My Science School

All sounds make invisible ripples, or waves, in the air. The ear collects sound waves and converts them first into vibrations, then into signals that the brain interprets as sounds.

Outer ear

Sound waves travel along the ear canal until they hit the eardrum and make it vibrate. The outer ear (pinna) ‘catches’ sound waves and directs them through the ear canal to the protected middle ear. These incoming sound waves cause the eardrum to vibrate. This is where the process of understanding these sound waves begins.

Middle ear

The vibrations pass through a series of bones, through the oval window, and into the cochlea. The middle ear is connected to the back of the nose and throat by the Eustachian tube. This means that when your loved one yawns or swallows, the Eustachian tube can open to equalise the pressure on both sides of the eardrum and prevent the membrane from being damaged. 

Inner ear

Microscopic hairs inside the cochlea convert the vibrations into nerve signals, which are sent to the brain. The middle ear is connected to the back of the nose and throat by the Eustachian tube. This means that when your loved one yawns or swallows, the Eustachian tube can open to equalise the pressure on both sides of the eardrum and prevent the membrane from being damaged. 

Loud and clear

The louder the sound, the bigger the vibrations it makes. Our ears are so sensitive that we can detect even the smallest sound, such as a paperclip dropping on the floor. We measure the loudness of sounds in decibels (dB).

 

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The ear is the body’s organ of hearing. It is larger than it looks – only a skin-covered flap is visible on the outside of the head, with the rest of the ear lying hidden from view inside the skill.

Ears come in many shapes and sizes. Typically, men’s ears are larger than women’s, according to a study in the journal Plastic and Reconstructive Surgery. Researchers also found that the average ear is about 2.5 inches (6.3 centimeters) long, and the average ear lobe is 0.74 inches (1.88 cm) long and 0.77 inches (1.96 cm) wide. They also noted that the ear does indeed get larger as a person ages.

The ear has three zones, each with different roles. The outer ear collects sounds and funnels them towards the middle ear, where they are converted into vibrations. In the inner ear, the vibrations are transformed again, into signals to send to the brain.

 

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Every human has a unique iris pattern, which is why many modern security systems use iris recognition technology.

Two sets of muscles in the iris contract and relax to control the amount of light entering the eye through the hole in its centre – the pupil. Circular muscles contract in bright light, making the pupil smaller to prevent a dazzling effect. In dim light, radial muscles (like spokes on a wheel) contract to make the pupil bigger so it allows in more light. Different amounts of melanin pigment inside the iris give eyes their different colours. Brown is the most common colour, found in more than half the world’s population.

The iris is usually strongly pigmented, with the color typically ranging between brown, hazel, green, gray, and blue. Occasionally, the color of the iris is due to a lack of pigmentation, as in the pinkish-white of oculo-cutaneous albinism,[1] or to obscuration of its pigment by blood vessels, as in the red of an abnormally vascularised iris. Despite the wide range of colors, the only pigment that contributes substantially to normal human iris color is the dark pigment melanin. The quantity of melanin pigment in the iris is one factor in determining the phenotypic eye color of a person. Structurally, this huge molecule is only slightly different from its equivalent found in skin and hair. Iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is found in brown-eyed people and of the latter in blue and green-eyed people.

 

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Sight is the key sense, so maintaining good vision is important to humans. Eyesight often deteriorates as the body ages and the number of light-sensitive rods and cones decreases. Two of the most common eye conditions are problems with focusing and with seeing certain colours.

Out of sight

The most common eye problems are short-sightedness and long-sightedness, where distant or near objects can appear blurred. Glasses or contact lenses can help the light to focus in the right place within the eye and make images sharp again.

Short-sightedness

Short-sighted people can focus on things that are close, but not on things that are further away.

Long-sightedness

Long-sighted people can focus on things at a distance but not on near objects.

Colour blindness

Most eyes can see millions of different colours, but some people cannot distinguish between colours because of injury, illness, or an inherited condition. More boys than girls have colour blindness.

 

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The brain’s task is to make sense of what the eyes see, and it usually gets it eight. However, optical illusions can play tricks on the brain as it tries to fill any gaps in the visual information it receives.

Pavement painting

Artists can create the illusion of depth by skilful use of techniques such as shadowing and perspective (making lines meet as they would if seen in the distance).

Moving image

This is caused by the eyes’ light-sensitive cells turning on and off as they react in different parts of the pattern. This fools the eye into thinking it is seeing movement.

 

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The left and right eye each have their own angled view, called the visual field. Data from the left half of each eye is compared by the brain’s visual centre, and similarly for the right halves of each eye. The process of combining the different views into one 3D image is called binocular vision.

