5.1.5 Plant Responses Flashcards
(51 cards)
define cell signalling
communication and coordiantion between cells to trigger a reaction in the cell
why do plants need to respond to their environment
to avoid abiotic stress- cold, heat, dryness and humidity
to maximise photosynthesis by obtaining more light and water
to avoid herbivory
what are the roles of auxins
control cell elongation, involved in tropisms and stimulate the release of ethene
what are the roles of gibberellins
cause stem elongation
what are the role of ethene
causes fruit ripening, promotes senescence
what is the role of ABA
stimulates stomatal closing
name 3 similarities between plant hormones and hormones in mammals
- hormones bind to receptors which cause enzyme reaction inside cells
- act on several target tissues
- may involve in switching genes on and off
name 3 differences between plant and mammals hormones
plants- produced by many tissues
animals- produced by endocrine tissues
p- move in xylem and phloem
a- move in bloodstream
p-act on most tissues
a- act on specific target tissues only
what is the food store in a
dicot
monocot
2x cotyledons
endosperm
explain the process of seed germination
1) seeds absorb water
2) water activates the embryo to start making the gibberelin
3) gibberelin activates genes to make protease, converts protein into amino acids, this is converted into amylase which converts starch into maltose, maltose is converted into maltase which converts maltose into glucose
4) these are used to respire and produce atp for building roots and shoots
what are the two pieces of evidence which shows that gibberelins are responsible
1:
plant species without the gene to make protease do not germinate
2:
if gibberellin biosynthesis inhibitors are applied to seeds they do not germinate
what are meristems
groups of immature cells which can divide and differentiate
what are apical meristems
tips of roots and shoots making them grow longer
what are lateral bud meristems
buds that could form a side shoot
what are lateral meristems
circular bands that make roots and shoots get wider
what are intercalary meristems
between the nodes, helps the shoots get longer
where are auxins made and what do they cause
made in the cells at the tips of shoots and tips of roots
(move down from the shoot top and up from the root tip via diffusion)
travel to the zones of elongation
stimulate elongation here
describe exactly how the auxins cause stem cell elongation
auxins bind to specific receptors in the cell surface membrane
they cause the active transport of H+ by an ATPase enzyme into the cell wall
low PH optimal for expansin enzymes that loosen cell walls
the expansin enzymes break bonds between microfibrils present in cellulose
allows for cell elongation
explain how positive phototropism occurs
1) shoot tip produces auxin, auxin diffuses down from shoot tip or is moved by active transport
2) light causes movement of auxin from light side to shaded side
3) higher auxin concentration on shaded side causes cell wall loosening and greater elongation of cells on shaded side
4) grows faster and causes shoot to bend towards the light
what happens if their is a high concentration of auxin in the root
high concentration of auxin inhibit elongation of cells in the root
what is apical dominance
high concentrations of auxins suppress growth of lateral shoots
what happens if the apical shoot was removed
auxin production stops apical dominance stops lateral buds develop side shoots grow plant becomes bushy
what effect on the stem do gibberellins have
affect the length of internodes (regions between leaves)
define tropism
directional growth of plants determined by the direction of external stimuli
