Stimuli And Responses

Question 1

What is a stimulus?

Answer 1

Any change in the internal or external environment

Question 2

Taxis response is

Answer 2

Directional movement in response to a stimulus

Question 3

Kinesis response is

Answer 3

Random, non directional movement in response to a stimulus

Question 4

The job of sensory neurones

Answer 4

Sensory neurones transmit electrical impulses from receptors to the central nervous system

Question 5

Job of motor neurones

Answer 5

Motor neurones transmit electrical impulses from the CNS to the effectors

Question 6

Job or relay neurones

Answer 6

Relay neurones transmit electrical impulses between sensory neurones and motor neurones

Question 7

Pathway of nervous communication

Answer 7

Stimulus
Receptors
Sensory neurone
CNS
Motor neurone
Effector
Response

Question 8

Reflex arc pathway

Answer 8

Stimulus
Receptor
Sensory neurone
Relay neurone in spinal cord (skipping conscious part of brain, making it involuntary)
Effector
Response

Question 9

If there’s a relay neurone involved in the simple reflex arc then it’s possible to override the reflex. True or false?

Answer 9

True, the brain can override it

Question 10

Tropism is

Answer 10

The response of a plant to a directional stimulus

Question 11

Positive tropism is

Answer 11

Growth towards the stimulus

Question 12

Negative tropism is

Answer 12

Growth away from the stimulus

Question 13

Phototropism in shoots

Answer 13

Grow and bend towards light

Question 14

Phototropism in roots

Answer 14

Grown and bend away from light

Question 15

Gravitropism in shoots

Answer 15

Grown and bend away from gravity

Question 16

Gravitropism in roots

Answer 16

Grow and bend towards roots

Question 17

Another name for gravitropism

Answer 17

Geotropism

Question 18

Auxins stimulate growth in shoots but high concentrations inhibit growth in roots

Answer 18

Auxins stimulate growth in shoots but high concentrations inhibit growth in roots

Question 19

What is IAA

Answer 19

A type of auxin

Question 20

What does IAA do in shoots

Answer 20

Causes shoot to grow on the side that IAA is on

Question 21

What does IAA do to roots

Answer 21

Inhibits growth on the side that IAA is on

Question 22

How do auxins stimulate growth of shoots?

Answer 22

By cell elongation

Question 23

What is cell elongation?

Answer 23

Cell walls become loose and stretchy so the cell gets longer

Question 24

How do receptors j the nervous system covert the energy of the stimulus into electrical energy used by neurone

Answer 24

When a nervous system receptor is in its resting state there’s a difference in charge between the inside and the outside of the cell. The inside of the cell is negative and the outside of the cell is positive. This means there’s a potential difference across the membrane. This is the resting potential.
When a stimulus is detected the cell is excited and becomes more permeable, allowing more ions to move in and out of the cell, altering the potential difference. The inside of the cell becomes positive and the outside of the cell becomes negative. This is called the generator potential.
A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference so a bigger generator potential is produced.
If the generator potential is big enough it’ll trigger an action potential. An action potential is only triggered if the generator potential reaches the threshold level

Question 25

How are the strength of action potentials measured?

Answer 25

Action potentials are all one size so the strength of the stimulus is measured by the frequency of action potentials

Question 26

Where are pacinian corpuscles found?

Answer 26

The skin

Question 27

Which stimuli do pacinian corpuscles detect?

Answer 27

Mechanical stimuli (e.g. Pressure and vibrations)

Question 28

What happens when a pacinian corpuscle is stimulated?

Answer 28

The lamellae are deformed and press on the sensory nerve ending. This causes the sensory neurones cell membrane to stretch, deforming the stretch mediated sodium ion channels. The channels open and sodium ions diffuse into the cell, creating a generator potential. If the generator potential reaches the threshold it triggers an action potential

Question 29

Describe the structure of pacinian corpuscles

Answer 29

Pacinian corpuscles contain the end of a sensory neurone called a sensory nerve ending. The sensory nerve ending is wrapped in loads of layers of connective tissue called lamallae

Question 30

How do parts of the eye work?

