Entire Topic 6 Flashcards
What is a stimulus?
What is tropism
A. What is IAA
Stimulus: Detectable change in the environment
Tropism: When plants respond to stimuli through growth
A.
IAA is a growth factor, it is a type of auxin which controls cell elongation in the shoots and inhibits growth of cell in the roots
What does phototropism do in shoots and roots ?
Shoots:
- Light is needed in the LDR so plants bend towards light - positive phototropism
1. IAA which is produced in the shoot tip causes cell elongation
2. IAA diffuses to other cells
3. As light is shining on one side, IAA will diffuse towards shaded side of shoot resulting in a higher conc. of IAA there
4. Cells in shaded side elongate more, therefore plant bends towards the light source
Roots:
- Roots do not require light however must anchor plant deep in the soil
1. high conc. of IAA inhibits cell elongation in roots, causing roots to elongate more on the ligher side and so roots bends away from light - negative phototropism
What does gravitropism do in shoots and roots?
Shoots:
1. iAA diffuse from upper to lower side of shoot
2. if plant is straight vertical this causes plant cells to elongate and plant grows upwards
3. If plant is on its side, shoot will bend upwards
This is negative gravitropism
Roots:
1. IAA moves to lower side of roots so upper side elongates and roots bend down towards gravity - this anchors plant in
This is positive phototropism
What are taxes?
What are kineses?
For both give examples
Taxes:
- organism moves entire body towards a favourable stimulus or away from an unfavourable stimulus - positive and negative taxis
E.g. Earthworms and sun
Kineses:
- an organism changes the speed of movement and rate it changes direction
- if it moves from benificial to harmful stimuli, its response is to increase rate it changes direction so it can return to favourable conditions quickly
- if organism is surrounded by negative stimuli, rate of turning decreases and moves at a straight line
-woodlice
What is a pacinian corpuscle and how does it work?
- they are pressure receptors located deep in the skin
- sensory neurone in pacinian corpscule are surrounded by plasma membrane which has stretch mediated sodium channels embedded within them
- when membrane is stretched/deformed the Na+ channels open and Na+ diffuses in leading to a generator potential
- What are Rod cells
- How do rod cells Create a generator potential
- what are the pros and cons of rod cells?
- Rods process images in black and white
- Rhodopsin is broken down by light energy
- They can detect light of VERY LOW intensity, as MANY rod cells are connected to 1 sensory neurone
HOWEVER - rod cells have low visual acuity
- What are cone cells
- How do cone cells Create a generator potential
- what are the pros and cons of rod cells?
- Cone cells process images in colour - there are 3 types which contain different iodopsin pigment which all absorb different frequencies of light (RGB)
- Iodopsin broken down by light energy
- They have high visual acuity as each cone cell is connected to one bipolar cell
HOWEVER
- iodopsin is only broken down if there is high light intensity, so action potentials can be generated with enough light
- this is because 1 cone cell is connected to 1 bipolar cell - thats why we cant see colour in the dark
how is heart rate controlled from SAN releasing wave of depolarisation
why is it an advantage that there is a delay between the apex of the heart then the ventricles to contract?
- SAN releases wave of depolarisation across atria causing it to contract
- When wave of depolarisation reaches AVN, another wave of depolarisation is released from AVN.
- Because there is nonconductive tissue between atria and ventricles, wave of depolarisation does not reach there
- So bundle of His conducts wave of depolarisation down the septum and through the purkinje fibres
- This result the apex and then the walls of the heart to contract
6.Finally all the cells repolarise and cardiac muscle relaxes
Because this allows enough time for atria to pump all blood into the ventrices
How does your body react to pH decrease?
- pH has decreased because of high respiratory rate, because of CO2 production or lactic acid - this can denature enzymes
To prevent this:
1. More impulses are sent via SYMPATHETIC nervous system to the SAN, to increase heart rate and therefore to remove CO2 by exhalation
How does your body react to blood pressure changes?
Too high:
Can cause damage to walls of artery
Parasympathetic nervous system sends more impulses to decrease heart rate
Too low:
Insufficient supply of Oxygenated blood for respiring cells and removal of waste
Therefore more impulses go via sympathetic nervous system to increase heart rate
How is resting potential maintained?
- By sodium potassium pump involving active transport and ATP
- pump moves 2K+ ions in and 3 Na+ ions out
- this creates an electrochemical gradient causing K+ to diffuse out and na+ to diffuse in
- as membrane is more permeable to K+, more move out resulting in 70mv
How are action potentials generated?
- stimulus provides Na+ voltage gated channels to open and na+ diffuse into axon
- potassium ion channels are already open, however as there is Na+ channels open, there is an increase in P.D
- when Na+ diffuses enough to reach -55mV, it reaches threshhold value, an action potential is generated
- this therefore makes even more Na+ voltage gated channels to open
- when we reach +40 mV, voltage gated na+ channels close, and because of open K+ channels P.D decreases - repolarisation
- repolarisation causes more K+ channels open, and they diffuse out, to lead to -80mV - hyperpolarisation
This follows the all or nothing principle
what is the importance of the refractory period?
refractory period is when the membrane cannot be stimulated because sodium channels are recovering
impotance:
- ensures discrete impulses are produced - so each action potential is seperate
- ensures action potential travels in 1 direction
- limits number of impulse transmission - prevents over reaction to stimulus
What affects speed of conductance and why?
- Myelination and saltotary conduction -
- action potential jumps from node to node - this means you dont need to produce that many action potentials across the whole length - wider diameter:
- diameter means less leakage of ions, therefore travels faster
3.Temperature
- ions diffuse faster
- more AtP for active transport for sodium potassium pump
Describe what happens in the synapse and why is this unidirectional?
Describe what is in cholinergic synapse
- action potential arrives at presynaptic knob and depolarisation leads to Ca2+ channels to open and Ca2+ diffuses into synaptic knob
- Vesicles containing the neurotransmitter moves towards and fuse with presynaptic membrane, neurotransmitter is released to synaptic cleft
- Neurotransmitter diffuses down conc. gradient across synaptic cleft to post synaptic membrane - neurtransmitter binds to receptors complementary in shape on post synaptic membrane
- Na+ ion channels open and Na+ diffuse in - if enough neurotransmitter, enough Na= diffuses in and when its above threshold membrane becomes depolarised
- Neurotransmitter is degraded and released from receptor by enzyme and transported back into presynaptic membrane
Unidirectional because vesicles are in pre - conc. gradient is from pre to post, receptors are only on post
Neurotransmitter- acetylcholine
Enzyme - Ach - breaks to choline and acetate
