Response to Stimulus

Question 1

What is a stimulus?

Answer 1

A change in the environment

Question 2

What is a receptor?

Answer 2

They detect different types of stimuli

Question 3

What is a co-ordinate centre?

Answer 3

Process information

Question 4

What is an effector?

Answer 4

Produces an appropriate response.

Question 5

What is kinesis?

Answer 5

A non-directional response to a stimulus such as the flatworm that moves in one direction to protect itself from predators.

Question 6

What is taxes?

Answer 6

A directional response to stimulus such as in organism like euglena flagella are light sensitive to light therefore are able to move towards light.

Question 7

What is Indoleacetic Acid (IAA)?

Answer 7

Most common naturally occurring plant hormone of the auxin class. Involved in elongation and important for plants growth repose to light, such as phototropism and gravitropism.

Question 8

What is phototropism?

Answer 8

A grow in response to light where greater concentration of IAA on shaded side results in greater rate of elongation causing the shoot to bend towards the light. This increases amount of sunlight absorbed so can generate more energy from photosynthesis.

Question 9

What is gravitropism?

Answer 9

Growth in response to gravity. Therefore in shoots, there’s a higher concentration of IAA result in a reduced cell elongation on the lower side of the root therefore the upside of the root grows causing the root to point in the direction of gravity.

Question 10

Types of neurones

Answer 10

Sensory neurones carry impulses from receptors to the CNS
Relay Neurones are found in the CNS, and connect the sensory neurone to the motor neurones
Motor neurones carry impulses from the CNS to effectors

Question 11

What is the reflex arc?

Answer 11

Pathway along which impulses are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain - Very quick, protective response

Question 12

Describe the process of the reflux pathway?

Answer 12

1. A pin (the stimulus) is detected by a pain receptor in the skin
2. The sensory neurone sends electrical impulses to the spinal cord (the coordinator)
3. Electrical impulses are passed on to relay neurone in the spinal cord
4. The relay neurone connects to the motor neurone and passes the impulses on
5. The motor neurone carries the impulses to the muscle in the leg (the effector)
6. The impulses cause the muscle to contract and pull the leg up and away from the sharp object (the response)

Question 13

What are receptors?

Answer 13

Receptors are groups of specialised cells that can generate an electrical impulse in a sensory neurone

Question 14

What is the structure of Pacinian Corpuscles?

Answer 14

Made of layers of membrane, separated with gel containing Na+ ions.

Question 15

How does pacinian corpuscles create an action potential?

Answer 15

There is an excess of Na+ ions surrounding the axon. Pressure is exerted on the PC and membrane layers become distorted causing the stretch mediated Na+ channels to open. Na+ ions enter the axon via facilitated diffusion and the influx of ions changes the potential difference causing depolarisation.

Question 16

What cells does the retina contain?

Answer 16

Rod cells which are sensitive to light intensity and clone cells which are sensitive to different wavelengths of visible light.

Question 17

Structure of the rod cells?

Answer 17

Rod cells contain rhodopsin that breaks down light in dim light and are very sensitive to low-intensity light- allows humans to distinguish between light and dark objects in dim light.

Question 18

Structure of clone cells?

Answer 18

Cone cells contain iodopsin and are less sensitive to light however are sensitive to different wavelength of light such as red sensitive, blue sensitive and green sensitive. The combined effect is that it allows humans to observe all the colours on the visible spectrum.

Question 19

What is visual acuity?

Answer 19

Being able to distinguish between two separate points

Question 20

The structure of the retina?

Answer 20

Rod and Clone cells are connected by synapses to bipolar neurones that then connect to bipolar neurones that connect to ganglion that is connected to optic nerve.

Question 21

Why is no individual connected to optic nerve?

Answer 21

Due to high number of receptors on the retina, it is not possible for there to be individual connections between brain and receptor.

Question 22

Why does the rod cells provide lower visual acuity?

Answer 22

Brain receive a general, not specific, understanding of the fields of vision that are light or dark. A single, stimulated rod is unlikely to produce a large enough to provide an elicit picture so requires a larger combined generator potential to reach the threshold and stimulate the bipolar nerve.

Question 23

Why are rod cells good?

Answer 23

Allow effects of summation that allows organisms the see in dimmer light that clone cells allows.

Question 24

Why do cone cells provide higher visual acuity?

Answer 24

Single cone cell with a single bipolar neurone therefore if two clone cells are stimulated able to interpret two different spots of light. Only able to detect only one of three colours the brain receives the information about the colour of light detected.

Question 25

What is the sinoatrail node?

Answer 25

A group of cells in the wall of the right atrium that can initiate waves of depolarisation.

Question 26

What is the atrioventricular node?

Answer 26

A region of conducting tissue between the atria and ventricles

Question 27

What is the Bundle of His?

Answer 27

A collection of conducting tissue in the septum of the heart

Question 28

What is purkyne fibres?

Answer 28

Spread around the ventricles and initiate depolarisation of the ventricles from the apex of the heart

Question 29

How does the heart pump?

Answer 29

SAN sends a wave of electrical activity, non-conducting tissue prevents immediate contraction of ventricles, atrioventricular delays blood from leaving atria, AVN sends a wave of electrical activity down the bundle of His causing the ventricle to contract from the apex.

Question 30

What is the cardioregulatory centre?

Answer 30

Controls heartbeat in the medulla its made of two parts an acceletory centre and an inhibitory centre.

Question 31

What does the acceletory centre do?

Answer 31

Acceletory centre is activated causing impulses to be sent to the SAN through the sympathetic neurones. Noradrenaline is secreted in the synapse increasing the frequency of the impulses produced caused the heart to beat faster

Question 32

What does the inhibitory centre do?

Answer 32

Inhibitory centre activated causing impulses to be sent down the parasympathetic neurone to the SAN, acetylcholine is secreted in the synapse reducing frequency of impulses

Question 33

What are factors that increase the hear rate?

Answer 33

Changes in pH caused by high carbon dioxide concentration, detected by chemoreceptors located in carted arteries. This causes the sympathetic pathway which increases the frequency of the impulses therefore increasing CO2 that can be expelled from the lungs.

Question 34

How does the body react to a change in blood pressure?

Answer 34

Changes in blood pressure, monitored by baroreceptors in the sinus. If the blood pressure increases then the a increased frequency of impulses are sent from the medulla via parasympathetic pathway causing the heart rate to decrease, lowering the blood pressure.