Biology revision notes

Cells are the building blocks of life. Knowing each organelle's job and how to compare animal, plant and bacterial cells is the foundation of biology.

Cells are organised into tissues, organs and systems. This topic covers digestion, the heart and circulatory system and transport in plants.

Pathogens cause communicable disease. The immune system fights them; vaccines and antibiotics support that defence.

Photosynthesis transfers light energy into chemical energy in glucose; respiration releases that energy for the cell to use.

Homeostasis keeps internal conditions constant. The nervous system responds quickly using electrical impulses; hormones give slower, longer-lasting control.

DNA carries the instructions to build an organism. Meiosis produces gametes with genetic variation, and Punnett squares predict inheritance patterns.

Evolution by natural selection explains the diversity of life. Advantageous variations become more common over generations as their carriers reproduce more.

Ecology studies how living things interact with each other and their environment. Human activity is now a major threat to biodiversity.