definitions - set 7 Flashcards
sex-linked gene
a gene found on the X chromosome but not on the Y chromosome
sexually-transmitted infection
an infection that is transmitted via bodily fluids through sexual contact
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
sink
a place to which substrates are transported in phloem
solvent
a liquid in which another substance is dissolved
source
a place from which substances are transported in phloem
species
a group of organisms with similar characteristics, which can interbreed with each other to produce fertile offspring
species diversity
the number of different species living in a habitat
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 photosynthesize, 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
stationary phase
a stage when the numbers in a population remain approximately constant
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
style
the connection between the stigma and ovary of a flower
substrate
the substance on which an enzyme acts
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
sustainable resource
one which can be removed form the environment without it running out
sustainable development
providing for the needs of an increasing human population without harming the environment
synapse
a point at which an impulse can be passed from one neurone to another
synaptic cleft
a tiny gap between two neurones
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
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
testis (plural: testes)
an organ in which sperm is made
testosterone
a hormone secreted by the testes, which causes male characteristics
tissue
a group of cells with similar structures, working together to perform a shared function
tissue fluid
the fluid that surrounds all the cells in the body, formed from blood plasma that leaks out of capillaries
toxin
a poisonous substance
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
transmissible disease
a disease caused by a pathogen that can be passed from one person to another
transmitter substance
a chemical that carries a nerve impulse across a synapse
transpiration
evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, though the stomata
transpiration stream
the pathway of water from the root hair of a plant, up the root and stem and out of the leaves into the atmosphere
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
a term used to describe a plant cell that has absorbed water ad ha cytoplasm that is pressing outwards on the cell wall
type 1 diabetes
a condition in which the pancreas is unable to make insulin
