Topic 8 Flashcards
(118 cards)
What will an exposure to red light trigger
Germination
What will an exposure to far-red light inhibit
Germination
What happens when a plant absorbs red (natural) light
Phytochrome is converted from inactive Pr to active Pfr
In the dark, Pfr slowly converts back into Pr
If exposed to far red light, it will change back rapidly
Define long day plants
Only flower when day length exceeds a critical value
When uninterrupted darkness is less than 12hrs
Need high levels of Pfr
Define short day plants
Only flower when uninterrupted darkness is greater than 12hrs
Need low levels of Pfr, therefore more Pr
What else, other than germination, does exposure of phytochromes to light stimulate
Development of primary leaves
Leaf unrolling
Production of pigments
How is greening of the shoot promoted
Causes the phytochromes to change shape through a series of interactions with other signal proteins
They activate transcription factors which cause the synthesis of enzymes that control chlorophyll production in greening of the shoot
What are phytochromes
Photoreceptors
That absorb red or far red light
Define the central nervous system
Part of the nervous system that consists of the brain and spinal cord
Define autonomic nervous system
Nervous response from his part of the nervousness system are involuntary and involve the smooth muscle
Define sympathetic nervous system
Prepares the body for fight or flight
Define parasympathetic nervous system
Prepared the body for rest and digest
What is the resting potential
The inside of an axon is more negative than the outside, making the membrane polarised at -70mV
Due to an uneven distribution of ions across the cell surface membrane
How is the resting potential created within an axon
1) Na/K+ pumps create a concentration gradient across the membrane
2) k+ diffuse out of the cell down the conc gradient, making the outside of the membrane positive and the inside negative
3) electrical gradient will pull K+ back into the cell
4) at -70mV there is no net movement of K+ as the electrical gradient balances the chemical gradient
How is an action potential generated in an axon
1) voltage dependent gated Na+ channels open, allowing Na+ to flow into the axon, depolarising the membrane
2) the Na+ channels close whilst the voltage dependent gated K+ channels open, allowing K+ to leave the axon, repolarising the membrane
3) the membrane is hyperpolarised
4) the K+ channels close but K+ diffuse back into the axon through K+ channels to recreate the resting potential
What is the place two neurones meet at known as
A synapse
What is the neurotransmitter called used at a Cholinergic Synapse
AcetylCholine
What is the sequence of events at a synapse
1) an action potential arrives
2) the membrane depolarises allowing Ca2+ channels to open
3) the influx of Ca2+ causes synaptic vesicles to fuse with the presynaptic membrane
4) the neurotransmitter binds with receptors on the post-synaptic membrane causing Na+ channels to open
5) membrane depolarises and initiates an action potential
How is the neurotransmitter removed from the synaptic cleft
It is either broken down by enzymes
Or reabsorbed into the presynaptic neurone
Define excitatory synapse
Makes a membrane more permeable to sodium ions and therefore leads to depolarisation and an action potential
What are inhibitory synapses
They make it less likely for an action potential to be produced in the post synaptic neurone
The channels for chloride and potassium ions are opens in the post, causing it to become hyperpolarised
Define summation
Each action potential adds to the effect
What are the two types of summation
Spatial
Temporal
Define spatial summation
A single exciting synapse typically does not depolarise the post synaptic membrane to generate an action potential