Chapter 14 - Response to Stimuli

Question 1

What is a stimulus?

Answer 1

A noticeable change in the external or internal environment that leads to a response

Question 2

What are stimuli detected by?

Answer 2

Receptors

Question 3

How many stimuli does each receptor detect?

Answer 3

1

Question 4

What is the name of the molecule that generates a response?

Answer 4

Effector

Question 5

Describe the sequence of events in the nervous system

Answer 5

Stimulus - receptor - coordinator - effector - response

Question 6

What is a taxis?

Answer 6

A response whose direction is determined by the stimulus

Question 7

What is a kinesis?

Answer 7

A response where the organism changes the speed at which it moves and direction

Question 8

What is a tropism?

Answer 8

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

Question 9

Why are plant growth factors not described as hormones?

Answer 9

They may be made throughout the plant, not just in organs

Some factors impact the tissues that release them rather than acting on a distant organ

Question 10

What hormone controls plant cell elongation?

Answer 10

IAA

Question 11

Describe how plants respond to unilateral light

Answer 11

Cells in the tip produce IAA, which is transported throughout the plant
Light causes the IAA to move to the unshaded region
A greater concentration of IAA builds up on the shaded region than the unshaded one
IAA causes the elongation of cells - cells on the shaded side grow more
This causes the tip to bend towards the light

Question 12

What impact does IAA have on roots?

Answer 12

It inhibits cell elongation

Question 13

Describe how plants respond to gravity

Answer 13

Cells in the root tip produce IAA, which is distributed throughout the root
It is transported to all sides of the root
Gravity means that a higher concentration of IAA gathers on the lower side
Cells on this side grow more slowly than those on the upper side
This causes the root to bend downwards

Question 14

What happens as plant cells mature?

Answer 14

Their responsiveness to IAA decreases - they become more rigid

Question 15

What is the Central Nervous System?

Answer 15

The brain and spinal cord

Question 16

What is the Peripheral Nervous System?

Answer 16

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

Question 17

What are the two neurones found in the peripheral nervous system?

Answer 17

Sensory and motor neurones

Question 18

What do sensory neurones do?

Answer 18

Carry nerve impulses away from receptors towards the central nervous system

Question 19

What do motor neurones do?

Answer 19

Carry nerve impulses away from the central nervous system to effectors

Question 20

What two nervous systems is the motor nervous system divided into?

Answer 20

The voluntary and the autonomic nervous systems

Question 21

What is the voluntary nervous system?

Answer 21

Carries nerve impulses to body muscles and is under voluntary control

Question 22

Describe the process of a reflex arc

Answer 22

Stimulus
Receptor
Sensory neurone
Coordinator
Motor neurone
Effector
Response

Question 23

What is the autonomic nervous system?

Answer 23

Carries nerve impulses to muscles and is not under voluntary control

Question 24

Why are reflex arcs important?

Answer 24

Rapid
Instinctive
Short neurone pathway and few synapses
Don’t require input from the brain - prevents the brain from being overloaded

Question 25

What do Pacinian Corpuscles respond to?

Answer 25

A change in pressure

Question 26

What type of receptor is a Pacinian Corpuscle?

Answer 26

Sensory

Question 27

How does a Pacinian Corpuscle act as a transducer?

Answer 27

Converts energy from the stimulus into nerve impulses that can be understood by the body (a generator potential)

Question 28

Where are Pacinian Corpuscles found?

Answer 28

Deep in the skin, joints, ligaments and tendons

Question 29

Describe the structure of a Pacinian Corpuscle

Answer 29

A single sensory neurone surrounded by layers of connective tissue with gel in between

Question 30

How does a stretch-mediated sodium channel work?

Answer 30

In its resting state, the channels are too narrow for Na+ ions to pass through When pressure is applied, it is deformed and the membrane surrounding the neurone stretches This widens the channels so Na+ ions can diffuse into the neurone The influx of ions depolarises the neurone and creates a generator potential This creates an action potential along neurones to the CNS

Question 31

How do rod and cone cells work as transducers?

Answer 31

Converting light energy into the electrical energy of an impulse

Question 32

Why do rod cells only show us images in black and white?

Answer 32

They can't distinguish between different wavelengths of colour

Question 33

Why do rod cells allow us to see at low light intensity?

Answer 33

Many rod cells are connected to a single bipolar cell so there is a greater chance that the threshold value will be exceeded to produce a generator potential. This provides the energy to break down rhodopsin

Question 34

What is a consequence of many rod cells linking to the same bipolar cell?

Answer 34

The light received by these cells will create just the one impulse and so rod cells can't distinguish between two points of light

Question 35

Why do cone cells only respond to high light intensity?

Answer 35

Each cell is connected to its own bipolar cell so the stimulation of a number of cone cells can't be combined to exceed the threshold potential and break down iodopsin

Question 36

What cells are found at the fovea?

Answer 36

Cone cells

Question 37

What cells are found at the periphery of the retina?

Answer 37

Rod cells

Question 38

What does stimulating the sympathetic nervous system result in?

Answer 38

An increase in activity

Question 39

What does stimulating the parasympathetic nervous system result in?

Answer 39

A decrease in activity

Question 40

Describe the sequence of events that cause the heart to beat

Answer 40

A wave of electrical impulses spread from the SAN across the atria, making them contract A layer of non-conductive tissue stops this impulse reaching the ventricles The impulse enters the AVN and travels along the Bundle of His to the base of the ventricles This causes the ventricles to contract from the bottom up

Question 41

What causes the heart rate to increase during exercise?

Answer 41

More respiration = more CO2 = lower pH Chemo-receptors in the carotid artery detect this Increases the frequency of impulse to the medulla oblongata This increases the frequency of impulses via the sympathetic nervous system to the SAN This causes the heart to beat more frequently so more CO2 is exhaled and the CO2 concentration returns to normal

Question 42

What happens when blood pressure is too high?

Answer 42

Pressure receptors send impulses to the centre in the medulla that decreases heart rate This centre sends an impulse through the parasympathetic nervous system to the SAN which decreases the heart rate

Question 43

What happens when blood pressure is too low?

Answer 43

Pressure receptors send impulses to the centre in the medulla that increases heart rate This centre sends an impulse through the sympathetic nervous system to the SAN which increases heart rate