6 Response To Changes In Environment

Question 1

Stimulus

Answer 1

A detectable change in the internal or external environment of an organism that leads to a response in the organism

Question 2

Coordinator

Answer 2

Acts like a switchboard, connecting information from each receptor with the appropriate effector

Question 3

Stimulus and response sequence of events

Answer 3

Stimulus -> receptor ->coordinator -> effector -> response

Question 4

Taxes

Answer 4

A simple response whose direction is determined by the direction of stimulus. As a result, mobile organisms respond directly to environmental changes by moving its whole body either towards a favourable stimulus (positive taxis)or away from an unfavourable one(negative taxis)

Question 5

Kineses

Answer 5

A form of response in which the organism doesn’t move towards or away from a stimulus
Instead it changes the speed at which it moves and the rate at which it changes direction

Question 6

Why is response to stimuli advantageous?

Answer 6

Organisms increase their chance of survival by responding to changes in their environment

Question 7

Tropisms

Answer 7

A tropism is the growth of part of a plant in response to a directional stimulus
In most cases the plant part grows towards (positive response) or away from (neg response) the stimulus
-Plant shoots grow towards light (pos phototropism) and away from gravity (neg gravitropism) so that their leaves are in the most favourable position to capture light for PS
-plant roots grow away from light (neg phototropism) and towards gravity (pos gravitropism) to increase probability that roots will grow into the soil, where they are better able to absorb water and mineral ions

Question 8

Indoleacetic acid (IAA)

Answer 8

Plant growth factor
Belongs to a group of substances called auxins
Controls plant elongation

Question 9

Phototropism in flowering plants

Answer 9

1. Cells in the tip of the shoot produce IAA, which is then transported down the shoot
2. The IAA is initially transported evenly throughout all regions as it begins to move down the shoot
3. Light causes the movement of IAA from the light side to the shaded side of the shoot
4. A greater conc of IAA builds up on the shaded side of the shoot than on the light side
5. As IAA causes elongation of shoot cells and there is a greater conc of IAA on the shaded side of the shoot, the cells on this side elongate more
6. The shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light

In roots a high conc of IAA inhibits cell elongation. As a result in roots the elongation of cells is greater on the light side and so the root bends away from light - negatively phototropic

Question 10

Gravitropism in flowering plants

Answer 10

1. Cells in the tip of the root produce IAA, which is transported along the root
2. The IAA is initially transported to all sides of the root
3. Gravity influences the movement of IAA from the upper side to the lower side of the root
4. A greater conc of IAA builds up on the lower side of the root than the upper side
5. As IAA inhibits the elongation of root cells and there is a larger conc of IAA on the lower side, the cells on this side elongate less than those in the upper side
6. The greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity

In shoots the greater conc of IAA on the lower side increases cell elongation and causes this side to elongate more than the upper side
So shoots grow upwards away from force of gravity

Question 11

Shoot tip removed

Answer 11

No response

Tip must either detect the stimulus or provide the messenger or both as its removal prevents any response

Question 12

Light proof cover placed on over shoot tip

Answer 12

No response

Light stimulus must be detected by the tip

Question 13

Thin, impermeable barrier of mica inserted on light side

Answer 13

Movement of chemical down shaded side
Shoot bends towards light

Mica on light side allows hormone to pass only down the shaded side where it increases growth and causes bending

Question 14

Mica inserted on shaded side

Answer 14

Movement of chemical down shaded side is prevented by mica

No response

Question 15

Tip removed, gelatin Block inserted and tip replaced

Answer 15

Movement of chemical down shaded side
Shoot bends towards light

Gelatin allows chemicals to pass through it, but not electrical signals, the bending which occurs must be due to chemical passing from tip

Question 16

Tips removed and replaced but displaced to one side

Answer 16

Shoots bend towards side where no tip is present

Question 17

Central nervous system

Answer 17

Made up of brain and spinal cord

Question 18

Peripheral nervous system

Answer 18

Made up of pairs of nerves that originate from either the brain or spinal cord
Divides into sensory nervous system and motor nervous system

Question 19

Two major divisions of nervous system

Answer 19

Central nervous system

Peripheral nervous system

Question 20

Sensory neurones

Answer 20

Carry nerve impulses (electrical signals) from receptors towards the CNS

Question 21

Motor neurones

Answer 21

Carry nerve impulses away from the CNS to effectors

Question 22

Motor nervous system divides into

Answer 22

Voluntary nervous system

Autonomic nervous system

Question 23

Voluntary nervous system

Answer 23

Carries nerve impulses to body muscles and is under voluntary (conscious) control

