My Science School

Zebra crossings on the road have black and white stripes in order that we can see them clearly. So you might think that having black and white stripes would make a real-life zebra a sitting target for animals that hunt zebras lived on their own, you would probably be right. But nature is cleverer than that. Zebras move about in herds. So when they are grouped together, their colouring makes a confusing pattern of mixed black and white stripes all moving in different directions at the same time. Any predator trying to single out one particular zebra for its next snack would get cross-eyed looking at that lot. That is what the zebras hope. As long as they keep together, their strange camouflage gives them great protection.

 

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The smart answer is by touching you! But when you find out that some of the largest of these fish can knock a man over with their electric shock, the question deserves a fuller answer.

The idea of fish producing electricity as strong as this is amazing, to begin with. Yet several species have this capability. Some of the smaller ones can produce currents able to light small bulbs while some of the larger fish have powered small electric motors for some minutes before getting tired.

Some fish have generating organs in their heads. Others have them on either side of their tails. These are supplied with nerves from wither the brain or the spinal cord. In all cases the parts of the fish that produce electricity are really modified muscles. In brief bursts, however, they provide a very useful weapon. Enemies can be frightened off with a quick electric shock. And when the same shock is used to stun small fish, the electric fish does not have to look any further for supper.

 

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One of the most unnerving things about a snake is its steady gaze. If you have ever had those unblinking eyes fixed on you, even through a zoo window, you will know what I mean.

For a snake, its penetrating stare is a terrific way of scaring prey. Some animals are turned rigid with fright when they see a snake’s eyes, glaring at them. But the reason they cannot blink is not quite as calculating. Snakes cannot blink because they do not have eyelids. They cannot even close them to go to sleep. Instead they have a permanent glassy stare that can turn most creatures cold with fear.

 

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Lizards have a brilliant way of escaping from predators – detachable tails. It sounds crazy, but that is what they are. A lizard’s tail has a special weak link. If it is unlucky enough to be caught by the tail, this link snaps. The lizard escapes and the predator is left with just a short piece of tail in its jaws. The stump of tail left does not take long to grow back to its correct length, and as nature intends it to snap, it does not cause the lizard any real harm. One kind of lizard called skink goes a stage further. It has a tail which thrashes around when it is pulled away from the rest of the body. This can be really confusing for a predator, which often, mistakes the bit of tail for a living creature. And while it is puzzling that out, the skink has bags of time to make a run for it.

 

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Even though whales look like fishes, they are related to you and me. We are all mammals, as are porpoises and dolphins. Whales are warm-blooded like us. They don’t have furry coats to keep warm like many land animals. Instead whales have a thick layer of oily blubber under their skin. Whales have hearts like yours and mine too – double hearts with four chambers.

The thing that really distinguishers whales from fish is the way they breathe. Fish get the oxygen they need from passing water through their gills. Whales, on the other hand, have lungs similar to ours. They can hold their breath for far longer than we can. But when they need to breathe again they have to come to the surface, they spout out a jet of mist which looks like a fountain or geyser. As it leaves their nostrils, the breath is a warm vapour. But as soon as it is released into the colder air, it condenses to form the mist we can see. Once the sued air is expelled, the whale can take another breath and dive again.

 

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Deep down in the oceans it is pitch-black. You cannot see a thing without artificial light, because sunlight cannot penetrate further than 460 metres below the surface. This could be a serious problem for fish living so deep, if they did not have lights of their own.

Some, like the angler fish, use light to catch their prey. The rat-tail fish sends out a cloud of light to dazzle an enemy while it makes a speedy getaway. Then there are those who use light just to keep in touch with friends and find a mate. They have ‘recognition lights’, rather like ships.

The light produced in these fish is like no other light on earth. For one thing, it’s cold. Almost every other sort of light we know of produces heat. Being cold makes it very energy efficient. Some fish produce their light by mixing chemicals with a little oxygen from their blood. These meet in glands in the fish’s skin. The chemicals form a combustion and light is produce in the gland, which turns into a lamp.

In other oceanic fish bacteria produce the light. The bacteria live and feed on tissue in the fish’s skin, which the fish is constantly replacing. However, the bacteria help the fish by producing substances that glow with bright light. So while the fish helps them, they help the fish.

 

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Every part of a camel's body is suitable for life in the desert from padded feet to blood cells to the hump. The idea of the hump as a reservoir of water is not true. It's rather a mound of fat which gives the camel energy to sustain itself when it has to go for days or weeks without food. The fact that the fat converts into water during metabolism may have given rise to this myth. But it does not help in supplying water to the camel. So, where do camels store water in the bloodstream.

An adult camel can drink up to 135 litres of water at one go. Much of it is stored in its blood. The corpuscles serve as a water tank from which the camel draws water every day. A bellyful of water can help a camel live for 17 days without a refill. The red blood cells of a camel are football-shaped and much smaller than the circular red blood cells of most animals.

These cells aid in continued circulation even when the camel is dehydrated and also allow gulping of such a vast quantity of water at one go. Their anatomical and physiological features are such that they can survive in extreme conditions. Their urine and faeces contain very little water. While most animals lose water while breathing, camels have an efficient respiratory system. Their nostrils trap moisture in their breath before it is exhaled. This moisture is then returned to their body fluids. Camels do not sweat and thereby conserve water.

When they need water, their body will first get it from all fluid parts, before going for the water reserves in the bloodstream. This allows their blood to continue to flow normally, even when they are relatively dehydrated.

So, what is the purpose of the hump? Having a hump of fat, instead of fat evenly distributed throughout their bodies, allows for better heat dissipation. It helps keep their body temperature down. If the camel goes for long without food, the hump will collapse and droop. It will take the camel a maximum of four months of proper eating for the hump to get back to normal.

 

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Ponds play host to a large number of frog species, especially during their mating season. And not surprisingly, the area is filled with different kinds of loud croaks of the males, fervently hoping the females out there would hear them. But when the place is filled with calls from a variety of species, is it even possible for the females to pick out those from the males of their own species? As incredible as it seems, it is possible! And how this plays out is just as fascinating. Come, let's find out.

Lungs and ears

Though we associate hearing with ears, in the case of frogs, lungs too seem to be at play. In fact, these two organs work together to behave much like the way noise-cancelling devices do amplifying the sound we want to hear, and blocking all or most other sounds.

A recent study observed female American green tree frogs during the mating season, and discovered that when they hear the cacaphony of calls, they inflate their lungs with air. When this happens, their eardrums are compressed, causing them to vibrate less in response to sounds that fall within a certain frequency range. It is important to note that the call of the male American tree frog falls outside this range, and so, it can be heard clearly. Not just that. Since the calls of other species fall within this frequency range, those calls are largely filtered out. This also helps the female American green tree frogs hear the males of their species acutely. It is suspected that the females also know to adjust the sensitivity of this in-built 'noise-cancelling' mechanism by altering the quantity of air used in their lungs. Scientists presume that many other frog species too could be equipped with similar mechanisms to identify their own species in a cacaphony of calls.

 

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