absorption: the movement of digested food molecules through the wall of the intestine into the blood or lymph.
accommodation: the change of shape of the lens, in order to focus on objects at different distances.
active site: the part of an enzyme molecule into which its substrate fits. active transport: the movement of ions in or out of a cell through the cell membrane, from a region of their lower concentration to a region of their higher concentration against a concentration gradient, using energy released during respiration.
adrenaline: a hormone secreted by the adrenal glands, which prepares the body for ‘flight or fight’.
aerobic respiration: the release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen.
allele: any of two or more alternative forms of a gene.
alveolus (plural: alveoli): an air sac in the lungs, where gas exchange occurs.
amino acids: molecules that can link together in long chains to form proteins; they contain carbon, hydrogen, oxygen and nitrogen, and sometimes sulfur.
amniotic fluid: secreted by the amnion, which supports and protects a developing fetus.
amylase: an enzyme which breaks down starch to maltose.
anaemia: an illness caused by a lack of haemoglobin.
anaerobic respiration: the release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen.
antagonistic muscles: muscles that work as a pair – for example, one may cause extension and the other flexing of a joint.
anther: the part of a stamen in which pollen is produced
antibiotic: a drug that kills bacteria in the human body, without damaging human cells.
antibodies: chemicals secreted by lymphocytes, which attach to antigens and help to destroy them
antigens: chemicals on the surfaces of pathogens, which are recognised as foreign by the body
artificial selection: the choice by a farmer or grower of only the ‘best’ parents to breed, generation after generation
asexual reproduction: the process resulting in the production of genetically identical off spring from one parent
assimilation: the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells
auxin: a plant hormone which causes cells to elongate
axon: a nerve fibre that conducts impulses away from the cell body
balanced diet: a diet containing some of each of the diff erent types of nutrients, in a suitable quantity and proportions
bile: a liquid made in the liver, stored in the gall bladder and emptied into the small intestine, where it helps to emulsify fats
bile salts: substances in bile that help to emulsify fats
biodegradable: able to be broken down (digested) by microorganisms
breathing: muscular movements which cause air to move into and out of the lungs
bronchioles the small tubes into which the bronchi branch
bronchus (plural: bronchi) one of the two tubes into which the trachea branches, carrying air into each lung
cancer a disease in which cells divide uncontrollably, producing lumps (tumours)
carbohydrase an enzyme that catalyses the breakdown of carbohydrates
carcinogen a substance which increases the risk of a person’s body developing cancer
cardiac muscle the muscle of which the heart is made
carnivore an animal that gets its energy by eating other animals carpel the female part of a fl ower
catalase an enzyme found in almost all living tissues, which catalyses the breakdown of hydrogen peroxide to water and oxygen catalyst a substance that speeds up a chemical reaction and is not changed by the reaction
cell sap a solution of sugars and other substances inside the vacuole of a plant cell
cell surface membrane a very thin layer of fat and protein that surrounds every living cell
cellulose a polysaccharide carbohydrate which forms fi bres and is found in the cell walls of plant cells
central nervous system the brain and spinal cord
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
chloroplast an organelle found in some plant cells, which contains chlorophyll and where photosynthesis takes place
chromosome a thread of DNA, made up of a string of genes
cilia tiny extensions on the surface of a cell, which can wave in unison and cause fl uids 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 eff ect on the phenotype
colon the first part of the large intestine, in which water and ions are absorbed
community all the organisms, of all the different species, living in an area at the same time
consumer an organism that gets its energy by 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
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, a 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
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
decomposer an organism that gest its energy from dead or waste organic matter
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
development an increase in complexity
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
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, water-soluble molecules using mechanical and chemical processes
diploid nucleus a nucleus containing two sets of chromosomes (e.g. in body cells)
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 a substance taken into the body that modifies or affects chemical reactions in the body
dry mass the mass of an organism after all water has been removed
ductless glands glands of the endocrine system, which secrete hormones directly into the blood