Answer 30

Light enters the eye through the pupil. The amount of light that entered is controlled by the muscles of the iris. Light rays are focused by the lens onto the retina, which lines the inside of the eye. The retina contains photoreceptor cells - these detect light. The fovea is an area of the retina where there are lots of photoreceptors. Nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve, which is a bundle of neurones. Where the optic nerve leaves the eye is called the blind spot - there aren't any photoreceptor cells, so it's not sensitive to light

Question 31

How do photoreceptors work?

Answer 31

Light enters the eye, hits the photoreceptors and is absorbed by light sensitive optical pigments. Light bleached the pigments, causing a chemical change and altering the membrane permeability to sodium ions. A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurones. Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain

Question 32

Two types of photoreceptors

Answer 32

Rods and cones

Question 33

Where are rods located within the eye?

Answer 33

Peripheral parts of the retina

Question 34

Where are cones found within the eye?

Answer 34

Packed together in the fovea

Question 35

Why are rods and cones sensitive to different wavelengths of light

Answer 35

They contains different optical pigments

Question 36

What vision do rods provide

Answer 36

Monochromatic vision - only gives information in black and white

Question 37

What vision do cones provide?

Answer 37

Trichromatic vision - only gives information in colour. There are three types of cone: red sensitive, green sensitive and blue sensitive. To see different colours they are stimulated in different proportions

Question 38

Why can rods fire action potentials in dim light?

Answer 38

They are sensitive to light. Three rods join to one neurone meaning mant weak generator potentials combine to reach the threshold and trigger an action potential

Question 39

Why can't cones fire action potentials in dim light?

Answer 39

Cones are less sensitive to light. One come joins to one neurone so it takes more light to reach the threshold and trigger an action potential

Question 40

Why do rods have a low visual acuity?

Answer 40

Rods give a low visual acuity because many rods join the same neurone, which means light from two points close together cannot be told apart

Question 41

Why do cones give a high visual acuity?

Answer 41

Cones give a high visual acuity because cones are close together and one come joins one neurone. When light from two points hits two cones two action potentials go to the brain so the points can be distinguished despite being close together

Question 42

The heart is myogenic, what does this mean?

Answer 42

It can contract and relax without receiving signals from nerves

Question 43

How does the heart beat?

Answer 43

The Soniatrial node sets the rhythm of the heartbeat by sending regular waves of electrical activity to the atrial walls. This causes the right and left atria to contract at the same time. A band of non conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles. Instead the waves of electrical activity are transferred from the sinoatrial node to the atrioventricular node. There is a slight delay while the atria empty before the atrioventricular node passes the waves of electrical activity on to the bundle of His. The bundle of His conduct the waves of electrical activity between the ventricles and the apex of the heart. The purkyne tissue carry waves of electrical activity into the muscular walls of ventricles causing them to contract simultaneously

Question 44

What controls the sinoatrial node?

Answer 44

Medulla oblongata

Question 45

How does the body respond to high blood pressure?

Answer 45

The baroreceptors detect high blood pressure. Impulses are sent to the medulla which sends impulses along parasympathetic neurones. These secrete acetylcholine which binds to receptors on the sinoatrial node. This effects the cardiac muscles and the heart rate slows down to reduce blood pressure back to normal

Question 46

How does the body respond to low blood pressure?

Answer 46

Baroreceptors detect low blood pressure. Impulses are sent to the medulla which sends impulses along sympathetic neurones. These secrete noradrenaline which binds to receptors on the sinoatrial node. This affects the cardiac muscles. The heart rate speeds up to increase blood pressure back to normal

Question 47

How does the body respond to high pH levels?

Answer 47

Chemoreceptors detect chemical changes in the blood. Impulses are sent to the medulla which sends impulses along parasympathetic neurones. These secret acetylcholine which binds to receptors on the sinoatrial node. This affects the cardiac muslces. Heart rates decreases to return pH levels back to normal

Question 48

How does the body respond to low pH levels?

Answer 48

Chemoreceptors detect chemical changes in the blood. Impulses are sent to the medulla which sends impulses along sympathetic neurones. These secrete noradrenaline which binds to receptors on the sinoatrial node. This affects the cardiac muscles. The heart rate increase to return pH levels back to normal

Question 49

How does CO2 affect pH levels?

Answer 49

High CO2 = low pH | Low CO2 = high pH