Biodiversity is the total number and variety of species in a given area. It can be studied using sampling techniques, and organisms can be classified according to morphological features.

Cells divide by mitosis for growth and repair. They divide by meiosis to produce gametes for sexual reproduction. Stem cells differentiate into specialised cells during the development of organisms.

Break down each step of mitosis with this guide and interactive activity from BBC Bitesize written to the GCSE WJEC biology specification.

What is DNA and how is the structure of this hereditary molecule responsible for its function? Scientists are using their knowledge of DNA to create and use genetic profiles.

Variation is the differences found within the same species. It can be caused by both sexual reproduction and environmental influences.

How can genes change? Mutations are caused by several factors and can cause genetic disorders. How can gene therapy help treat these disorders?

Evolution by natural selection was proposed as a theory by Darwin and Wallace. What evidence is there in the world today to suggest that species evolve by this mechanism?

Our nervous system allows us to detect and react to changes in the environment. Sense organs, like the eyes, detect changes and our central nervous system co-ordinates a response.

Conditions inside our body need to be maintained in a steady state. Blood sugar level and temperature are regulated carefully. Lifestyle choices such as drugs and alcohol can affect this homeostasis.

Our kidneys regulate the water concentration in our blood and excrete toxic waste. When they fail to work properly, dialysis treatment or a transplant is required.

Handling micro-organisms safely requires specific techniques. Growing and studying micro-organisms gives us vital information about their rapid growth and their possible uses.

Communicable diseases are caused by the spread of micro-organisms. How do they spread, and what future developments will come from the study of the immune system and the treatment of diseases?