3D Vision

Many animals, such as horses, have eyes on the sides of their head, but humans have forward-facing eyes. Each eye sees from a different angle to provide an overlapping view of the scene. The brain uses this to create an image with height, width, and depth.

Movie magic

The ultimate cinematic experience is a 3D movie. The film is made by copying what the eyes so. Scenes are shot with two cameras, then special glasses are worn to put the images together. The result makes the audiences feel as though they are “in” the film.

 

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Human eyes can see in colour, thanks to 127 million light-sensitive cells on the back of the retina. These light detectors, called rods and cones, capture light rays from the lenses to create coloured images.

Rods and cones

About 120 million rods are sensitive to low light. They see in black and white and provide only minimal detail. About 7 million cones see colour and detail, but only in bright light.

Rod cells

The rods work well in dim light. They provide information about the whole image in shades of grey.

Cone cells

The cones detect colour and detail at the centre of the image, but only work in bright light.

Final image

Information from the rods and cones is gathered and transmitted via the optic nerve to the brain. This creates a full-colour image with fine detail.

Three colours

There are three types of colour-detecting cones inside the eyes. They are sensitive to red, blue, or green. But combined, they can detect millions of colours, all made of mixtures of these three basic colours.

Blue, green and red are known as the primary colours. Secondary colours are where two primary colours mix. White is a mix of all three primary colours. Yellow is a mix of red and green.

 

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The human eye is excellent at picking up different colours and fine details. The position of the two eyes also means they can provide a tremendous range of visual information about what is being looked at. The powerful vision-processing areas of the brain then interpret this torrent of data into highly detailed mental images – which your memory then helps you to recognize.

The iris of the eye is the color portion behind the cornea. Our eye color is a function of the amount of pigment within the iris (brown eyes have the most pigment, while blue eyes have the least). The iris contains muscles that open and close its central opening called the pupil in response to decreases and increases in light exposure (exactly like the camera aperture).

Light then travels through the lens, where it is fine-tuned to focus properly on the retina, the nerve layer that lines the back of the eye and connects to the brain. The retina acts like the film in a camera, and clear vision is achieved only if light from an object is precisely focused onto it. If the light focuses either in front of or behind the retina, the image you see is blurred. A refractive error means that the shape of eye structures does not properly bend the light for focusing.

 

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The average eyeball is about 2.5 cm (1 in) in diameter and is made up of two fluid-filled cavities – a small space in front of the lens and a larger area behind it. Light enters the eye through the pupil, which is an adjustable window between the cornea and the lens.

Superior rectus muscle

This muscle controls upward movements. This group of muscles serves to move the eyes within the orbit. It includes the superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique and inferior oblique muscles. 

Lateral rectus muscle

Lateral rectus muscle is one of the 4 straight muscles of the orbit responsible for the movement of the eye in the cardinal directions. The eye is pulled from side to side by this muscle.

Superior oblique muscle

Superior oblique is the longest muscle in this group, spanning from the body of sphenoid bone to the super lateral aspect of the eyeball. This rotates the eye upwards and towards the nose.

Inferior oblique muscle

Like the other eye muscles, inferior oblique is named by its position within the orbit, relative to the eyeball. This muscle rotates the eye downwards and towards the outside of the head.

Inferior rectus muscle

The inferior rectus muscle originates from the common tendinous ring, and goes on to attach at the lower anterior surface of the eyeball. The eye is pulled downwards by this muscle.

Sclera

The outer coating is also called the white of the eye.  In fact, the sclera forms more than 80 percent of the surface area of the eyeball, extending from the cornea all the way to the optic nerve, which exits the back of the eye. Only a small portion of the anterior sclera is visible.

Retina

This layer contains millions of cells that detect light. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.

Fovea

The central part of the retina, this contains colour-detecting cones. The fovea is responsible for sharp central vision (also called foveal vision), which is necessary in humans for activities for which visual detail is of primary importance, such as reading and driving. The fovea is surrounded by the parafovea belt and the perifovea outer region.

Vitreous humour

The vitreous humour (also known simply as the vitreous) is a clear, colourless fluid that fills the space between the lens and the retina of your eye. 99% of it consists of water and the rest is a mixture of collagen, proteins, salts and sugars. This is a thick jelly that fills the back of the eye.

Pupil

The pupil is the opening that allows light into the eye. While your two pupils will usually be roughly the same size, pupil size overall can fluctuate. Factors that cause your pupils to become bigger or smaller are light (or the lack of it), certain medications and disease, and even how mentally interesting or taxing you find something.

