Osmosis is the movement of a thinner liquid into a thicker liquid through a semipermeable partition or membrane when physical external pressure is applied. The thinner liquid dilutes the thicker solution.
Osmosis is a process that occurs in our bodies all the time. For example, after the food we eat is broken down in the stomach, it passes through the intestines. The intestines contract to force the nutrients, which are thinner, to pass through the walls of the intestines into the blood, which is a thicker solution.
In reverse osmosis, exactly the opposite happens. Water that has a high concentration of impurities is put under pressure and forced through a semipermeable partition leaving all the larger particles behind. This process renders the impure water as well as salty water (here the process is called desalination) potable enough to drink.
This is why RO is used in water purifiers. In a purifier, water passes through several stages-a sediment filter, activated carbon filter and ultraviolet light. RO is the final stage. The larger molecules cannot pass through these various filters and RO removes the harmful particles, metal ions and bacteria in the water that remains. This cleans the water thoroughly and prevents diseases caused by contaminated water.
Reverse osmosis is also used in the food industry to make concentrated juices. The traditional heat treatment reduces the quality of heat-sensitive fruits such as oranges. RO reduces the quantity of water in the juice, so it doesn’t need to be thickened by heating. For instance, in the production of maple syrup, RO is used to remove the water from the sap before it is boiled into a syrup. Dairy industries use RO to make concentrated milk and whey protein powders.
Since RO units are also manufactured in compact sizes, they can be installed easily which is why a number of home water filters come equipped with it.
RO removes almost all the minerals in the water, which leaves it tasteless. Some RO systems come with a remineralisation filter that adds minerals to the water and makes it more flavourful!
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There are red cells, used for carrying oxygen, white cells, which fight any infection by invading bacteria or viruses, and platelets, which make the blood clot when a vessel is damaged, so sealing the wound. Different kinds of white cell work together to protect you from disease: T-cells, which identify invaders; B-cells, which make deadly proteins called antibodies that surround the invaders; and macrophages, which swallow them up and destroy them.
What job does the brain do? 
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The pancreas is an important organ found in the bodies of human beings and all animals with backbones. It lies crossways behind the stomach. This organ resembles a flask lying on its side. The human pancreas is a pinkish yellow gland about 12 to 15 cm long, 3.8 cm. wide and 2.5 cm. thick. It is joined to the small intestine behind the stomach. Do you know the function of the pancreas?
Cholesterol is an organic compound belonging to the steroid family and occurring either in a free state or as esters of fatty acid in practically all animal tissues. The molecular formula for cholesterol is
. In a normal man it is about 0.3 percent of his average weight. It is the starting material from which the body produces bile acids, steroid hormones and pro-vitamin substances in the body. It is used by our body to help the digestive system as well.
It was because of the use of such modern techniques and apparatus that the first human hearts transplant became possible. It took place on December 3, 1967, at Groote Schuur Hospital, Cape Town, South Africa. A team of 30 surgeons, headed by Dr. Christian Barnard, operated on Louis Washkansky, aged 55. The donor was 25 year old Denise Ann Darvall who had been killed in a road accident. 
The commonest type of cirrhosis is known as Laennec’s cirrhosis. Although it can occur at any age, it usually affects the people between 40-60 years of age. It is more commonly found among the males than among the females. To begin with, this involves an abnormal increase in liver fat. Soon the liver starts degenerating and in the end only a little fat is left.
Anaemia is a particular physical condition in which the amount of haemoglobin in the blood or the number of red blood cells in a person falls below the normal level. More specifically, it is a condition caused by the deficiency of iron in the blood. In fact, haemoglobin is a protein in the red cells that contains iron. It is carried in the red blood cells of the human blood and imparts it the red colour. Haemoglobin makes it possible for the blood to carry oxygen. The body’s tissues need oxygen to function properly. The lack of the minimum amount of red blood cells or haemoglobin would result in a poor oxygen supply to the body and hence people suffering from anaemia look pale and feel tired as they become oxygen-starved.
It is a matter of common experience that we shiver in winter if we are not wearing woollen clothes. And even if we want to stop it we cannot do much about it. Do you know why do we shiver on a cold day? 
