Cell Biology: Cells are the basic unit of life. Prokaryotic cells (bacteria) lack a nucleus and membrane-bound organelles, while eukaryotic cells (plants, animals) have a nucleus and organelles. Diffusion is the movement of particles from high concentration to low concentration, while osmosis is the movement of water across a membrane. Mitosis is the process of cell division in which two identical daughter cells are produced. Organisation: Tissues are made up of cells with similar functions. Organs are made up of different tissues working together. Organ systems are made up of organs working together. Plants have a root system, shoot system, and reproductive system. Infection and Response: The immune system defends the body against pathogens. White blood cells, such as phagocytes and lymphocytes, play a key role in the immune response. Vaccines can be used to protect against infectious diseases. Antibiotics can be used to treat bacterial infections, but not viral infections. Bioenergetics: Photosynthesis is the process by which plants produce glucose and oxygen from carbon dioxide and water. Respiration is the process by which cells release energy from glucose. Aerobic respiration requires oxygen, while anaerobic respiration does not. Homeostasis and Response: Homeostasis is the maintenance of a stable internal environment. The nervous system and endocrine system work together to regulate body functions. The menstrual cycle is controlled by hormones. Inheritance, Variation, and Evolution: Genes are segments of DNA that code for specific traits. Alleles are different forms of a gene. Natural selection is the process by which organisms with advantageous traits survive and reproduce more successfully. Evolution is the process by which species change over time. Ecology: Ecosystems are made up of biotic (living) and abiotic (non-living) factors. Food chains and webs show the transfer of energy between organisms in an ecosystem. Human activities, such as deforestation and pollution, can have a negative impact on the environment.