The word "biology" comes from two Greek words:

• Bios — meaning "life"
• Logos — meaning "study"

So, biology literally means "the study of life." A person who studies biology is called a biologist.

Living Things and Non-living Things

Living things are organisms that show all the characteristics of life. Non-living things do not have these characteristics.

Unicellular and Multicellular Organisms

Unicellular organisms are very small organisms made of only one cell. Examples include bacteria, amoeba, and protozoa. They are also called microorganisms because they can only be seen with a microscope.

Multicellular organisms are larger organisms made of many cells. Examples include humans, fish, trees, and cows.

The Cell as the Basic Unit of Life

All living things are made up of cells. A cell is the smallest unit that can carry out all life processes. Cells are so small that they can only be seen using a microscope.

All living things share seven characteristics that distinguish them from non-living things:

1. Nutrition — obtaining and using food materials from the environment
2. Respiration — releasing energy from food inside the cells
3. Excretion — removing harmful waste materials from the body
4. Growth and Development — increasing in size and becoming more complex
5. Sensitivity — detecting and responding to changes in the environment
6. Movement — moving parts of the body or moving from one place to another
7. Reproduction — producing new individuals of the same kind

These characteristics are also called the life processes.

Biology is divided into branches that focus on different areas of study.

Main Branches

• Botany — the study of plants
• Zoology — the study of animals

Minor Branches

Biology is important in our daily lives for many reasons:

• Health and Medicine — Biology helps us understand how the human body works, why we get sick, and how to treat diseases. Doctors, nurses, and pharmacists all rely on biological knowledge.
• Agriculture — Understanding plant and animal biology helps farmers grow better crops, keep livestock healthy, and control pests.
• Environmental Conservation — Biology helps us protect wildlife, manage forests, and conserve natural resources in Tanzania's national parks and reserves.
• Food Security — Biological knowledge is used to improve food production, preserve food, and develop new crop varieties.
• Biotechnology — Biology is the foundation for making vaccines, antibiotics, and other products that improve human life.

Biology connects with many other subjects and fields of study:

• Biology and Chemistry — Chemistry helps us understand how nutrients, medicines, and cellular chemicals work in living organisms.
• Biology and Physics — Physics explains how light enters our eyes, how sound travels to our ears, and how muscles work.
• Biology and Mathematics — Mathematics is used to count cells, measure growth rates, and analyze data in biological research.
• Biology and Geography — Geography helps us understand how climate and soil affect the distribution of plants and animals.
• Biology and Agriculture — Biology provides knowledge about crops and livestock, while agriculture applies this knowledge to food production.
• Biology and Medicine — A career in medicine (becoming a doctor, nurse, or pharmacist) requires deep knowledge of human biology.

These connections make biology a central science that supports many other fields.

In Tanzania, biological knowledge is used every day in local markets. For example, when a farmer at the Mbeya or Arusha market checks if fruits are ripe or damaged, they are applying their understanding of plant biology — knowing how fruits grow, ripen, and decay. Similarly, when a mother at home prepares vegetables for lunch, she uses knowledge of nutrition biology to choose food that keeps her family healthy. Understanding biology also helps local health workers at dispensaries recognize symptoms of common diseases like malaria or typhoid, which are caused by microorganisms.