Immunity is described as the ability of the body to resist or to recover from the invasion of disease-causing microbes (bacteria, viruses, and protozoas) and larger parasites (helminthes). Thus a person said to be immune to a particular disease would not contact it although others might do so.
The people who live in very noisy areas also get their hearing power impaired. They are able to hear only loud sounds. In the Second World War, 58,000 soldiers developed deafness because of the fierce sounds of tanks and machine guns. Deafness can be caused by ear diseases also. Sometimes due to the bad effects of the diseases in other parts of the body also cause deafness. Even aging reduces the power of hearing. Excessive use of some intoxicating medicines can also affect the power of hearing. At times undesirable growth of some bones inside the ear also causes deafness because these prevent the sound waves from reaching the main parts of the ear. 
The process of digestion is very complex and elaborate. It starts from our mouth itself. When we chew food the saliva produced in the mouth moistens it. The saliva contains a substance called ptyalin which converts the starch of the food into sugar. This is the first stage of digestion. Therefore we should swallow the food only after properly chewing it. 
As he grows, hair becomes harder. Boys and girls reach puberty at the age of 11 to 13 years. There is faster growth of sex glands at this age. In man, the testes and other sex glands, produce a group of hormones known as ‘androgens’. In woman, the ovaries and other sex glands, produce another group known as ‘estrogens’. The function of the androgens is to regulate secondary male sex features such as the growth of facial and chest hair and deepening of the male voice at puberty. The function of the estrogens is to regulate secondary female features, such as the change in the size of breasts, growth of pubic hair and onset of the menstrual cycle. There are various other changes in men and women brought about by these hormones. For example female body becomes soft and tender whereas, male body turns hard and strong. A special group of hormones called the ‘progestrogens’; are responsible for the regulation of pregnancy. Hence women do not have beards due to the absence of androgens.
The 4 main tastes are – sweet, salty, sour and bitter. All other tastes are a combination of two or more of these. These 4 main tastes are felt by different portions of our tongue. For example, salty and sweet tastes are felt by the tip of our tongue. Similarly, a sour taste is detected by the buds on the sides of the tongue and bitter taste, by the back portion of the tongue. The tongue is also sensitive to irritants such as pepper.
Fourth type of learning is insight learning. It means solving a problem through understanding how the different parts of a problem fit together. A simple example is that of a young child wanting to climb on the top of a table. The child may use a stool to get on to the chair and then use the chair to climb onto the table.
There are many theories regarding baldness. Some people treat baldness as the indication of the arrival of old age while some are of the view that bald men are intelligent. Baldness is also treated as a sign of richness. Some people think that bald men are fools. Whatever may be the significance of baldness, one thing is certain that by losing hair, man is deprived of his natural charm.
During the past two decades bio-engineers have developed a number of artificial substitutes for diseased tissues and organs. Some of these, such as, kidney dialyzers are external devices. Other such as plastic heart valves and artificial blood vessels are implanted inside the body, replacing the diseased or damaged ones. Two devices – the dialyzer and artificial heart valves are of special interest.
In 1984-1985, several artificial heart implants were performed in the United States and Sweden. Good life spans have been achieved but against a tremendous cost.
It is the store of things learned and retained from our activity or experience. Our memory is a collection of knowledge, experiences, impressions, skills, habits, and many other things. It gives us the ability to learn and adapt from previous experiences as well as to build relationships. It has a lifelong storage capacity, and no computer of the world can match its performance. Short-term memory is the information that we are currently thinking of and it lasts for only a few seconds. Important things which we have experienced and would not like to forget are transferred from short-term memory into long-term memory.
The brain is made up of two halves. Different areas of the brain have different functions. All nerve cells in the brain, about 100 billion of them, are connected to one another and transmit information. This network of the nerve cells is expanded through learning and training. Our brain controls our actions, regulates our sleep, and allows us to feel sensations like pain and joy. If it is damaged, maybe due to a stroke, one has to relearn a lot of things like speaking, walking, or eating.
Our balancing organs in the inner ear are three semicircular canals filled with fluid and with fine sensory hair. These hairs sway with our movement and transmit the changes to the brain. The eyes and the foot confirm these movement signals. When we spin around and then stand still, our brain gets confused with different messages: the balancing organs say that we are still moving, but eyes and body convey a different message – and we become dizzy.
