Biology Revision for "O" level examinations

Biotechnology  is the application of biological organisms, systems, or processes by various industries to help in the improvement of the value of materials and organism such pharmaceuticals, crops, and livestock (ASC-Chemistry for life). Biotechnology is not a new concept. It can be dated back to more than 6000 years ago (Biotechnology Industry Taken from:  unidigest.com Organization) when man first began to breed and domesticate plants and animals. However, modern biotechnology involves more genetic engineering, where an organism's genome is altered. Because of this technology, Biotechnology may allow man to reshape the future of his planet. We may very well be able to reduce the imminent threat global climate change by modifying organisms so that they are better adapted to survive in their ecosystems, and improve quality of agricultural crops and livestock. With Genetic engineering, we may even be able to extend our lives, either by improving our diet and health care, ...

What is cholesterol? Cholesterol is found in every cell of the body and has important natural functions. It is manufactured by the body but can also be taken in from food. It is waxy and fat-like in appearance.  Cholesterol is Source:  GetaLife  oil-based and so does not mix with the blood, which is water-based. It is therefore carried around the body in the blood by lipoproteins. There are basically two types of cholesterol 1.   Low-density lipoprotein (LDL - cholesterol carried by this type is known as 'bad' cholesterol).   A high LDL level leads to a buildup of cholesterol in your arteries. (Arteries are blood vessels that carry blood from your heart to your body.) 2.High-density lipoprotein (HDL - cholesterol carried by this type is known as 'good' cholesterol).   HDL cholesterol sometimes is called “good” cholesterol. This is because it carries cholesterol from other parts of your body back to your liver. Your liver removes the cholesterol ...

Sexually transmitted diseases (STDs) are infections that you can get from having sex with someone who has the infection. The causes of STDs are bacteria, parasites and viruses. There are more than 20 types of STDs. In the developing world, STDs are an even greater public health problem as the second leading cause of healthy life lost among women between 15 and 44 years of age 1 . 1. AIDS (Acquired Immune Deficiency Syndrome) Cause: By Human Immunodeficiency Virus (HIV) through contact with infected person's body fluid e.g. during sexual intercourse, blood transfusion. AIDS Symptoms: Opportunistic infections : body immune system becomes weakened and cannot defend itself. Person usually die from infections rather than HIV itself. Control / Treatment:  No treatment available. (Control by preventing causes e.g. use of condom, Avoid contact with infected persons, test blood before transfusions) 2. Genital Herpes Genital Herpes Cause: virus spread durin...

Our first line of defense against foreign organisms is barrier tissues such as the skin (mechanical barrier) that stop the entry of organism into our bodies. If, however, these barrier layers are penetrated, the body contains cells that respond rapidly to the presence of the invader. Other mechanical barriers include:             -Movement of cilia in respiratory track             -Peristalsis in alimentary canal             -Flushing action of tears and saliva             -Acidic stomach to kill microorganisms 1 If these barriers did not stop the invaders (pathogens) then the blood would play an important role in defending the body (second line of defense). E.g. phagocytes (WBC) would engulf microbe and kill them, or lymphocytes would produce ant...

Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift ( Berkeley )  It is a  process in nature in which organisms possessing certain genotypic characteristics that make them better adjusted to an environment tend to survive, reproduce, increase in number or frequency , and therefore, are able to transmit and perpetuate their essential genotypic qualities to succeeding generations . This theory was put forward by Charles Darwin, trying to explain how evolution of species occurs . Look at an example to help make the concept natural selection clearer:  Industrial melanism is a phenomenon that affected over 70 species of moths in England. It has been best studied in the peppered moth, Biston betularia . Prior to 1800, the typical moth of the species had a light pattern. Dark colored or melanic moths were rare and were therefore collectors' items. During the Industrial Revolution, soot and other industri...