Cornea

A clear layer, the cornea helps to focus light. Your cornea can also filter out some of the sun's ultraviolet light. But not much, so your best bet to keep it health is to wear a pair of wraparound sunglasses when you're outdoors.

Lens

This structure changes shape to focus light on the retina. In other words, it focuses the light rays that pass through it (and onto the retina) in order to create clear images of objects that are positioned at various distances. It also works together with the cornea to refract, or bend, light.

Iris

The iris is a circle of muscle that controls how much light enters the eye. Together with the pupil, the iris is responsible for regulating the amount of light that gets into the eye. Too much or too little light can hamper vision. 

Ciliary muscles

The ciliary muscle occupies the biggest portion of the ciliary body, which lies between the anterior border of the choroid and iris. These contract or relax to adjust the shape of the lens.

Optic nerve

The optic nerve is located in the back of the eye. It is also called the second cranial nerve or cranial nerve II. It is the second of several pairs of cranial nerves. Signals from receptors in the retina are carried to the brain along this nerve.

Light detectors

Rods and cones are two types of light receptor cell on the retina. Rods pick up dim light, while cones detect colour and detail. Then they send information about what they record to the brain via the optic nerve.

 

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When rays of light from an object hit the cornea (outer shell of the eye) they are bent (refracted). The rays then refract more as they pass through the transparent lens. With distant objects, light is refracted mainly by the cornea – then thin lens only refracts light a little. With nearer objects, the lens becomes wider and it does more of the refraction.

The surface of the cornea is where light begins its journey into the eye. The cornea’s mission is to gather and focus visual images. Because it is out front, like the windshield of an automobile, it is subject to considerable abuse from the outside world.

The cornea is masterfully engineered so that only the most expensive manmade lenses can match its precision. The smoothness and shape of the cornea, as well as its transparency, is vitally important to the proper functioning of the eye. If either the surface smoothness or the clarity of the cornea suffers, vision will be disrupted.

 

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The role of the eyes is to collect vast amounts of visual information, which the brain turns into 3D pictures of the world around us.

Each eye has a built-in lens to give a picture of the world and a bank of sensors to record it. Human eyes can focus on anything from a close-up speck of dust to a galaxy across the universe, and work in both faint moonlight and dazzling sunshine. The lens in each eye focuses light rays together on the back of the eyeball. Receptors record the patterns of light, shade, and colours, then send them to the brain to make an image.

Three pairs of muscles control the movements of each eye, allowing it to swivel and roll to look up, down, or from side to side. The muscles are fast-acting, so the eye can easily follow a moving object.

 

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Different animals use their tails for different purposes. Animals such as monkeys and opossums have what is called a prehensile tail, which allows them to grasp tree branches. Grazing animals like horses and cows use tails to swat flies. Cats like lions and tigers use it for balance, especially when running. Kangaroos too use their tails for balance. Tails are also used for communication – dogs wag their tails to express affection; deer flash their white underside of their tail to warn other deer in the vicinity of possible danger, and female deer do so when they are ready to breed; and beavers slap the water with their tails to indicate danger.

Some species use their tail to escape from their enemies (lizards detach their tails to prevent an attack from its predator), while others use it to attack their enemies (Scorpions have venom at the end of their tail, while rattlesnakes have a special organ at the end of their tail that enables them to warn intruders and keep enemies at bay).

Did you know crocodiles and alligators store fat in their tails?

 

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Spanning two countries and spread over 2,00,000 sq.km., it is no surprise that Thar Desert is one of the largest deserts in the world. While easily much more than three-fourths of the desert spans four States in India – Rajasthan, Gujarat, Punjab and Haryana.

However, despite its dry conditions and low rainfall, it hosts a large number of people, and a variety of flora and fauna. In fact, it is said that about 40% of the people in Rajasthan call the region home. The scrub, water-resistant trees and sparse grasslands support a variety of fauna.

Wildlife

At least 300 species of resident and migratory birds can be found here. Among them are the critically endangered great Indian bustard and lesser florican. Raptors include critically endangered red-headed vulture, white-rumped vulture and Indian vulture. Blackbuck, chinkara, Indian wild ass, desert fox, sloth bear, wild cat, several species of reptiles such as snakes and lizards, and insects such as beetles too can be spotted here.

Desertification

Desertification refers to the gradual degradation of dryland ecosystems caused due to soil and vegetation loss, resulting in more areas turning into dry regions. This happens due to continuous human activity such as agriculture, overgrazing, deforestation etc., and change in climate. This phenomenon is being observed globally, and it is no different in Thar Desert. A changing landscape with diminishing vegetation affects the various birds and animals too dependent on the region for survival. The Central Arid Zone Research Institute studied various aspects of desertification, including wind erosion/deposition, vegetation degradation etc. in the Thar Desert, especially in Rajasthan. The report released by the Institute in 2019 said that the damage is so severe that it could take a long while for the landscape to recover.

