Secondary 4 Biology

A biomolecule made of carbon, hydrogen and oxygen, covering monosaccharides, disaccharides and polysaccharides; the main energy source of organisms.

A common six-carbon monosaccharide; the usual substrate of cell respiration, absorbed directly by the digestive tract.

The storage polysaccharide of plants, a long chain of glucose units; it turns blue-black with iodine solution.

The storage polysaccharide of animals, kept mainly in the liver and muscles and quickly broken down to top up blood glucose.

The polysaccharide of plant cell walls; human digestive enzymes cannot break it down, so it counts as dietary fibre.

Water-insoluble biomolecules made of glycerol and fatty acids, used for energy storage, insulation and cell membranes.

The building blocks of proteins; twenty kinds are common, chained in different orders to form different proteins.

Biomolecules made of amino acids, responsible for growth and repair, catalysis, transport and defence.

Nucleotide-based biomolecules that store genetic information, including DNA and RNA.

A food test for reducing sugars: heated with Benedict's solution, a positive result gives a brick-red precipitate.

The boundary of every cell; a selectively permeable membrane of phospholipid bilayer and proteins that controls the movement of substances.

The model of membrane structure: a fluid phospholipid bilayer with proteins embedded like mosaic tiles.

A thread of DNA and proteins in the nucleus; it carries the genetic information.

The organelle where aerobic respiration takes place, releasing energy as ATP.

The tiny particle that assembles amino acids into proteins, either free in the cytoplasm or on the endoplasmic reticulum.

A network of membranes in the cytoplasm that transports materials; rough ER has ribosomes on its surface.

The plant organelle containing chlorophyll, where photosynthesis takes place.

A fluid-filled sac; the large central vacuole of plant cells stores cell sap that keeps the cell firm.

The tough outer layer of plant cells, made of cellulose, providing support and protection.

A cell without a membrane-bound nucleus (such as bacteria); its genetic material lies free in the cytoplasm and it lacks other membrane-bound organelles.

The net movement of particles from a higher to a lower concentration, a passive process requiring no energy.

The difference in concentration between two regions; moving down it means going from high to low concentration.

The diffusion of water molecules across a semi-permeable membrane from a higher to a lower water potential.

A membrane that lets some molecules such as water pass but holds back others such as sucrose.

A measure of the tendency of water to move; pure water has the highest water potential and concentrated solutions the lowest.

The movement of substances against the concentration gradient by carrier proteins, requiring energy from respiration.

The shrinkage of the cytoplasm and membrane away from the cell wall as a plant cell loses water.

The bursting of red blood cells that take in too much water in a hypotonic solution, releasing haemoglobin.

The firm, swollen state of a plant cell whose contents press against the cell wall after taking in water.

The energy-consuming process by which a cell wraps its membrane around and engulfs large particles such as bacteria.

The whole sequence from the end of one division to the end of the next, covering interphase and the division phase.

The longest stage of the cell cycle (G1, S and G2), in which the cell grows and replicates its DNA.

A DNA-and-protein structure carrying genetic information; it condenses into a visible form during division.

One of the two identical copies of a replicated chromosome, the pair joined at the centromere.

The fibrous structure formed between the poles of a dividing cell that moves the chromosomes.

Nuclear division that distributes replicated chromosomes equally to two daughter cells, used for growth and repair.

The division of the cytoplasm after nuclear division, forming two daughter cells.

The structure formed at the equator of a dividing plant cell that develops into the new cell wall.

Two successive divisions producing four cells with half the chromosome number, used to make gametes.

The sex cells (sperm or egg) produced by meiosis, carrying half the chromosome number of body cells.

The sum of all chemical reactions in a cell, covering catabolism and anabolism.

The breakdown of large molecules into smaller ones, releasing energy.

The building of large molecules from smaller ones, consuming energy.

A protein biological catalyst that speeds up reactions without itself being changed.

The molecule an enzyme acts on; it binds to the enzyme's active site.

The groove on an enzyme whose shape is complementary to the substrate, giving the enzyme its specificity.

The temporary combination of enzyme and substrate in which the reaction takes place.

The permanent loss of an enzyme's shape — and hence active site — caused by high temperature or extreme pH.

A substance shaped like the substrate that competes for the active site; its effect is reduced by adding more substrate.

An inhibitor that binds away from the active site and changes its shape; extra substrate cannot remove its effect.

The process by which cells oxidise food molecules step by step, releasing energy captured as ATP.

The energy currency of the cell, storing and transferring the energy released in respiration.

The oxygen-independent reactions in the cytoplasm: glucose is split to triose phosphate and oxidised to pyruvate, with a net gain of 2 ATP.

The three-carbon compound at the end of glycolysis; it enters the mitochondrion when oxygen is available, or becomes lactic acid or ethanol when not.

The two-carbon compound formed from pyruvate in the mitochondrion; the entry molecule of the Krebs cycle.

The cyclical reactions in the mitochondrial matrix that release carbon dioxide and produce energy carriers and a little ATP.

The process on the inner mitochondrial membrane that uses energy carriers to build large amounts of ATP, with oxygen as the final acceptor.

The oxygen-dependent pathway of respiration, yielding much energy and producing carbon dioxide and water.

The pathway used when oxygen is short, relying on glycolysis alone and yielding little energy.

The substance pyruvate becomes in oxygen-starved muscles; its build-up causes aching and fatigue.