chapter 14- response to stimuli

Question 1

what is a stimulus

Answer 1

a detectable change in the internal or external environment of an organism that leads to a response in the organism

Question 2

what is a coordinator

Answer 2

formulates a suitable response to a stimulus

Question 3

what is an effector

Answer 3

produces the response

Question 4

taxis

Answer 4

a movement response whose direction is determined by the direction of the stimulus

Question 5

example of positive phototaxis

Answer 5

algae moving towards light for maximum light for photosynthesis

Question 6

example negative phototaxis

Answer 6

earthworms moving away from light. can easier preserve water and food in the soil and avoid predators

Question 7

example of positive chemotaxis

Answer 7

bacteria moving towards and area where glucose is more highly concentrated to use as a food source

Question 8

kinesis

Answer 8

organism does not move towards or away from the stimulus
Changes the speed at which it moves and the rate at which it changes direction but movement is random

Question 9

tropism

Answer 9

growth of part of a plant in response to a directional stimulus

Question 10

Phototropism in flowering plants

Answer 10

• cells in tip of shoot produce IAA which is transported down shoot
• IAA is initially transported evenly throughout all regions
• light causes the movement of IAA from the light side to the shaded side of the root
  -IAA causes the shoot to elongate on the shaded side
• shoot elongates faster on the shaded side causing shoot to bend towards light

Question 11

gravitropism in flowering plants

Answer 11

• cells in tip of root produce IAA which is transported along not
  -IAA is initially transported to all sides of root
• gravity causes IAA to move from upper side of root to lower
  -IAA builds up on lower side
• IAA inhibits elongation of root cells so cells on lower side of root elongate less than cells on upper side of root
• this causes the root to bend downwards

Question 12

what does the central nervous system consist of

Answer 12

brain and spinal cord

Question 13

what is the peripheral nervous system made up of

Answer 13

pairs of nerves that originate from either the brain or the spinal cord

Question 14

what is peripheral nervous system divided into

Answer 14

sensory nervous system- carry nerve impulses from receptors to CNS
motor nervous system- carry nerve impulses from CNS to effecter

Question 15

what is the motor nervous system divided into

Answer 15

voluntary nervous system- carries nerve impulses to body muscles under conscious control
autonomic nervous system-carries nerve impulses to glands, smooth muscle and cardiac muscle and is involuntary

Question 16

what is a reflex arc

Answer 16

pathway of neurones involved in a reflex

Question 17

describe the events of a reflex arc

Answer 17

1. Stimulus- heat from hot object
2. Receptor- temperature receptors on the skin which generate nerve impulses in sensory neurone
3. sensory neurone- passes nerve impulse to spinal cord
4. coordinator- link sensory neurone to motor neurone in spinal cord
5. motor neurone- carries nerve impulses from spinal cord to muscle in upper arm
6. effector- muscles in upper arm which is stimulated to contract
7. response- pulling hand away from hot object

Question 18

Importance of reflex arcs

Answer 18

protect the body from harm
effective from birth and do not have to be learnt
fast

Question 19

How does the pacifism corpuscle function

Answer 19

• resting potential is maintained as in the resting state stretch mediated sodium channels are too narrow to allow sodium ions to diffuse in
  -when pressure is applied the membrane around its neurones becomes stretched
• sodium ion channels are widened and sodium ions diffuse into the neurone
• influx of sodium depolarises the membrane leading to the production of a generator potential
• generator potential produces an action potential

Question 20

Rod cells

Answer 20

• cannot distinguish between different wavelengths of light so images only seen in black and white
• help us see at low light intensities

Question 21

why do rod cells respond to low light intensities

Answer 21

• rhodopsin needs to be broken down in order for a generator potential to be produced
  -rhodopsin can be broken down at very low light intensities

Question 22

why is there a greater chance that the threshold value will be exceeded than if each rod cell was individually connected to its own neurone

Answer 22

the cumulative stimulation of more than one rod cell can create an action potential in the bipolar neurone. This is called spatial summation. Larger stimulus intensity would be needed to create an action potential if each rod cell was individually connected to its own neurone

Question 23

why do rod cells give low visual acuity?

Answer 23

light received by multiple rod cells connected to the same bipolar cell will only generate a single impulse regardless of how many neurones are stimulated

Question 24

Cone cells

Answer 24

• three different types each responding to a different wavelength of light

Question 25

why do cone cells only respond to high light intensities

Answer 25

- stimulation of a number of cone cells cannot be combined to help exceed the threshold value as each cone Is connected to its own bipolar cell - iodopsin requires a higher light intensity in order to be broken down and produce a generator potential

Question 26

why do cone cells provide high visual acuity

Answer 26

- each cone cell has its connection to a single bipolar cell, so if two adjacent cone cells are stimulated, the brain receives two separate impulses - the brain can therefore distinguish between two separate sources of light

Question 27

where are the cone cells found

Answer 27

fovea

Question 28

where are rod cells found

Answer 28

peripheries of the retina

Question 29

differences between rod and cone cells

Answer 29

-cone cells have high visual acuity rod cells have ow visual acuity -rods are sensitive to low intensities of light but cones aren't - only one type of rod but 3 types of cone - more rods than cones

Question 30

role of the sympathetic nervous system

Answer 30

stimulates effectors so speeds up activity eg. fight or flight response

Question 31

role of the parasympathetic nervous system

Answer 31

inhibits effectors so slows down activity

Question 32

describe the myogenic control of heart rate

Answer 32

- SAN releases wave of electrical activity - Atria contract at the same time -AVN passes electrical activity after a short delay via Purkyne tissue and bundle of His - ventricles contract at the same time from bottom upwards

Question 33

how is blood carbon dioxide concentration controlled

Answer 33

- blood pH lower than normal - chemoreceptors in coroted arteries and aorta detect this and increase the frequency of action potentials to centre in medulla oblongata that increases heart rate - centre increases frequency to action potentials to SAN leading to increased electrical impulses and heart rate - increased blood flow means more CO2 removed by lungs -blood pH returns to normal so receptors decrease the frequency of action potentials to medulla oblongata - decreased frequency of APs to SAN

Question 34

Describe how blood pressure is controlled when it is too high

Answer 34

- pressure receptors transmit more action potentials to the centre in the medulla oblongata that decreases heart rate - this sends action potentials via the parasympathetic nervous system to the SAN leading to a decrease in heart rate

Question 35

Describe how blood pressure is controlled when it is too low

Answer 35

- pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate this sends action potentials via the sympathetic nervous system to the SAN which increases heart rate