produce this
kind of light?
No. There are many organisms that can produce
bioluminescence. There are bacteria that can emit light.
There are glowing mushrooms. Tiny organisms called
dinoflagellates residing in the deep ocean can also
produce light. The light produced is mostly blue-green in
colour though some can produce red, yellow, pink, violet
and white coloured light too.
Dinoflagellates, unlike fireflies, produce light only
when they are disturbed. One of the theories is that
these organisms produce light to startle their predator.
The copepods are small organisms that live on the
ocean floor and prey on the dinoflagellates. Therefore,
the dinoflagellate has to evolve strategies to escape the
copepods. The production of a brief flash of light is one
such strategy. An alternative theory is that production of
light actually signals the enemies of copepods and thus, is

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 used to attract the organisms that prey on the copepods.
Finally, there is a group of scientists, which believes that
the light production has no value to the dinoflagellate.
In the ocean floors live tiny bacteria belonging to
Photobacterium and Vibrio genera (e.g. Photobacterium
phosphoreum, Vibrio fischeri) that can produce
bioluminescence. These bacteria live in close association
with other organisms like fish. The fish provides food
and a place to live to the bacteria. In turn, the fish uses
the light produced by the bacteria for hunting, or as a
camouflage, or in attracting potential mates. This kind of
association where both the organisms benefit from each
other is known as ‘symbiosis.’

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 Let us move from the ocean floors to the rain forests
of Brazil. In some places the forest is so thick that sunlight
never penetrates. In these dark forests, scientists have
found new species of tiny glowing mushrooms. Just as
the fireflies and dinoflagellates do, these mushrooms
also use luciferase to convert luciferin into light in the
presence of ATP and oxygen. The light, just as in the case
of fireflies, is green in colour. There are 71 such species
of mushrooms found not only in Brazil but in Japan
too. Unlike dinoflagellates and fireflies, the mushrooms
produce light continuously, which is visible only when it is
dark. We do not know the reason why these mushrooms
glow. It could be a signal to tell other organisms that it
is poisonous and therefore, should be left alone. It could
glow to attract insects, which would pick up the spores
and help to spread them far and wide. Or just as in case
of dinoflagellate, there might be no particular reason why
the light is produced. Only further research will enable us
to understand why these mushrooms produce light.

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 THE FLIGHT
OF THE BIRDS

Stray birds of summer come to my window

To sing and fly away
-Tagore

The peahen landed gracefully on my patio. Using the patio

as a runway, she braked in front of my rose plant, just as
a plane would land on an airstrip. How do birds fly? Is it
really similar to a flight of an aeroplane?
Let us first look at the flight of an aeroplane. To do so
we need to understand Bernoulli’s principle. Bernoulli was
a Swiss mathematician who discovered that a slow-moving
fluid (could be liquid or gas) exerts more pressure than
a fast-moving fluid.
An aeroplane wing is rounded at the leading edge and
sharp at the trailing edge. If we look at the cross-section
of a wing, we would see that it is slightly curved. Due to
this curvature, the airflow is faster on the upper surface
as compared to the lower surface. Applying Bernoulli’s

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 principle, we realize that the pressure will be more on the
lower surface than on the upper surface, thus developing
a pressure difference between the two surfaces. The higher
pressure on the lower surface allows the aeroplane to be
lifted.
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 Birds too follow Bernoulli’s principle. Their wings are
curved such that the airflow on the upper surface is more
than on the lower surface allowing a pressure difference
to develop. But there are differences between a bird
and an aeroplane. The wings of an aeroplane are fixed
whereas the wings of a bird are not fixed. The wings of
a bird, unlike that of an aeroplane, have a sharp leading
edge. The wings also contain many microscopic features
like fold, gaps, and ridges. Besides, a bird can alter the
dimensions of the wings by drawing them closer to their
body or extending them fully outwards from the body.
Birds can glide and soar in the air as well as use
flapping motion. During gliding, the wings do not flap.
They are instead held out to the side of the body at a
slight angle that allows the air to be deflected downwards.
The downward movement of the air causes a reaction
force, called lift, to be set up in the opposite direction.
The lift allows the bird to glide through the air. The angle
at which the wing is held is very critical. If the angle is
too large, then it will produce a dragging force that will
impede the motion of the bird. If the angle is too small,
then the downward movement of air will not be sufficient
to create lift.
Soaring is a kind of gliding and takes place only under
certain specific conditions. During soaring the bird flies
in a rising air current. For example, the Sun can heat up

