Answers to last issue's Do You Know?

1. I love eating ice cream. Can I survive by just eating different flavours of ice cream (and nothing else)?
Answer: The short answer is yes, you can, but it will not be a pleasant life.
Health experts recommend that women consume at least 1200 calories a day, and men consume at least 1500 calories a day. Ice cream contains milk, cream, and sugar. Let us say you have a plain vanilla flavour, it has about 200 to 250 calories per 100g, so you would need to eat at least half a litre of it each day to get enough calories. But 100 gm of icecream contains about 4 g of protein, 28 gm of carbohydrate (mostly sugar) and14 gm of fat. So half a litre of ice cream would give you only about 20 grams of protein per day, which is smaller than the 40 gm of protein that a 50 kg person needs. But milk protein contains all the ten essential amino acids your body needs. These are the amino acids that cannot be made (synthesised) by our own body and are required for normal growth and development as well as metabolic and physiological functions of the body.
Milk also contains vitamins A, D (usually added extra to toned milk), E, and K which are the fat soluble vitamins although it is not a major source of E and K. It also contains most of the B vitamins, and small amounts of vitamin C. You could take care of the rest with different ice cream flavours. If you could include real fruit pulp and nuts, instead of flavour extracts like vanilla, you should get enough vitamin C and E.
Unfortunately, an ice cream-only diet would give you too much saturated fat and sugar, increasing your risk of coronary heart disease and diabetes. You are also likely to suffer from constipation as you will be short on dietary fibre (which come from vegetables and fruit). Your teeth will rot fast as well, so you will not even enjoy the ice cream!
So while you may be able to survive, it is not a recommended diet!

2. Why do clothes look darker when they get wet?
Answer: Actually , wet fabric is not actually darker than dry fabric. Rather, it just *looks* darker to the human eye. The same goes for other surfaces, like wet cement after a rainstorm, or wet beach sand after waves splash over it. 
To understand how colour in material changes in the presence of moisture, it is important to recall how colours are perceived by us in the first place. When light from the sun strikes a blade of grass, we perceive the grass to be green because the light energy is only partially absorbed. The grass absorbs wavelengths of light in the blue, red, yellow and orange range of the electromagnetic spectrum, but reflects green light wavelengths (560-520 nanometres). Thus, the light that bounces back from the grass is taken in by our eyes, where it hits the cone cells in our retina, and is translated in your brain to green grass. So how we perceive colour is completely dependent on how light is either absorbed or reflected. 
Additionally, the texture and composition of the material can affect how we see colour. An article of clothing is composed of many layers of tiny fibers, which provides a lot of surface area for light to be reflected. Even though a material may be partially transparent, the multiple layers and individual fibres reflect the colour back at you. A white T-shirt, for example, is composed of fibres that are mostly transparent, but in such large numbers and concentrations, they generate a vibrant white colour. The interaction of all that fabric, light and air creates the appearance of a solid colour to your eyes. Even if fabric feels smooth, they have a rough surface on a microscopic level and the falling light has more angles to bounce off, generating more reflection and creating a brighter appearance.
Now let us examine how things change when a material or surface is wet. Most importantly, when a material is wet, that additional layer of water acts like a second reflective surface.
Consider a bright red T-shirt for example. When light strikes the dry T-shirt, all the wavelengths of light are absorbed except for those that appear red (700-635 nanometres), which bounce back to our eyes. When that T-shirt gets wet and light strikes the fabric, it must then pass back through the layer of water on the fabric. The water has filled in all the gaps of the fibres that had previously been filled with air. As a result, the light is more likely to be bent away from the eye by the water. This condition is called total internal reflection, a situation in which the light that would normally bounce back at the observer can instead be re-absorbed by the water.
If fewer photons of light bounce off the fabric and return to your eye, then the material appears to be "darker" in colour. The amount of light being reflected by the material is the same, but less of it is being sent back to your eye. 
As the fabric dries, more air returns to the pockets of space between the fibres, allowing falling light to bounce and reflect more freely, rather than being absorbed or re-reflected by any water present on the material. So the colour becomes "lighter".

3. Can we genetically modify an animal so that it could live on another planet or on the moon?
Answer: This is an interesting question. Firstly, rather than animals, if we consider bacteria, there may already be microbes on Earth that could survive on Mars. Bacteria from the Dead Sea and the Arctic tundra have been shown to survive in a simulated Martian atmosphere. Venus has a cooler upper atmosphere, but surviving on this planet is difficult, as it has no ice or water. 
Alien life might have its own completely different biochemistry, but we would not be able to genetically engineer it, since DNA molecules themselves require water.
Moving on to more complex, multicellular life, the lack of atmospheric oxygen on Mars would probably rule out this planet. The organisms on Earth that do not need oxygen are almost all single-celled because anaerobic metabolisms produce much less energy.
Jupiter's moon Europa has a liquid water ocean underneath its icy crust, and in 2009, some scientists suggested that there might be oxygen too. How survivable this ocean is for Earth life will depend on what other toxins and nutrients are dissolved in it. If we do wish to attempt genetic engineering to survive the cold and pressure in Europa, deep-sea fish and invertebrates would be good candidates.
How do scientists study the mechanisms by which human beings might survive in environments outside the Earth? In 2015 there was a study of the Kelly twins, one of whom spent more than a year aboard the International Space Station while his twin brother stayed back on Earth. From his scientists have obtained a wealth of data on how space affects the human body. The major question in this line of research is to figure out a way to make human cells more resilient to the effects of radiation.
However, the idea of tinkering with animal genes is controversial, so nobody has a definite answer to the question. 

