- abscisic acid:plant growth substance that bringd about the dormanvy of seeds
- abortion:termination of pregnancy before the full term of pregnancy(280 days)
- acid rain:rain having a ph of betwwen 5 and 2.2 and which is formed when gases such as sulphur dioxide and nitrogen oxide dissolve in the atmosphere moisture
- accommodation:ability of the lens of the eye to alter its shapefor clear vision when viewing both near and distant objects
- acrosome:part of a sperm cell that contains enzymes which help digest the outer layer of the ovum during fertilisation
- acromegaly:disease caused by over secretion of the growth hormone in adults, characterised by lengthening of the bones of the hands, feet and chin
- adaptive radiation:change in characteristics of organisms of a population as they move into difference environments and became suited in different ways to the different environments
- adenine:one of four nitrogenous bases found in DNA and RNA; in DNA it always joins with thymine
- ADH:hormone that controls the amount of water absorbed by the kidneys and witch is therefore responsible for osmoregulation
- adrenal glands:gland situated on the kidney which produces the hormones adrenalin and aldosterone
- adrenalin:hormone that is secreted by the adrenalin gland during emergencies
- advantageous mutation:mutations that lead to new characteristics that are beneficial to the organism
- African apes:refers to gorillas, chimpanzees and the bonobos
- albinism:genetic disorder caused by lack of pigmntation due to mutation
- aldosterone:hormone that is produced by the adrenal gland and regulates salt concetration in the blood
- algal bloom:an increased growth of algae duw to sudden increase in the avaliability of nutrients due to eutrophication
- alien invasive species:a species thta is introduced into an area where it does not naturally occur ; usually outcompetes the natural species of that area
- alleles:alternate forms of a gene that control the same chararteristic but in different ways e.g a gene for height may have an allele for tallness and an allele for shortness
- allopatric speciation:formation of two or more species as a result of separation of the original species into different groups by a geographic barrier
- allantois:structure in a developing embryo normally used in gaseous exchange; non-functional in the foetus of humans
- alternation of generations:the alternation of a diploid, spore-producing phase with a haploid, gamete-producing phase
- altricial development:the development of the eggs of birds into young birds which are poorly-developed with their eyes closed; without down feathers; unable to move for themselves
- anaerobic respiration:respiration that takes-place in the absence of oxygen
- ancestor:a species that may have undergone change over a period of time to for new species
- amino acid:the monomers which serve as building blocks for the synthesis of proteins; made up of an amino group(NH2) and a carboxylic acid group
- amniocentesis:the process by which amniotic fluid, which contais cells of the embryo are drawn out of uterus and studies to see if theh unborn baby has any disorder
- amnion:the inner membrane of the embryo of birds, mammals and reptiles
- amniotic egg:an egg which has four membranes, namely amnion, chorion, allantois and yolk sac, together called extra embryonic membranes
- amniotic fluid:the fluid which lies inside the amniotic cavity; it protects the developing embryo
- ampullae:swellings at the base of the semi-circular canals of the ear within which the cistae (receptors for balance are found)
- analogous:similar structure that have come about by convergent evolution from different ancerstors e.g wings of an insert and that of a bird
- anaphase:phase in mitosis and meiosis during which chromatids or whole chromosomes are pulled to opposites poles
- aneuploidy:a mistake in the process of meiosis causing one gamete to receive two chromosomes, while the other gamete receives no chromosome because of non-disjunction od sister chromatids during anaphase 2 of meiosis
- anthropology:study of the natural history and development of humans from their very earily beginnings
- antibiotics:a drug formed from living organisms (usually bacteria and fungi)whichs stops or slows down the growth of disease causing microbes
- anticodon:sequence of three consective bases on tRNA which complement the bases on the codon found in mRNA
- aphrodisiac:substances that increase the sex drive
- aquatic:living in or around water
- aquifer:a wet underground layer of water-bearing, permeable rock or unconsolidated materials from which groundwater can be extracted using a borehole
- aqueous humour:fliud in the aqueous chaber of the eye that transports nutrients to the cornea and provides shape to the eye
- arboreal:living on trees
- archaeology:study of things that are very old
- artificail selection:the process by which animals or plants are selected and allowed to breed with other selected animals plants to produce characteristics that are desirable or useful to humans
- asteriod:small, airless rocky worlds that revolve around the sun and are too small to be called planets
- astigmatism:eye defect caused by an uneven corneal surface
- auditory canal:tube leading from the pinna to the tympanic memebrane in the human ear carrying sound waves
- autonomic nervous system:part of the nervous system which acts by double innervatition of the organs
- autosomes:all chromosomes besides the sex chromosomes
- autrophic:having the ability to manufacture it own food
- auxin:plant growth substances that may be considered to be hormones
- axon:part of neuron that carries impulses aways from the cell body.