Our sense of smell in responsible for about 80% of what we taste. The taste buds present on our tongues are limited to only the basic sensations: sweet, salty, sour, and bitter. All other flavours that we experience come from smell. This is why, when our nose is blocked, as by a cold, most foods seem bland or tasteless. Our sense of smell can normally detect up to 10,000 smells.
We can judge the direction of sound only because we have two ears. The sound waves reach the right and the left ear with a small time difference because the ears are at slightly different distances from the source of the sound. The eardrums vibrate, and the ear ossicle transmits the impulse to the inner ear. The inner ear sends it further to the brain where the signals from both ears reach at marginally different times. The brain calculates the direction of the sound from the tiny difference in these times.
Without the sense of touch we would be quite helpless. We would not be able to feel one, we would not feel our feet hitting the floor while walking and injuries would go unnoticed because no pain would be felt. We would also be deprived of many pleasant experiences important for social interaction. For blind people the sense of touch is very important. They move around safely by feeling and touching objects in their surroundings. Blind people compensate for their lack of sight by highly developed sense of touch.
We can think of the eye as a kind of camera. The iris behind the cornea is light-sensitive and corresponds to the aperture of the camera. This can be set near or far, depending on the amount of light falling on it. The light rays penetrate the lens of the eye, and fall on the retina. Millions of light-sensitive cells convert the light into signals sent to the brain via the optic nerve. These are put together to make images, and are interpreted by the brain. There are two types of cells in the retina: the light-sensitive rods that help us see in the dark and the less sensitive cones that help us see colours.
Whatever we perceive is not always real. For example, in a magic show, we may think what we see is real, but actually it is an illusion. Even our sense of balance can be deceived, and then one would react with uncertainty and dizziness. Hallucinations often occur because things do not happen the way we expect them to, and the brain gets ‘confused’.
Just as each human being is unique; his grooved fingertips are also unique. Even identical twins do not have the same patterns of grooves on their fingertips. Minor cuts and some skin diseases may cause temporary changes in the patterns, but on healing, the same pattern appears. Since 1901, police have used this knowledge to compare the fingerprints found at a crime site with those of the suspects. In early days, this comparison was done manually and used to be very cumbersome and time-consuming. Today, fingerprints are matched by the computer in a fraction of the time used earlier. 
The skin, as a sense organ, perceives all kinds of touch sensations as signals. These signals are sent to the brain, are interpreted, and the body reacts accordingly. The brain can differentiate between the touch stimuli that we create ourselves and the stimuli given by others. If we try to tickle ourselves, our brain anticipates this type of touch from our hands and prepares itself for it. Since the element of unexpectedness is missing, the body does not respond the same way as it would if someone else were to tickle us.
The colour of a person’s skin depends on his environment. In regions with abundant sunlight, a dark skin colour is necessary to provide protection against the harmful UV rays. Light-skinned people in north Europe, where there is very little sunlight, do not need this protection. UV rays are not always harmful: they are needed for the formation of vitamin D, which the body needs for building bones. The darker the skin, the less sunlight can enter the skin and vitamin D formation is reduced. A dark skin may, therefore, result in Vitamin D deficiency in areas where there is not much sunlight. 
Goose pimples help in regulating the body temperature. When we are exposed to cold temperature or get scared, our body hairs stand up so that the air between them can form an insulating layer. Each hair is permanently anchored to the skin with its root. Small muscles are present at these roots, which contract in case of cold or fear. This is visible on the skin as small bumps. The contraction of the muscles also produces heat in the body. This was an excellent warm-up device for our thickly haired curly ancestors who did not wear clothes. 
In the summers, our skin is often exposed to UV radiation from strong sun that can damage the skin. A pigment, called melanin, is produced in the skin to protect against the harmful radiations from the sun. The more this pigment is produced, the darker, i.e., more tanned, is the skin and the higher is the protection against sunburn. That is why; many light-skinned people get sunburnt very quickly. Sunburn always means damage to the skin. Even when the skin has apparently recovered from the burn, it remains damaged from inside and there is always a high risk of getting skin cancer later. 
