1. What Is Biology?
Biology is the study of living things. It explores how organisms grow, function, reproduce, and
interact with their environment.
2. Characteristics of Living Things
All living organisms share key features:
● They are made of cells.
● They respond to their environment.
● They grow and develop.
● They reproduce.
● They use energy.
● They maintain internal balance (homeostasis).
● They evolve over generations.
3. The Cell
Cells are the basic units of life.
There are two main types:
● Prokaryotic cells (like bacteria) do not have a nucleus.
● Eukaryotic cells (like plant and animal cells) do have a nucleus.
Important cell parts include:
● The nucleus, which controls the cell and contains DNA.
● Mitochondria, which produce energy.
● Ribosomes, which make proteins.
● The cell membrane, which controls what enters and exits the cell.
● Cytoplasm, the jelly-like fluid inside the cell.
● Chloroplasts, which do photosynthesis (in plant cells only).
● Cell wall, which gives structure and protection (in plant cells only).
● Vacuoles, which store water and nutrients.
4. Levels of Organization in Living Things
Living organisms are organized in increasing complexity:
Cell → Tissue → Organ → Organ system → Organism
5. Photosynthesis vs. Cellular Respiration
● Photosynthesis happens in plants. It uses sunlight, carbon dioxide, and water to make
glucose (a sugar) and oxygen.
● Cellular respiration happens in all living cells. It breaks down glucose using oxygen to
release energy, and it produces carbon dioxide and water.
6. Genetics
DNA is the material that carries genetic information. A gene is a piece of DNA that determines a
trait, like eye color. Chromosomes are long strands of DNA found in the nucleus. Humans have
46 chromosomes.
Gregor Mendel is known as the father of genetics. He discovered that traits are passed from
parents to offspring through dominant and recessive patterns.
7. Classification of Living Things
All living things are grouped into categories to help scientists study them. These levels, from
largest to smallest, are:
Kingdom → Phylum → Class → Order → Family → Genus → Species
Humans belong to the species Homo sapiens.
8. Human Body Systems
Your body is made up of several systems that work together:
● The circulatory system moves blood around your body.
● The respiratory system helps you breathe.
● The digestive system breaks down food.
● The nervous system sends signals using your brain and nerves.
● The muscular system helps your body move.
● The skeletal system gives your body structure and protects organs.
● The immune system protects your body from disease.
9. Ecology
Ecology is the study of how living things interact with each other and their environment.
An ecosystem includes all the living things (like animals and plants) and nonliving things (like air
and water) in an area.
In an ecosystem:
● Producers make their own food (like plants).
● Consumers eat other organisms (like animals).
● Decomposers break down dead material (like fungi and bacteria).
10. Evolution and Natural Selection
Evolution is the process of change in species over time.
Natural selection is the idea that the organisms best suited to their environment are more likely
to survive and reproduce. This concept was introduced by Charles Darwin.
Bonus Fact:
Your body contains more bacterial cells than human cells — and most of them help keep you
healthy!