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 poikilothermic; 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 faeces, through the anus
egg a female gamete
embryo a young organism before birth, and before all the body organs have formed
emphysema a disease in which the walls of the alveoli in the lungs break down, reducing the surface area for gas exchange
emulsification breaking large globules of fat into tiny droplets, so that they mix easily with water
endocrine system the endocrine glands, which secrete hormones
endothermic homeothermic; able to regulate body temperature; the body temperature is independent of the temperature of the environment
environment all the living (biotic) and non-living (abiotic) factors an organism encounters during its life
enzymes proteins that function as biological catalysts
epidermis (mammal) the outer layer of the skin
epidermis (plant) a tissue made up of a single layer of cells which covers the top and bottom of a leaf, and the outside of the stem and root
epithelium a layer of cells covering a surface in an animal, e.g. the cells lining the trachea
euphoria a condition in which a person forgets all their worries and feels completely happy
excretion removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements
F1 generation the offspring from a parent homozygous for a dominant allele and a parent homozygous for the recessive allele
fermentation the breakdown of glucose by yeast, using anaerobic respiration; it produces carbon dioxide and alcohol
fertilisation the fusion of the nuclei of two gametes
fetus a young organism before birth, once all the body organs have formed
filament the stalk of a stamen
flaccid a term used to describe a cell that has lost a lot of water, becoming soft
follicle a space inside an ovary in which an egg develops
food chain a chart showing the flow of energy (food) from one organism to the next beginning with a producer (e.g. mahogany tree → caterpillar → song bird → hawk)
food web a network of interconnected food chains showing the energy flow through part of an ecosystem
fossil fuel a substance that can be combusted to release energy, formed millions of years ago from the partially decomposed and compressed bodies of organisms
fruit an ovary of a plant after fertilisation; it contains seeds
FSH follicle stimulating hormone; a hormone secreted by the pituitary gland which causes the development of eggs in the ovaries
fully permeable able to let most substances pass through
gametes sex cells, e.g. eggs and sperm
gas exchange the entry of oxygen into an organism’s body, and the loss of carbon dioxide
gene a length of DNA that is the unit of heredity and codes for a specific protein. A gene may be copied and passed on to the next generation
genetic diagram the conventional way to set out a genetic cross
genetic engineering taking a gene from one species and putting it into another species
genotype the genetic makeup of an organism in terms of the alleles present (e.g. Tt or GG)
geotropism a response in which a plant grows towards or away from gravity
glomerulus a tangle of blood capillaries in a Bowman’s capsule in the kidney
glucagon a hormone secreted by the pancreas, which increases blood glucose level
glycogen the polysaccharide that is used as an energy store in animal cells and fungi
goblet cells cells which secrete mucus
greenhouse effect the warming effect of carbon dioxide, methane and other greenhouse gases, on the Earth
growth a permanent increase in size and dry mass by an increase in cell number or cell size or both
guard cell one of two sausage-shaped cells in the epidermis in plants, between which there is a hole called a stoma; the guard cells can change shape to open and close the stoma
habitat the place where an organism lives
haploid nucleus a nucleus containing a single set of unpaired chromosomes (e.g. sperm and egg)
hepatic relating to the liver
herbivore an animal that gets its energy by eating plants
heterozygous having two different alleles of a gene (e.g. Tt or Gg), not pure-breeding
HIV/AIDS HIV is the human immunodeficiency virus, which causes AIDS
homeostasis the maintenance of a constant internal environment homeothermic endothermic; able to regulate body temperature; the body temperature is independent of the temperature of the environment
homologous chromosomes the two chromosomes of a pair in a diploid cell; they have genes for the same features at the same positions
homozygous having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding
hormone a chemical substance produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver
hypha (plural: hyphae) one of the long, thin threads of which the body of a fungus is made; each hypha is just one cell thick
immune: able to fight off a particular type of pathogen before it causes any symptoms in the body
implantation the movement of a young embryo into the lining of the uterus, and its attachment there infection the entry of a pathogen to the body
infectious disease a disease caused by a pathogen, which can be passed from one person to another
ingestion taking substances (e.g. food, drink) into the body through the mouth
inheritance the transmission of genetic information from generation to generation