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 warm air such that it rises up from the earth forming
what is known as ‘thermal.’ Birds can use this rising air
current to fly.
During flapping, the wings produce a downstroke and
an upstroke. During downstroke, the wings beat down
and forward creating lift. The upstroke involves lifting the
wings up and extending it so that it is ready for the next
downstroke.
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 Bats are the only mammalian species that can fly.
Scientists in Lund, Sweden, used a wind tunnel created
specifically to study animal flight. The field created by
airflow during animal flight was recorded using a special tool
called ‘digital particle image velocimetry.’ After recording
the image, the scientists calculated the force generated by
downstroke as well as upstroke. They found, much to their
astonishment, that the force created by downstroke and
upstroke was equal suggesting bats, unlike birds, use both
downstroke and upstroke to create a lift.
One of the most intriguing flying patterns is created
during migration of the birds. If you look at the birds, you
will find that some of them fly in V-shape. Why V-shape?
The V-shape helps in conserving energy as well as in
better communication. The first bird, called ‘the lead bird,’
in the V-shape pushes against a wall of air, thus, reducing
resistance. At the same time, the swirling air caused by
the lead bird’s movement helps the bird behind it to
push forward. Hence, every bird behind the lead bird
gets assistance and push to move forward. When the lead
bird gets tired, it falls back, and another bird becomes
the lead bird.

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 THE CAT’S TONGUE

The Owl and the Pussy-cat went to sea

In a beautiful pea-green boat.
-Edward Lear

My neighbour feeds two stray cats. One of them is striped

and the other is black and white in colour. Both cats wait
outside my neighbour’s house for their daily ration of
milk and chicken pieces. The striped cat is a male and
the black and white is a female. Interestingly cats do
not possess cheeks, which are essential for drinking. The
cheeks provide suction power so that the liquid enters
the mouth. If an animal does not possess cheeks, then
how are they able to drink?
There are many animals that do not possess cheeks
like we do. For example, dogs do not have cheeks so
they drink water using a spoon-like action. They curl their
tongue in such a manner that it forms a ladle and with
this ladle they scoop up the liquid. This implies that the

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 tongue should be submerged into the liquid. Most of
the animals lacking complete cheeks employ this trick.
But not cats.
The tongue of a cat is known to be rough and for a long
time scientists had assumed that the cats employ their
rough tongue in the same way, as does a dog. However,
one day, a researcher, Roman Stocker, was watching his
cat, Cutta, drink milk and he wondered if the assumption
that cats and dogs use the same method to drink was true.
To test this assumption, Roman Stocker and his
colleagues used a high-speed camera to study the way

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 cats drink milk. What they found was astonishing. The
tongue of the cats does not penetrate the liquid. This
implies that they do not form ladle like structure with
their tongue. So how do they drink?
The cats extend their tongue towards the liquid and as
it touches the surface of the liquid, the tip of the tongue
is curled backwards. This movement allows it to pick a
droplet. Now, the cat starts withdrawing the tongue from
the liquid. As it does so, a column of liquid is pulled-up.
The cat clamps its jaws close and the liquid is trapped
inside the mouth.
This action of cats has a profound implication. When
the column of liquid is being pulled up, it is being
pulled against the gravity. Therefore, to understand the
mechanism better, the researchers built a robotic tongue
that could mimic the cats’s tongue. Using this instrument,
the researchers found that two forces play an important
role in the drinking mechanism. One is the inertia of the
liquid that tends to keep the liquid moving upwards. The
other is the gravitational force that tries to pull the liquid
downwards. Thus, the inertia and gravitational forces
are acting on opposite directions. The cat must balance
between these two forces such that it pulls up the liquid
into its mouth before the gravitational force pulls it down.
If it closes its jaws too early, it would miss the column
of water as the inertia pulls it up. If it closes its jaws too

