1
Q
Importance of reflex
A
- avoids damage to tissues;
- escape from predators;
- plays a role in homeostasis
2
Q
How does a pacinian corpuscle produce a generator potential in response to a stimulus
A
- when pressure is applied, it stretches membrane, causing the PC to change shape
- stretch-mediated sodium ion channels open
- this causes sodium ions to enter,
- this results in depolarisation
- a generator potential is formed
3
Q
Why can rod cells allow us to see in dim light
A
- several rods are connected to 1 bipolar neurone
- many generator potential combine (spatial summation)
- this can then exceed threshold for an action potential;
- individual generator potentials won’t exceed threshold;
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4
Q
Benefits of having a large fovea
A
- High cone cell density on Fovea
- Enables high visual acuity
- As one cone linked to one bipolar neurone;
- Wider area of clear vision;
5
Q
Explain the high visual acuity of cone cells
A
- Each cone cell connects to 1 bipolar neurone
- The brain recieves impulse from each cone cell individually
6
Q
Define visual acuity
A
Resolving power, the ability to distinguish close objects
7
Q
How do plants shoot respond to illumination and explain the benefit of this
A
- IAA moves to the shaded area
- Causes this side to grow faster, leading to positive phototropism
- This causes the shoot to bend towards the light source
- Light is needed for photosynthesis
8
Q
How do plants roots respond to gravity?
A
- Gravity causes IAA to accumulate at bottom of root, leading to high conc of IAA
- This inhibits cell elongation on the lower side
- Less inhibition on upper side so it grows more
- This causes the root to bend downwards
9
Q
Kinesis definition
A
- A non-directional response to a stimulus;
- Results in an increased speed of movement and repeated change in direction
- Organism keeps until it is in a more favourable environment;
10
Q
Explain why it takes time for rod cells to recover their sensitivity to light after moving into darkness
A
- rhodopsin broken down by light;
- takes time to resynthesis it;
11
Q
Similarity/Difference between taxis and tropism
A
- Similarity – directional response to a stimulus
- Difference –Taxis occurs in animals organisms and tropism occurs in plants
12
Q
Explain the poor visual acuity of rod cells
A
- Spatial Summation of rod cells
- the brain cannot distinguish between impulse from different rod cells
13
Q
Benefits of kinesis
A
- stays longer stays in favourable conditions ;
- remains near food source
14
Q
Explain trichromatic vision
A
- three types of cones cells
- each sensitive to different wavelength of light