inorganic a term used to describe substances that are not made by living organisms
insulin a hormone secreted by the pancreas, which reduces blood glucose level
intercostal muscles muscles between the ribs, which help to produce breathing movements
iris the coloured part of the eye, which controls the amount of light allowed through to the lens and retina
islets of Langerhans groups of cells in the pancreas which secrete insulin and glucagon
lactase an enzyme that breaks down the disaccharide lactose into glucose and galactose
lactation production of milk by mammary glands
LH luteinising hormone; a hormone secreted by the pituitary gland which causes an egg to be released from an ovary
lignin a tough, waterproof material that makes up the walls of xylem vessels; wood is mostly lignin
limiting factor something present in the environment in such short supply that it restricts life processes
lipase an enzyme that digests fats (lipids) to fatty acids and glycerol
lumen the space in the centre of a tube
lymph the fluid found inside lymph vessels, formed from tissue fluid
lymph nodes organs in which large numbers of white blood cells (which can destroy bacteria or toxins) collect
lymphocytes white blood cells that secrete antibodies
maltose a disaccharide produced by the digestion of starch
mechanical digestion the breakdown of large pieces of food to smaller ones, increasing their surface area; it is done by teeth in the mouth and by the contraction of muscles in the stomach wall
meiosis reduction division in which the chromosome number is halved from diploid to haploid
menstruation the loss of the uterus lining through the vagina
mesophyll the tissues in the centre of a leaf, where photosynthesis takes place
metabolic reactions the chemical reactions that take place inside a living organism
micropyle a tiny hole in the testa of a seed
mitosis nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosomes
monosaccharide a simple sugar; a carbohydrate whose molecules are made of one sugar unit
movement an action by an organism or part of an organism causing a change of position or place
mucus a viscous, sticky substance which is secreted in many parts of the body for lubrication or the removal of dust or bacteria
mutagen a substance that causes mutations mutation a change in a gene or a chromosome
mycelium the mass or network of hyphae that makes up the body of a fungus
myelin a fatty substance surrounding the axons of many neurones, enabling the nerve impulse to travel faster
natural selection the greater chance of passing on of genes by the best-adapted organisms
nectary a gland producing a sugary fluid, found in many insect- or bird-pollinated flowers
negative feedback a mechanism used in homeostasis, in which a change in a parameter brings about actions that push it back towards normal
nephron one of the thousands of tiny tubules in a kidney, in which urine is produced
nerve a bundle of axons or dendrons belonging to many different neurones
neurone a nerve cell; a cell specialised for the rapid transfer of electrical impulses
niche the role of an organism in an ecosystem
nitrifying bacteria bacteria that obtain their energy by converting ammonia or nitrite ions to nitrate ions
nitrogen-fixing able to change unreactive nitrogen gas into a more reactive nitrogen compound such as nitrates or ammonia
nitrogenous waste excretory products containing nitrogen – for example, ammonia, urea, uric acid
non-biodegradable not able to be broken down by microorganisms
nutrition the taking in of nutrients which are organic substances and mineral ions, containing raw materials or energy for growth and tissue repair, absorbing and assimilating them
oestrogen a hormone secreted by the ovaries that helps to control the menstrual cycle
omnivore an animal that eats food of both animal and plant origin
optimum temperature the temperature at which something happens most rapidly
organ a structure made up of a group of tissues, working together to perform specific functions
organ system a group of organs with related functions, working together to perform body functions
organelle a structure within a cell
organic a term used to describe substances that have been made by living organisms, or whose molecules contain carbon, hydrogen and oxygen organism a living thing
osmosis the diffusion of water molecules from a region of their higher concentration (dilute solution) to a region of their lower concentration (concentrated solution), through a partially permeable membrane
ovary an organ in which female gametes are made
oviduct the tube leading from an ovary to the uterus
ovulation the release of an egg from an ovary
ovule a structure in the ovary of a flower which contains a female gamete
oxygen debt the extra oxygen that must be taken in by the body following strenuous exercise, when anaerobic respiration took place; the oxygen is needed to break down the lactic acid that accumulated as a result of anaerobic respiration
oxygenated blood blood containing a lot of oxygen; in humans, blood becomes oxygenated in the lungs
palisade layer the upper mesophyll layer in a leaf, made up of rectangular cells containing many chloroplasts
