Cells, Organ Systems and Ecosystems (WJEC)

Cell

A cell is the basic unit of life. It carries out functions needed for an organism to survive and grow.

Unicellular vs. Multicellular Organisms

Unicellular organisms, like bacteria, consist of a single cell, while multicellular organisms, like humans and plants, have many specialized cells working together. 

Cytoplasm

A jelly-like fluid inside the cell where chemical reactions take place. It contains organelles and enzymes. 

Nucleus

Controls cell activities and contains genetic material (DNA). 

Cell Membrane

A thin layer that controls what enters and leaves the cell. 

Mitochondria

Organelles that release energy by breaking down food during respiration. 

Plant Cell Wall

A rigid outer layer made of cellulose that gives strength and prevents bursting. 

Vacuole

A large sac filled with cell sap (water, sugars, and minerals) that helps keep the plant cell firm. 

Chloroplasts

Contain chlorophyll, which captures sunlight for photosynthesis. 

Magnification

The measure of how much bigger an image appears compared to the actual object. 

Resolution

The smallest details that can be clearly seen in an image. 

Light Microscope

Uses light to magnify cells, allowing basic cell structures to be seen. 

Electron Microscope

Provides much greater detail, allowing scientists to see tiny cell structures. 

Cell Differentiation

The process where cells become specialized for specific functions, like red blood cells carrying oxygen. 

Tissue

A group of similar cells working together for a specific function, like muscle tissue. 

Organ

A structure made of different tissues that work together, like the heart or brain. 

Organ System

A group of organs working together, like the digestive system. 

Diffusion

The movement of molecules from high to low concentration without needing energy. 

Osmosis

The movement of water molecules from high to low water concentration across a partially permeable membrane. 

Active Transport

The movement of molecules from low to high concentration, requiring energy. 

Enzymes

Biological catalysts that speed up chemical reactions without being used up. 

Lock and Key Hypothesis

The idea that each enzyme has a specific shape that fits only one substrate. 

Aerobic Respiration

A process that releases energy using oxygen: 

Glucose + Oxygen → Carbon dioxide + Water + Energy 

Anaerobic Respiration

A process that releases energy without oxygen, producing lactic acid: 

Glucose → Lactic acid + Energy 

Oxygen Debt

The extra oxygen needed to break down lactic acid after exercise. 

Alveoli

Tiny air sacs in the lungs where oxygen enters the blood, and carbon dioxide is removed. 

Peristalsis

Wave-like muscle contractions that push food through the digestive system. 

Bile

A substance produced by the liver that helps break down fats. 

Red Blood Cells

Transport oxygen using haemoglobin and carry carbon dioxide back to the lungs. 

White Blood Cells

Defend the body by fighting infections and producing antibodies. 

Platelets

Help blood clot to prevent excessive bleeding. 

Arteries

Carry blood away from the heart under high pressure. 

Veins

Carry blood back to the heart and contain valves to prevent backflow. 

Capillaries

Tiny blood vessels where gas and nutrient exchange occur. 

Cardiovascular Disease

A condition caused by fatty deposits in arteries, leading to heart disease or strokes. 

Photosynthesis

The process by which plants make food using sunlight: 

Carbon dioxide + Water → Glucose + Oxygen 

Xylem

Transports water and minerals from roots to leaves. 

Phloem

Transports sugars from leaves to other parts of the plant. 

Transpiration

The loss of water from leaves through evaporation and diffusion. 

Carbon Cycle

The movement of carbon between the atmosphere, plants, animals, and decomposers. 

Producer

An organism, like a plant, that makes its own food through photosynthesis. 

Consumer

An organism that eats other organisms for energy. 

Decomposer

An organism, like bacteria or fungi, that breaks down dead matter and recycles nutrients. 

Homeostasis

The regulation of internal conditions to maintain a stable environment in the body. 

Hormone

A chemical messenger that travels in the blood to regulate body processes, like insulin for blood sugar control.