Cambridge O Level / IGCSE Biology (Chapters 1–9)

Comprehensive vocabulary flashcards covering key terms, processes, definitions, and formulas across Chapters 1 to 9 of Cambridge O Level / IGCSE Biology.

Movement

An action causing a change in position or place of the whole organism or a part of it.

Respiration

Chemical reactions in cells that break down nutrient molecules and release energy.

Sensitivity

Detecting and responding to changes in the internal or external environment.

Growth

A permanent increase in size and dry mass, caused by an increase in cell number, cell size, or both.

Excretion

The removal of toxic materials, waste products of metabolism, and substances in excess of requirements.

Egestion

The removal of undigested food from the alimentary canal as faeces.

Species

A group of organisms that can reproduce with one another to produce fertile offspring.

Dichotomous key

A tool that identifies organisms using a sequence of paired, contrasting statements based on observable characteristics.

Mitochondria

Organelles in the cytoplasm that serve as the site of aerobic respiration, releasing energy for cell processes.

Ribosomes

Cellular structures that serve as the site of protein synthesis.

Tissue

A group of similar cells working together to perform a specific function.

Organ

A structure containing different tissues working together to carry out specific functions.

Magnification formula

$\text{Magnification} = \frac{\text{image size}}{\text{actual size}}$, where both measurements are converted to the same units ($1\,\text{mm} = 1000\,\mu\text{m}$).

Diffusion

The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.

Osmosis

The net movement of water molecules from a region of higher water potential (a more dilute solution) to a region of lower water potential (a more concentrated solution), through a partially permeable membrane.

Plasmolysis

The pulling away of the plant cell membrane from the cell wall when placed in a concentrated solution due to water loss by osmosis.

Active transport

The movement of particles through a cell membrane from a lower concentration to a higher concentration, against the concentration gradient, using energy released by respiration and carrier proteins.

Biuret test

A chemical food test for proteins where the reagent turns from blue to lilac/purple in the presence of protein.

Benedict's test

A test for reducing sugars where a food sample mixed with Benedict's solution is heated, changing from blue to a green, yellow, orange, or brick-red precipitate.

Emulsion test

A chemical test for lipids where the sample is shaken with ethanol and then mixed with water, forming a milky-white emulsion if lipids are present.

Gene

A length of DNA that codes for a protein or functional product.

Enzyme

A biological catalyst that speeds up a chemical reaction without being used up by the reaction.

Denatured

The state of an enzyme when extreme temperatures or pH permanently or substantially alter the shape of its active site so the substrate no longer fits.

Photosynthesis

The process by which plants use light energy absorbed by chlorophyll to make carbohydrates from carbon dioxide and water ($6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$).

Limiting factor

The factor in shortest supply that restricts the rate of a physiological process, such as photosynthesis.

Peristalsis

The wave-like contraction and relaxation of circular and longitudinal muscles that pushes food along the alimentary canal.

Mechanical digestion

The breakdown of food into smaller pieces without changing its chemical composition, which increases surface area for enzyme action.

Chemical digestion

The breakdown of large, insoluble molecules into small, soluble molecules that can be absorbed, using digestive enzymes.

Bile

An alkaline fluid produced by the liver and stored in the gall bladder that neutralises stomach acid and emulsifies fats into smaller droplets.

Assimilation

The movement and incorporation of absorbed nutrients into the cells of the body to be used for energy, growth, and repair.

Xylem

A plant transport tissue made of dead, hollow, lignified vessels that carries water and mineral ions upwards from roots to stems and leaves, providing mechanical support.

Transpiration

The loss of water vapour from a plant, mainly from leaves through stomata by evaporation from mesophyll surfaces and subsequent diffusion.

Translocation

The transport of sucrose and amino acids through the phloem from sources to sinks.

Double circulatory system

A circulatory system where blood remains in vessels and passes through the heart twice during one complete circuit (pulmonary circulation and systemic circulation).

Artery

A blood vessel that carries blood away from the heart at high pressure, characterised by thick muscular and elastic walls and a relatively narrow lumen.

Vein

A blood vessel that carries blood towards the heart at low pressure, featuring thinner walls, a wide lumen, and valves to prevent backflow.

Capillary

A tiny blood vessel with walls that are one cell thick, connecting arteries and veins to permit efficient exchange of substances between blood and tissue cells.

Tissue fluid

Fluid forced out of blood capillary walls at the arterial end under high pressure that surrounds cells, allowing exchange of oxygen, nutrients, and waste products.