pancreas an organ lying close to the stomach, which is both an endocrine gland (producing insulin and glucagon) and an exocrine gland (producing pancreatic juice)
pancreatic juice the liquid secreted into the pancreatic duct by the pancreas; it flows into the duodenum where its enzymes help with digestion of fats, proteins and carbohydrates
particulates tiny pieces of carbon and other substances found in smoke, which can irritate the lungs
pathogen a microorganism that causes disease
penicillin an antibiotic which destroys bacteria by damaging their cell walls
pepsin a protease enzyme found in the stomach
peristalsis rhythmic contractions of muscles that ripple along a tube – for example, peristalsis pushes food through the alimentary canal
petiole a leaf stalk
phagocytes white blood cells that surround, engulf and digest pathogens
phenotype the physical or other features of an organism due to both its genotype and its environment (e.g. tall plant or green seed)
phloem tubes long tubes made up of living cells with perforated end walls, which transport sucrose and other substances in plants
photosynthesis the fundamental process by which plants manufacture carbohydrates from raw materials using energy from light
phototropism a response in which a plant grows towards or away from the direction from which light is coming
pigment a coloured substance – for example, chlorophyll, haemoglobin
placenta in mammals, an organ made up of tissues of both the mother and embryo, through which the mother’s and embryo’s bodies exchange nutrients and waste materials
plasma the liquid part of blood, in which the cells float
plasmolysed the condition of a plant cell that has lost so much water that its cytoplasm shrinks and pulls the cell membrane away from the cell wall
platelets tiny fragments of cells found in blood, which help with clotting
pleural membranes two strong, slippery membranes which surround the lungs
plumule the young shoot in an embryo plant
poikilothermic ectothermic; unable to regulate body temperature physiologically; the organism’s temperature varies with that of its environment
pollen grains tough, resistant structures containing the male gametes of a flower
pollination the transfer of pollen from the male part of the flower (anther of stamen) to the female part of the plant (stigma)
polysaccharide a carbohydrate whose molecules are made of hundreds of sugar units linked in long chains – for example, starch, glycogen and cellulose
population a group of organisms of one species, living in the same area at the same time
predator an animal that kills and eats other animals
primary consumers herbivores producer an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
progesterone the pregnancy hormone; a hormone secreted by the ovaries and placenta which maintains the lining of the uterus
prostate gland a gland close to a male’s bladder, that secretes fluid in which sperm can swim
protease an enzyme that catalyses the breakdown of proteins protein a substance whose molecules are made of long chains of amino acids; proteins contain carbon, hydrogen, oxygen and nitrogen, and sometimes sulfur
puberty the stage of development during which sexual maturity is reached
pulmonary relating to the lungs
pure-breeding homozygous
pyramid of biomass a sideways-on graph, in which the size of the boxes represents the dry mass of organisms in each trophic level of a food chain
pyramid of numbers a sideways-on graph, in which the size of the boxes represents the number of organisms in each trophic level of a food chain
radicle the young root in an embryo plant
receptor a cell that is able to detect changes in the environment; often part of a sense organ
recessive an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g)
reflex action a fast, automatic response to a stimulus
reflex arc the arrangement of neurones along which an impulse passes during a reflex action
relay neurone a neurone in the central nervous system which passes an impulse between a sensory neurone and a motor neurone
renal relating to the kidneys
renal capsule the cup-shaped structure at the start of a nephron, where filtration occurs
reproduction the processes that make more of the same kind of organism
respiration the chemical reactions that break down nutrient molecules in living cells to release energy
retina the part of the eye that contains receptor cells
rickets a disease caused by a lack of vitamin D or calcium, in which bones are not as hard as they should be and can grow in a bent shape
root cap a tough, protective covering over the tip of a root
sebaceous gland an oil-producing gland in the skin
secondary consumers carnivores that eat herbivores
secondary sexual characteristics features of the body that develop at puberty, as a result of the increased secretion of sex hormones
seed an ovule after fertilisation; it contains an embryo plant
selection pressure an environmental factor that causes organisms with certain characteristics to have a better chance of survival than others
self-pollination the transfer of pollen from the anther to the stigma on the same plant (but not necessarily the same flower)
semen a mixture of sperm and fluids from the prostate gland and seminal vesicles seminal vesicles glands that secrete fluid in which sperm can swim
sense organs groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals
