Answers to last issue's Do you know?

1. Which is the slowest animal on Earth?

Ans: There are a lot of animals that never move. Corals and sponges are examples, but there are many more. Clearly, these animals are the slowest on earth, since they don't move at all!
Of the animals that do move, a lot depends upon size. Small animals might seem fast when they dart across your field of view in the microscope, but they are covering a very small distance. So their speeds are low.
Speed generally increases as size increases, just like an adult human can run faster than a child. However, there is one medium-sized animal that is particularly slow. This is the sloth, especially the three-toed sloth.
The sloth is an arboreal (tree living) animal mostly found in Central and South America, that moves very slowly. Because of this, its name has taken on the meaning of a slow, lazy person.
However the sloth is not moving slowly because it is lazy. It lives in an area where eagles are the major predator. Eagles, like most predators, have very keen eye-sight which is particularly suited to detect movement. When the sloth moves through the trees very slowly, it is hard to detect its presence.
Sloths don't do much walking on the ground, though -- they spend their lives hanging upside down from tree branches with the help of their long claws. They eat, sleep, and even have babies upside down!
This is because their legs and feet are shaped to hang from trees. It's actually hard for sloths to walk on the ground. They can't run or stand upright on their feet. On the rare ocassions when on the ground the sloth generally moves at 15-30 cm per minute with its maximum speed being 150 cm per minute.
2. Who invented the Internet?
Ans: The Internet is a global system of interconnected computer networks. The Internet is a global data communications system. You can think of it as a network of networks.
As it turns out, there is no one inventor of the Internet. The Internet was created in the 1960s as a huge network linking big university and government computers. The science behind the Internet was invented during the Cold War, when the United States was in competition against Russia for weapons and technology.
Shown is a very crude diagram of the internet - a computer network that connects two computers. Because the internet is so complex it is shown simply as a cloud (it's too complex to draw).
The first idea is that of packet switching: packets of data are "routed" or sent from one place to another. The destination is chosen based on address information that is also carried in the data, much like the address on a letter. The theoretical idea of packet switching was due to Leonard Kleinrock in 1961.
All telephone exchanges at that time worked on the basis of "circuit switching" where there is an actual electrical circuit all the way from the source to the destination. So this was a very radical idea.
Larry G. Roberts created the first functioning long-distance computer network in 1965. He also designed the Advanced Research Projects Agency Network (ARPANET), the seed from which the modern Internet grew, in 1966.
Bob Kahn and Vint Cerf invented a technique called the Transmission Control Protocol (TCP) to move data on the modern Internet, in 1972 and 1973. E-mail was invented around that time.
It wasn't until 1989 that Tim Berners-Lee, a scientist at the European Laboratory for Particle Physics in Geneva, proposed the World Wide Web (WWW).
While the internet is an infrastructure that provides connectivity between computers, the Web is one of the services communicated via the Internet. WWW is just the culmination of a series of ideas over more than 40 years.
3. What's the difference between the flu and a common cold?
Cold and flu (or influenza) are both respiratory illnesses and many people use the terms interchangeably. However, they are both caused by different viruses.
Ans: Common cold is caused by viruses such as adenoviruses, coronaviruses or rhinoviruses while flu is caused by the influenza virus. A picture of the molecular surface of a rhinovirus and a photo (under transmission electron micrograph) of influenza virus, magnified approximately 100,000 times, are shown.
Flu symptoms, typically high fever, can appear in 3-6 hours, unlike colds, which set in more gradually, although both have an incubation period (time taken for symptoms to develop after being infected) of a few days.
Sneezing and sore throat, stuffy nose is common in colds but rare with flu, which can cause headaches (and many other aches!) instead. Flu can also lead to serious health complications such as pneumonia and bacterial infections.
Most importantly, vaccination is possible against flus. Every year, only a handful of strains of the influenza virus cause most of the flu across the world. You may have heard of "bird flu" and "swine flu" recently.
On the other hand there is no cure for the common cold: there are lots of viruses which cause colds. Moreover, they keep on changing or transforming themselves (called mutation) from generation to generation. So it is not possible to find a vaccine that prevents every variety. The good news is that the cold just slowly goes away by itself.
4. I read that plants absorb water through osmosis and later I heard someone talking about reverse osmosis ! What are these ?
Ans: Osmosis is a physical force. It is the natural tendency of water with a low concentration of dissolved particles to move across a semi-permeable membrane to an area of water with a high concentration of dissolved particles.
Osmosis may occur when there is a partially permeable membrane, such as a cell membrane. Impermeable means that the object doesn't allow things through it, so a membrane has to be permeable so food gets in and waste gets out.
The water will try to reach an equilibrium on both sides. So both sides of the semi-permeable membrane will have the same concentration of dissolved particles.
When the membrane has a volume of pure water on both sides, water molecules pass in and out in each direction at exactly the same rate; there is no net flow of water through the membrane.
Plants use osmosis to absorb water and nutrients from the soil. The solution in the roots of the plants has high levels of water, and hence draws in water from the surrounding soil that has low levels of water. Roots are designed as selectively permeable membranes, admitting not only water, but some useful minerals that the plant needs for survival. Osmosis also plays a critical role in plant and animal cells, with fluids flowing in and out of the cell wall to bring in nutrients and carry out waste.
The flow may be stopped, or even reversed by applying external pressure on the side of higher concentration. In such a case the phenomenon is called reverse osmosis. Reverse osmosis (RO) is a filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution.
Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing salt and other substances from the water molecules. This is the reverse of the normal osmosis process.
The ability of the membrane to reject or repel dissolved particles, while allowing water to readily permeate, is based on the incredibly small size of the multitude of pores that penetrate its surface. Such pores are able to reject substances as small as 0.0005 microns.
5. Why does the Moon seem to follow you when you move?
Ans: Yes indeed, does the Moon not seem to follow you when you move? The answer is simple, it does so because it's so far away!
This sounds all wrong. After all, how could something far away seem to follow along at all?
To understand this, start with objects that are much closer. When you are riding in a bus, close things seem to move by rapidly as you pass them. A tree or house by the road starts out ahead of you. It comes up fast, and in a few moments, it's far behind you.
Objects that are far away do not seem to move very fast. If you can see a far-away building or a mountain from a moving bus, notice how long it takes for that object to pass by. If you live near big mountains, you can sometimes ride toward mountains that never seem to get any closer.
The Moon is nearly 4 lakh km away. It is so far away that the motion of your bus doesn't change its position enough for you to notice. So the Moon just seems to follow you wherever you go.
The next time you're traveling on a moonlit night, roll up a piece of paper into a narrow tube. Watch the moon through it, staying in the same position in the bus. The moon will appear to pass by very quickly, just like the trees and houses nearby, because your field of vision will be very narrow.