How Does Scratching Stop Itching?

When our cells get damaged itching results. Due to this small damage substances such as histamine (the amine that plays a role in allergic phenomena and the widening of blood vessels) are freed and which irritates the nerves and fibers in the skin. This irritation sends signals similar to pain to the central nervous system. There is a similarity between telephone lines and a switchboard. The function of a switchboard is to route incoming calls and to ensure that only one line at a time is connected to a particular numbered telephone. This effectively blocks the telephone from other incoming calls. Similarly, the itch signal can be blocked by occupying the central nervous system by another incoming message like the sensation of scratching, which is less irritating.

How Is Blood Grouping Done?

The broad classification of the groups or types is based on the presence or absence of particular antigens that are carried on the surface of red blood cells. Corresponding antibodies are carried in the blood plasma. Broadly the types are A, B, AB and O but the International Society of Blood Transfusion recognizes some thirty types fro the purposes of blood transfusion - the process of transferring blood taken from one person to another person.

A person with a particular antigen in his blood cannot have the same antibody. Thus a person with  blood containing the antigen A cannot have the antibody A in his blood.

A person of the blood group A has the antigen A and the antibody B. Similarly a person belonging to the blood group B will have the antigen B and the antibody A. The person belonging to the blood group AB will have only the antigens A and B and  no antibodies. The person of the blood type O has only the antibodies A and B and no antigens.

Another type of blood group is the Rh blood group. This name is derived from the group first discovered in the Rhesus monkey. In this group there is the Rh Positive and the Rh Negative blood groups.

The other blood groups include the A1 Positive (A1 +ve), A1 Negative (A1 -ve), A2 Positive, A2 Negative, B Positive, B Negative, O Positive and O Negative to name a few.

How Long Can Humans Survive Without Oxygen?

On the whole, oxygen is absolutely required for survival. Loss of oxygen to any part of the body is known as hypoxia. Total loss of oxygen results in anoxia.

Due to the susceptibility of the human brain to oxygen, humans can survive for only a short period of time without a supply of oxygen to the brain. In spite of the fact that the brain weighs only 5% of the body's weight, it consumes some 20% of all the oxygen intake. Oxygen is supplied to the brain by blood. It takes only about 8 to 10 seconds of loss of oxygen to the brain to make us lose consciousness. Loss of oxygen to the brain for a period of 4 to 6 minutes results in destruction of the brain cells. Extended periods of time results in brain damage and ultimately death.

The brain can survive for longer periods of time at lower temperatures. That is due to the fact that at lower temperatures the brain requires less oxygen for its survival. This fact is made of use in major surgeries and is known as induced hypothermia.

The other tissues of the body can survive for longer periods of time without oxygen, which make organ transplantation possible.

How Do Fruits Ripen?

Senescence or biological aging of plants is associated with the ripening of fruits. It is influenced by the hormone ethylene and involves changes in acidity, color, flavor, texture and content. The production of ethylene increases nearly a  hundred times.

When the ripening of a fruit begins, it involves a climacteric change ( a stage of fruit ripening associated with the production of ethylene and increased cell respiration). It sets off a series of biological changes such as lateral growth and loosening of cell walls. Fruits such as bananas, melons, apples, apricots and tomatoes. There are other fruits that are non-climacteric such as citrus, grapes and strawberries. These non-climacteric fruits do not require the production of additional ethylene nor do they have respiration bursts.

Color changes are due to the synthesis of carotenoids (organic pigments) and result in yellow or red color. Other compounds such as anthocyanins that give a fruit a red, blue or purple color depending on it pH value.

Textural changes are due to the limited degradation of cell walls and the activity of enzymes such as polygalacturonase and pectinesterase which plays an important role in the ripening of fruits.

Acidity in plants are due to the presence of citric acid (gooseberry, peaches and tomatoes), malic acid (plum, cherry, banana, apricot and apple) and both of these acids in grapes.

How To Optimize Your Flight

You have to plan your flight long before you are actually going to take it. More so if you intend to go on an long international flight. Book your tickets as early as possible and get yourself a seat by the aisle. It saves you the trouble of stepping over your co-passenger's feet.

Get to the airport as early as possible. Usually, if you're on an international flight you'll have to be at the airport three hrs before the flight. Try to get there a mite earlier so that you can avoid the long lines at the check in counters and the security clearance points. Most of the airline staff will be in a good mood and your checking will go off smoothly.

First get your check in luggage out of your hands. They are the heavy ones and make sure that they are checked through to your final destination if you have to change flights. You don't have to travel by the same airline to do so. Less luggage more the comfort.

