biology topic 9 homeostasis and plants 9.1 9.2

homeostasis

internal conditions maintained in dynamic equilibrium within its limit

why does core temp need to be maintained

maintain rate of enzyme reactions

why does blood pH need to be maintained

maintain rate of enzyme reactions

why does water potential need to be maintained

prevent osmotic lysis

negative feedback

self regulatory

return the internal environment to optium if there is change

positive feedback

a fluctuation triggers change which results in greater change from normal

what are hormones

proteins secreted by endocrine glands and transported in blood stream

specific tertiary structure so only complementary to certain cell receptors

stage of negative feedback pt 1

receptors detect deviation

stage of negative feedback pt 2

coordinator

stage of negative feedback pt 3

corrective mechanism by effector

stage of negative feedback pt 4

receptors detect that conditions have returned to normal

why separate feedback systems control fluctuations in different directions

provides more control

stops overcorrection

why is there a time lag between hormone production and response by effector

produce hormone

transport hormone in blood

cause required change to protein

mode of action of adrenaline pt 1

hormone receptor complex forms

mode of action of adrenaline pt 2

conformational change to receptor activates g- protein

mode of action of adrenaline pt 3

activates adenylate cyclase which converts ATP to cyclic AMP

mode of action of adrenaline pt 4

cAMP activates protein kinase A pathway

mode of action of adrenaline pt 5

results in glycogenolysis

mode of action of estrogen pt 1

steroid hormone diffuses through cell membrane

mode of action of estrogen pt 2

forms hormone receptor complex with ER receptor in cytoplasm

mode of action of estrogen pt 3

complex enters nucleus and acts as transcription factor

3 groups of plant growth factors

auxins

cytokinins

gibberellins

functions of auxins

involved in trophic responses

controls cell elongation

supresseslateral buds to maintain apical domiance

promote root growth

how do auxins cause cell elongation acid growth hypothesis pt 1

IAA causes active transport of H+ ions into cell wall

how do auxins cause cell elongation acid growth hypothesis pt 2

disruption to H- bonds between cellulose molecules and action of expansins make cell more permeable to water

how do auxins cause cell elongation acid growth hypothesis pt 3

cells with higher turgor pressure elongate faster

functions of gibberellins

stimulates germination

elongation at cell internodes

fruit growth

rapid growth

how is germination stimulated pt 1

seeds absorbs water activating embryo to secrete gibberellins

how is germination stimulated pt 2

gibberellins diffuse to aleurone layer which produces amylase

how is germination stimulated pt 3

amylase diffuses to endosperm layer to hydrolyse starch

how is germination stimulated pt 4

hexose sugars act as respiratory substrate to produce ATP

functions of cytokinins

stimulate development of lateral buds by promoting cell division at apical meristems

how does plant growth hormones interact

synergistically

antagonistically

synergistically

to achieve same effect

antahonistically

with inverse effects eg auxins and cytokinins

phytochrome

plant photoreceptor with bilin chromophore group

phytochrome 2 forms - inactive

biologically inactive Pr absorbs red light

phytochrome 2 forms - active

biologically active Pfr absorbs far- red light

when are phytochromes abundant- darkness

Pr abundant

when are phytochromes abundant- aunlight

Pfr abundant

how does phytochrome control flowering

Pr absorbs red light and converts it to Pfr which stimulate flowering as it signifies that light intensity is high enough for photosynthesis

what is photomorphogenesis

pattern of plant growth and development determined by light intensity

how does phytochrome control photomorphogenesis

the transition from Pr to Pfr

localisation of proteins within cells

transcription of certain genes

phosphorlyation of proteins

how does phytochrome control photomorphogenesis - affects

germination

circadian rhythm

flowering