4. Do fish feel pain?
Answer: This has been debated for a long time and people have believed for long that fish do not suffer. But in the last two years, scientific evidence is coming in showing that this wisdom might be faulty.
Fish have neurons known as nociceptors, which detect potential harm, such as high temperatures, intense pressure, and caustic chemicals. Fish produce the same opioids (the body's innate painkillers) that mammals do. Also, their brain activity during injury is analogous to that in vertebrates on land: sticking a pin into goldfish or rainbow trout, just behind their gills, stimulates nociceptors and a cascade of electrical activity that surges toward brain regions essential for conscious sensory perceptions (such as the cerebellum, tectum, and telencephalon), not just the hindbrain and brainstem, which are responsible for reflexes and impulses. So fish do demonstrate a sharp reaction.
Fish also behave in ways that indicate they consciously experience pain. In one study, scientists dropped clusters of brightly coloured Lego blocks into tanks containing rainbow trout. These trout typically avoid any unfamiliar object coming suddenly, in case it is dangerous. But when scientists gave the rainbow trout a (painful) injection of acetic acid, they were much less likely to exhibit these defensive behaviour, probably because they were distracted by their own suffering. In contrast, fish injected with both acid and morphine maintained their usual caution. Like all analgesics, morphine dulls the experience of pain, but does nothing to remove the source of pain itself, suggesting that the fish's behaviour reflected their mental state, not mere physiology. If the fish were reflexively responding to the presence of caustic acid, as opposed to consciously experiencing pain, then the morphine should not have made a difference.
In another study, rainbow trout that received injections of acetic acid in their lips began to breathe more quickly, rocked back and forth on the bottom of the tank, rubbed their lips against the gravel and the side of the tank, and took more than twice as long to resume feeding as fish injected with benign saline. Fish injected with both acid and morphine also showed some of these unusual behaviour, but to a much lesser extent, whereas fish injected with saline never behaved oddly.
All this makes you shudder? Skipping more such details, it is becoming increasingly clear to biologists and veterinarians that fish do feel pain. 
Should we care how fish feel? Philosophers discussing our ethical obligations to other animals say, yes if we know that they suffer. Now that scientists talk of fish showing indications of a form of fish-suffering, many say that this cannot be compared with human pain. True enough, but though we do not know whether cats, dogs, lab animals, chickens, and cattle feel pain the way we do, yet we still afford them increasingly humane treatment, so the considerations may apply to fish as well.
Consider this. Annually, about 70 billion land animals are killed for food around the world. That number includes chickens, other poultry, and all forms of livestock. In contrast, an estimated 10 to 100 billion farmed fish are killed globally every year, and about another one to three trillion fish are caught from the wild. The number of fish killed each year far exceeds the number of people who have ever existed on Earth.

5. How far do we travel through space every day?
Answer: The first and simple answer is found by calculating the circumference of the Earth's orbit around the sun and dividing by the number of days in a year. 
The average distance from the sun to the Earth is 150 million kilometers. Multiplying by 2 Pi gives 942.5 million km for the circumference. Dividing this by 365.25 days/year gives 2.58 million km per day. 
The actual average orbital velocity is closer to 29.77 km/second, accounting for the fact that the orbit is slightly elliptical. Using this value gives a more accurate 2.57 million km per day average. 
Actually this apparently simple question also touches on some fundamental principles of relativity and even questions in cosmology. There is no universal reference frame. So, when talking about the motion of the Earth, we have to declare which object the motion is with respect to. At the Earth's equator you travel approximately 40,000 km a day with respect to the Earth's centre. Each day, the Earth's orbit takes you about 4.02 million kilometres with respect to the Sun's centre. 
Our solar system is in motion relative to the Milky Way galaxy and our entire galaxy, along with the local cluster of galaxies is in motion relative to the Cosmic Background Radiation. This last motion is measured by observing a red-shift in the background radiation. 
The entire solar system, including the Earth, moves through the "cosmic background radiation" (the leftover radiation from the birth of the Universe) at about 596 km per second for a total of 51.5 million km per day. This is much larger than the orbital motion, but it is not yet known what is the cause or meaning of this relative velocity. (To be precise, the directions of all these velocities are always changing, it is meaningless to simply add them together.)
Sources: BBC's Science Focus, Physics Links, ABC Science, Hakai magazine