Section 6:Response to stimuli

Question 1

Define stimulus

Answer 1

A detectable change in the environment that leads to a response

Question 2

What is the response pathway?

Answer 2

Stimulus~Receptor~Coordinator~Effector~
Response

Question 3

How can a response lead to evolution and natural selection?

Answer 3

Response leads to evolution due to organisms that survive pass on their allels to the next generation
Therefore, there is always a selection pressure that favours organisms with more appropriate responses

Question 4

What are animal and plants responses?

Answer 4

• Animals=taxis and kinesis
• Plants=Tropism

Question 5

What are taxis and what is the difference between positive and negative?

Answer 5

Directional response to a stimulus
* Positive=movement towards a stimulus
* Negatuve=movement away from a stimulus

Question 6

What is a kinesis and how does it work in different environments?

Answer 6

A non-directional response to a stimulus,organisms will either increase or decrease speed of movement and the rate in which it changes the direction
* Favourable environment=slower movement
* Unfavourable environment=faster movement,straight lines and turning sharply

Question 7

What are tropisms?

Answer 7

A growth movement of a plant in response to a directional stimulus

Question 8

What are comercial uses of auxins?

Answer 8

selective weed killer, flower initation and development

Question 9

What is the main auxin in plants?

Answer 9

Indoleacetic acid (IAA)

Question 10

Give examples of each animal and plant response

Answer 10

• Taxes=moving away from the light
• Kinesis=woodlice moving to stay in a favourable environment
• Tropism=shoots grow towards light

Question 11

What are the plants growth factors and what are their tropisms?

Answer 11

• light~phototropism
• gravity~geotropism
• water~hydrotropism

Question 12

Five points (concentration)

How does phototropism work in flowering plants with IAA?

Answer 12

• IAA is initally transported evenly throughout all regions as it begins to move down the shoot
• Light causes movement of IAA from the light side to the shaded side of the shoot
• Greater concentration of IAA builds up on the shaded side of the shoot then the light side
• IAA causes elongation of shoot cells, since there is a grater concentration on the shaded side, the cells elongate more
• Shaded side elongates faster than the lgiht side, causing the shoot tip to bend towards the light

Question 13

Where is IAA produced?

Answer 13

Shoot tips or Root tips

Question 14

How does gravitropism work in flowering plants, involving IAA?

Answer 14

• Cells in the tips produces IAA, which is then transported along the root
• IAA is initially transported evenly throughout the plant
• Gravity causes IAA to move from the upper side to the lower side
• Greatr conc of IAA build up on lower side
• IAA inhibits elongation of root cells of lower side

Question 15

What are the types nervous system?

Answer 15

peripheral~sensory + motor~voluntary + autonomic
central~brain + spinal cord

Question 16

What are nerves?

Answer 16

Collections of neurons that are joined together by connective tissues. They are responsible for transfering impulses from receptors to CNA and back to effectors

Question 17

What are the three types of neuron and where are they located?

Answer 17

• Sensory neuron=located near receptor organs
• Motor=located near effectors
• Intermediate=most often in the brain and spinal cord

Question 18

What are the different types of neuron stimulated by and where do they transmit impulses to?

Answer 18

• Sensory~receptor detecting a stimulus=coordinator-intermediate neuron(brain/spinal cord)
• Intermediate~sensory neuron or another intermidiate neuron=motor neurone or another intermediate neuron
• Motor~intermediate neuron=effector organ

Question 19

What is the detailed response pathway?

Answer 19

stimulus-receptor-sensory neuron-coordinator-intermediate neuron-motor neurone-effector-response

Question 20

What is reflex?

Answer 20

An automatic, rapid response to an adverse stimulus that protects the body tissues from injury

Question 21

What is the reflex arc important?

Answer 21

• Prevents injury to the body
• Make survival more likely :allows animal to find food or mates
• Effective from birth
• Fast (synapes aren’t included and they are the slowest link)

Question 22

Three points

What are the features of a receptor?

Answer 22

• They are tansducers
• They are specific
• They respond to stimuli

Question 23

What are the two types of receptors?

