Answers to last issue's Do You Know?

1. How and why do chameleons change colour?
Ans: Chamleons are a wonder of nature, in their technicolour splendour. But there is a lot of myth about them too.
There is this myth that chameleons change colour to blend in with their surroundings, but this is actually not true. Most of the reason why chameleons change colour is as a signal, a visual signal of mood and aggression, territory and mating behaviour.
The way that chameleons actually do this is really molecular --- they are molecular masterminds, really. If you look closely at the skin of a chameleon, you find that they have several layers of specialised cells called chromatophores and these are cells that can change colour. On the outer surface of the chameleon, the skin is transparent and just below that surface is the first layer of these cells, and they contain various pigments. These are xanthophores, containing particular specialised pigments that have a yellow colour. Beneath that are pigment cells which are called erythrophores which have a red colour in them. Beneath that, another layer of cells called iridiphores have a blue coloured pigment called guanine, which is actually also used in making DNA. Underneath all this is another layer of cells called melanophores which have a brown pigment --- melanin --- in them.

Now, how does the chameleon change colour? Well, those chromatophores are wired up to the nervous system. They are also sensitive to chemicals that are floating around in the blood stream of the chameleon. What happens is that the colours are locked away in tiny vesicles, little sacs inside the cells that keep them in one place, so the cells do not look coloured. But when a signal comes in from the nervous system or from the blood stream, the granules or vesicles can discharge, allowing the colour to spread out across the cell, and this alters the colour of the cell. The chameleons mix different contributions of these chromatophores to get different colours. That is how the chameleon changes colour, and usually does so to convey mood.
So a calm chameleon is a pale greeny colour. When it gets angry, it might go bright yellow, and when it wants to mate, it basically turns on every possible colour it can, to attract its mate. This is not unique to chameleons. Other animals also have these chromatophores. Cuttlefish are another very elegant example of how this works. So it is not so much to do with camouflage. It has more to do with communication.

2. When you yawn, why do your eyes water?
Ans: Part of the reason is that when you yawn, you squeeze your eyes tightly shut. The way that tears flow is that they come out of your lacrimal gland, which is on the upper outer side of the top of your eye; they then flow - in a film - across your eye obliquely downwards and inwards.
The tiny black dot on your lower eyelid is called a punctum, and that is where your tear duct starts and where the tears drain away.
But if you squeeze your eyelids tightly shut, you close off the punctum, stopping the tears flowing across your eye and into the tear duct, so they build up in the eye. This makes you cry a little bit, which is why tears appear when you yawn.
Some scientists give an alternative explanation. During a yawn, there is a slight increase in pressure inside the skull (likely caused by slight increases in the amount of oxygen taken in during a deep yawn). This causes the cerebrospinal fluid, the fluid that surrounds the brain and flows through the brain's ventricle system, to be forced out faster than normal. That fluid enters the lachrymal (tear) system. That increase in fluid pushes out the tears.
Mostly scientists prefer the simpler explanation, based on squeezing the eyelids tightly shut.

3. If solar panels were put in space, how could the energy produced be sent back to earth?
Ans: While the idea is not as definite as construction of solar panels, it is a very attractive one: solar energy `captured in space' could be a great source for us.
In space near Earth, sunlight has roughly 30 percent more energy than the sunlight we see, because of weather and haze in the atmosphere. When one adds the impact of the day / night cycle and the natural changes between summer and winter in some locations, the difference between Earth-based and space-based solar power grows to a factor of 20 or more.
It is possible that in the future, space solar power could deliver hundreds of thousands of megawatts - enough to power tens of millions of homes around the world.
First, just as on earth, sunlight in space will be converted into electricity by solar rays, that in turn power electronic devices that produce radio waves in what is known as the "microwave" region - a wavelength of about one to ten centimetres.
This microwave energy is then transmitted from many thousands of small antennas, very much like thousands of musicians all playing the same note on their instruments. By orchestrating the individual transmitters - like an orchestra conductor with his baton guiding many musicians, a coherent beam can be formed, and the converted solar energy directed to a desired location on Earth. 
Radio waves of this size have virtually no interaction with our atmosphere, and very little with our weather; in other words, the atmosphere is almost invisible to them. As a result, more than 90 percent of the radio wave energy from space will reach Earth in a low intensity, but precisely pointed transmission.
Once there, the microwave energy can be converted back into electricity by a large but simple receiver known as a rectifying antenna, or "rectenna" which will look a lot like mesh fencing, just like one of the goals in International football, but laid out flat, like a semi-transparent ceiling.
That is all it takes - how solar energy collected in space can be transmitted efficiently and safely back to Earth for our benefit.

