Biology is the science that deals with the study of living things. The word Biology is derived from two Greek words, Bios which means Life, and logos which means study of. Thus biology is the study of life and living organisms.


Biology can be defined as a branch of science that deals with the study of life. The term biology can also be defined as a branch of science that deals with the study of living things or organisms.

Biologist: A person specializing in the study of biology

Life means being alive or existing. Something is alive or existing if it possesses life processes which include movement or locomotion, respiration, excretion, reproduction, sensitivity, and nutrition.

The organism is anything that has life. It is the other name of a living thing. Organisms are made up of cells.

A cell is a basic unit of living things. Cells that make up plants are called plant cells and those which make up animals are called animal cells.

Some organisms are made up of one cell and are called unicellular or single-celled organisms e.g. amoeba, euglena, and yeast. Some organisms are made up of many cells and are called multicellular organisms e.g. animals, plants, and most fungi.



Movement is the change of position of the whole organism or just part of an organism. For animals and unicellular organisms, the movement is of the whole body. This is known as locomotion. Most animals move about using their legs, wings, or fins.

Unicellular organisms such as amoeba, paramecium, and euglena use the locomotory structures pseudopodia, cilia, and flagella respectively.

In plants, only part of it may move towards different factors such as light, water, gravity etc. They move by growing. Their roots grow down in the soil and their shoots grow up into the air or towards a source of light.

Irritability (sensitivity)

Irritability is the ability of an organism to respond to a stimulus. Stimulus (plural; stimuli) is anything that causes a response in an organism. Examples of stimuli include an alarm clock, a smell of breakfast cooking, and a fly landing on your skin. 

All living things are sensitive to certain changes in their surroundings, that is, they are aware of what is happening around them.

This is possible because they have special organs known as sense organs by which they detect these changes. Examples of sense organs include eyes for vision (sight); skin for temperature, touch, and pressure detection; tongue for tasting; nose for smelling; and ears for hearing and body balance.

Plants do not have sense organs but are still able to detect and respond to things like gravity, water, and light.

Feeding (Nutrition)

All living things need food to provide energy for activities such as growth, repair, and health. Animals get their food by eating other living things or food materials that were once living things. 

Herbivores (e.g. rabbits) eat plants, carnivores (e.g. lions) eat other animals, and omnivores (e.g. humans) eat animals and plants.

Plants make their own food through the process called photosynthesis. The process of taking in food, synthesizing it, digesting, and oxidizing it to release energy or build the body is called nutrition.


Respiration is the breaking down of food materials within cells to release energy. Respiration usually involves the use of oxygen. All living things need energy for movement, growth and development, and functioning of body organs.


Excretion is the process of removing metabolic waste products from the body of living organisms. All living things produce wastes such as carbon dioxide, water, urea, and ammonia.

Some of these chemicals if left to accumulate in the cells would seriously poison the living organism hence they need to be removed. Waste products are removed from the body by excretory organs such as the skin, kidneys, lungs, and liver.


Reproduction is the process by which living things produce new individuals of their kind. All living things reproduce, to replace organisms lost by death. 

If a group of organisms does not reproduce fast enough to replace those which die, the group becomes extinct.

Reproduction ensures the continuation of life when the parent generation dies. Human beings bear babies; birds hatch chicks; and plants produce seedlings as new organisms, which eventually grow to mature organisms to replace those lost by death.


Growth is defined as an irreversible (permanent) increase in size and dry weight of an organism involving differentiation. All living things need food in order to grow and build up their bodies. Animals grow until they reach a certain adult size, but most plants can grow continuously throughout their lives.

A table of differences between living things and non-living things

Living things

Non-living things

They respire

Do not respire

They grow

Do not grow

They respond to

Do not respond to

They reproduce

Do not reproduce

They excrete

Do not excrete

They feed

Do not feed

They move

Do not move


is a subject and it has many branches. The main branches are botany and

is a branch of biology that deals with the study of plants. A person who studies botany is called a botanist.

Zoology is a branch of biology that deals with the study of animals. A person who studies zoology is called a Zoologist

Other branches of biology

Mycology: this is the study of fungi. A person who studies mycology is called a mycologist.

Bacteriology: this is the study of bacteria. A person who studies bacteriology is called a bacteriologist.

Virology: this branch of biology deals with the study of viruses. A person who studies virology is called a virologist.

Immunology: is concerned with the body's defense against diseases and foreign substances. A person who studies immunology is called an immunologist.

Entomology: refers to the study of insects A person who studies entomology is called an entomologist.

Parasitology: this branch deals with the study of parasites and their effects on living organisms. A person who studies parasitology is called a parasitologist.