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 close, it will lose the water, as the gravitational force would
pull it back towards the ground.
How do cats acquire this behaviour? Is it genetic? That
is to say, are cats born with this instinct to balance inertial
and the gravitational force? Or, is it learnt in the same way
as birds learn to fly and we learn to walk? Researchers
believe that cats learn this behaviour the same way as we
learn to walk. So, the drinking behaviour is instinctive. It
is not in-built but learnt through trial and error.
Is this only true of the cats? What about tigers, lions and
other animals that belong to the feline genera along with
the cats? Well, the researchers went to a zoo to study the
behaviour of these animals and found that this behaviour
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 extends to all the animals belonging to the feline genera.
Thus tigers, lions, leopards, cheetahs, employ the same
trick to drink liquids. The only difference is the timing.
As these animals possess a longer tongue and are taller
than cats, they lap much slowly so that the inertia and
gravitational force could be balanced properly.
This study has helped in designing better robots.
Robots are used for cleaning oil spills and scientists are
now designing robots that would be able to clean up the
oil spills using the same principle as the cat’s tongue.

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 THE POWER OF SUGARS

Tardigrades don’t care!

-Hank Green

Of all the animals abounding our Earth, I find the

tardigrades the most fascinating. The name itself is
mesmerizing. Tardi means ‘slow’ and grade means ‘step.’
The organism is a slow stepper and extremely hardy. It is
found in hot springs as well as beneath layers of ice at the
poles. It is found on the ocean floors where the pressure
is 1000 times more than that on the Earth’s surface. It
is also found on the top of Himalayan peaks where the
oxygen level is one-third of that found at sea level. How
is it able to survive in such tough conditions?
Tardigrades, also known as water bear or moss piglet,
are capable of going into suspended animation whenever
they are faced with adversity. There are several organisms
that can do this. For example, certain bacteria possess this
behaviour. When these bacteria face lack of food supplies,
they transform themselves into a form known as ‘spores.’
As spores, they can survive for a long time. When these

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 spores are provided plenty of food resources, they revert
to their bacterial form.
Tardigrades, however, are not bacteria. Tardigrades, in
fact, are closely related to cockroaches. They belong to a
family known as arthropods. However, unlike cockroaches,
which we can see with our naked eye, we need a
microscope to observe tardigrades.
How do tardigrades go into suspended animation?
The process of going into suspended animation is known
as ‘cryptobiosis.’ During cryptobiosis, all the metabolic
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 processes come to a standstill. It is a death-like state.
However, under right conditions, the process can be
reversed, and the organism can revive. Cryptobiosis takes
place when there is lack of water (anhydrobiosis), lack
of oxygen (anoxybiosis), low temperature (crybiosis) and
increase in salt concentration (osmobiosis). Tardigrades
undergo anhydrobiosis.
During anhydrobiosis, the tardigrades lose water
and start drying up. However, each organism contains
molecules that need to be present in hydrated form. If
these molecules lose water, then they lose their structure
and therefore, their function. So, the tardigrades had to
evolve a mechanism by which these essential molecules
would not lose their structure when water is lost. The
tardigrades came up with an interesting solution. During
anhydrobiosis, sugar molecules replace the lost water
molecules. There are many kinds of sugar molecules. The
sugar that we eat is one type. Glucose is another type
and the sugar that tardigrades use is known ‘trehalose.’
Trehalose is an interesting molecule. It is classified as a
disaccharide, which means two sugar molecules are linked
together. Glucose is a monosaccharide as is fructose.
These molecules contain one sugar residue. Sucrose is a
disaccharide. It is made of glucose and fructose. Trehalose,
on the other hand, is made up of two glucose units. It
can retain a large amount of water.

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 Replacing trehalose with water appears to prevent
structural deformities in tardigrades, though no one is
sure how trehalose is able to do so. Some believe that
the ability of trehalose to retain water molecules reduce
the water loss. Some believe that it is because trehalose
can interlink between various molecules. Whatever be the
reason what we do know is that tardigrades can survive
for a long period of time after cryptobiosis. The earliest
observations were made by Anton van Leeuwenhoek
in 1702, when he observed these animals under his
microscope. He saw that by adding water, these animals
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 could slowly be revived and the removal of water led to
suspended animation.
The tardigrades are part of an important experiment.
Can they survive in space and if they can, what features
enable them to do so. The space has extreme conditions,
it is extremely dry and creature in space will have to face
harmful solar and ultraviolet radiations. The extreme dry
climate implies that the organism needs to be equipped
to survive under desiccating conditions. And we know
that tardigrades are superbly equipped to do so. The first
experiment was carried out in 2007 and it was found that
tardigrades could indeed survive in space. In May 2011,
they were carried in the space shuttle ‘Endeavour’ to
understand further the ability of this organism to survive
in the harsh environmental conditions of space. We have
to wait and see what further surprise the organism reveals.