- Binocular vision- the process of looking at an object with both eyes, gives rise to depth perception i.e stereoscopic vision.
- Bio-accumulation- the increase in concentration of substances in organisms as we progress from one trophic level to the next.
- Biogeography- the distribution of species in different parts of the world.
- Biological control- the use of the natural enemy of a pest to control the pest population.
- Biodiversity-the range of species and the number of organisms making up each species within communities.
- Biological evolution- the change that occurs in living organisms over a period of time due to changes in the environmental conditions.
- Bipedal- describes an organism that walks on two legs.
- Biotechnology- use of the latest advancements in technology to promote research and development in the life sciences.
- Bivalent- a pair of homologous chromosomes that come to lie next to each other during crossing over.
- Blastocyst- hollow sphere of cells that implants in the uterus wall and from which the embryo and extra embryonic membranes develop.
- Blind spot- area of the retina from which the optic nerve arises,contains no rods and cones and therefore not sensitive to light.
- Borehole- a hole drilled from the top of the surface of the soil until it reaches the permeable layer of rock saturated with water in order to extract the water.
- Brachiation- swinging from branch to branch with arms overhead.
- Brain haemorrhage- the rupture(breaking open) of a blood vessel in the brain.
- canines:sharp, pointed teeth that are well developed in carnivores for tearing meat
- carbon footprint:the total amount of carbon dioxide each person releases into the atmosphere each month from the use of various energy sources.
- carbon tax:a tax imposed on companies depending on the amount of carbon dioxide released
- cataract:a clouding that develops in the lens of the eye or in its envelope (lens capsule), obstructing the passage of light
- cell body:part of a neuron that contains the nucleus
- cell cycle:the series of events that occur during the life span of a cell
- cells of Leydig:cells in testes that secrete testosterone
- cellular respiration:process by which glucose is broken down in a stepwise fashion to release energy
- central nervous system:part of the nervous system made up of the brain and pinal cord
- centrioles:structure resulting from the splitting of the centrosome to form spindle threads division
- centromere:structure that holds two chromatids of a chromosome together after DNA replication
- centrosome:structure in an animal cell that forms spindle thread during cell divison
- cerebellum:part of the brain responsible for co-ordination of muscular movements, muscle tone and balance
- cerebrospinal fluid:fluid found in the cavities of the brain and spinal cord
- cerebrum:the region of the brain associated with judgement, intelligence, memory,interpretation of the sensations and co-ordination of voluntary actions
- cerumen:the wax that lines the auditory canal to prevent desiccation
- cervix:neck of the uterus just above the vagina
- chemotherapy:the use of various chemicals in combination with each other to either destroy the canal cells directly, or by destroying their DNA and preventing the cells from reproducing
- chiasma:the point at which the chromatids or homologous chromosomes cross-over during the first prophase of meiosis
- chorion:the outer membrane of the embryo,which together with uterine tissue of the mother, forms the placenta
- choriod:pigmented layer in the eye that absorbs lights, thus prevents the internal reflection of light
- chromatid:half a chromosome; the two halves are held together by a centromere; these two halves have actually been formed from one chromosome by DNA replication
- chromatin network:an entrangled mass of threads found in the nucleus of cells which are in the "resting stage"
- chromosome:string like structure found in the nucleus of dividing cells; formed from chromatin network contains the hereditary material DNA
- chromosomal aberation:a change in the normal number or structure of chromosomes in an individuals
- ciliary body:thickened circular rim of the choriod which contains ciliary muscles
- ciliary muscle:muscles found within the ciliary body; contraction and relaxation of the ciliary muscle alters the shape of the lens, thus bringing about accommodation
- clone:an organism or a group of organisms that are identical to the organism from which they were produced
- cloning:the process by which genetically identical individuals are formed
- cochlea:spirally colled portion of the inner ear responsilbe for the receptors of sound
- co-dominance:condition in which two alleles of a gene have equal expression in the phenotype of an organism
- codon:a sequence of the three consecutive bases found in DNA or mRNA onto which fit three complementary bases of tRNA during protein synthesis
- colour blindness:an inherited condition found mainly in males; a colour blind person cannot see certain colours.