Question 24

Autonomic nervous system

Answer 24

Carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control , that is involuntary (subconscious)

Question 25

spinal cord

Answer 25

column of nervous tissue that runs along the back and lies inside the vertebral column for protection. emerging at intervals along the spinal cord are pairs of nerves

Question 26

reflex arc

Answer 26

involuntary response to sensory stimulus involve three neurones e.g. 1. the stimulus- heat from hot object 2. a receptor- temp receptors in skin on back of hard, which generates nerve impulses in the sensory neurone 3. a sensory neurone- passes nerve impulses to spinal cord 4. a coordinator (intermediate neurone)- links the sensory neurone to the motor neurone in the spinal cord 5. a motor neurone- carries nerve impulses from the spinal cord to a muscle in the upper arm 6. an effector- the muscle in the upper arm, which is stimulated to contract 7. the response- pulling the hand away from hot object

Question 27

importance of reflex arcs

Answer 27

- involuntary and therefore do not require the decision-making powers of the brain, thus leaving it free to carry out more complex responses - they protect the body from harm. effective from birth and dont have to be learnt - they are fast, because the neurone pathway is short with very few synapses where neurones communicate with each other - absence of any decision-making process also means the action is rapid

Question 28

pacinian corpuscle

Answer 28

responds to changes in mechanical pressure - specific to a single type of stimulus - produces a generator potential by acting as a transducer

Question 29

pacinian corpuscle- specific to single type of stimulus

Answer 29

only responds to mechanical pressure

Question 30

pacinian corpuscle- produces a generator potential by acting as a transducer

Answer 30

PC transduces the mechanical energy of the stimulus into a generator potential

Question 31

pacinian corpuscle structure and function

Answer 31

Pacinian Corpuscles are located deep in the skin, and are mostly found on fingers, soles of the feet as well as external genitalia. They are also found in joints, tendons and ligaments. Pacinian Corpuscles have a single sensory neurone, located in the centre of connective tissue called lamellae which forms layers separated by a gel. The Pacinian Corpuscle contains stretch mediated sodium channels in the cell surface membrane. When not under pressure these channels are closed, however under pressure these become deformed. As a result they open and allow the rapid influx of sodium ions to occur. The positive charge on the sodiums changes the membrane potential, causing the membrane to become depolarised. This results in an generator potential being created which goes on to create an action potential in the axon.

Question 32

pacinian corpuscle function

Answer 32

- in its normal state, the stretch-mediated sodium channels of the membrane around the neurone of a pacinian corpuscle are too narrow to allow sodium ions to pass along them. in this state, the neurone of the pacinian corpuscle has a resting potential - when pressure is applied to the PC, it is deformed and the membrane around its neurone becomes stretched - this stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone - the influx of sodium ions changes the potential of the membrane (it becomes polarised), thereby producing a generator potential - the GP in turn creates an action potential (nerve impulse) that passes along the neurone and then, via other neurones, to the CNS

Question 33

receptors in the eye

Answer 33

light receptor cells of the mammalian eye are found on its innermost layer, the retina. the millions og light receptor cells found in the retina are of two main types: rod cells and cone cells both act as transducers by conserving light energy into the electrical energy of a nerve impulse

Question 34

rod cells

Answer 34

cannot distinguish different wavelengths of light and so lead to images being seen only in black and white more numerous than cone cells many are connected to a single sensory neurone in the optic nerve rod cells are used to detect light of very low intensity a certain threshold has to be exceeded before a generator potential is created in the bipolar cells to which they are connected as a number of are connected to a single bipolar cell, there is a much greater chance that the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell so rod cells allow us to see in low light intensities (ie night) but only in black and white

Question 35

rod cells- generator potential

Answer 35

in order to create a GP the pigment in the rod cells must be broken down. there is enough energy from low light intensity to cause this breakdown.

