21

In the respiratory organ, blood receives oxygen, and then transports it to all the living parts of the body where it is used in tissue respiration..To function efficiently, a respiratory organ has a large surface area for rapid oxygen uptake and a very good supply of blood in a dense network of blood capillaries, which are separated from the surrounding air or water by an epithelium made up of a very thin layer of cells..

22

The scientific investigation method is important as it provides a systematic and complete way to acquire scientific knowledge. It also teaches us to think critically and analytically..Science discoveries help us to understand and appreciate our environment and improve the quality of life.

23

Diseases are caused by the presence of bacteria or viruses in the body. The symptoms may be due to the antigen or foreign proteins of the bacteria or the toxic chemicals produced by the bacteria. Recovery from the disease followed by immunity depends mainly on the production of antibodies in the blood. Antibodies are proteins released into the blood which destroy kills or rids the body of these disease causing microorganisms different ways..

21

Rubbish is produced daily by human. Rubbish such as domestic wastes (leftover food) is classified as biodegradable while glass, plastic and metals are classified as non-biodegradable. Non-biodegradable rubbish is imperishable and remains in rubbish dump sites for a long time. Problems associated with the improper disposal of rubbish are foul-smelling dump sites, as well as the dump sites becoming a breeding place for microorganisms which cause diseases.

17

In the making of soap, a vegetable oil such as palm oil is boiled with a concentrated alkali solution in a reaction known as saponification. The alkali reacts with the oil and breaks it down into glycerol and fatty acids. These fatty acids react with the alkali to form sodium or potassium salt of the fatty acids.

17

The radioactive decay of uranium was first discovered by Antoine Henri Becquerel in 1896. The Paris physician accidentally discovered that photographic plates wrapped in dark paper were blackened by invisible radiation was capable of discharging an electroscope. In 1898, a France couple, Marie and Pierre Curie, discovered the radioactive elements radium and polonium. Marie Curie also discovered the radioactive element thorium..

29

Endocrine glands are also known as ductless glands. They secrete hormones directly into the bloodstream. The endocrine glands I in both males and females are the same except for the testis (male) and the ovary (female). The majority of endocrine glands are controlled by the pituitary gland but some are stimulated by the nervous system or by chemical substances.

24

Variation gives rise to variety, diversity and uniqueness in organisms. Variation enables organisms to adapt and survive in the changing environment. This allows the organisms to breed and pass these adaptations to the next generation. Variation helps to prevent the complete extinction of animals and plants species.

34

The brain is made up of very soft and delicate tissues. It is protected from injury by the cranium and layers of membranes called meninges. The brain consists of two layers. The outer layer is called the grey matter and the inner layer is called the white matter. The grey matter is made up of cell bodies of neurons while the white matter consists of nerve fibers..

23

The use of nuclear energy to generate electrical energy is a controversial issue in many countries but over half of the electricity in France is generated by nuclear power stations..People are against the production of nuclear energy because past nuclear – related tragedies still haunt them. The effects caused by nuclear disasters such as Chernobyl and Three Mile Island are still fresh in the minds of most people.