IGCSE Biology

• Active transport


  The process in which energy is used to move the particles of a substance against a concentration gradient, that is, from a region where they are of lower concentration to a region where they are of higher concentration.

  
• Adaptation


  Any characteristic of an organism that improves its chances of surviving in its environment.

  
• Aerobic respiration


  Respiration with oxygen. It's the oxidation of food substances in the presence of oxygen with the release of a large amount of energy. Carbon dioxide and water are released as waste products.

  
• AIDS


  An abbreviation for Acquired Immune Deficiency Syndrome.

  
• Alleles


  Different forms of a gene which occupy the same relative positions on a pair of homologous chromosomes.

  
• Anaerobic respiration

  Respiration without oxygen. It's the oxidation of food substances in the absence of oxygen. Anaerobic respiration releases less energy than aerobic respiration.

  
• Anaesthetics


  Drugs that make the body unable to feel pain

  
• Arteries


  Blood vessels which carry blood away from the heart.

  
• Artificial selection


  A method used by human beings to produce plants and animals with desired qualities.

  
• Asexual reproduction


  The process resulting in the production of genetically identical offspring from one parent, without the fusion of gametes.

  
• Assimilation


  The process whereby some of the absorbed food materials are converted into new protoplasm or used to provide energy.
• Axon


  A nerve fibre that transmits impulses away from the cell body of a neurone.

  
• Bioaccumulation


  The process by which substances collect in all parts or part of a living organism.

  
• Breathing


  The process that brings about an exchange of gases between an organism and its environment.

  
• Capillaries


  Microscopic thin-walled (one cell thick) blood vessels which carry blood from a small artery (arteriole) to a small vein (venule).

  
• Codominance


  A condition where both alleles express themselves in a hybrid, as they are both either dominant or recessive to one another. (Roughly equal expression.)

  
• Community

  Populations of organisms living together and interacting with one another under the same environmental conditions.

  
• Conservation

  The protection and preservation of natural resources of the environment.

  
• Consumers


  Organisms which obtain their energy by feeding on other organisms.

  
• Continuous variation


  Traits with phenotypes ranging from one extreme to the other. It is brought about by combined (or additive) effects of many genes. It is affected by environmental conditions, e.g. intelligence, height and skin colour in human beings.

  
• Cross-pollination


  The transfer of pollen grains from one plant to the stigma of a flower in another plant of the same species.

  
• Decomposers


  Saprotrophs and detritivores. Organisms which obtain energy by breaking down dead organisms, faeces and excretory products.

  
• Dendron


  A nerve fibre that transmits impulses towards the cell body of a neurone.

  
• Desertification


  The destruction of land leading to desert-like conditions.

  
• Detoxification


  The process of converting harmful substances into harmless ones in the body.

  
• Differentiation


  The process by which a cell becomes specialized for a specific function.

  
• Diffusion

  The net movement of particles (atoms, ions or molecules) from a region of higher concentration to a region of lower concentration, that is, down a concentration gradient.

  
• Digestion


  The process by which large food molecules are broken down into small, soluble and diffusible molecules that can be absorbed by the body cells.

  
• Diploid


  Cells that contain the full number of chromosomes.

  
• Discontinuous variation


  Traits that show limited variation in their phenotypes which are easily distinguishable. It is usually controlled by only one or a few genes. It is not affected by the environment. E.g. detached earlobes-it's either yes or no.

  
• Dominant


  A form of a gene that is expressed and masks the recessive gene. It gives the same phenotype in both homozygous and heterozygous conditions as it expresses itself.

  
• Ecology


  The study of the relationships between living organisms and the natural environment.

  
• Ecosystem


  An ecological system formed by the interaction of living organisms (biotic) and their non-living (abiotic) environments.

  
• Egestion


  The removal of undigested matter from the body. Egestion would be like pooing-you're egesting faeces which are basically undigested food.

  
• Endocrine glands


  Ductless glands that secrete hormones into the bloodstream.

  
• Enzymes

  Biological catalysts made of protein. They alter the rate of (mostly catalyse) chemical reactions without themselves being chemically changed at the end of the reactions.

  
• Eutrophication


  The profuse growth and multiplication of algae and green plants as a result of the enrichment of nutrients in the water. Often leads to depletion of oxygen levels.

  
• Excretion


  The process by which metabolic waste products and toxic materials are removed from the body of an organism. E.g. sweating, sweat is a metabolic waste product.

  
• Fertilisation


  The process by which the male gamete fuses with the female gamete to form a zygote.

  
• Focusing/accommodation


  The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina.