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.

Food chain

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

Food web

Two or more food chains interlinked together.

Gamete

A reproductive cell containing the haploid number of chromosomes.

Gene

A hereditary factor found on a particular locus in a chromosome. It controls a particular characteristic and codes for a specific protein.

Genetic engineering

A technique used to transfer genes from one organism to another.

Genotype

The combination of genes in an individual.

Gland

A cell, tissue or an organ that secretes chemical substances.

Habitat

The place where an organism lives.

Haploid

Cells that contain half the number of chromosomes as the parent cells which produced them.

Heterozygous

A condition where you have different alleles for a particular trait. E.g. if B codes for brown eyes (dominant allele is always upper case) and the recessive allele is b (always the lower case of the dominant alleles' letter), then a person with a Bb genotype for eye colour is heterozygous dominant, so will have brown eyes.

Homeostasis

The maintenance of a constant internal environment.

Homologous pairs

Chromosomes which have the same genes, shape and length.

Homozygous

Having identical alleles for a particular trait. E.g. BB-homozygous dominant, or bb-homozygous recessive.

Hormone

A chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organ(s) where it exerts its effects

Irritability/sensitivity

The ability of an organism to respond to a stimulus.

Meiosis

A form of cell division such that the daughter cells contain half the number of chromosomes as the parent cell. -will be haploid, e.g. to form sex cells/gametes (Chromosomes are in the nucleus.)

Mitosis

Cell division such that the daughter cell produced contains the same number of chromosomes as the parent cell. -will be diploid, e.g. to form somatic (body) cells

Mutation

The sudden or spontaneous change in gene structure or a chromosome, or even the chromosome number, and may be inheritable.

Nerve

A collection of nerve fibres.

Nerve fibre

A long cytoplasmic extension of the cell body of a neurone. It serves to transmit impulses.

Neurone

A nerve cell.

Nutrition

The intake of food and the processes that convert food substances into living matter.

Osmoregulation

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

Osmosis

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, i.e. down a water potential gradient. Or, from a region of high concentration to a region of low concentration, through a partially permeable membrane, i.e. down a concentration gradient.

Oxygen debt

The amount of oxygen required to oxidize the lactic acid produced in muscles during anaerobic respiration and convert it into harmless substances.

Partially/selectively permeable membrane

A membrane that allows selected substances to pass through.

Peristalsis

The rhythmic wave-like contractions of the walls of the gut.

Phagocytosis

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

Phenotype

The physically expressed trait in an individual, e.g. outward appearances such as height and eye colour.

Photosynthesis

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

Pollination

The transfer of pollen grains from an anther to a stigma.

Pollution

The addition of substances to the environment that damage it, making it unfit for life.

Population

A group of organisms of the same species living together in the same habitat.

Producers

Organisms which convert energy from the sun, or light energy, into chemical energy and store it as food during photosynthesis. They are the start of the food chain.

Recessive

A form of a gene that expresses itself only in the homozygous condition. E.g. Bb, it won't be expressed because the dominant 'B' allele masks it and is expressed instead. But in 'bb', this is homozygous recessive, so it will be expressed.

Reducing sugars

Sugars that produce a red precipitate when boiled with Benedict's solution. E.g. glucose, maltose, fructose, lactose.

Reflex action

An immediate response to a specific stimulus without conscious control.

Reflex arc

The shortest pathway by which impulses travel from the receptor to the effector in a reflex action.

Respiration

The oxidation of food substances with the release of energy in living cells.

Self-pollination

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

Sexual reproduction

The process involving the fusion of two gametes to form a zygote, resulting in the production of genetically dissimilar offspring-as in there will be variation.

Species

A group of similar organisms. Organisms within a species can breed. They produce healthy offspring that are able to grow, develop and reproduce normally.

Synapse

A junction between two neurones.

Tissue

A group of similar cells which work together to perform a specific function.

Tissue respiration

The process in living cells by which food substances are oxidized with energy released for the vital activities of the cells. Basically: C6H12O6 + 6O2 à 6CO2 + 6H2O + energy (ATP)

Translocation

The transport of manufactured food substances such as sugar and amino acids in plants (in phloem.)

Transpiration

The loss of water vapour from aerial parts of a plant, especially through the stomata of the leaves.

Transpirational pull

The suction force caused by transpiration that is the main factor causing water movement up the xylem.

Turgor pressure

The pressure exerted outwards on the cell wall due to the water in the cell-hence the cell becomes turgid.

Variation

The differences that can be observed within a species.

Veins

Blood vessels which carry blood towards the heart.

Voluntary action

An action that is under the control of the will, requires thinking so it's obviously slower than involuntary/reflex actions.