Topic 6 - Stimuli and Response

Question 1

What stimuli do plants respond to ?

Answer 1

Light, gravity and touch

Question 2

what is tropism in plants ?

Answer 2

a growth response to an external directional stimulus

Question 3

what is positive tropism

Answer 3

growing towards the stimulus

Question 4

what is negative tropism

Answer 4

growing away from the stimulus

Question 5

what is phototropism

Answer 5

• the growth of plant in response to light.
• shoots grow towards light - positively phototrophic
• roots grow away from light - negatively phototrophic.
• IAA moves to the shaded side of the shoots stimulating cell elongation, causing growth towards the light.
• IAA moves to the shaded parts of roots, inhibiting growth, causing growth away from the light.

Question 6

what is gravitropism

Answer 6

• the growth of a plant in response to gravity
• shoots grow upwards - negatively gravitropic
• roots go downwards - positively gravitropic.
• IAA moves to the underside of the shoots, stimulating cell elongation so the shoot grows upwards.
• IAA moves to the underside of roots, inhibiting growth cell elongation so roots grow downwards.

Question 7

what are growth factors in plants

Answer 7

• hormone like chemicals that speed up or slow down plant growth.
• they’re produced in growing regions of the plants - shoot tips.
• they move to other parts of the plant where they’re needed.

Question 8

what are auxins in plants

Answer 8

• hormone like growth factors that stimulate the growth of shoots by cell elongation by expansion - cell walls become loose and stretchy so cells get longer.
• high concentration of auxins in roots inhibits plant growth.

Question 9

what is IAA

Answer 9

• indoleacetic acid is an auxin which is produced in the tips of shoots.
• it moves around the plant to control tropism by diffusion and active transport over short distances and via the phloem on long distances.
• This results in an uneven distribution of IAA in the plant so there’s an uneven growth of the plant.

Question 10

what are abiotic factors to a plant

Answer 10

• temperature
• water availability
• pH
• light intensity
• minerals
• c02 concentration

Question 11

what is taxes

Answer 11

directional movement in response to an external stimulus

Question 12

what is kinesis

Answer 12

non-directional response to presence and intensity of external stimulus

Question 13

what is the purpose of taxes and kinesis

Answer 13

maintain optimum environment for survival and reproduction

Question 14

what is a stimulus

Answer 14

any change in the internal or external environment

Question 15

what are receptors

Answer 15

cells or proteins in the cel surface membranes that detect stimuli.

Question 16

what are effectors

Answer 16

cells that bring about a response to a stimulus, to produce the effect. They include muscle cells and cells in glands, e.g. the pancreas

Question 17

what is the nervous system

Answer 17

a complex network of cells and neurones

Question 18

what are sensory neurones

Answer 18

transmitt electrical impulses from receptors to the central nervous system - the brain and spinal cord.

Question 19

what is the motor neurones

Answer 19

transmit electrical impulses from the CNS to the effector

Question 20

what are relay neurones

Answer 20

transmit electrical impulses between sensory neurones and motor neurone

Question 21

how does a nervous response happen

Answer 21

• a stimulus is detected by receptor cells on the cell surface membrane.
• an electrical impulse is sent along the sensory neurone
• when the electrical impulse reaches the end of a neurone chemicas called neurotransmitters take information across to the next neurone, which sends and electrical impulse.
• The CNS (the coordinator) processes the information and sends impulses along motor neurones which stimulate muscle of gland cells an effector produces a response

Question 22

what is the central nervous system

Answer 22

made up of the brain and the spinal cord

Question 23

what is the periphoral nervous system

Answer 23

made up of neurones that connect the CNS t the rest of the body, it also has 2 systems.

Question 24

what are reflexes

Answer 24

the body responds to the stimulus without making a conscious decision to respond. it is a rapdi, automatic response.

Question 25

why is a reflex very fast

Answer 25

you dont have to spend time deciding how to respond, information travels very fast from receptors to effectors

Question 26

what is the pathway of neurones linking receptors to effectors in a reflex called

Answer 26

reflec arc

Question 27

what happens during the reflex arc

Answer 27

* receptor cells on the cell surface membrane detect the stimulus. * the sensory neurone carries impulses to a replay neurone * the relay neurone in the spinal cord connects to the motor neurone * the motor neurone sends impulses to the effector * the effector produces a reponse to stop the body from being damaged

Question 28

how is the nervous system response localised

Answer 28

when an electrical impulse reache sthe end of a neurone, neurotransmitters are secreted directly onto target cells, e.g. muscle cells - so the nervous response is localised.

Question 29

how is the nervous system response short lived

Answer 29

neurotransmitters are quickly removed once they've done their job

Question 30

how does the nervous system create quick reactions

Answer 30

electrical impulses are really fast so the response is rapid

Question 31

what is resting potential

Answer 31

* when a nervous system receptor is in its resting state there is a difference in charge between the inside and outside of the cell - this is generated by ion pumps and ion channels * meaning that there's a voltage across the membrane (potential difference).