- common ancestor:a common species that gave rise to two or more other species through evolution
- complementary base pairs:nitrogenous bases that always pair with each other and are joined by hydrogen bonds in a DNA molecule
- complementary strand:the new DNA strand that is developed during DNA replication according to the template strand of DNA, using free DNA nucleotides
- complete dominance:condition in which one allele of a gene is dominant over the other (recessive) such that only the dominant allele influences the phenotype in the heterozygous condition
- cones:receptor cells; sensitive to other colour, found in the retina of the eye
- conjunctiva:thin outer covering located in front of the cornea of the eye that helps to protect the eye
- connector neuron:neurons found within the grey matter of the spinal cord which carry impulses from the sensory neuron to the moter neuron
- continuous variation:variation in a characteristic among individuals of a popluation in which differences are slight and grade into each other e.g skin color
- conservation:the wise and cautious use of our resources so that they are available to current as well future generations
- contraception:methods which may be used to prevent fertilisation of the egg cell by the sperm cell
- contrasting:different phenotype expression of the same characteristic
- characteristics:different phenotype expressions for flower colour
- control:an additional set up used in scientific invesigation used to verify results
- convergent evolution:process by which similar structures have evolved independently from diferent ancestors
- co-ordination:linking of various system and activities within the body
- cord blood:blood found in the umbilical cord; it is a rich source of stem cells
- cornea:the transparent disc-like ortion of the sclera which allows light to enter the eye
- corpus callosum:a mass of white fibres which connect the right and left sides of the brain
- courtship behaviour:is the special behaviour that animals use to attract a mating partner when they are ready to breed
- cowper's gland:one of the glands of the male reproductive system of humans that produces a secretion that nourishes the sperm cells and assists in their movement
- cranial nerves:the twelve pairs of nerve that arise directly from the brain; it inclides the optic and auditory nerves
- cranium:part of the skull that contains and protects the brain
- creationism:theories that suggest that all life forms have been created by supreme being and that organisms have not changed since their creation
- cristae:receptors for balance found within the ampullae of the semi-circular canals
- crossing-over:a process that takes place in the first prophase of meiosis, involving the exchange of genetic material between members of each homologous pair of chromosomes
- cross-fertilistion:the fusin of male gametes from one individuals with the female gametes of another individual
- cross-pollination:transfers of pollen from the anther to the stigma of flowers of different plants of the same species
- culling:removal of an animal from flock due to inferior quality or of it is too old for breedig or if the population size exceeds the carrying capacity
- cytokinesis:division of the cytoplasm of cells which follows division of the nucleus during the final stages of mitosis and meiosis
- cytokinins:plant growth substances that simulates cell division
- cytosine:one of the four nitogenous bases found in DNA and RNA it always joins with guanine in DNA
- Decompose- The breakdown of dead plant and animal material by bacteria and fungi into simple nutrients.
- Decomposition- the process by which dead plant and animal material is broken down by bacteria and fungi into simple nutrients.