Topic 6: Stimuli & Response

Question 1

What is a stimulus?

Answer 1

A detectable change in the environment

Question 2

What are the cells that detect stimulus called?

Answer 2

Receptors

Question 3

What increases when organisms can respond to stimulus?

Answer 3

Chance of survival

Question 4

What is a tropism?

Answer 4

Term given when plants respond via growth to a stimulus

Question 5

What are the 3 types of tropism?

Answer 5

Positive and Negative
Can grow towards or away from stimulus (light or gravity)

Question 6

What are tropisms controlled by? And give an example

Answer 6

Growth factors
IAA (indoleacetic acid)

Question 7

What is IAA?

Answer 7

Type of auxin that can control cell elongation in shoots and inhibit growth of cells in the roots

Question 8

Where is IAA made?

Answer 8

In the tip or the roots and shoots but can diffuse to other cells

Question 9

What is the term given to the tropism when the plant responds to light?

Answer 9

Phototropism

Question 10

In shoots why does a phototropism help growth?

Answer 10

Light is needed in the LDR in photosynthesis so plants grow and bend towards the light
This is a positive phototropism

Question 11

What happens in the shoots phototropism?

Answer 11

1) Shoot tip cells produced IAA, causing cell elongation
2) The IAA diffuses to other cells
3) If there is unilateral light (one sided) IAA will diffuse towards the shaded side of the shoot resulting in a higher conc of IAA there
4) The cells on the shaded side to elongate more and results in the plant bending towards the light source

Question 12

Do roots photosynthesise? Why?

Answer 12

No, as they don’t require light they must anchor the plant deep in the soil

Question 13

What does IAA do in the roots?

Answer 13

High conc inhibits cell elongation, causing root cells to elongate more on the lighter side and so the roots bend away from the light
(Negative phototropism)

Question 14

What name is given to the responses to gravity in plants?

Answer 14

Gravitropism

Question 15

What happen due to gravitropism’s in shoots?

Answer 15

IAA will diffuse to the lower side from the upper side
If the plant is vertical this causes the plant cells to elongate and plant grows upwards
If the plant is on it’s side, it will cause the shoot to bend upwards
(Negative gravitropism)

Question 16

What happen due to gravitropism’s in roots?

Answer 16

IAA moves to the lower side of the roots so that the upper side elongates and the root bends down towards gravity and anchors the plant in
(Positive gravitropism)

Question 17

What is a reflex?

Answer 17

Rapid, automatic response to protect you from danger

Question 18

What is a reflex arc made from?

Answer 18

Motor, sensory and relay neuron

Question 19

What is one reason why reflexes are so fast?

Answer 19

As there’s only 3 neurons that means that there’s only 2 synapses

Question 20

Give 2 examples of a simple response?

Answer 20

Taxes and kinesis

Question 21

What is meant by a taxes?

Answer 21

An organism will move its entire body towards (positive) a favourable stimulus or away (negative) from an unfavourable stimulus

Question 22

What is meant by a kinesis?

Answer 22

An organism changes the speed of movement and the rate it changes direction
Non-directional (random) movement

Question 23

Why are taxes and kinesis important?

Answer 23

They keep organisms within the favourable conditions of their environment (light, moisture and chemicals)

Question 24

With kinesis what happens when an organism moves from with beneficial stimuli to harmful stimuli?

Answer 24

It’s kinesis response will be to increase the rate it changes direction to return to the favourable conditions quickly
(vise versa)

Question 25

What does the stimulation of a receptor cause?

Answer 25

Leads to the establishment of generator potential which can cause a response e.g action potential

Question 26

Name the 3 receptors we must know about

Answer 26

Pacinian corpuscle Rods Cones

Question 27

What is the Pacinian corpuscle's job?

Answer 27

Pressure receptor: detect changes in pressure located deep in skin, mainly in hands and feet

Question 28

What does the sensory neuron in the Pacinian corpuscle have?

Answer 28

Special channel proteins in it's plasma membrane

Question 29

What type of neuron is the Pacinian corpuscle?

Answer 29

Sensory?

Question 30

What are the special channel proteins in it's plasma membrane called?

Answer 30

Stretch-mediated sodium channels

Question 31

What does the Stretch-mediated sodium channels in the Pacinian corpuscle cause to happen?

Answer 31

Allow Na+ ions to enter the sensory neuron only when they are stretched and deformed

Question 32

What causes the neuron plasma membrane on the Pacinian corpuscle to deform?

Answer 32

When pressure is applied it deforms

Question 33

What happens due to the pacinian corpuscle being deformed?

Answer 33

When it deforms the neuron stretches and widens the Na+ channels so Na+ diffuses in which leads to the establishment of a generator potential

Question 34

What 2 receptors are found in the human retina?

Answer 34

Rods and cones

Question 35

What type of receptors are rods and cones?