Dermatology: It is concerned with the medical study of skin and its diseases. A person who studies dermatology is called a dermatologist.

This is a branch of biology that deals with relationships among living things and between organisms and their surroundings. A person who studies ecology is called an ecologist.

Anatomy: This is the study that deals with the structure of living things. A person who studies anatomy is called an anatomist.

Endocrinology: This is the study of the structure of endocrine glands and the hormones associated with them. A person who studies endocrinology is called an endocrinologist.

Histology: The study of the structure of tissues A person who studies histology is called a histologist.

Cytology: The study of the structure, composition, and function of cells. A person who studies cytology is called a cytologist.

Microbiology: Is devoted to the study of organisms that can be seen only with a microscope e.g. bacteria, viruses, some fungi, and some protoctists. A person who studies microbiology is called a microbiologist.

Taxonomy: This is the scientific classification of organisms. A person who studies taxonomy is called a taxonomist.

Genetics: Study of heredity and variation in organisms. A person who studies genetics is called a geneticist.


The following is an outline of why the study of biology is important:
a)It helps us to understand ourselves better since we are living things.

b)Skills and knowledge of biology can be applied to other scientific fields such as agriculture, forestry medicine, nutrition, pharmacy, and veterinary science.

c)It helps us to understand our environment better and the principles of conserving it.

d)Biology helps to answer some important questions such as, what do living things need, why do we resemble a monkey, and why do frogs lay many eggs but only a few become adults?

e)Knowledge of biology helps us to improve our health since causes, symptoms,
transmission and treatment of various diseases are studied in biology.

f)Knowledge of biology helps us to avoid magical beliefs, superstitions, and other traditional taboos.

g)Knowledge of genetics helps us to clear some common doubts about certain inherited characteristics e.g. albinism, sickle cell anemia, and hemophilia.

h)Knowledge of the structure and chemical composition of the organisms enables us to acquire food, clothes, and shelter from them.


Veterinary science (Veterinary medicine)

Veterinary medicine is the branch of medicine that deals with the diseases of animals. Doctors that treat animals are called Veterinarians.

Veterinarians are trained to prevent, diagnose and treat illness in large and small animals. Their work is valuable because many animal diseases can be transmitted to human beings e.g. rabies, tuberculosis, tularaemia (rabbit fever) anthrax. 

Basic knowledge of biology is required for successful study of veterinary science.


Agriculture is concerned with the production of useful plants and animals through farming systems. Agriculture uses knowledge of biology to improve plant and animal breeding. Genetically modified organisms (GMOs) ensure better quality, early maturity, and high-yield products. 

Crop and animal diseases and pests can only be overcome by applying biological knowledge.


A forest is a large area of land covered with trees. It is much more than just trees. It also includes smaller plants such as mosses, shrubs, and wildflowers. Forestry is the science of managing forest resources for human benefit.

Biology helps in improving the quality of the trees by manipulating the genetic constitution of the particular plant species. Climate, soil, and water determine the type of plants to be grown which entirely applies biological knowledge. 

The use of biological control to combat tree pests applies biological principles.


Pharmacy is the profession concerned with the preparation, distribution, and use of
drugs. Members of this profession are called pharmacists or druggists. A pharmacy also refers to a place where drugs are prepared or sold. 

Knowledge of biology also helps to know the effects of drugs on living things (pharmacology) and possible remedies to be taken.


Medicine is the science and art of preserving health and treating illness. Medicine is a science because it is based on knowledge gained through careful study and

Biological knowledge helps doctors, surgeons, and nurses diagnose, treat and
prescribe the right medicine to cure the disease.

Biological knowledge will also help them to offer education to the patients on how to prevent themselves from diseases e.g. purifying drinking water, and vaccinating against polio, measles, and other diseases.


Nutrition is the science that deals with food and how the body uses it. Food supplies energy for every action we perform. Knowledge of biology helps to identify the type of food required by an individual based on its quality and quantity.

A table showing differences between plants and animals.



(i)They are autotrophic, i.e. they can make
their own food

They are heterotrophic i.e. they feed on
complex organic compounds

(ii)Contain chlorophyll, can undergo

No chlorophyll, cannot undergo

(iii)Growth occurs in some parts only i.e.
root and shoot tips.

Growth occurs in all parts of the body.

(iv)They have branched bodies

They have compact bodies

(v)No nerves, muscles, blood system or
special sensory cells.

Have nerves, muscles, blood system and special sensory cells.

(vi)Usually rooted in the ground and do not move from place to place.

Not rooted in the ground, move to get food and escape enemies.

(vii) Have no digestive system.

Have digestive system.

(viii) Cells of plant have cell walls.

Cells of animal have no cell wall.



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