Paper 2 Flashcards
(47 cards)
What is phototropism?
The growth of a plant in response to light direction.
What is gravitropism?
The growth of a plant in response to gravity.
In shoots, what effect does IAA have?
IAA causes cell elongation.
In roots, what is the effect of IAA?
IAA inhibits cell elongation.
How is light detected in plants?
Light is detected by receptors in the shoot.
What happens to IAA when light is detected?
IAA diffuses to the darker side.
What occurs on the darker side of the shoot in response to IAA?
IAA increases on this side.
What is the result of IAA causing cells on the darker side to elongate?
The shoot bends towards the light.
What type of phototropism is exhibited when a shoot bends towards the light?
+ve phototropism.
How does a receptor work?
Pressure is applied to the receptor causing the lamellae to bend and presses against the sensory neurone ending. This increase in pressure and so causes the stretch mediated sodium ion channels to open, allowing sodium ions to diffuse into the sensory neurone ending. Causes depolarisation of the sensory neurone ending and if current is high enough and passes threshold an action potential is triggered
Do rod cells have high or low sensitivity to light?
High
Do cone cells have high or low sensitivity to light?
Low
why do cone cells have low sensitivity to light?
One cone cells is connected to one bipolar neurone
why do rod cells have high sensitivity to light?
Many rod cells are connected to one bipolar neurone (spatial summation)
What does it mean that the heart is myogenic?
it can contract by itself without receiving signals from nerves
How do atria contract?
Sinoatrial node sends impulses to the atria walls so they contract SIMULTANEOUSLY
Why is there a short delay when atria contact?
It is to make sure the atria are empty and the ventricles are full of blood
What does the Atrioventricular node do?
It sends impulses via the Purkyne fibres in the hundle of his to the ventricles so they contract simultaneously
What happens to heart rate during increased exercise?
ph decreases this detected by chemoreceptors in carotid bodies.
• send more impulses to the medulla via the cardiac centre (cardio acceleratory)
• increases the heart rate by sending more impulses from the medulla via SNS to the SAN.
What happens to heart rate during increased exercise? (blood pressure)
during increased exercise the heart contracts more strongly and therefore presses on the veins and so increasing the rate at which Venus blood returns to the heart.
this also increases stroke volume
What is resting potential and why?
-70 mv , 3 Na out, 2 K in (inside more negative)
What 2 factors allow resting potential to be maintained?
• permeability - more permeable to 3Na in then 2k out
• electrochemical gradient - actively transports 2K in and 3Na out
what is depolarisation?
• Na ion gates open
• Na ions diffuse in
• enough Na ions must diffuse in to pass threshold to generate an action potential
What is repolarisation?
• Na ion channels close
• K ion channels open
• k ions diffuse out
• making the inside of axon more negative (hyper polarised)
