Biology

The Seven Characteristics of Living Organisms (MRS GREN) All living organisms carry out seven life processes. These are often remembered using the mnemonic MRS…

Plant and Animal Cell Structures All living organisms are made of cells. Cells are the basic units of life. Plant and animal cells share several structures but…

The Magnification Formula When viewing specimens under a microscope, magnification is used to describe how many times larger the image appears compared to the…

What is Diffusion? Diffusion is one of the most important transport processes in living organisms. It requires no energy input from the cell. Diffusion is the…

Water as a Solvent in Organisms Water is the most important solvent in living organisms. Many vital processes depend on substances being dissolved in water:…

What is Active Transport? Unlike diffusion and osmosis, active transport moves particles against the concentration gradient - from a region of lower…

Chemical Elements in Biological Molecules All biological molecules are built from a small set of chemical elements. You need to know which elements are found in…

Catalysts and Enzymes A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction An enzyme is a protein that is…

What is Photosynthesis? Photosynthesis is the process by which plants synthesise carbohydrates from raw materials using energy from light. It is the basis of…

Overview of Leaf Structure Leaves are the main organs of photosynthesis. Most leaves have a large surface area and are thin - these are both adaptations for…

Balanced Diet A balanced diet contains all the necessary nutrients in the correct proportions to maintain health - providing enough energy for daily activities,…

The Digestive System The digestive system consists of the alimentary canal - a continuous tube from mouth to anus - and associated organs that help process…

What is Physical Digestion? Physical digestion is the breakdown of food into smaller pieces without any chemical change to the food molecules. Physical…

Functions of Xylem and Phloem Plants have two types of vascular (transport) tissue that run throughout the plant body, together forming the vascular bundles…

Root Hair Cells Root hair cells are specialised cells on the surface of roots that have long, thin extensions (root hairs), which greatly increase the surface…

What is Transpiration? Transpiration is the loss of water vapour from the leaves of a plant. Water evaporates from the surfaces of the mesophyll cells into the…

The Circulatory System The circulatory system is a system of blood vessels with a pump (the heart) and valves to ensure the one-way flow of blood around the…

Structure of the Mammalian Heart The heart is a muscular pump that drives blood around the body. Left and right atria - the upper chambers, which receive blood…

Structure of Blood Vessels Feature Artery Vein Capillary Wall thickness Very thick, muscular and elastic Thinner than arteries, with less muscle and elastic…

Components of Blood Blood is a liquid tissue made up of four main components: Component Description Functions Red blood cells Biconcave disc shape; no nucleus…

Pathogens and Transmissible Disease A pathogen is a disease-causing organism (e.g. bacteria, viruses, fungi, protoctists) A transmissible disease is a disease…

Features of Gas Exchange Surfaces The lungs are specialised for efficient gas exchange between air and the blood. Effective gas exchange surfaces share four key…

What is Aerobic Respiration? Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules, releasing energy. Aerobic…

What is a Drug? A drug is any substance taken into the body that modifies or affects chemical reactions in the body. Antibiotics Antibiotics are used to treat…

Structure of an Insect-Pollinated Flower The parts of an insect-pollinated flower can be identified in diagrams and images, and their functions stated: Sepals -…

The Male Reproductive System The parts of the male reproductive system can be identified on diagrams, along with their functions: Testes - produce sperm cells…

The Sun as the Energy Source The Sun is the principal source of energy input to biological systems. The Flow of Energy Through Living Organisms Light energy…

Food Chains A food chain shows the transfer of energy from one organism to the next, beginning with a producer. Worked Example: Constructing and Interpreting a…

The Carbon Cycle The carbon cycle can be described in terms of: Photosynthesis - carbon dioxide is removed from the atmosphere and fixed into organic molecules…

Ecosystems and Biodiversity An ecosystem is a unit containing the community of organisms and their environment, interacting together Biodiversity is the number…

Why Organisms Become Endangered or Extinct Cause How it threatens species Climate change Alters habitats and food availability faster than some species can…