Biology is the study of life.
Biology comes from two Greek words namely: Bios-life, and logos –knowledge or study of, hence Biology means the study of living things.
Biology as a science is very wide and has many specialized branches. These include:
Some of the specialized branches of biology
Botany Study of plants
Zoology Study of animals
Cytology Study of cells
Morphology Study of form and structure of organisms
Ecology Study of organisms in relation to their environments
Entomology Study of insects
Parasitology Study of organisms which live on or in the bodies of other organisms and get their nutrients from them
Genetics Study of heredity
Pathology Study of diseases of animals and plants
Physiology Study of process and functioning of body parts
Taxonomy Study of naming, grouping and classifying of organisms

Biology as a subject is a single science based on the study of living things. Therefore by studying it helps us to:
1. Acquire knowledge which enables one to answer questions about life and living things e.g. can identical twins be of different sexes?
2. Acquire scientific attitudes and methods, which help to solve problems. This is achieved by increasing the powers of observing, which enables one to make critical evaluations hence drawing correct conclusions.
3. Understand the basic principles of life which influence all events in the world
4. Improve our general health standards through skills acquired in preventing germs that cause diseases.
5. Develop and promote conservation program which enables the use of available resources sustainably
6. Understand and explain the different behaviors showed by different organisms
7. Get introduced to different biological occupations and fields such as veterinary medicine, human medicine, pharmacy, forestry, agriculture, etc.
A living thing is biologically called an organism. Examples of organisms include: man, housefly, cockroach, maize plant, mushroom, etc. there is no absolute definition of a living thing. However, all living things share certain basic features called characteristics of living things.
There are seven basic characteristics of living things summarized as;
“MRS GREN’’- Movement, Reproduction, Sensitivity, Growth, Respiration, Excretion, nutrition.
1. Movement
This refers to the displacement in space all or part of an organism e.g. young shoot bending towards light, roots growing towards water. Animals move from one place to another and this type 0of movement is called locomotion. Plants and other organisms that are fixed in one place do not loco mote but can move parts of their bodies. Movements of living things involve expenditure of energy derived from respiration.
2. Reproduction
This is the production of new individuals similar to parents. This is important for the continuity of life and formation of new generations.

3. Sensitivity or irritability
This is the ability of an organism to respond to changes in the environment and within themselves. Such a change in the environment is termed as stimulus. Some of the signs of sensitivity include locomotion of animal, crying of a child on seeing a fierce looking dog, growing towards light by a plant shoot. Sensitivity is very essential in the survival of an organism.
4. Growth and development
Growth is the permanent increase in size of an organism. It is brought about by taking substances from the environment and incorporating them into internal structure of an organism. Growth results in changes in shape and form of an organism which causes as development.
5. Respiration
This is the release of energy into the body due to the breakdown of substances in the body. It often involves oxygen, which must therefore be obtained by the organism from the surrounding and in turn gives out carbon dioxide
6. Excretion
This is the process by which waste products of metabolism are removed out of the body. Metabolism refers to the chemical reaction that occur in organisms. The disposal of metabolic waste products is important because some of the waste products are poisonous.
7. Nutrition or feeding
This is the process by which a living things (organism) obtains nutritive substances from the environment. These substances are used to build up the organism and provide energy for various activities.
Food for thought
A motorcycle moves, takes in oxygen and gives out carbon dioxide, consumes fuel but nevertheless it is not the living thing
Discuss the truth of this statement.

Most of the organisms belong to two broad groups namely: plants and animals
Examples of plants: grasses, simsim, mosses, ferns, mango etc.

Examples of animals:
Rabbits, cows, monkeys, goats, cats, man etc.
Plants and animals have in common the seven basic characteristics of living things (MRS GREN)
However, these two groups of organisms show fundamental differences between them as summarized below:
PLANTS Animals
Have chlorophyll Lack chlorophyll
Make their own food Un able to make their own food
Do not locomote Do locomote for various reasons
Have cell walls around their cells Show a quick response to stimuli
Response to stimuli is slow
Growth is localized to the tips Growth occurs through out the body
Have external organs e.g leaves Their organs are located mostly inside the body


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