CSEC Human and Social Biology key terms

The process by which green plants use sunlight trapped by chlorophyll to combine carbon dioxide and water into glucose, releasing oxygen as a by-product.

The controlled release of energy from glucose inside living cells, using oxygen in aerobic respiration and producing carbon dioxide and water as waste products.

Release of energy from glucose without oxygen, producing lactic acid in human muscle cells and ethanol plus carbon dioxide in yeast, with less energy released than aerobic respiration.

A small energy-carrying molecule made in cells during respiration; breaking it down supplies the energy needed for processes such as muscle contraction and active transport.

The green pigment in chloroplasts that absorbs light energy for photosynthesis, mainly in the blue and red parts of the spectrum.

A green organelle found in plant cells that contains chlorophyll and is the site where photosynthesis takes place.

Tiny openings, mostly on the underside of leaves, that let carbon dioxide in and oxygen and water vapour out; each is controlled by two guard cells.

Pairs of specialised epidermal cells that swell with water to open a stoma and lose water to close it, controlling gas exchange and water loss.

Loss of water vapour from the leaves of plants, mainly through stomata, which pulls water up the xylem and cools the plant.

Movement of dissolved sugars and other solutes through the phloem from sources such as leaves to sinks such as roots, fruits and growing tips.

Plant tissue made of dead, hollow, lignified vessels that transports water and dissolved minerals upward from the roots to the leaves.

Living plant tissue with sieve tubes and companion cells that carries sugars and amino acids from leaves to other parts of the plant.

A protein that speeds up a specific chemical reaction in living things by binding its substrate at an active site; it is unchanged by the reaction.

The specially shaped region of an enzyme molecule where its substrate binds, forming an enzyme-substrate complex before products are released.

Loss of an enzyme's shape and function when temperature or pH moves far from the optimum, so the active site can no longer fit its substrate.

The molecule that an enzyme acts on, fitting into the enzyme's active site and being converted into products.

The net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient, without needing energy.

The movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution, down a water potential gradient.

Movement of substances across a cell membrane against a concentration gradient, using energy from respiration and carrier proteins in the membrane.

A thin barrier that lets small molecules such as water pass through but blocks larger solute molecules, controlling what enters and leaves a cell.

Shrinking of the cytoplasm away from the cell wall when a plant cell loses water by osmosis in a concentrated solution.

The firm, swollen state of a plant cell when it is full of water; turgor pressure keeps soft plant tissues upright and stiff.

The difference in concentration of a substance between two regions, which drives diffusion and osmosis; the steeper the gradient, the faster the movement.

Long, thin cells on plant roots with a large surface area that absorb water by osmosis and mineral ions by active transport from the soil.

Millions of tiny air sacs in the lungs with thin, moist walls and a rich blood supply, where oxygen and carbon dioxide are exchanged by diffusion.

The red, iron-containing protein in red blood cells that binds oxygen in the lungs and releases it in tissues that need it.

Disc-shaped cells without a nucleus that are packed with haemoglobin and carry oxygen from the lungs around the body.

Colourless blood cells that defend the body, either by engulfing microbes or by making antibodies and antitoxins against specific pathogens.

The control systems that keep conditions inside the body steady, such as temperature, blood glucose and water balance, despite changes outside.

A control mechanism in which a change from the normal level triggers a response that reverses that change, bringing conditions back towards the set point.

A hormone made by the pancreas that lowers blood glucose by making liver and muscle cells take up glucose and store it as glycogen.

Widening of blood vessels near the skin surface, increasing blood flow and heat loss to cool the body when it is too warm.

Narrowing of blood vessels near the skin surface, reducing blood flow and heat loss to help keep the body warm.

A short section of DNA on a chromosome that codes for a particular protein or characteristic and is passed from parents to offspring.

One of the different versions of the same gene, such as the tall and short forms in pea plants; an organism inherits one from each parent.

An allele that shows its effect in the phenotype even when only one copy is present, masking the recessive allele paired with it.

An allele whose effect appears in the phenotype only when two copies are present, because a dominant allele masks it.

The combination of alleles an organism carries for a gene, written as pairs of letters such as AA, Aa or aa.

The observable features of an organism, produced by its genotype interacting with the environment.

Having two identical alleles for a particular gene, for example both dominant or both recessive.

Having two different alleles for a particular gene, one dominant and one recessive.

A thread-like structure in the nucleus made of DNA and protein, carrying genes; humans have 46 in most body cells, arranged in 23 pairs.

The molecule shaped as a double helix that stores genetic information as a sequence of bases and is copied before a cell divides.

Cell division that produces gametes with half the normal chromosome number, creating genetic variation through independent assortment and crossing over.

Cell division that produces two genetically identical daughter cells with the same chromosome number, used for growth and repair.

A change in the base sequence of DNA that may alter a protein and produce a new characteristic, sometimes harmful, sometimes useful.

A microorganism that causes disease, such as certain bacteria, viruses, fungi and protozoa, which can spread from host to host.

An organism that carries a pathogen from one host to another without being affected itself, such as a mosquito spreading malaria.

A protein made by white blood cells that binds specifically to an antigen on a pathogen and helps destroy it.

Resistance to a particular pathogen, gained after infection or vaccination when the body produces antibodies and memory cells against it.

Introducing a weakened or inactive form of a pathogen so the body makes antibodies and memory cells, giving protection against later infection.

A disease caused by a protozoan parasite, spread by the bite of infected female Anopheles mosquitoes, producing fever and chills.

A condition in which blood glucose is not controlled properly, either because the body makes too little insulin or cells do not respond to it.

The release of harmful substances or energy into the environment, such as untreated sewage, factory smoke or excess noise, damaging organisms and habitats.

Over-enrichment of water with nutrients such as nitrates, causing rapid algal growth that later decays and removes oxygen, killing fish.

Warming of the Earth as gases such as carbon dioxide and methane trap outgoing heat in the atmosphere, increasing with human emissions.

The large-scale clearing of forests for farming, timber or building, which destroys habitats, reduces photosynthesis and can increase soil erosion and flooding.