Why do leaves change color, especially in autumn?

Three factors influence autumn leaf color
  - leaf pigments, length of night, and weather.

In leaf pigments, Chlorophyll gives leaves their basic green color, Carotenoids produce yellow, orange, and brown colors  and Anthocyanins gives reddish color. Both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed. The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors. So the leaves look colorful in autumn.  Temperature and moisture also influence the leaf color. During sunny days, lots of sugars are produced in the leaf, which tapers off as colder days start. This in turn spur production of the brilliant colors in leaves.

How is sugar and jaggery different?

Both  sugar and jaggery (gur) are made from the same sources, generally sugarcane. But there is a lot of difference in their properties and benefits.
- Color :  Sugar is bright white color, whereas the color of jaggery can range from golden-yellow to golden brown, brown, dark brown like dark chocolate.
- Texture : While sugar crystals are solid and hard, jaggery is semi solid, softer than sugar and also amorphous.
- Processing : To make sugar, the syrup is treated to remove the unwanted particles, so that after condensation and crystallization, the product is white color. On the other hand, in case of jaggery, there is no treatment given to the juice and it also does not undergo the crystallization process. The sugarcane juice is boiled continuously, until thick paste is formed, after which the paste is poured into molds and blocks of desired size.
- Composition : While sugar is made only of sucrose, jaggery is made up of predominantly sucrose, mineral salts, iron and some fiber. Hence, consumption of jaggery is recommended in case of iron deficiency anemia.

- Sugar is instantly absorbed in the blood while jaggery is digested slowly. Jaggerry is also rich source of iron. It acts as a cleansing agent and cleans the lungs, stomach, intestines, esophagus and respiratory tracts.

Why do we sneeze?

A sneeze begins with a tickling sensation in the nerve endings that sends a message to your brain that it needs to rid itself of something irritating the lining of your nose. Sneezing is a procedure of expelling the harmful bacteria and virus which has entered the body and multiply themselves during cold, allergic reactions or when dust blows on our face.The high velocity of the airflow is achieved by the buildup of pressure inside the chest with the vocal chords closed. Sudden opening of the cords allows the pressurized air to flow back up the respiratory tract to expel the irritants. This helps to remove offending particles in the nose. It is an important reflex action to remove an irritant and to keep our air passages open and free of obstructions.

People don’t sneeze when they are asleep because the nerves involved in nerve reflex are also resting.

Is there a difference between words - smart, clever and intelligent?

Clever, Smart and Intelligent are attributes which are used interchangeably and synonymously. They express different levels of formality but essentially they may mean the same.

Smart is being quick-witted or "bright". A smart person is usually someone who is quick in thinking though not necessarily having high level knowledge in a broad base of subjects. 

Intelligence is the ability to learn, understand and make judgments or have opinions that are based on reason, and is something which you are born with i.e genetic. A person's intelligence level has to do with how well informed they are, how educated and knowledgeable they have become.

Clever people are born with above-average mental ability using their knowledge creatively. Cleverness is having or showing the ability to learn and understand things quickly and easily. 

Clever person know what works, smart person know when it works, and intelligent person knows why it works :)

Why does a liquid remain hot or cold for a long time inside a thermos flask?

Thermos flask consists of double walled glass bottle. The inner side of outer wall and the outer side of inner wall are silvered. The air is pumped out between the two walls of bottle to create a vacuum.

Generally, a hot substance gets cold by releasing its heat to the surroundings. Likewise a cold substance gets hot by absorbing the heat from the surroundings. The most important function of the thermos flask is to prevent the flow of heat to and from the bottle. Conduction, convection and radiation are the three processes by which heat can flow from one place to another. Thermos flask doesn’t allow heat exchange to take place. Glass is used to make up a thermos flask which is a bad conductor of heat; hence heat is prevented from escaping out by conduction. Due to the presence of vacuum within the walls, heat loss due to convection is also ruled out. Since the walls are also silvered heat is also not lost due to radiation. Due to all these reasons mentioned above, a hot thing remains hot and a cold thing remains cold for many hours.

Why do doctors examine the pulse of a patient?

The pulse can be felt by placing fingers on the inside of the wrist over the radical artery. When a doctor checks the pulse, heart beats are counted for a minute. Since the rate of contractions felt at the wrist would be same as the heart rate, the pulse tells us about the health of the heart. This tells the doctor about the health of the patient’s heart. The pulse rate depends on the blood requirement of the body and this indicates the pressure on the circulatory system. An irregular pulse rate indicates a fault in the normal functioning of the heart. A good practitioner of Ayurveda can simply measure the pulse of a person and understand all about the ailments in the body.

Which time zone applies to Antarctica where all time zones meet?

