definitions - set 2 Flashcards
cellulose
a polysaccharide carbohydrate which forms fibres and is found in the cell walls of plant cells
central nervous system
the brain and spinal chord
chemical digestion
the breakdown of large molecules of food into smaller ones, done by enzymes
chlorophyll
a green, light-absorbing pigment found inside chloroplasts in plant cells
chloroplasts
an organlelle found in some plant cells, which contains chlorophyll and where photosynthesis takes place
chromosome
a thread-like structure of DNA, made up of a string of genes
cholera
a disease caused by a waterborne nacterium. which causes severe diarrhoea
chyme
the partly-digested food, that moves from the stomach into the small intestine
cilia
tiny extentions on the surface of a cell, which can wave in unison and cause fluids to move
ciliary muscle
a ring of muscle around the lens, which can change its shape
cirrhosis
a disease of the liver in which the cells are permanently damaged
clone
a group of genetically identical organisms
codominance
a situation in which both alleles in a heterozygote have an effect on the phenotype
common ancestor
a species that lived long ago that is thought to be a distant ancestor of two or more species living today
community
all the organisms, of all the different species, living in an area at the same time
cone cell
a light-sensitive cell in the retina, which responds to light of a particular color
consumer
an organism that getsits energy from feeding on other organisms
continuous variation
differences in the features of a group of organisms in which there are no definite categories; each individual’s features can lie anywhere between two extremes
coronary heart disease
a condition in which the coronary arteries become partly blocked
corpus luteum
the structure that forms in an ovary after an egg has been released; it secretes progesterone
cortex
in a kidney, the outer layer; in a plant stem or root, aa tissue made of typical plant cells (usually, however, without chloroplasts)
cotyledons
food storage structures in a seed, which sometimes come above ground during germination and begin to photosynthesise
cross-pollination
the transfer of pollen from the anther of one plant to the stigma of another plant of the same species
cuticle
a layer of wax on a leaf
cytoplasm
jelly-like material that is found in cells
deamination
a metabolic reaction that takes place in the liver, in which the nitrogen-containing part of amino acids is removed to form urea, followed by the release of energy from the remainder of the amino acid
death phase
a stage where the number in a population falls rapidly towards zero
decomposer
an organism that gets its energy from dead or waste organic matter
deforestation
the destruction of large areas of forest
denatured
an enzyme is said to be denatured when its molecule has changed shape so much that the substrate can no longer fit into it
denitrifying bacteria
bacteria that obtain their energy by converting nitrate ions into nitrogen gas
deoxygenated blood
blood containing only a little oxygen
depressant
a drug that inhibits the nervous system and slows it down
dialysis
exchange of substances between two solutions through a partially permeable membrane; dialysis machines are used in the treatment of people with kidney failure
diastole
the stage of a heart beat in which the muscles in the heart relax
dichotomous
branching into two
diffusion
the net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement
digestion
the break-down of large, insoluble food molecules into small molecules using mechanical and chemical processes
diploid
having two sets of chromosmoes
disaccharide
a complex sugar; a carbohydrate whose molecules are made of two sugar units
discontinuous variation
differences in the features of a group of organisms where each fits into one of a few clearly defined categories
DNA
the chemical from which genes and chromosomes are made
dominant
an allele that is expressed if it is present (e.g. T or G)
dormant
a condition in which an organism shuts its metabolism down, so that it can survive in adverse conditions
double circulatory system
a system in which blood passes twice through the heart on one complete circuit of the body
drug
any substance taken into the body that modifies or affects chemical reactions in the body
ecosystem
a unit containing all of the organisms and their environment, interacting together, in a given area
e.g. decomposing log or a lake
ectothermic
unable to regulate body temperature physiologically; the organism’s temperature varies with that of its environment
effector
a part of the body that responds to a stimulus, e.g. a muscle or a gland
egestion
the passing out of food that has not been digested, as feaces, through the anus