When you take a long distance flight, the commencement of your flight may be at noon but it may already be night at your destination just about ten or eleven hours away. And at times when you take a very long flight there may be stopovers or you may have to change flights and the tediousness of changing terminals etc. tend to bog you down. And this is where you get the jet lag etc. when your circadian clock goes out of sync.

All of the tiredness accompanying a long flight can be avoided if you are the exercising type. I am suggesting that you train to be a marathon runner just before your flight date, but starting a small exercising routine will definitely help. All you have to do is to move around and perform some simple exercises. Stretch yourself a bit and get the adrenalin and your heart pumping. Limber up and make yourself flexible. You'll find out why.

Most of us usually travel by the economy class and if you are a regular traveler, even in short distance flights, you'll know what economy. They really do not meant the price, it is the economy of space that the airlines mean, but for the first flighter, this may come as a surprise only when he sits down and find out that he's supposed to be contortionist. So to keep yourself from getting the cramps, you'll have to stretch your legs, wriggle your toes and move your shoulders and at convenient intervals get up and short walk down the aisle.

As much as possible try not to drift off into sleep during the initial few hours of the flight. Look at the miniscule that is in front of you and check out the entertainment menu laid out for your benefit. Eat what is given, though airline foods are not something to go gaga about. Drink a lot of water. Try to get some sleep after the meal. They'll wake you up for the next meal.

Just follow these tips and try to get some more from seasoned travelers if you know any of them. As you continue to take more flights you will learn more tricks of the trade. Till then have a good flight.

How Do Wells In A Beach Give Good Drinking Water?

Beaches are made up of sand which has a high permeability and porosity. As such, when there is rainfall, the rain water percolates into the ground through this porous medium. It saturates the sand. Fresh water has a lower density when compared to sea (saline) water and so fresh water remains on the top. Hence the fresh water in wells in beaches.

How Are Rainbows Formed?

Rainbows are arc shaped and can be seen in that part of the sky opposite the sun. A rainbow is made up of 7 colors - violet, indigo, blue, green, yellow, orange and red but most of the time these colors are blended together and as such we normally see only 4 or 5 of them clearly. Rainbows are caused by refraction (bending) and reflection of the rays of the sun as it falls on the raindrops. The tiny drop of water acts as a prism and as the rays of the sun pass through these drops of rain they are refracted and are separated into different colors and as the rays of the sun strikes the inner surface of the raindrops, they are further refracted and this causes the rainbow. At times when the rainfall is heavy, the rainbow may be spread in such a way that its ends seem to meet the earth at the horizon.

How Are Ocean Depths Measured?

Depths of oceans are measured using a technique known as Ultrasound measurements. A transmitter is mounted at the bottom of a ocean going vessel which is capable of transmitting ultrasonic waves. These ultrasonic waves are reflected from the floor of the ocean and a sensor receives and records them. since the speed of these ultrasonic waves in water is known, the time taken by these waves to travel to the bottom of the ocean and back gives the depth of the ocean at the point where the measurements was taken. By taking different measurements at various points of the ocean floor, the surface of the ocean bottom can be accurately measured and mapped.

How Do CFCs Damage The Ozone Layer?

One of the everyday activities that we indulge in is the use of chlorofluorocarbons (CFCs) that damage the environment especially the ozone layer that protects us from the harmful effects of the cosmic rays emitted by the sun and other celestial bodies and maintains the radioactive balance of the atmosphere. CFCs are used in a variety of ways such as refrigerants, coolants, insulants propellants in aerosol sprays cleaning agents etc.

Ozone (O3) is a blue gas that is very unstable and lies roughly 10 to 50 Kms. above the earths atmosphere with a maximum concentration between 20 to 25 Kms and is a very unstable form of oxygen and is split up into free oxygen (O) and O2 (the Oxygen that we breathe) when ultraviolet (UV) radiation hits its molecules. The energy of the UV radiation, on the splitting of the ozone molecule is converted into harmless heat and never reaches the earth. The O and the O2 recombine into new molecules of ozone (O3).

The CFCs that we release can remain as CFCs for up to a hundred years. As it is, it is harmless but the trouble starts when it slowly drifts upwards to the ozone layer where it is split apart by the UV radiation into molecules of chlorine etc. This chlorine combines with the free O in the ozone layer forming chlorine monoxide; thus effectively stopping the reformation of the ozone molecules depleting the already scarce ozone, causing a hole in the ozone layer.

The resulting passing of UV radiation into the atmosphere reaches the earth causing increase in eye cataract, skin cancer and other harmful effects to both flora and fauna of the earth.