My Science School

Dialysis is a process of separating dissolved substances from a solution using a semi-permeable membrane which allows only some dissolved substances to pass through. Many substances such as cell walls and cellophane act as semi-permeable membranes.

Dialysis is used to remove waste-products from the blood of patients with impaired kidney function. Accumulation of waste products especially urea, in the blood can prove fatal.

Dialysis of blood is carried out using a dialysis machine. Blood drawn from the artery in the forearm of the patient is passed through a semi-permeable membrane. The tubing is placed in a solution called dialysis fluid. Since the blood has a high concentration of impurities compared to the dialysis fluid, a concentration gradient builds up. This results in a flow of soluble impurities from the blood into the dialysis fluid. This continues till the concentrations on each side of the membrane are balanced. To prevent clotting of blood in the dialysis machine, the anti-clotting substance heparin is used.

 

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DTP or Desk-top Publishing is a method of designing, editing and laying out a publication electronically using a personal computer and word processing, graphics and page layout software. This term, DTP, was first coined by Paul Brainerd, a British pioneer in this field.

In a DTP process, whatever be, the matter or layout of a page, it is composed electronically and stored in the computer with the help of a page making software. Corrections of any type or changes can be easily done any number of times on the computer and the desired output is then obtained from a laser printer on paper. The camera ready text matter is then converted into photographic film (negative or positive) from which plates are made for printing. In newspaper publishing, it provides for incorporation of text, as it arrives by e-mail, directly into the pages being prepared. DTP is a versatile technology for applications in the advertising, designing and publishing business.

 

Endoscopy is a harmless and painless method of diagnosing diseases of any of the hollow organs of the body (like throat, stomach or intestine) by looking directly into the affected organ using a probe called endoscope. It is a hollow metallic tube fitted with a light source and a viewing system.

Modern endoscopes make use of flexible bundles of optical fibres both for transmitting light to the organ and transmitting the image to the eyepiece outside for viewing.

Since the endoscope gives a direct view of the affected body parts, patients need not go for complicated investigations.

Advanced endoscopes may have surgical attachments to carry out minor operations or biopsy.

 

The biological clock is an in-built timing system found in all living organisms. It times the various activities of the organisms and keeps them in harmony with the regular changes in their surroundings, such as the day-night cycle. The cycle of sleep, wakefulness and many other body activities repeats over a period of roughly 24 hours. That is why it is also known as the circadian rhythm. It works by keeping track of the rhythmic changes in the environment such as day and night, movement of ocean tides, phases of the moon, and seasons of the year. These rhythms can be shifted and the biological clock can be reset by changing, for example, the temperature at which a plant is grown or the duration of light exposure an animal gets.

There can be cycles of more than 24-hour duration too. Human beings have daily, weekly, monthly and yearly biological rhythms. The level of hormones and other chemicals in blood varies over each of these periods.

One of the effects of the biological clock is jet lag felt while travelling long distances by air.

 

It is a diagnostic technique to check for genetic abnormalities in unborn babies. The test involves taking a sample of the amniotic fluid which surrounds the growing baby inside the womb. It is usually done about the 16th week of pregnancy as by this stage there is enough amniotic fluid to allow the test to be carried out and enough time to terminate the pregnancy in case genetic abnormalities are detected. This can help prevent later suffering of the baby and the family.

For obtaining a sample a hollow needle is carefully inserted under local anaesthesia through the expectant mother’s abdomen. The amount of fluid withdrawn is only about 20 ml. This fluid contains cells from the developing baby. Chemical and microscopic examinations of these cells can provide invaluable information, revealing the presence or absence of genetic disorders which cannot be detected otherwise.

The chromosome analysis of the cells in the amniotic fluid can also reveal the sex of the baby.

Allergy is a state of hypersensitivity acquired through the exposure to a particular substance, called allergen. Spores, pollen, cat’s hair and proteins of egg, milk, and fish are some common allergens. The most common allergen is the house-dust mite.

Usually only parts of the body which are exposed to allergens show signs of allergy in the form of rashes or weals. However, if an allergen gets into the blood stream, it can cause reactions almost anywhere in the body.

Practically all allergies are caused by an over-reaction of the body’s defence mechanism when white blood cells react with allergens considering them as dangerous infectious organisms, it leads to allergy. Under normal conditions, the white blood cells (lymphocytes) on coming in contact with foreign substances like bacteria, viruses and proteinaceous matter produce what are called antibodies. The antibodies combine with the foreign substance and neutralize it. But when an antibody is formed against a harmless protein it attaches itself to mast cells which contain chemical— histamine. When the particular protein enters the body again, histamine is released. Due to the action of histamine blood capillaries are dilated, their walls become leaky and fluid from the blood comes out in the nearby tissues and they swell. The characteristic redness and itching in an allergy is due to dilation of blood capillaries.