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 THE COLOURFUL CHAMELEON

We are like chameleons, we take our hue and the

color of our moral character, from those who are around us.
-John Locke

The chameleon sat motionless on the bark of the tree.

It was brown in colour. I moved slowly, trying to capture
it on my camera. Alas, I was not very careful, and the
chameleon moved. It now sat hidden amongst the leaves
and as I watched it breathless, it turned from brown to
pale green. Soon it was invisible.
How does the chameleon do this trick? Does it

it switches on, as the need be? How does it realize that

the surrounding has changed and therefore, it should now
change its colour? How many colours can a chameleon
turn into?
Yes, the chameleons do possess different colour
pigments. These creatures contain cells that possess the
ability to make red, yellow or brown pigment. These

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 cells are called chromatophores (chroma: colour). The
chromatophores are present just beneath the outer layer
of the skin and are arranged in layers. Thus, the layer just
beneath the outer layer of skin contains cells that can
make red and yellow pigments. Beneath this layer further,
is a layer of cell that has the ability to scatter light. Finally,
is the layer of cells that has two characteristics. The first
characteristic is the ability of these cells to make a brown
pigment called ‘melanin.’ Melanin is universally present in
all organisms and has the capacity to absorb all colours
comprising light. However, the melanin that is produced
in chameleons has the ability to move around the cell
and thus, redistribute itself. The melanin can be present

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 bunched together as a clump or widely distributed through
the cell. The second characteristic of these cells is that
they have branches and these branches extend upwards,
invading the other layer of cells.
When melanin is bunched up together as a clump, the
light that strikes the chameleon, is scattered by the scatter
layer. The colour we see is the colour that is reflected
by the yellow pigment. When melanin is distributed
throughout the cell, all the colours are absorbed by this
pigment and the chameleon appears dark in colour. When
melanin is partially distributed, then the chameleon can
adopt brown or green colour depending upon the extent
of distribution.

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 How does the chameleon decide when it should change
colour? The chameleon senses light, temperature and
mood. For example, the chameleon that I was observing
moved from the branch that was partially exposed to
the sunlight into the thickset leaves, where the sunlight
could not penetrate. The extent of light available as
well as the temperature changed with the movement of
the chameleon. And this change was sensed by it and
accordingly it changed its colour. Besides, mood is also a
determinant of the colour. A species of chameleon called
‘Panther chameleon’ becomes red when it is angry.
That brings us to the third question. Does each
chameleon species possess the ability to change into any
colour? The answer is ‘no.’ Each species possesses a set of
colour pigments that is characteristic to that species. So,
some can adopt exotic colours while others have more
restricted range.
Why did chameleons evolve this ability? Was it because
the ability to change colour helped it to hide better
from its enemies? Or, was it to help in courtship? For a
long time, scientists believed that, chameleons change
their colour to blend into the surrounding and thus,
be camouflaged. However, recent research has shown
that this hypothesis is false. Researchers now believe
that the chameleons evolved this ability to attract other
chameleons and to warn potential rivals. Devi Stuart-Fox,

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 a researcher at University of Melbourne, Australia, studied
the chameleons in South Africa for four years and found
that the males that possessed the ability to change into a
wide of range of colours usually used the most eye-striking
colour during courtship.
Chameleons are not unique in possessing the
ability to change colours. There are other organisms like
cephalopods, which reside in the oceans. These organisms,
also called ‘chameleons of the oceans,’ possess a much
wide colour palette than chameleons. Furthermore,
cephalopods can change their colour within milliseconds.