Two sides to locust attack

The Thar Desert was in the news a few months ago for locust invasion in the region. Considered one of the worst in decades, the attacks were reported from a few other neigbouring regions too, and the locusts made short work of the crop farmers had raised over several acres. The farmers were advised to spray pesticides on the crops to keep these hungry locusts at bay. This was of concern because while the insecticide killed the locusts, it could harm birds and other creatures eating locusts that die thus.

Meanwhile, it was lucky time for birds and animals that could feast on locusts while they were still alive and untouched by the pesticide. Locusts are said to be rich in protein. Apparently, several creatures in the wild – from the great Indian bustard to lizards, foxes, desert cats, jackals and wolves 0 had hearty and nutritious meals, thanks to the invasion. In fact, it is said that the insects helped increase reproduction rates in the bustards under the captive breeding programme.

 

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Life cycle refers to the development stages through a creature’s life. As you perhaps know already, the life cycle of most insects, including ants, wasps, bees, flies, butterflies and moths, consists of four stages – egg, larva, pupa and adult. This transformation is called metamorphosis. Metamorphosis is derived from the Greek word that means “to change shape”. Well after an adult lays eggs, the larvae or the caterpillars wiggle out. And they’re very hungry caterpillars! So at this stage, their singular purpose is to eat and grow. Depending on the species, what they feed on changes. For instance, the mosquito larvae usually feed on leaves. After growing considerably in size and shedding skin many times, the larvae pupate. During this stage, they have a protective covering, are attached to a surface, do not feed and the structures for adults are formed. Finally, adults emerge. It’s during the pupal stage that the question of chrysalis or cocoon comes up.

Chrysalis

Chrysalis refers to the pupal stage of a butterfly. Just before its final molting, the caterpillar attaches itself to a surface – usually a stem or under a leaf – using a tiny pad of silk that it spins. Some of these hanging caterpillars resemble letters such as C, J, etc. depending on the species. When it sheds its skin one last time, the new skin that emerges gradually becomes the outer covering for the chrysalis, which looks like a small lump of shimmer or plain colour. Inside this, slowly some parts of the caterpillar liquefy to give way to new organs. For instance, antennae and wings form while chewing mouthparts turn into sucking mouthparts to enable the butterfly to sip on nectar.

Cocoon

Cocoon is the hard covering spun usually by moth caterpillars. Before their last molting, the moth caterpillars spin these silky cases, and inside these, the caterpillars turn into pupae before emeriging as moths. Some of the caterpillars even add bits of dry leaves and tiny twigs to these cases for camouflage. Silk is obtained from the cocoon of the silk moth. Some of the insects too spin cocoons.

Not all the spinners!

It is said that butterflies never spin cocoons. However, there are apparently a few moth varieties too that do not build a cocoon. Instead they pupate underground – burrowing in the soil, molting into pupae and remaining burrowed until finally emerging out of the soil as moths.

 

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If you are a regular follower of news, you would have often come across pictures or videos of thousands of dead fish floating in a lake or a river. Sudden appearance of dead fish is a clear sign of environmental stress in the water body and it prompts officials to investigate the underlying cause. Called fish kill or fish die-off, such events can result from a variety of reasons.

Oxygen depletion

Dead zone: Most fish kills happen due to low oxygen level triggered by water pollution. Some regions in river, lakes and oceans become too depleted in dissolved oxygen that they can no longer support aquatic life. These areas are called dead zones.

When humans channel agricultural runoff, sewage and industrial effluents into waterways, the amount of nutrients in the water increases. The excess nutrients, especially nitrogen and phosphorous, lead to a spurt in the growth of microscopic algae called phytoplankton. This phenomenon is called algal bloom. Phytoplanktons use up all the nutrients, grow, die and sink to the bottom, where they are decomposed by bacteria. The bacteria respire using the dissolved oxygen in the water, leading to the depletion of oxygen available for other marine organisms, which eventually suffocate and die, mostly en masse.

Algae can also form infamous red tides, large toxin-releasing blooms that can accumulate in fish and spread through the food web.

High water temperature: Most dissolved oxygen-related fish kills occur in the summer months. In general, warm water holds less dissolved oxygen than cold water, so summer is the time when fish can have a hard time getting enough oxygen.

Other causes

Apart from oxygen, depletion, drought, overpopulation, infectious diseases, and release of high concentrated toxins into the water body cam contribute to fish kill. More often than not, fish kill is a result of a combination of several such factors.

 

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