Since Antarctica is at the South Pole, and all of the time zones have a common point there, logically, there would be a part of Antarctica that would occupy each of the time zones simultaneously. Antarctica has no official time zones .
There is no specific time zone for Antarctica and neither could there be any. Therefore , researchers in the Antarctic regions of the earth usually use the time zone associated with their research stations. For example , since nearly all flights to Antarctica and the South Pole are from New Zealand , New Zealand time is the most commonly used time zone in Antarctica .
Some prefer to follow the time zone of their nation’s capital.

Why do ants walk in a line?

Ants are social insects. They live in big colonies and have a very organised social life. Red ants make their nests inside the walls of our houses. They generally travel large distances in search for food. In absence of any maps or navigation aids, they have to rely on other mechanisms to find their way around. 

As they walk the ants leave behind a scent that they use to trace their way to a food source or back to their home. The scent that the ants leave behind is called pheromone. The ants walk in a line because they follow the scent left behind by the leader. They are following a trail laid out by another ant that will take them to food, water or their home. As more ants travel the trail the scent gets stronger (easier to follow) and the random bumps are smoothed out making the trail straighter.

Once the food source is depleted,the returning ant will not leave any trail pheromone and hence the concentration of trail pheromone in that particular path gets faded. Thus the other worker ants stop following that path and look for a new source.

How does soap work to clean body or clothes?

Most of the time, dirt comes in the form of grease or oil which sticks itself onto surfaces and will not come off if only water is just used. This is because oil and grease are non-polar, which means that the oil molecules are not charged and therefore are not attracted to polar substances such as water. Because of this, oil tends to stick with its own molecules or other non-polar substances. Oil and grease will stick onto plates and cutlery during cleaning, and no amount of water can completely remove it.

In order to remove oil from clothes or from your dishes with water, the oils must be made soluble by the process of emulsification. Soap is an excellent cleanser because of its ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed. 

Why does mosquito bite itch and produces red bump?

Most people experience some kind of skin reaction after being bitten by a mosquito. Only the female mosquito feeds on blood. When the female mosquito stabs her needle-like proboscis (a straw-like mouthpart) into our skin to suck out our blood, she injects us with her saliva. This is filled with digestive enzymes and anticoagulants, and it keeps blood flowing until she is finished with her meal. Our body reacts to the saliva by producing histamine. This makes the blood vessels near the bite enlarge, and so a pink, swollen, and itchy bump appears. When the blood vessels expand, nerves in the area become irritated by the swelling. We feel this irritation as an itchy sensation.

Why can't we remember most of our dreams?

Throughout our sleep we are thinking or dreaming and yet upon awakening we tend to forget most of it. Something about the way the brain/mind functions during sleep makes recall difficult. 

Dreams are basically your brain thinking while your body sleeps (subconscious). It's usually a mix up of all your thoughts, concerns, and late experiences- which is why a dream sometimes reminds you of something you forgot - like a review of a movie you saw. You can't remember your dreams because they are less of an experience than they are a thought. You only dream at a certain level of sleep, but your dreams can still last several hours. You forget your thoughts when you sleep just as fast as you do when you're awake. Most remembered dreaming occurs during a phase of sleep called Rapid Eye Movement (REM) sleep, which occurs about every hour-and-a-half. 

Why do we have lines on the palms of our hands?

Our hands can bend, they can stretch, they can wiggle, and they can wave! To be able to do that, the skin that covers our hands needs to be able to adjust to the changing shapes. The lines are just folds of skin that allow the hand to bend. Observe that all the lines appear at locations where our skin folds over. They are technically called 'flexion creases', and many of them are on our hands from before we are born. When our hands bend, the creases help fold the skin. A baby will have fewer, softer, lines, since it has not moved its hand as much. 

Feet are very similar in structure to hands but do not bend as much. The lines on the bottom of our feet are not as severe, because sole of feet does not have so much flexibility as hand.

Is the ice in the polar ice cap, fresh or of saltwater?

Even though the glacier ice comes from salty ocean water, the sea ice that forms in the Arctic and Antarctic is fresh water. The presence of salt lowers the freezing point of ocean water and it does freeze. However, the salt molecules are rejected back into the liquid as the ice forms, resulting in freshwater ice floating. The land ice over Greenland and Antarctica is also fresh water, and results from the accumulation of snowfall over long time periods.

Why do we rub our eyes when we are tired?

When we are tired, our tear ducts produce less fluid, which dries out our eyes. If we are really tired, we may drift off mentally, causing us to stare. Having our eyes open for prolonged periods of time increases dryness.

When we rub our eyes, we stimulate the tear ducts, which spreads moisture over our eyes. This pressure also triggers a reduction in blood pressure, which helps us relax and get ready for sleep. 

