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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.

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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..

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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.

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By the time sunlight reaches our eyes, most of the blue light has been scattered out. This leaves only light from the red end of the spectrum which travels towards us with little or no scattering. This is why the Sun appears red during sunsets..In dim light, everything appears to be in shades of black and white because the cone cells in our eyes which are responsible for detecting color do not work well in dim light.

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Nuclear energy will be one of the alternative sources of energy in the future. Nuclear energy is the heat energy produced from the changes in an unstable nucleus. A large amount of nuclear energy is produced when a heavy nucleus splits in two light nuclei join to form a heavier nucleus.

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Mutation is classified as somatic (when it occurs in somatic cells) and gametic (when it occurs in gametes). Somatic mutation, for example the brown spots in the iris of the eye cannot be passed on to the next generation while gametic mutation such as albinism can be passed on. An organism which has undergone mutation is called a mutant.