Our skin is the largest, heaviest, and the most versatile organ. The skin forms the outer covering of our bodies. The colour of the skin and hair determines our appearance. Without the skin, we would not have any protection against UV rays, injuries, and germs invading from outside. Our sense of touch would not work without it. The skin reacts to the outside stimuli and becomes red, brown, or gets goose pimples. Each person has a unique set of fingerprints, and police can often catch criminals by matching their fingerprints. 
Muscle stiffness is a painful result of overstrained muscles. It frequently occurs on days when the body suffers very strong physical stress. Physical strain causes micro cracks in the muscle fibres, which slowly get filled with water. As a result of this, the tissue gets stretched, which causes pain, and gives rise to inflammation. After a few days of recuperation, the pain usually subsides. 
Many of our bones are joined to one another through joints, which permit different kinds of movements. The ball joints of our hips and shoulders offer the highest freedom of movement. Here, the ball-shaped end of one bone moves inside the bowl-shaped end of the other. Knees and elbows are joined by means of a hinge joint, which permits only the back and forth movement, like the hinge in a door. Our head sits on a condyloid joint, which allows it to move sideways, front or back, but not rotate. Fluid is present in the joints as a lubricant so that the joints and the bones do not rub against each other. 
Most of our organs are protected by the skull and the body skeleton. Some of our most sensitive organs lie embedded in the powerful cranial bone of the skull—the brain, the eyes, and the hearing organs. The mouth cavity protects the only movable bone of the skull, the lower jaw. The body skeleton with the ribs fanning out of the backbone protects the area of the chest. Internal organs such as the heart, lung, liver, and spleen are protected behind the rib cage, and the backbone covers the vital spinal cord. 
An adult has 206 bones, which together weigh about 9 kg. A baby has 350 bones. Many bones in a baby’s skeleton are not fully grown, such as those of the skull. Cartilages are present at these points, and turn into bone at a later point. Bones are made up of different materials, and provide strength and elasticity. The bone mass is covered by a periosteum (bone skin), which contains nerves, blood vessels, and bone-building cells. The bone marrow, which makes the red blood cells, is present inside long bones. The longest bone in our body is the thigh bone. 
Urine is a waste product, which is formed in the kidneys after the purification of blood. Kidneys contain millions of very tiny canals, called nephrons, which filter out harmful substances as well as excess water from the blood to form primary urine. This liquid still contains some useful components that are reabsorbed into the body in the kidneys. The remaining fluid that can no longer be used flows through the ureters into the bladder. Once the bladder is full, we need to go to the toilet and relieve ourselves.
Stress, an unhealthy way of life, bacteria, and viruses are the most important causes of intestinal problems. Bacteria and viruses reach the body via food or water and cause sickness, vomiting, and diarrhoea. Diarrhoea is caused because the body fights against these invaders and wants to get rid of them as quickly as possible. Sometimes, with diarrhoea, we have fever too, since an increase in the body temperature accelerates the healing processes of the body. 
After the absorption of the nutrients in the small intestine, the 1.5 m long large intestine absorbs water from the remaining undigested food and converts it into a solid mass. The solid mass of waste matter is stored in the lowermost part of the large intestine, the rectum, and is then excreted as ‘stools’ through the anus.
The function of the small intestine is to digest the food into simpler nutrients, and to absorb these nutrients. If food stays longer in the small intestine, it will have more time to get digested completely and will also enable the body to absorb all the nutrients. The very long length (more than 6 m) of the small intestine enables the food to stay there longer. The finger-like ‘intestinal villi’ on the inner wall of the small intestine help in absorbing the nutrients in the bloodstream. The liver and pancreas produce enzymes that travel to the small intestine to help break down proteins, fats, and carbohydrates into sugar. This process is known as metabolism.
After the food has been chewed and mixed with saliva, it reaches the stomach through the oesophagus. The food is prepared for actual digestion in the small intestine, which is connected to the large intestine, and ends in the rectum. The undigested remains of the food and urine are excreted from the body. We can survive without water only for a few days, but the body can manage without food for quite some time. If the starvation goes on for a very long time, the body becomes weak and prone to diseases.
