Bio 3.6

Created by

Maisie Green

Cards (85)

What is a stimulus?
a detectable change in the environment
What is a tropism?
growth in response to a stimulus in plants
Describe a positive phototropism in plant shoots?
Shoot tip produces IAA, causing cell elongation
The IAA diffuses to other cells
The IAA diffuses towards the shaded side of the shoot
Cells on the shaded side elongate more, causing them to bend towards the light source
Describe a negative phototropism in plant roots?
IAA inhibits cell elongation
This causes cells to elongate more on the lighter side so the root bends away from the light
Describe a negative gravitropism in plant shoots?
IAA diffuses from the upper side to the lower side of a shoot
If the plant is vertical it causes the cells to grow upwards
If the plant is on its side, it will cause the shoot to bend upwards
Describe a positive gravitropism in plant roots?
The IAA moves to the lower side of roots in response to gravity so that the upper side elongates and the root bends down towards gravity and anchors the plant in.
What is a reflex?
a rapid, automatic response to protect you from danger
What is a taxes?
when an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus
What is kinesis?
an organism changes the speed of movement and the rate it changes direction to return to the favourable stimulus quickly
if an organism is surrounded by negative stimuli, the rate of turning decreases to keep it moving in a relatively straight line
What are the 3 receptors we must know?
Pacinian corpuscle
Rods
Cones
Where are pacinian corpuscle's located 
deep in the skin, mainly in fingers and feet
Describe the membranes of the pacinian corpuscle
Contain stretch-mediated sodium channels
Describe the structure of the pacinian corpuscle.
- There are layers of tissue surround a neurone ending.
- With Sodium rich gel between the layers..
- There are stretch mediated sodium channels in the tissue.
Describe how the pacinian corpuscle works
During resting potential sodium channels are too narrow to allow sodium ions through;
When pressure is applied, membrane stretches and becomes deformed;
Sodium ion channels open;
Sodium ions enter causing depolarisation of membrane;
Causing generator potential which creates an action potential
What colour do rods process images in?
black and white
what is the pigment of rod cells?
rhodopsin
How do rod cells create a generator potential?
pigment of rod cells, rhodopsin, must be broken down by light energy
what intensity do rod cells detect 
low
what is retinal convergence
a number of rod cells are connected to a single bipolar cell
what impact does retinal convergence have on vision?
it means that the brain cannot distinguish between the separate sources of light - causing low visual acuity
How do cones process images?
in colour
What is the pigment for cone cells?
iodopsin - three types - red, green and blue
what intensity does iodopsin work at?
high
how many cone cells attach to a bipolar cell, what does this mean in terms of vision? 
one
the reason why we can't see colour in the dark
high visual acuity because the brain can distinguish between separate sources of light detected
Where are most cone cells located?
near the fovea
what does myogenic mean in the heart?
it contracts on its own accord
Where is the sinoatrial node (SAN) located?
the right atrium, also known as the pacemaker
where is the atrioventricular node located?
near the border of the right and left ventricle, still within the atria
Where is the bundle of His?
runs through the septum
Where are the Purkyne fibres?
walls of ventricles
Describe the process of the control of heart rate?
- SAN releases wave of depolarisation across atria, causing contraction
- AVN releases wave of depolarisation
- bundle of His conducts wave down the septum and purkyne fibres
-the apex and walls of the ventricles contract
-short delay before this happens which allows the atria to pump all blood into ventricles
-the cells repolarise and cardiac muscle relaxes
What in the brain controls the heart rate and how?
the medulla oblangata, via the autonomic nervous system
What are the 2 parts of the autonomic nervous system
1. a centre linked to the sinoatrial node to increase HR via the sympathetic nervous system
2. another that decreases heart rate via the parasympathetic nervous system
what does heart rate respond to?
pH and blood pressure
How is heart rate decreased?
Impulses are passed down parasympathetic nerves
How is heart rate increased?
more impulses via the sympathetic nervous system
Describe the structure of a myelinated motor neurone
Cell body - contains organelles
Dendrites - carry action potentials
Axon - conductive long fibre that carries nervous impulses along neurone
Schwann cells - wrap around axon to form myelin sheath
Nodes of Ranvier - gaps between myelin sheath
What is the resting potential of a neurone?
-70mV

when a neurone is not conducting an impulse
How is a resting potential established?
- sodium potassium pump, involving ATP and active transport
- pump moves 2 K+ ions in and 3 Na+ ions out
- this creates an electrochemical gradient causing K+ to diffuse out and Na+ to diffuse in
- membrane is more permeable to K+ so more moved out
What is an action potential?
When a neurones voltage increases beyond a set point from the resting potential
An increase in voltage, depolarisation, is due to membrane becoming more permeable to Na+
Once an action potential is generated it moves along the axon