4. If we could make all mosquitoes to be of one sex, we can solve the mosquito menace, can't we?
Ans: A brilliant idea, and one that has occurred to some scientists as well!
The idea is that if you progressively shift the sex ratio of a population towards males and there are fewer and fewer females in the population then the overall size of the population will decrease to such a point where the population cannot sustain itself any more and will actually crash. 
Scientists introduced into the mosquito a gene which essentially destroys the X chromosome. We know that, as in humans, also in mosquitoes, there are two types of sperm produced by males: sperm that carry the Y chromosome and sperm that carry the X chromosome. The sperm that carry a Y chromosome produce sons. The sperm that carry X chromosome produce daughters. So, we found a way to specifically eliminate the sperm that carried the X chromosome so that only the sperm that carried a Y chromosome would be functional and would make these males produce only sons. 
This is a very promising technology but scientists are very far away from making it work on an everyday basis. There are many technical hurdles to overcome, but the biggest difficulty is to ensure all aspects of biosafety, safety, ethical concerns and regulatory concerns are addressed. The big challenge is to take these mosquitoes and test them at a larger scale. Apparently a special facility has been built in Italy with large cages that create a field-like control environment.
We wish the scientists good luck, we need all the help we can get to combat mosquitoes and malaria, not to mention dengue and chikungunya!

5. When lightning hits the sea or a lake, do any fish get electrocuted?
Ans: After all, we do have reason to worry. Lightning is a massive electrostatic discharge, the sudden flow of electricity. During a thunderstorm, regions of positive or negative charge build up within or between clouds and the surface of the planet. This charge is eventually discharged by a lightning flash or strike, carrying a huge 30,000 amperes of current and transferring 500 megajoules of energy. This is the equivalent energy striking in a split second as a colossal 1,400 100-watt bulbs running for an hour. 
So, humans are concerned about being fried when lightning strikes on land, are fish not worried in water?
Let us look at what happens when a thunderstorm develops and what happens just prior to the lightning strike. There is a charge that builds up in the cloud and there is an opposite charge that builds up on the surface of the water. So, when a lightning flash occurs, the discharge discharges along the surface. The effect of the lightning is pretty much contained to the surface of the water and in fact, the fish that are swimming below the water are safe. They are completely unaffected by the lightning. 
Thus the lightning electricity mostly stays on the surface of the water. This has to do with the fact that salt water is such a good conductor, so the electricity will quickly be dispersed or spread out to the surrounding water close to the surface. The fish below are safe.

6. Do tears run down one's face at the same speed as normal water?
Ans: This is a very interesting phenomenon, and worth closely watching. The only trouble is that the person crying is not going to be much amused by your wanting to measure the speed of the tears.
Note that if you put droplets of water on your face, they tend to be bigger before they run down. Also remember that a big river will flow a lot faster than a small river. So a big droplet of water has much more gravity pulling on it, thus a much larger force pulling it down your face, but the forces which slow it down increase much more slowly. Tear droplets contain some surfactants and some proteins, so they break up and start running down your face when they are smaller than normal droplets of water.
To summarise: teardrops are smaller than water droplets because tears contain chemicals; the smaller droplets are less heavy, so they get dragged down our face slightly more slowly, so they run more slowly.