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 ECHOLOCATING yOUR
WAy IN DARK
Bumblebee bat, how do you see at night?
I make a squeaky sound that bounces
back from whatever it hits. I see by hearing.
-Darrin Lunde, Hello, Bumblebee Bat

During summers, in the night, I can sometimes see the

bats flying about. I am not overtly fond of the bats and
when they flap their wings as they sweep up and down,
I have to control the urge to scream.
However, bats are special creatures. Along with dolphins
and whales, they are one of the few mammals that use
echolocation for navigation. Bats are nocturnal creatures
and are of different types. For example, the Old World fruit
bats have large eyes with good light-gathering capacity
while the insect-eating bats possess small eyes and depend
on echolocation to find their food. It was in 1799 that the
Italian scientist Lazzaro Spallanzani discovered that bats
do not use sight, but instead use hearing to locate preys.
What is echolocation? Sound, like light, travels as waves.

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 When we speak, a wave of air pressure is created that
moves forward. When this wave hits a solid object, the
object reflects back the sound wave, exactly as though it
were a light wave. The reflected wave is known as ‘echo.’
You can get echo in canyons and in man-made structures.
The Bara Imambara in Lucknow is famous for its echo. If
you stand at end of the balcony and call out ‘Hello’, you
will be able to hear the echo of the word ‘Hello’. This is
because the structure on the opposite end reflects back
the sound waves. Bats use the same principle to locate
their food. They produce a sound either through their
mouth or through their nose. This sound creates waves
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 that traverse through the air until it hits a solid object like
an insect. The insect reflects back the sound wave which
the bat hears and thus, finds out the exact position of
the insect.
How do bats use this property of the sound waves?
Well, bats emit sound through their nose using their
larynx or mouth by clicking their tongues. These sounds
are made in the form of pulses. We cannot hear these
sounds because these are very loud sounds in the range
of 9 kHz to 200 kHz while the human ear can only hear
sounds in the range of 20 Hz to 20 kHz. Hertz (Hz) is the
unit of sound frequency, which merely means how many
waves pass through a given point. Different species of bats
emit different frequencies of sound. When a bat emits

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 these sounds, the sound wave travels through the air until
it hits the object, for example, an insect. The insect body
reflects back the sound wave which is then received by
the bat. The distance between the two objects is equal
to the velocity of the sound multiplied by the time taken
for the sound to be received. Thus, if a bat emits a sound
and hears its echo back in 1 second, then the distance is
given by:
d = vt (where d is distance, v is velocity of sound in
air, and t is the time taken for the bat to hear the echo).
d = 343 m/s x 1 s
d = 343 m
But, the time has to be divided by two because the
bat emits a sound which travels through air to the object
that then reflects back. Therefore,
d =172 m.
Thus, the bat can estimate the position of the insect
accurately. Bats can emit sounds either at constant
frequency or at varying frequencies. The calls also vary in
repetition rate, intensity and length, hence allowing the
bats to estimate not only the distance but also minute
details such as size, hardness and the flutter of the prey’s
wings.
The ear of the mammal has a specialized structure
known as cochlea to amplify and detect sound. The
cochlea of bats is adapted to hear high frequency sounds.

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 Further, the auditory center in the brain appears to have
become specialized to interpret the data received from
echoes.
The discovery of echolocation in bats and dolphins is
the basis of SONAR (Sound navigation and ranging) used
for navigating, detecting and communicating with vessels/
objects under the surface of water.
Can humans use echolocation? A group of visually-
challenged persons have been trained by scientists to
use echolocation very successfully to navigate. Basically,
these people actively create sounds, either by clicking their
tongue, or by tapping their canes, or by lightly stomping
their feet. Then they listen to the echo from the nearby
objects to orient themselves and thus, navigate.

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 THE THIRSTy CROW

If men had wings and bore black feathers,

few of them would be clever enough to be crows.
-Henry Ward Beecher

Remember Aesop’s fable about the thirsty crow? The crow

finds a pitcher with water, but the level is so low that he
cannot drink water from it. Then the crow decides to throw
stones into the pitcher until the water level rises and it
can drink water. The moral of the story is that where there
is a will, there is a way or that necessity is the mother of
invention.
For a long time, birds were believed to be of lesser
intelligence than mammals. However, recent studies have
shown that our traditional belief might be wrong.
The brain is a complex structure composed of neurons
and glial cells. Of these two cells, neurons are considered
most important. The brain is subdivided into many parts
of which the neocortex is present only in mammals and
is believed to be the seat of higher cognitive processes
such as problem solving and memory formation. The