Answer 23

Pacinian corpuscles and light recepotrs

Question 24

Six points

What happens when pressure is applied to pacinian corpuscles?

Answer 24

1. Applying pressure open the sodium channels
2. More sodium on the outside of the axon
3. When channels are open Na enters by FD
4. Influx of sodium by FD causes depolorisation
5. This creates generator potential which creates an action potential causes depolorisation
6. This nerve impulse is passed along to the CNS

Question 25

What is the function of the retina, fovea and blind spot?

Answer 25

* Retina=contains light-sensitive (photo) receptors (rod and cone cells) * Fovea=part of the retina that is directly opposite the pupil and contains only one cells/is responsible for good visual acuity * Blind spot=where the optic nerve leaves the eye/ contains no light-sensitive receptors

Question 26

Give three differences between rod cells and cone cells

Answer 26

* Rods= outer-segment rod shaped, poor visual acuity and are not sensitive to different wavelengths of light=does not distinguish colour * Cones=outer-segment cone shaped, good visual acuity and are sensitive to different wavelengths of light=does distinguish colour

Question 27

Define visual acuity and how is high visual acuity attained

Answer 27

Visual acuity is the amount of detail that can be seen To get high visual acuity, we constantly move our eyes so the image focuses on the fovea

Question 28

# Six points How does a pacinian corpsucle work?

Answer 28

1. Pressure on the skin changes the shape 2. Deformes the membrane~strech mediated Na+ channels open 3. Sodium ions diffuse in via FD 4. This causes depolorisation of the membrane 5. Generator potential occurs 6. Action potential created (nerve impulse) which is passed along the neurone to the CNS

Question 29

What is the autonamic NS responsible for and what parts are included in it?

Answer 29

Autonamic NS controls involuntary activities of internal muscles and glands * sympathetic NS and parasympathetic NS

Question 30

What does the sympathetic NS and parasympathetic NS?

Answer 30

* Sympathetic=stimulates effectors and speeds up any activity~copes with stressful situations by hightening awarness * Parasympathetic=inhibits effectors and slows down activity~conserves energy and replenishes the body's reserves/controls normal resting conditions

Question 31

What does the sinoatrial node (SAN) do?

Answer 31

Generates a wave of electrical activity which spreads around the heart, inital stimulus for contraction originates

Question 32

What is cardiac conduction?

Answer 32

The rate at which the heart conducts electrical impulses

Question 33

# Six points Describe the cardiac cycle sequence | SAN and AVN

Answer 33

* SAN generates a wave of electrical activity~spreads out over the heart * Wave spreads from SAN to atria causing them to contract * This wave reaches AVN but is delayed~allow atria to contract and empty its contents into the ventricles * Wave sent down bundle of Hs directing the wave throught the interventricular septum of the heart * At the base bundle of Hs divides further into purkyne fibres * When the wave reaches these fibres the heart contracts from the bottom upwards

Question 34

How is heart rate changed through the SAN by the NS?

Answer 34

* Centre in medulla oblongata speeds up heart rate=sympathetic nerves~increases frequency of nerve impulses to SAN via sympathetic nerves SAN initiates heart beat at an increased rate leading to increased heart rate

Question 35

Desrcibe the role and location of chemoreceptors

Answer 35

Located in the walls of the aorta carotid artery Sensitive to changes in pH~may be a result of increased CO2 conc due to exercise

Question 36

How does exercise effect cardiac output?

Answer 36

1. Increased musuclar activity=increased CO2 conc 2. Blood pH is lowered 3. Chemoreceptors send an impulse to the centre of the medulla oblongata that speeds up heart rate 4. Centre sends impulses via sympathetic to the SAN 5. Increase in frequency of electrical activity to SAN 6. Increase in heart rate=increases blood flow=removes CO2 quicker 7. Blood CO2 conc lowered=blood pH is normal

Question 37

What happens to the SAN when blood pressure is higher than normal?

Answer 37

* Centre that slows down heart rate * Via parasympathetic nerve system * Descreases frequency SAN initiates heart rate * Decreases heart rate * Decreases blood pressure