This is the same reason we rub our eyes when we're under a lot of stress.

Why do bananas turn black when put in a refrigerator?

Green banana peels contain a plant hormone called ethylene. This is a gaseous chemical that is responsible for helping ripen the banana to yellow. At the same time, a few different natural acids are also being produced that add balance to the ripening process and make the banana sweet.

When you put a banana in the fridge, the acid production slows down because of the cold temperature and, as a result, the ripening process slows down. Yet ethylene production continues to escape, eventually breaking down the cell walls of the peel until it becomes black.

Why does sunflower always face towards the Sun?

Facing of sunflower towards the sun is known as phototropic movement. Sunflower plant contains a growth hormone named Auxin which is sensitive to the sun-rays. This chemical accumulates on the shaded part of stem and boosts the growth of cells on the shaded part of stem. So the sunflower automatically leans in the opposite direction i.e. towards the Sun. As the direction of shade changes with the direction of the Sun, Auxin hormones also shift their own position on the stem to remain away from the sun-rays. This keeps sunflower always facing the Sun.

Why do we stop growing after certain age?

Our body grows with the help of proteins. The proteins get converted into amino acids during the process of digestion. The cells and tissues are produced by these amino acids. Proteins along with minerals produce and repair muscles, tissues and bones. 

Growth of our body is controlled by the endocrine glands that we have. After a certain age, the body gets the full maturity. It takes too much food and energy to keep on growing after we have hit maturity. So after maturity, the body stops growing up, because after this age the glands which are responsible for growth become less active. But there is very slow continuous growth.

Why are the two sides of a coin known as heads and tails?

Generally, one side has the imprint or embossing of the official head of state or an insignia or emblem and hence it is called the head side. It is the main side of a coin carrying the portrait head of the ruler or a Symbol and name of the country. Since the opposite of the head is the tail, the reverse side is naturally called 'tails'. It depicts the denomination or issue price of the coin with year and mint mark underneath. 

Technically, the heads and tails sides are known as the obverse and reverse, respectively. The tail side name possibly originated from the British ten pence coin, the reverse of which shows a heraldic lion with its tail raised.

Why does sugar dissolve faster in hot water than cold water?

Sugar dissolves by water molecules surrounding sugar molecules and separting in from the rest of the solid. When sugar is added to water, energy is used up to break apart the molecules in the sugar. The water molecules then begin to spread out to make room for the sugar. This way the sugar gets dissolved in the water.

When the water is hot, the sugar molecules break apart faster, and the water molecules move around the sugar faster. With increased temperature, the water molecules are moving more rapidly, increasing the speed at which hydrated sugar molecules are transported away from the solid, increasing the rate at which the solid dissolves. In cold water, this process is slow, hence the sugar does not get dissolved faster.

Why do we sweat on a hot day?

When the body temperature rises, the sweat glands are stimulated to secrete perspiration. It is nature's way to keep the body cool. During the process of evaporation of sweat, body heat is taken away, thus giving a sense of coolness.

Sweating is therefore the human body's primary cooling mechanism. Because this mechanism uses water, we need to replace lost fluids by drinking more fluids in hot weather. This is especially true after exercising or working in hot weather.  When we sweat, our skin and clothing become covered with water. If the atmospheric humidity is low, this water evaporates easily. The heat energy needed to evaporate the water comes from our bodies. So this evaporation cools our bodies.

Why do owls have three eyelids?

Owls are equipped with 3 eyelids. They have a normal upper and lower eyelid, the upper closing when the owl blinks, and the lower closing up when the Owl is asleep. The third eyelid is called a nictitating membrane, and is a thin layer of tissue that closes diagonally across the eye, from the inside to the outside. This cleans and protects the surface of the eye.

Why does a wet cloth appear darker than when dry?

We see a cloth's colour by the light which hits it. For example, when white light (containing all colours) hits a green shirt, all the colours in the light are absorbed by the shirt,except green, which gets emitted. This emitted green light is why the shirt looks green to our eyes.
When the shirt becomes wet, water is absorbed in the fabric, including the outer layer of the material. When white light hits the surface of the material where it is wet, some of the light will scatter (refract) from the water. This light doesn't make it back to our eye. Less light coming from the wet region means it will look darker. Not all of the light that is emitted by the green fabricreaches your eyes now. Because there is less light coming from the wet area (some was refracted in a different direction), that area will look darker than the material around it.

Why water droplets are formed outside a glass containing cold water?

The cold water reduces the temperature of the glass. The cold glass reduces the temperature of the air around the glass. The moisture in this surrounding air gets condensed into liquid droplets. Hence we see a layer of water droplets on the outer surface of the glass.