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 neocortex is absent in birds and therefore, for a long time
it was believed that birds do not have the ability to solve
problems or the skill to form concepts.
This view has now been challenged. Experiments done
with many species of birds have begun to show that
birds can indeed do problem-solving. The most amazing
experiment came from a New Caledonian crow named
‘Betty.’ The New Caledonian crow is similar to our house
crow, but it possesses an unusual ability to fashion tools.
Three scientists from Oxford University studied Betty,
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 who was captured as a youngster and bred in captivity.
However, Betty’s ability to make tools was discovered by
accident. The scientists were testing the ability of Betty
and another New Caledonian crow named ‘Abel’ to retrieve
food by using wires. The food was placed in a cage and
the birds were provided with different kinds of wires to
retrieve it. While Abel used a hooked wire to get the food,
Betty took a straight wire, bent it into a hook shaped
tool and used it to retrieve the food. This was the first
time, a bird bred in captivity, had exhibited such power.
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 This ability was even more fascinating because Betty had
no role model to learn from as it had been reared in a
laboratory.
Betty is not the only example in the world of birds. Nor
is the tool-making the only ability that birds display. One
of the cognitive abilities that mammals possess is memory
formation, a trait that corvids, the group to which crows
belong, also display. Corvids live in large societal groups
and in a study with Pinyon Jays, which are also corvids, it
was found that these birds can recognize individuals within
their group. Another member of the Corvidiae family is the
Clark’s nutcracker, which has a remarkable spatial memory.
It can store its nuts in 20,000-30,000 separate places and
yet, accurately retrieve each one of them months later.
So what region of the brain in birds provides this
ability? It appears that the birds possess a region
that goes by the tongue-twister name ‘nidopallidium
caudolaterale,’ which functions in a comparable manner
as neocortex in mammals. Furthermore, the birds also
seem to possess similar neural substrates required for
skills such as imagination and reasoning in neocortex and
nidopalladium caudolaterale.
Do all birds possess cognitive abilities similar to
mammals? We do not know. What we know is that the
cognitive abilities seem to be maximal in birds that live in
large complex societies. Further, a comparison of neural

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 densities between different species of birds has shown
that the ‘intelligent’ birds contain a higher neural density.
However, it needs to be confirmed whether a higher neural
density does indeed provides higher cognitive skills.

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 References

navigate-stars.html

news030630-5.html
http://en.wikipedia.org/wiki/Dung_beetle

http://en.wikipedia.org/wiki/Signalling_theory

honest-and-dishonest-signaling-in-animals-a-
biological-game-theory/

Fibonacci/fibnat.html#spiral

title/Snail_in_shining_armor

why-do-fireflies/

glowing-mushroom-species

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 do-migratory-birds-fl

shows-how-bats-manoeuvre

/how-bats-fly/#.XIH2brjhWM8

cat-tongues/

html

.pdf

change-their-colors

chameleon-camouflage-color-change-myth-news/

how-do-chameleon-s-change-color

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 2011/05/25/the-brain-on-sonar-%E2%80%93-how-
blind-people-find-their-way-around-with-echoes/

intelligence/

avian-intelligence/

Printed at India Offset Press, New Delhi

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Facinating-Eng NEW 04-02-2020.indd 61 20/02/2020 11:15:22
 Nature is endowed with creativity, so are wonderful its phenomena
which we see around us. From the flight of birds to the light emitted by
glow-worms to the chameleons changing their colour, they have always
captured the imagination of humans. The present book explores the
fascinating world of insects, birds and animals and explains in a lucid
manner the principles of science and mathematics behind these various
phenomena. An interesting read for young and curious readers who not
only admire Nature but also wish to know more about it.

Rohini Muthuswami is a teacher and a researcher at the School of Life

Sciences, Jawaharlal Nehru University. She is also the author of book
Exploring the Biological World, published by National Book Trust, India.
Atul Srivastava Vardhan is a freelance illustrator with over 30 years of
experience. He has illustrated many children’s books and magazines.
Currently, he is working with Hindustan Times Ltd.

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Facinating-Eng NEW 04-02-2020.indd 63 20/02/2020 11:15:23