Acquired Immune Deficiency Syndrome (AIDS) is the most devastating and fatal disease of the 21st century. It is a viral disease caused by the Human Immune Deficiency Virus (HIV). What makes it different from other viruses is that, it strikes at the body’s own defence machinery (the immune system) that constantly fights the vast array of microbial enemies invading our bodies. The virus may remain dormant upto 10 years until some event activates it. On awakening, it disarms the immune system. With its main line of defence shattered, the body now falls easy prey to even the common infecting agents that it would otherwise ward off. The patient usually dies of these infections.

            HIV spreads from an infected person to a healthy person through body fluids. Sexual transmission of HIV is most common. Contaminated blood and blood products besides passage of the virus from infected mother to unborn baby are other ways by which the virus spreads.

The naphthalene balls used for keeping away harmful insects from damaging clothes are basically volatile chemicals having a strong odour. These compounds include a wide variety of aromatic chemicals which are mainly derived from petroleum and coal tar. These chemicals are toxic. As they are highly volatile, they produce vapours which repel insects such as moths and silverfish which damage clothes during storage.

Wool fibres are made of a particular protein (Keratin) which is a bad conductor of heat and as a result does not allow body heat to escape. This helps us in keeping warm during winter. These fibres are wavy in structure, the property commonly known as crimp. Crimp imparts resilience to the fibre due to which fibres quickly recover from wrinkling and crushing. Because of this wavy structure the fibres do not come perfectly close and as a result a large number of air pockets are formed. The air entrapped within these pockets acts as an insulator and traps body heat inside.

Hail is formed in thunder clouds when ice pellets formed near the freezing level in the atmosphere are caught in air currents. They are tossed up and down by air currents within the thundercloud where these pellets collide and fuse with one another. Further deposition of water or ice, causes them to grow into hailstones. Certain conditions such as vertical upward air currents help prevent hail falling too quickly and results in the increase in the size of hailstones.

 

Plants have special structures called root hairs for absorbing water and other nutrients from the soil. The root-hairs are thin-walled extensions of the outer layer of cells in the root. Deep underground they are surrounded by solutions of various minerals and nutrients in the moist soil. Some of these nutrients such as the nitrogen compounds simply pass through the root-walls when they are present in high concentrations in the soil. The process can be likened to the natural flow of water from the high hills to low valleys. Other nutrients such as minerals which are present in lesser quantities in the soil than inside the cells are transported into the root hairs by special proteins located on the cell-walls, a process which can be likened to pumping of water from wells to tanks higher up. 

The annular rings or the alternating dark light circles seen in a cross section of a tree are produced because of differences in the rate of growth in different seasons. As it happens, the entire tissue in the trunk of a tree does not divide or grow to increase the girth of the tree. There is a layer of dividing tissue called the cambium sandwiched between the fibrous xylem (the water carrying tissue) and the phloem (the food carrying tissue). However, the cambium divides at different rates in different seasons. In winter, its growth is slower than in other seasons, say in spring, when conditions for growth are fairly favourable. Thus, the relatively small number of cell produced in winter remain compacted together producing a dark band while the cells produced during the spring season spread out into a broader light band. These growth patterns are repeated at annual intervals and hence the name. The annular rings thus indicate the age of a tree as well as the changes in climate that might have occurred in the tree’s life time.

Cells in the root hairs of plants contain dissolved sugars and salts. Water surrounding the root moves into them to equalize the pressure. This is called osmosis. The increased water pressure in root hairs forces water upward, cell by cell through the roots and trunk to reach the leaves.

In addition to this, during the growing season, a tree passes tonnes of water into the atmosphere from its leaves through transpiration.

This creates a partial vacuum that is quickly filled by the water being pushed up from the roots. Water molecules stick together, and as water is lost during transpiration, this cohesion causes a chain reaction that is transmitted all the way down.

Most medicines, which are chemical compounds and their combinations, degrade with time. This process is usually accelerated by heat and exposure to light. So the stability of every new formulation has to be checked over a period of time to evaluate its effective shelf-life. Ideally this should be done by storing the medicine at room temperature for some time. However, this method is time consuming. So what is done instead is that the medicine is stored at four different temperatures and under controlled conditions of light and humidity. The rates at which the medicine deteriorates are monitored. The compound’s stability at room temperature is calculated from the accelerated degradation tests made at higher temperatures. This allows scientists to fix a date beyond which the medicine may not be effective. 

Herbicides are chemicals used to destroy weeds without harming the useful crops. This is possible because of the different rates at which herbicides are absorbed by the weeds and crop plant.

Some crops have a dormancy period during which there is very little physiological activity. Herbicides can be safely used during this time. Some weeds have chemicals called enzymes that break down apparently harmless compounds into toxic products. Peas and other pod bearing plants, which do not contain this enzyme, remain unaffected. Such compounds are used as herbicides in legume fields. On the other hand, some crops contain compounds which convert the toxic herbicides into harmless compounds; most weeds lack this compound and are therefore killed. Factors like soil type, leaf shape, and method of application also affect the action of herbicides.