351 terms

Biology key terms

For IGCSE students. Also a good reference for IB DP students
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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
AIDS
acquired immune deficiency syndrome; a disease caused by an HIV infection which causes white blood cells numbers to reduce to such a degree that secondary infections become life threatening
alimentary canal
the tube of the digestive system through which food passes
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
amnion
a sac (which surrounds the foetus and holds the amniotic fluid.
amniotic fluid
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
animals
multicellular organisms which do not possess cell walls, they are motile, heterotrophs
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
anus
the opening at the end of the alimentary canal (surrounded by sphincter muscle) through which faeces are egested
artificial selection
the choice by a farmer or grower of only the 'best' parents to breed, generation aft er 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 fi bre that conducts impulses away from the cell body
bacteria
single-celled organisms many are harmless or beneficial, some are pathogens, e.g. Streptococcus with causes sore throats, they have cell walls, but lack organelles such as a nucleus (DNA/RNA is stored in the cytoplasm), they reproduce by fission
balanced diet
a diet containing some of each of the diff erent types of nutrients, in a suitable quantity and proportions
biceps muscle
a muscle in the upper arm which causes the arm to bend when it contracts
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
carbohydrates
starches and sugars
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 flower
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 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 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
competition
an interaction between organisms that occurs when both need the same resource which is in short supply
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
duodenum
the upper region of the small intestine, mainly concerned with the digestion of large insoluble nutrients
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
exhale
to breathe out
extensor muscle
a muscle that causes a limb to straighten when it contracts
F1 generation
the offspring from a P1 generation, usually the parents are homozygous for a dominant allele and a parent homozygous for the recessive allele
faeces
waste matter made from undigested food
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
flexor muscle
a muscle that causes a limb to bend when it contracts
follicle
a structure 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 membrane
a membrane able to let most substances pass through
fungi
organisms that reproduce by spores or budding, and live as saprotrophs or parasites, examples include moulds, yeasts, and mushrooms, they possess cell walls made from chitin
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. It 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
global warming
a theory that the greenhouse effect is being accelerated by the activities of humans causing a overal rise in global temperatures
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 in the epithelium (e.g. in the trachea) 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
is the human immunodeficiency virus, which causes AIDS
homeostasis
the maintenance of an internal environment within normal limits
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)
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 broken down 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
ileum
the lower region of the small intestine, mainly concerned with the absoption of nutrients
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
inhale
to breathe in
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
lactose
disaccharide made from the simple sugars/monosaccharides glucose and galactose
large intestine
the lower region of the intestine where final absorption water occurs
LH
luteinising hormone; a hormone secreted by the pituitary gland which causes an egg to be released from an ovary
ligament
a strong, stretchy cord that joins two bones together at a synovial joint
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 metabolic reactions
lipase
an enzyme that digests fats (lipids) to fatty acids and glycerol
lumen
the space in the centre of a tube, e.g. the space in a blood vessel through which blood flows
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
nuclear division in which the chromosome number is halved from diploid to haploid, this process is used to create gametes in humans
menstruation
the loss of the uterus lining through the vagina
meristem
undifferentiated plant tissue found directly behind the shoot and root tips from which new cells are formed by cell division (and mitosis)
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
microbe
abbreviation of the term microorganism
micropyle
a tiny hole in either the ovule through which pollen can enter to fertilise the egg cell or the testa of a seed through which water can enter to start germination
mitosis
nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosomes, this process supports growth in multicellular organisms
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 sheath
the insulating substance (secreted by Schwann cells) surrounding the axons of many neurones
natural selection
the process by which the best adapted organisms are more likely to reproduce and and pass on their genes
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 bacteria
bacteria 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
the point 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 selectively 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
P1 generation
the parental generation, usually consisting of one parent homozygous for a dominant allele and a parent homozygous for the recessive allele
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 (the upper region of the small intestine) where its enzymes help with digestion of fats, proteins and carbohydrates
partially/selectively/semi permeable membrane
a membrane able to let some substances pass through, but not all
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
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
Plants
multicellular organisms which possess cellulose cell walls, they are not motile, they obtain energy by photosynthesis
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
strong, slippery membranes which surround each lung
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, organisms that consume producers
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 and neutralises the acids present in the vagina
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
protoctists
unicellular organisms considered separate from fungi, plants and animals, but which have features shared with the animal plant kingdoms
puberty
the stage of development when secondary sexual characteristics arise and 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 energy
a sideways-on graph, in which the size of the boxes represents the energy contained in organisms at 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
recessive
an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g)
rectum
the final region of the large intestine which stores faeces before egestion
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 ultrafiltration 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 (photo) 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
root tuber
a swollen part of a root which stores food, e.g. carrot
saprotrophs
an organism that feeds on dead or dying organic matter, typically by excreting enzymes and absorbing the digested nutrients
secondary consumers
carnivores that eat herbivores/primary consumers
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 embryonic plant
selection pressure
an environmental factor that causes organisms with certain characteristics to have a better chance of survival than others
selectively/semi/partially permeable membrane
a membrane able to let some substances pass through, but not all
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
semi/partially/selectively permeable membrane
a membrane able to let some substances pass through, but not all
seminal vesicles
glands that secrete fructose to provide the sperm with an energy source ad fluids 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
sensory
receptor a cell that is able to detect changes in the environment; often part of a sense organ
sexual reproduction
the process involving the fusion of haploid nuclei usually from two different organisms) 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
small intestine
the upper region of the intestine where most chemical digestion and absorption of nutrients and water occurs
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 to aid gas exchange
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, e.g. potato
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
stomach
a muscular sac which holds undigested food and secretes hydrochloric acid (to kill pathogens) and a protease called pepsin (to chemically digest proteins)
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
synovial joint
a joint at which the two bones can move freely
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
tendons
strong, inelastic cords of tissue, which attach muscles to bones; they are also found in the heart, where they attach the atrioventricular valves to the wall of the ventricle
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
ventilation
the movement of air in and out of the lungs
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
viruses
parasites consisting of a DNA/RNA core surrounded by a protein coat, not considered to be living
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
nutrients
components in foods that an organism uses to survive and grow (includes carbohydrates, lipids, proteins, vitamins and minerals)
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