Question 32

what is generator potential

Answer 32

* when a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference. * The change in the potential difference is called the generator potential.

Question 33

what is action potential

Answer 33

* if the generator potential is big enough it will trigger an action potential - an electrical impulse along the neurone. * An action potential is only triggered if the generator potential reaches a certain level called the threshold level. * Action potentials are all one size, so the strength of the stimulus is measured by the frequency of action potentials.

Question 34

what are pacinian corpuscles

Answer 34

* pressure receptors in the skin * they detect mechanical stimuli such as pressure and vibrations, so are mechanoreceptors

Question 35

what is the structure of pacinian corpuscles

Answer 35

they contain the end of a sensory neurone which is wrapped in lots of layers of connective tissue called lamellae.

Question 36

what is the function of pacinian corpuscles

Answer 36

* when they are stimulated lamellae deform and press on the sensory nerve ending. * this causes the sensory neurone's cell membrane no stretch deforming the stretch mediated soidum ion channels. * The chanlles open and sodium ions diffuse into the cell, creating a genertor potential. * If this reaches the thresholf it triggers an action potential

Question 37

What is the pathway of light through the eye

Answer 37

* light enters the eye through the pupil, the amount of light that enters 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 photoreceptors cells.

Question 38

what is the fovea

Answer 38

an area of the retina which has lots of cone photoreceptors

Question 39

how are nerve impulses in the eye transported

Answer 39

* 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 photoreceptors cells so it is not sensitive to light

Question 40

How is light converted into an electrical impulse

Answer 40

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

Question 41

what are the 2 types of photoreceptors

Answer 41

rods and cones

Question 42

where are rods and cones found

Answer 42

rods - found in the peripheral parts of the retina cones - found packed tightly together in the fovea

Question 43

what are the main facts of rods

Answer 43

* they are very sensitive to light (they work well in dim light) * this is because many rods join to one neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential. * they give low visual acuity because many rods join to the same neurone so light from two points close togher cannot be told apart

Question 44

what are the main facts of cones

Answer 44

* cones are less sensitive to light than rods (they work best in bright light) * this is because one cone joins to one neurone so it takes more light to reach the threshold to trigger the action potential * cones give high visual acuity because cones ae close together and one joins to one neurone so you can distinguish two points that are close together. * there are 3 types of cones esch containing a different optical pigment red sensitive, blue sensitive and green sensitive. when they are stimulated in different proportions you see colours.

Question 45

what does the heart muscle being myogenic mean

Answer 45

it can contract and relax without receiving signals from nerves.

Question 46

how is the beating of the heart controlled

Answer 46

* The process starts in the SAN which is in the upper wall of the right atrium. The SAN is like a pacemaker and sends out waves of electrical impulses to the atria walls. * This causes the atria to contract in a downward movement. * Non conducting collagen tissue prevents the electrical impulses from being passed immediately to the ventricles to allow them to fill with blood. * The waves of electrical impulses are sent from the SAN to the AVN which is in the lower right atrium wall * It passes the waves of electrical activity to the bundle of His. * The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity up the walls of the ventricles allowing it to contract upwards.

Question 47

what is the role of the SAN

Answer 47

generates electrical impulses for the cardiac muscle to contract.

Question 48

How does the heart respond to high or low blood pressure

Answer 48

* The rate of the SAN fires is unconsciously controlled by a part of the brain called the medulla oblongata * pressure receptors called baroreceptors in the aorta and the carotid arteries are stimulated by high and low blood pressure. * high blood pressure - baroreceptors detect high blood pressure. impulses are sent to the medulla which sends impulses along parasympathetic neurones which secrete acetylcholine which binds to receptors on the SAN. Heart rate slows down to reduce blood pressure to normal. * low blood pressure - baroreceptors detect low blood pressure and impulses are sent to the medulla which sends impulses along the sympathetic neurones which secrete noradrenaline which binds to receptors on the SAN. Heart rate speeds up to increase blood pressure back to normal.

Question 49

how does the heart respond to low or high, oxygen, carbon dioxide and pH levels

Answer 49

* Chemical receptors called chemoreceptors in the aorta, the carotid arteries and the medulla monitor oxygen levels in the blood and carbon dioxide and pH. **High** * chemoreceptors detect chemical changes in the blood. * impulses are sent to the medulla which sends impulses along the parasympathetic neurones which secrete acetylcholine which binds to receptors on the SAN. * Heart rate decreases to return oxygen, carbon dioxide and pH levels to normal. **Low** *- chemoreceptors detect a chemical change in the blood. impulses are sent to the medulla which sends impulses along the sympathetic neurones which secrete noradrenaline which binds to receptors on the SAN. * Heart rate increases to return oxygen, carbon dioxide and pH levels back to normal.

Question 50

where are chemoreceptors found

Answer 50

the aorta, the carotid arteries and the medulla

Question 51

where are baroreceptors found

Answer 51

the aorta and the carotid arteries

Question 52

what are advantages of simple reflexes

Answer 52

* rapid * protection against damage * enables control of homeostasis * dont have to be learmt