Gce O-Level Biology Definitions

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Biology

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The science of life. It involves the study of living things and the theories that describe the world of life.

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Adaptation

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

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Tissue

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A group of cells with similar structures which work together to perform a specific function. There are two types of tissues: simple tissue and complex tissue.

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Concentration gradient

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The net movement of particles (ions or

molecules) from a region of a higher

concentration to a region of of lower

concentration, down a concentration gradient.

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Osmosis

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The net movement of water molecules from a solution of higher water potential to a solution of lower water potential, through a partially

permeable membrane.

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Active transport

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The process in which energy is used to move the particles of a substance across a membrane against its concentration gradient, from a region of lower concentration to a region of higher

concentration.

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Hydrolysis

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A reaction in which a water molecule is needed to break up a complex molecule into smaller molecules.

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Carbohydrates

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Organic molecules made up of the elements

carbon, hydrogen and oxygen. The hydrogen and oxygen atoms are present in the ratio 2:1.

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Fats

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Organic molecules made up of the elements carbon, hydrogen and oxygen. But unlike carbohydrates, fats contain much less oxygen in proportion to hydrogen.

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Proteins

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Organic molecules made up of the elements carbon, hydrogen and nitrogen. Another

element, sulphur, may also be present.

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Catalyst

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A substance that can alter or speed up a

chemical reaction, without itself being chemical changes at the end of the reaction.

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Enzymes

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Proteins that function as biological catalysts. They can alter or speed up a chemical reaction, and being chemical changes at the end of the reaction.

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Denaturation

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The change in the three-dimensional structure of an enzyme or any other soluble protein, caused by heat or chemicals such as acids or alkalis.

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Nutrition

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The process by which organisms obtain food and energy for growth, repair and maintenance of the body.

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Peristalsis

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The rhythmic, wave-like muscular contractions in the wall of the alimentary canal.

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Digestion

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The process whereby large food molecules are broken down into smaller, soluble molecules that can be absorbed into the body cells.

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Absorption

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The process whereby digested food substances are absorbed into the body cells.

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Assimilation

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The process whereby some of the absorbed food substances are converted into new

protoplasm or used to provide energy.

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Deamination

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The process by which amino groups are

removed for amino acids and converted to urea.

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Photosynthesis

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The process in which light energy absorbed by chlorophyll is transformed into chemical energy. The chemical energy is used to synthesise

carbohydrates from water and carbon dioxide. Water and carbon dioxide are the raw materials for photosynthesis. Oxygen is released during the process.

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Phagocytosis

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The process of engulfing or ingesting foreign particles such as bacteria, by the white blood cells.

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Transpiration

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The loss of water vapour from a plant, mainly through the stomata of the leaves.

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Respiration

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The breakdown (oxidation) of food substances (molecules) with the release of energy in living cells.

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Aerobic respiration

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The breakdown of food substances (molecules) in the presence of oxygen with the release of a large amount of energy. Carbon dioxide and

water are released as waste products.

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Anaerobic respiration

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The breakdown of food substances (molecules) in the absence of oxygen. Anaerobic respiration releases less energy than aerobic respiration.

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Gas exchange

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The exchange of gases between an organism and the environment.

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Excretion

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The process by which metabolic waste products and toxic substances are removed from the body of an organism.

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Osmoregulation

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The control of water and solute concentrations (levels) in the blood to maintain a constant water potential in the body.

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Homeostasis

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The maintenance of a constant internal

environment.

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Reflex action

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An immediate response to a specific stimulus without conscious control.

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Focusing

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

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Hormone

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A chemical substance produces in minute

quantities by an endocrine gland. It is

transported in the bloodstream to target

organ(s) where it exerts its effect(s). After

hormones have performed their functions, they are eventually destroyed by the liver.

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Mitosis

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A form of nuclear division that produces

daughter nuclei containing the same number of chromosomes as the parent nucleus. The

daughter nuclei are genetically identical.

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Meiosis

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A form of nuclear division that produce daughter nuclei containing half the number of chromosomes as the parent nucleus.

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Asexual reproduction

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The process resulting in the production of

genetically identical offspring from one parent, without the fusion of gametes.

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Sexual reproduction

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A process involving the fusion of two gametes to form a zygote. It produces genetically dissimilar offspring.

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Pollination

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The transfer of pollen grain from the anther to the stigma.

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Self-pollination

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The transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the the same plant.

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Cross-pollination

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

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Puberty

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The stage of human growth and development in which a person becomes physically mature.

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Monohybrid inheritance

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An inheritance involving only one pair of contrasting traits.

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Chromosome

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A rod-like structure visible in the nucleus during cell division. It is made up of the molecule deoxyribonucleic acid (DNA)

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Gene

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A unit of inheritance, born on a particular locus (position) of a chromosome. It is a small

segment of DNA in a chromosome that controls a particular characteristic or protein in an

organism.

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Allele

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Different forms of the same gene. They occupy the same relative position on a pair of

homologous chromosomes.

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Phenotype

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The expressed train in an organism, for example, the outward appearance of an organism.

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Genotype

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The genetic make-up (pairs of alleles) of an organism, that is, the combination of genes in an organism.

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Multiple alleles

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A term used for a gene that exists in more than two alleles.

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Mutation

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A sudden random change in the structure of a gene or in the chromosome number.

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Genetic engineering

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A technique used to transfer genes from one organism to another. Individual genes may be cut off from the cells of one organism and inserted into the cells of another organism of the same or different species. The transferred gene express itself in the recipient organism.

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Habitat

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The place where an organism lives.

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Population

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A group of organisms of the same species that live together in a habitat.

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Community

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All the population living and interacting with one another in habitat.

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Ecosystem

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A community of organisms interacting with one another and with its abiotic environment.

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Food chain

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A series of organisms through which energy is transferred in the form of food.

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Food web

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Interlinked food chains.

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Carbon sink

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An area that store carbon compounds for an indefinite period. It store more carbon than it

releases.

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Pollution

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The addition of a substance to the environment that damage it, making it undesirable or unfit for life. Substances that cause pollution are called pollutants.

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Eutrophication

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The process where water receives excess

nutrients like phosphates and nitrates, which causes excessive growth of algae and water plants.

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Bioaccumulation

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The process where certain chemicals like

insecticides are not excreted, but are accumulated in the bodies of organisms.

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Bioamplification

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The process where accumulated chemicals are passed along the food chain, increasing its

concentration in the bodies of organisms along the trophic levels.

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Biodiversity

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The range of species that are present in a

particular ecosystem.

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Conservation

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The protection and preservation of natural resources in the environment.