Organs are parts of the body having specific tasks. An example is the intestine, in which food is broken down and the nutrients are absorbed in the blood. Another important organ is the liver, which utilizes the components of food. Other organs are the kidneys, the spleen, the heart, and our biggest organ, the skin. They are all made up of different kinds of tissues, such as muscular tissue, fatty or supportive tissue, and blood vessels. The tissue in each organ is specifically designed to perform the tasks assigned to that organ. Thus, the muscular tissue of the heart is different and performs different functions as compared to that in the upper thigh. Each organ interacts with other organs to keep the body healthy.
The different cells of our body have very different tasks, but they are all similar in their structure. They have a cell wall or a cell membrane, which protects the inner matter of the cell and controls what goes in the cell and what comes out of it. The nucleus inside the cell controls all the processes in the cell. The energy for these processes comes from mitochondria, the power house of the cell. They are responsible for cell respiration. The endoplasmic reticulum takes care of the conversion of substances and for detoxifying the cells. All these organelles are embedded in the liquid cytoplasm inside the cell. If we drink less fluid, the cytoplasm will dry out and the cell may die. 
When we breathe, the oxygen reaches our lungs via the mouth, nose, and trachea. The lungs have a number of very tiny cavities known as air sacs which are covered by a network of very fine blood vessels. An exchange of gases takes place here. Impure blood reaches these capillaries and releases the waste gas carbon dioxide in the air sacs. This is exhaled out of the body, and freshly inhaled oxygen is absorbed into the air sacs. This oxygen is released into the blood via the capillaries. 
The heart, a hollow organ with four chambers, can be imagined as an unbelievably strong pump. It is about the same size as a fist. Electrical signals coming from the brain cause the heart muscle to contract about 70 times in a minute in an adult. The contractions are more frequent in children and while we are playing sports. These contractions pump the blood through the whole body through the circulatory system. This system consists of two types of vessels: arteries with blood rich in oxygen and veins with blood poor in oxygen. While the arterial blood supplies oxygen to every cell in the body, the venous blood is sent to the lungs where it is purified by removing the waste product carbon dioxide and absorbing new oxygen. 
Our body consists of millions of cells, which must be supplied with water properly. This supply is the responsibility of the blood. The red blood cells transport vital oxygen around the body. The blood also absorbs nutrients from the digestive tract, distributes them to the organs, and in return, takes away the waste products from the organs. Blood contains platelets that seal the wounds and white blood cells that help us fight disease-causing germs.
The human body is made up of 80% water, which is present in blood and other cells. Since we lose a lot of fluid through sweat, urine, and breath, we need to replenish it constantly. Drinking less water can cause immediate problems. The body cells become dry, and the skin wrinkles. Blood becomes thicker, and the heart has to make more effort to pump it through the body. Since the blood is responsible for transporting oxygen around the body, oxygen is not supplied adequately to the organs. The heart and the brain react immediately to a lack of oxygen—they get damaged in just a few minutes. 
The Neanderthals were people who lived 130,000-30,000 years ago, but then died out due to unknown reasons. One theory is that other lines of humans were stronger and eliminated them. The Neanderthals were about 1.70 m tall, had a heavily built body and were very powerful. They needed this power and strength to hunt woolly mammoths and rhinoceros with their home-made spears and knives. They made clothes of animal skins, lived in caves, and used fire. Their name is derived from the place where their remains were found, the Neander valley near Dusseldorf. 
Today, one can think of the apes and humans as cousins. They have common ancestors, but have not descended directly from each other. About 5-7 million years ago, a line of man-like apes grew apart, and evolved independently of the other apes. The oldest, almost completely intact skeleton of an upright ancestor of human – the Australopithecus – was found in 1974 in Ethiopia (Africa). The scientists named it ‘Lucy’.
Biologists classify humans as animals and part of the animal kingdom. Like our nearest relatives, the apes, humans are also mammals. Humans have evolved from apes, but there are features that differentiate us from other animals—including apes. These include the upright walk, our opposable thumb, our special ability to communicate by a language, and our highly developed brain. Our brain allowed our ancestors, like the Neanderthals, to invent tools.