9.1 Chemical Control in Plants and Mammals Flashcards
Homeostasis
The maintenance of a constant internal environment
Involves constant changes around an optimum point
pH + temp
Changes affect protein structure
Changes can cause a reduction in the rate of reaction or denaturation
Water
Changes in WP of tissue fluid or blood cause changes in the volume of cells due to osmosis
plasmolysed if shrunk + turgid if expanded
Control Mechanism
1) Optimum- point at which the reaction works best
2) Receptor- detects change from optimum
3) Coordinator- links the receptor + effector
4) Effector- muscle or gland which brings changes to return system back to optimum
Negative Feedback
System deviates from the optimum
Change is detected by the receptor
A change is produced which returns the system back to the optimum
Positive Feedback
System deviates from the optimum
Change is detected by the receptor
A change is produced which causes an even greater deviation from the optimum
Second Messenger
1) Hormones bind to a receptor on the target cell membrane
they aren’t lipid soluble so can’t cross membrane
2) This triggers a series of intracellular membrane bound reactions
3) This stimulates the release of a 2nd messenger
4) 2nd messenger activates enzymes to alter the metabolism of the cell
Adrenaline Second Messenger
1) Adrenaline binds to a receptor
2) Activates an enzyme called adenyl cyclase
3) cAMP acts as a 2nd messenger
4) Triggers an increase in respiration + muscle contraction
Hormone Entering the Cell
1) Hormone passes through membrane + binds to receptor inside the cell
2) They form a hormone- receptor complex which passes into the nucleus + acts as a TF to regulate gene expression
Oestrogen Hormone Entering the Cell
1) Oestrogen binds to a TF known as an oestrogen receptor
they bind together to form an oestrogen-oestrogen complex
2) This then moves to the nucleus where it binds to the promoter region of the target gene
3) This then acts as a promoter
Apical Dominance
Suppress the growth of lateral buds
Auxins
Promote root growth
Trophic response of plant shoots to unilateral light
Auxin Steps
1) Cells in the shoot tip produce IAA
2) IAA diffuses back down into the zone of elongation
3) IAA molecules bind to specific receptors on the cell membrane
this activates the pumping of H+ into cell walls spaces
4) This lowers pH + allows the breaking of the cellulose microfibrils
5) Cell can absorb more water by osmosis
cell elongates + expands
Phototropism
1) When a shoot is exposed to light from 1 direction
Auxins tend to diffuse to the unilluminated side
2) There is a greater conc of auxins of the dark side
this stimulates cells to grow towards the light
Cytokinins
Promote cell diviion in the apical meristems
Promote lateral bud growth
Work with ethene in the abscission of leaves
Gibberellins
Stimulate elongation at cell internodes
Stimulate germination
Gibberellin Steps
1) When the seed absorbs water it activates the embryo which secretes gibberellins
2) Gibberellins diffuse to the aleurone layer
3) The aleurone layer produces amylase
4) Amylase diffuses into the endosperm layer + breaks down starch into glucose
Phytochrome
A plant pigment that exists as 2 interconvertible forms
Pr
Inactive form
absorbs red light (sunlight)
Pfr
Active form
Absorbs far red light
Long day plants
Pfr stimulates flowering
Short day plants
Pfr inhibits flowering
Plants grown in dark
No Pr
Plants will be:
Tall and thin
Fragile stems
Small yellowed leaves
little root growth
In the soil
Internodes grow
Seed has plenty of Pr but no Pfr so no leaves or chlorophyll forms
