JCE Biology key terms

Movement of dissolved substances across a cell membrane from a region of lower concentration to a region of higher concentration, using energy released by respiration and carrier proteins in the membrane.

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

Net spreading of particles from a region of higher concentration to a region of lower concentration, caused by their random motion, until the particles are evenly distributed.

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

State of a plant cell in which water has entered by osmosis, swelling the vacuole so that it presses the cytoplasm against the cell wall and keeps the cell firm.

Comparison of an object's outer absorbing surface with its internal volume. A small ratio makes exchange by diffusion too slow, which is why large organisms need transport systems.

Protein that acts as a biological catalyst, speeding up a reaction by lowering the energy needed, and that is specific to one substrate because of the shape of its active site.

Loss of the shape of an enzyme's active site at high temperature or unsuitable pH, so the substrate no longer fits and the reaction rate falls sharply.

Process in chloroplasts in which green plants use light energy to combine carbon dioxide and water into glucose, releasing oxygen as a by-product.

Green pigment inside chloroplasts that absorbs mainly red and blue light and transfers the energy to the reactions of photosynthesis.

The factor, such as light intensity, carbon dioxide concentration or temperature, that is in shortest supply and therefore currently restricts the rate of a process like photosynthesis.

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

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

Tiny pores, mostly in the lower leaf surface, each surrounded by two guard cells; they open to let carbon dioxide in and water vapour and oxygen out.

One of many tiny air sacs in the lungs whose thin, moist, richly supplied walls give a large surface for gas exchange by diffusion.

Finger-like fold of the small intestine lining that increases the surface for absorbing digested food and contains a rich blood supply.

Green alkaline liquid made in the liver, stored in the gall bladder and released into the small intestine, where it emulsifies fats and neutralises stomach acid.

Release of energy from glucose using oxygen, producing carbon dioxide and water, and yielding far more energy per glucose molecule than anaerobic respiration.

Release of a small amount of energy from glucose without oxygen, forming lactic acid in muscles or ethanol and carbon dioxide in yeast.

Extra oxygen needed after vigorous exercise to break down the lactic acid that built up in muscles during anaerobic respiration.

Maintenance of a stable internal environment, such as constant body temperature, blood glucose concentration and water content, despite changes outside the body.

Control mechanism in which a change from the normal level triggers a response that reverses the change and brings the value back towards normal.

Control of the water and salt content of body fluids, carried out mainly by the kidneys by adjusting how much water is reabsorbed and how concentrated the urine is.

Rapid automatic response to a stimulus that does not involve conscious thought, travelling through a reflex arc from receptor to effector.

Junction between two neurones, or between a neurone and a muscle, across which a chemical transmitter diffuses to carry the impulse in one direction only.

Chemical messenger secreted by an endocrine gland into the blood, which carries it to a target organ where it alters that organ's activity.

Cell division that halves the chromosome number and produces four genetically different gametes, with new combinations of chromosomes created by independent assortment and crossing over.

Cell division producing two daughter cells with the same chromosome number and genes as the parent cell; it is used for growth, repair and asexual reproduction.

Permanent increase in size and mass of an organism, brought about by cell division and cell enlargement, often measured as length or mass over time.

One of two or more different forms of the same gene, occupying the same position on a chromosome and producing different versions of a characteristic.

The combination of alleles an organism carries for a particular gene, for example homozygous dominant, heterozygous or homozygous recessive.

The observable features of an organism, produced by the interaction between its genotype and the environment.

Allele whose effect appears in the phenotype even when only one copy is present, masking the effect of a recessive allele.

Random change in the base sequence of DNA or in chromosome structure, which may produce a new allele and so new variation.

Process in which individuals with characteristics better suited to their environment are more likely to survive and breed, so those alleles become more common in later generations.

Differences between individuals of the same species, caused by genes, by the environment, or by a combination of both.

Diagram of feeding relationships in which an arrow points from each organism to the one that eats it, showing the transfer of energy and biomass.

Position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer; energy available falls at each higher level.

Organism such as a bacterium or fungus that breaks down dead material and waste, releasing mineral ions and carbon dioxide back to the environment.

Over-enrichment of water with nitrate or phosphate, often from fertiliser run-off, causing algal blooms that die and decay, using up oxygen and killing fish.

Ability of a bacterium to survive a drug that would normally kill it, arising by mutation and spread by natural selection, often because antibiotics are overused.

Introducing weakened or inactive pathogen material so the body makes antibodies and memory cells, giving immunity to later infection without the full disease.

Factor kept the same in all trials of an experiment so that any measured change can be attributed to the variable being tested.

How consistent repeated measurements are; it is improved by repeating readings and by taking a large enough sample, and is judged by how close results are to each other.