Answer 35

Photoreceptors

Question 36

How do rods process images?

Answer 36

Black and White

Question 37

To create generator potential what must happen in a rod?

Answer 37

The pigment of rod cells (rhodopsin) must be broken down by light energy They can detect light of very low intensity, as many rod cells connect to one sensory neuron (retinal convergence)

Question 38

What is meant by retinal convergence?

Answer 38

When many rod cells connect to one sensory neuron

Question 39

What is the pigment in rod cells?

Answer 39

Rhodopsin

Question 40

What happens due to retinal convergence?

Answer 40

Meaning the brain cannot distinguish between the separate sources of light in low visual acuity

Question 41

What is meant by low visual acuity?

Answer 41

Its difficult for the brain to distinguish between the different light sources

Question 42

How do cones process images?

Answer 42

Colour

Question 43

What are the 3 types if cone cells?

Answer 43

Red, blue and green

Question 44

Why is there 3 different type of cone cells?

Answer 44

They contain different types of iodopsin pigment, which all absorb different wavelengths of light

Question 45

In cone cells iodopsin is only broken down if... (why?)

Answer 45

If there is a high light intensity, so action potentials can only be generated with enough light

Question 46

Do cone cells give a high or low visual acuity?

Answer 46

High

Question 47

Why can cone cells give a high visual acuity?

Answer 47

As each cone is connected to one bipolar cell, the brain can distinguish between separate sources of light detected

Question 48

What is the distribution of rods and cones like in the retina?

Answer 48

Uneven

Question 49

Why is the distribution of rods and cones in the retina uneven?

Answer 49

As light ids focused by the lens on the fovea, which will receive the highest intensity of light

Question 50

Where are most cone and rod cells located?

Answer 50

Cones near the fovea But rods further away

Question 51

What is cardiac muscle known as?

Answer 51

Myogenic

Question 52

What is meant by the term myogenic?

Answer 52

It contracts on its own accord, but the rate of contraction is controlled by wave of electrical activity

Question 53

Where is the SAN located?

Answer 53

in the right atrium

Question 54

What is the SAN known as?

Answer 54

Pacemaker

Question 55

What does the SAN stand for?

Answer 55

Sinoatrial node

Question 56

What does the AVN stand for?

Answer 56

Atrioventricular node

Question 57

Where is the AVN located?

Answer 57

Near the boarder of the right and left ventricle within the atria still

Question 58

Where does the bindle of Hid run through?

Answer 58

Septum

Question 59

Where is the purkyne fibres found?

Answer 59

In the walls of the ventricles

Question 60

What is the process of controlling heart rate? (STEPS 1+2)

Answer 60

1) SAN releases a wave of depolarisation across the atria 2) AVN releases another wave of depolarisation when the first reaches it. A non-conductive layer between the atria and ventricles prevents the wave of depolarisation travelling down to the ventricles

Question 61

What is the process of controlling the heart? (STEPS 3,4+5)

Answer 61

3) Instead the bundle of His, conducts the wave of depolarisation down the septum and purkyne fibres 4) As a result, the apex and walls of ventricles contract, there's a short delay before this happens whilst the AVN transmits the 2nd wave of depolarisation 5) Allowing enough time for the atria to pump all the blood into the ventricles and then the cells can repolarise and cardia muscles relax

Question 62

What part of the brain controls HR, via what?

Answer 62

Medulla oblongata via the autonomic NS

Question 63

What are the 2 parts of controlling HR?

Answer 63

1) A centre linked to the SAN to increase HR via the sympathetic NS 2) Another that decreases the HR via the parasympathetic NS

Question 64

What 2 stimulus lead to a change in HR and what detects them?

Answer 64

pH and blood pressure detected by chemoreceptors and pressure receptors in the aorta and carotid artery

Question 65

When does pH of the blood decrease?

Answer 65

pH of the blood would decrease during times of high respiratory rate due to the production of lactic acid/co2.

Question 66

Why do we have to remove excess acid/co2 from the blood?

Answer 66

To prevent denaturation of enzymes

Question 67

How do we remove excess acid/co2 from the blood?

Answer 67

Increasing HR (more impulses via sympathetic NS to SAN) So CO2 can diffuse out into the alveoli more rapidly

Question 68

Why is it important to decrease pressure in the heart if it gets too high?

Answer 68

As if it is too high this can cause damage to the walls of the arteries and it is important to put mechanisms in place to reduce the blood pressure

Question 69

What is done to decrease pressure in the heart?

Answer 69

More impulses via parasympathetic NS to decreases HR

Question 70

Why is it important to increase pressure in the heart if it goes too low?

Answer 70

May be insufficient supply of oxygenated blood to respiring cells and removal of waste

Question 71

What is done to increase pressure in the heart

Answer 71

More impulses via sympathetic NS to increases HR