Question 36

rod cells- cons

Answer 36

having many rod cells linking to a single bipolar cell is that light received by rod cells sharing the same neurone will only generate a single impulse travelling to the brain regardless of how many neurones are stimulated so in perception, the brain cannot distinguish between the separate sources of light that stimulated them two dots close together cannot be resolved and so will appear as a single blob rod cells therefore give low visual activity

Question 37

cone cells

Answer 37

of three diff types, each responding to a diff wavelength of light depending on the proportion of each type that is stimulated, we can perceive images in full colour often cone cells have their own separate bipolar cell connected to a sensory neurone in the optic nerve so the stimulation of a number of cones cannot be combined to help exceed the threshold value and so create a generator potential cone cells only respond to high LI they contain diff types of pigment from that found in rod cells pigment requires higher LI for its breakdown if 2 adjacent cone cells are stimulated, the brain receives 2 separate impulses

Question 38

where are cone and rod cells found

Answer 38

distribution of RC and CC in the retina is uneven light is focused by the lens on the part of the retina opposite the pupil. this point is known as the fovea. the fovea therefore receives the highest intensity of light. therefore cone cells, but not rod cells, are found at the fovea the conc of CC diminishes further away from the fovea at the peripheries of the retina, where light intensity is at its lowest, only rod cells are found

Question 39

what are the divisions of the autonomic nervous system?

Answer 39

- sympathetic NS | - parasympathetic NS

Question 40

sympathetic NS

Answer 40

stimulates effectors and so speeds up any activity acts like an emergency controller it controls effectors when we exercise strenuously or experience powerful emotions ie it helps us to cope with stressful situations by heightening our awareness and preparing us for activity(the fight or flight response)

Question 41

parasympathetic NS

Answer 41

this inhibits effectors and so slows down any activity it controls activities under normal resting conditions it is concerned with conserving energy and replenishing the body's reserves

Question 42

antagonostic

Answer 42

oppose each other e.g. sympathetic and parasympathetic NS if one system contracts a muscle, the other relaxes it

Question 43

what makes the heart myogenic?

Answer 43

its contraction is initiated from within the muscle itself, rather than by nervous impulses from outside (neurogenic), as is the case with other muscles

Question 44

what controls heart rate

Answer 44

within the wall of the right atrium of the heart is a distinct group of cells known as the sinoatrial node it is from here that the initial stimulus for contraction originates the SAN has a basic rhythm of stimulation that determines the beat of the heart

Question 45

sequence of events that controls the basic heart rate is

Answer 45

- a wave of electrical excitation spreads out from the sinoatrial node across both atria, causing them to contract - a layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing the ventricles - the wave of excitation enters a second group of cells called the atrioventricular node, which lies between the atria - the AVN, after a short delay, conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively make up a structure called the bundle of His - the bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of Purkyne tissue - the wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards

Question 46

modifying the resting heart rate

Answer 46

the rate can be altered to meet varying demands for oxygen during exercise the resting heart rate may need to more than double changes to the rate are controlled by a region of the brain called the medulla oblongata

Question 47

what are the two centres within the medulla oblongata concerned with heart rate?

Answer 47

- a centre that increases heart rate, which is linked to the sinoatrial node by the sympathetic NS - a centre that decreases heart rate, which is linked to the sinoatrial node by the parasympathetic NS

Question 48

chemoreceptors

Answer 48

found in the wall of the carotid arteries (arteries that serve the brain) sensitive to changes in the pH of the blood that result from changes in carbon dioxide conc in solution, CO2 forms an acid and therefore lowers the pH

Question 49

control by chemoreceptors

Answer 49

- when the blood has a higher than normal conc of CO2, its pH is lowered - the chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the freq of nervous impulses to the centre of the medulla oblongata that increases heart rate - this centre increases the freq of impulses via the sympathetic NS to the SAN. this, in turn, increases the rate of production of electrical waves by the SAN and therefore increases the heart rate - the increased blood flow that this causes leads ot more CO2 being removed by the lungs and so the CO2 conc of the blood returns to normal - as a consequence the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the freq of nerve impulses to the medulla oblongata - the medulla oblongata reduces the freq of impulses to the SAN, which therefore leads to a reduction in the heart rate

Question 50

control by pressure receptors

Answer 50

- when blood pressure is higher than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate. this centre sends impulses via the parasympathetic NS to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heart beats - when blood pressure is lower than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate. this centre sends impulses via the sympathetic NS to the SAN, which increases the rate at which the heart beats

Question 51

pressure receptors

Answer 51

occur within the walls of the carotid arteries and the aorta