sensitivity the ability to detect or sense changes in the environment (stimuli) and to make responses
sexual reproduction the process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring
sickle cell anaemia a condition caused by a codominant allele of the gene that codes for haemoglobin, in which a person has two copies of the gene and suffers serious health problems
simple sugar a monosaccharide; a carbohydrate whose molecules are made of one sugar unit
species a group of organisms with similar characteristics, which can interbreed with each other to produce fertile offspring
sperm a male gamete
sphincter muscle a muscle surrounding a tube, which can contract to close the tube
spongy layer the tissue beneath the palisade layer in a leaf; it is made up of cells that contain chloroplasts and can photosynthesise, with many air spaces between them
stamen the male parts of a flower
starch the polysaccharide that is used as an energy store in plant cells
stem tuber a swollen part of a stem, which stores food
stigma the part of a flower that receives pollen
stimulant a drug that makes the nervous system work faster
stimulus a change in an organism’s surroundings that can be detected by its sense organs
stoma (plural: stomata) a gap between two guard cells, usually in the epidermis on the lower surface of a leaf
stroke damage caused to the brain by an interruption in blood supply, caused either by a blood vessel bursting or a blood vessel becoming blocked by a blood clot
style the connection between the stigma and ovary of a flower
substrate the substance on which an enzyme acts
succulent a plant with swollen stems or leaves, in which water is stored
sucrase a carbohydrase found in the small intestine, which breaks down sucrose to glucose and fructose
sucrose a disaccharide, non-reducing sugar, made of a glucose molecule and a fructose molecule linked together; the form in which carbohydrates are transported in the phloem of plants
suspensory ligaments a ring of ligaments linking the ciliary muscles to the lens
systole the stage of a heart beat in which the muscles in the walls of the heart chambers contract
target organ an organ that is affected by a hormone
tertiary consumers organisms that feed at the fourth stage in a food chain; they eat carnivores
test cross breeding an offspring with the dominant phenotype with an organism with the recessive phenotype; the offspring of the cross can help to determine the genotype of the parent with the dominant phenotype
testa the tough waterproof covering of a seed
testis (plural: testes) an organ in which sperm are made
testosterone a hormone secreted by the testes, which causes male characteristics
tissue a group of cells with similar structures, working together to perform specific functions
tissue fluid the fluid that surrounds all the cells in the body, formed from blood plasma that leaks out of capillaries
trachea the tube that carries air from the nose and mouth down to the lungs
translocation the movement of sucrose and amino acids in phloem, from regions of production to regions of storage, or to regions of utilisation in respiration or growth
transpiration evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata
transpiration stream the pathway of water from the root hairs of a plant, up the root and stem and out of the leaves into the atmosphere
triceps muscle a muscle in the upper arm which causes the arm to straighten when it contracts
trophic level the position of an organism in a food chain, food web or pyramid of biomass, numbers or energy
tropism a plant growth response to a stimulus, in which the direction of growth is related to the direction of the stimulus
trypsin a protease enzyme found in pancreatic juice
turgid cell a plant cell that has absorbed water and has cytoplasm that is pressing outwards on the cell wall
umbilical cord an organ linking an embryo to the placenta, containing blood vessels
urea the main nitrogenous excretory product of mammals, produced in the liver from excess amino acids
ureter a tube that leads from a kidney to the bladder
urethra a tube that leads from the bladder to the outside
urine a solution of urea and other excretory products in water, produced by the kidneys
uterus the organ in a mammal in which the embryo develops
vaccination the introduction to the body of dead or weakened pathogens, to make a person immune to an infectious disease
vascular bundle a vein in a plant, containing xylem vessels and phloem tubes
vasoconstriction narrowing of blood vessels
vasodilation widening of blood vessels
villus (plural: villi) a tiny, finger-like process on the inner wall of the small intestine; villi increase the surface area for digestion and absorption
water potential gradient a difference in the concentration of water molecules; a dilute solution has a high water potential, and water tends to move from this, down a water potential gradient, into a concentrated solution
xerophyte a plant adapted to live in dry conditions
xylem vessels long hollow tubes made up of dead, empty cells with lignified walls, which transport water in plants and help to support them
zygote the diploid cell produced when two gametes fuse
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