BIOLOGY
SKIN
The entire surface of the body is covered by skin. In man, the skin is about 1 to 2mm thick except the skin of the palm and soles with thickness of about 6mm. The skin is the most extensive organ in the body. The mammalian skin consists of two major layers: the outer epidermis and inner dermis. Epidermis This is further divided into three layers known as cornified, granular and malpighian layers. Cornified layer: This is the upper-most layer of the skin and consists of flat dead cells. Cornified layer protects the body against loss of water and entering of foreign bodies. Granular layer: Contains living cells. It…
CARTILAGE
A cartilage is a tough elastic and semitransparent tissue devoid of blood vessels and nerves. Functions of cartilage It prevents friction between two bones and allows smooth and free movement. It absorbs shock between bones. For example the shock resulting from the vertebral bones are absorbed by cartilaginous intervertebral discs. It keeps open the trachea (windpipe) so that air flows into the lungs always. The cartilage of the nose also keeps the nostrils open for in-take of fresh air and output of waste air. The cartilage of the ribs allows contraction and expansion of the thorax thus enhancing breathing mechanism. It forms cushion in the sockets of bones such…
CARBOHYDRATES
Carbohydrates are organic compounds containing carbon, hydrogen and oxygen atoms. The ratio of hydrogen to oxygen is 2:1 in all carbohydrates. Starch, sugar, glycogen and cellulose are carbohydrates. They are classified into three major groups namely:- Monosaccharides Disaccharides and Polysaccharides. 1) Monosaccharides (one molecule sugars) These are simple sugars which consist of one molecule each. These sugars may contain six or less carbon atoms per molecule. Examples are glucose, fructose both with chemical formula (C6H12O6) and ribose (C5H10O5). 2) Disaccharides (Double molecule sugars) When two molecules of simple sugar combine and one molecule of water is removed, a disaccharide is formed. When one molecule of glucose combines with…
NASTIC AND TACTIC MOVEMENT
Nastic/sleeping movements The pinnate and bipinnate leaves of many leguminous plants open and close as a result of certain changes in temperature, light intensity or humidity of the atmosphere. The process which is however gradual is known as “sleeping movement” and occurs in such leaves as St. Thomas plant, and cassia. Flowers of certain plants are known to open only at certain time of the day. A good example is the “Four O’clock” plant which opens at about 4 pm daily. Sunflower changes its direction to face the sun. The flowers of”Snake tomato” remain closed during hot day and open at night or under conditions of high humidity. These flowers…
DIGESTIVE ENZYMES
Enzymes are organic catalysts of protein origin produced by living cells which help to speed up or slow down the rate of chemical reactions but remain chemically unchanged at the end of the reaction. Classes of enzymes Enzymes are usually classified according to the type of food they act upon. Generally three classes are known. They are amylases, proteases and lipases. 1) Amylases Amylases act on carbohydrates (starches and complex sugars) changing them to glucose which the body can absorb. Some amylase enzymes are: Maltase, sucrase, lactase and ptyalin. Maltase changes maltose to glucose. Sucrase changes sucrose to glucose and fructose. Lactase changes lactose to galactose and glucose.…