Why do plants respond to simuli
Increase chance of survival e.g towards light for more photosynthesis
Define tropism
Response of a plant to a directional stimulus
How do plants perform a tropism
- Use growth factors such as auxins (Indoleacetic acid, gibberelins)
What does IAA do?
Cause cell elongation in the shoots and inhibit cell growth in the roots
What do gibberellins do?
Control flowering and germination
Where are growth factors made?
In growing regions of the plants
How do growth factors move?
Short distances by diffusion and active transport and long distance by phloem
Summarise phototropism
- IAA moves to shadow side
- Cell elongation in shoots
- Inhibits cell growth in roots
Summarise gravitropism
- IAA moves to underside
- Cell elongation in shoots
- Inhibits cell growth in roots
What is the purpose of taxes and kineses
Keep mobile organisms in a favourable environment
Define taxes
A Mobile organisms moves away from or towards a directional stimulus
Define kinesis
When mobile organisms change their movement and speed in response to a non-directional stimulus
Speed faster/turn more in unfavourable and slower in favourable
Define reflex
A rapid response to a stimulus without conscious control
Summarise a reflex
Stimulus detected by receptor, travels along sensory neurone, then relay neurone, then motor neurone, then effector then response where the relay neurone is in the CNS
Advantages of a reflex
Avoid damage or danger
No thinking so faster
No learning so protects infants
What is the pacinian corpuscle
A receptor in skin detecting pressure touch and vibration
Summarise how a pacinian corpuscle causes a generator potential
- Pressure causes lamellae to stretch and deform
- Sodium ion channels are stretch mediated and hence open
- Na+ diffuse into neurone
- Greater stimulus, more deformation so more channels open
- Depolarisation occurs (generator potential)
- If threshold reached, AP occurs
What does the fovea consist of
Lots of photoreceptors, mostly cones
Summarise what happens when light hits a photoreceptor
- Light focuses on retina by lens
- Light absorbed by pigments in photoreceptor
- Causes sodium ion channels to open (generator potential)
If threshold is reached, AP occurs, travels across bipolar neurone and optic nerve to CNA
Summarise ROD cells
- Monochromatic
- More sensitive to low light
- Low visual acuity
- Edges of the retina
Why do ROD cells have low visual acuity?
Spacial summation to the bipolar neurone, so many rod cells to one bipolar neurone, so one AP generated, regardless of the number of ROD cells
Summarise CONE cells
- Trichromatic
- Less sensitive to low light
- High visual acuity
- Focused on the fovea
When do atrioventricular valves open?
When atria pressure is higher than ventricle pressure
What is the purpose of valves?
Blood flows in one way and no back flow
