revision
what takes blood to the heart
coronary arteries
function of insulin
lowers blood sugar and converts excess glucose into glycogen
features of villi
large network of capillaries
epithelical layer is only one cell thick (fast diffusion)
large surface area
order of neurons
sensory -> inter -> motor
functions of neurons
sensory - carry signals from receptor to cns
inter - process info from sensory and pass it onto the motor
neuron
motor - carries impulses from cns to an effector (muscle/gland) => response
specialised cell
red blood cell- biconcave shape increases surface area for more oxygen uptake
what is fertilisation
fertilisation is the fusion of the nuclei of the two haploid gametes to produce a diploid zygote which divides to form an embryo
how many chromosomes does an egg cell have
23
where are animal gametes produced
sperm- testis
egg- ovary
where is the plant gametes produced
pollen- anther
ova- ovary
what is haploid
haploid is a cell with only one set of chromosomes
what is diploid
diploid is a cell with two sets of chromosomes
what is an allele
an allele is different versions of the same gene
what is continuous variation
continuous variation is when there is a range of values between a maximum and a minimum (i.e. height)
what is discrete variation
discrete variation is when you can put seperate individuals into distinct groups (i.e. eye colour)
what does xylem transport
xylem transports water and minerals
what does phloem transport
phloem transports sugar
what direction does xylem travel
xylem travels upwards
what direction does phloem transport
phloem transports up and down
structure of xylem
it has lignified cells to withstand the pressure changes from water
structure of phloem
cells have seive plates and associated companion cells