Stimulus

Question 1

Importance of reflex

Answer 1

• avoids damage to tissues;
• escape from predators;
• plays a role in homeostasis

Question 2

How does a pacinian corpuscle produce a generator potential in response to a stimulus

Answer 2

• 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

Question 3

Why can rod cells allow us to see in dim light

Answer 3

• 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;
  *

Question 4

Benefits of having a large fovea

Answer 4

• High cone cell density on Fovea
• Enables high visual acuity
• As one cone linked to one bipolar neurone;
• Wider area of clear vision;

Question 5

Explain the high visual acuity of cone cells

Answer 5

• Each cone cell connects to 1 bipolar neurone
• The brain recieves impulse from each cone cell individually

Question 6

Define visual acuity

Answer 6

Resolving power, the ability to distinguish close objects

Question 7

How do plants shoot respond to illumination and explain the benefit of this

Answer 7

• 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

Question 8

How do plants roots respond to gravity?

Answer 8

• 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

Question 9

Kinesis definition

Answer 9

• 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;

Question 10

Explain why it takes time for rod cells to recover their sensitivity to light after moving into darkness

Answer 10

• rhodopsin broken down by light;
• takes time to resynthesis it;

Question 11

Similarity/Difference between taxis and tropism

Answer 11

1. Similarity – directional response to a stimulus
2. Difference –Taxis occurs in animals organisms and tropism occurs in plants

Question 12

Explain the poor visual acuity of rod cells

Answer 12

• Spatial Summation of rod cells
• the brain cannot distinguish between impulse from different rod cells

Question 13

Benefits of kinesis

Answer 13

• stays longer stays in favourable conditions ;
• remains near food source

Question 14

Explain trichromatic vision

Answer 14

• three types of cones cells
• each sensitive to different wavelength of light