Chapter 3.6 Response To Change In Conditions

Question 1

Why do plants need to respond to the environment?

Answer 1

• prevent water loss
• reproduce
• increase chance of survival
• maximise photosynthesis
  -reduce damage

Question 2

Types of stimuli that a plant can respond to

Answer 2

Plants respond to; light, gravity and water to avoid abiotic stress
Also respond to predication by producing chemical toxins

Question 3

How do plants respond to change in stimulus?

Answer 3

Plants change orientation of roots/leaves/stems to favourable conditions
By producing growth factors called tropism from growing regions to other tissues, where they regulate growth in response to stimuli

Question 4

How do plants respond to light
+ what is it called

Answer 4

Stems respond to light by moving towards it = positive phototropism
Roots respond to light by moving away from= negative phototropism

Question 5

How do plants respond to gravity
+what is it called

Answer 5

Stems respond by moving upwards = negative geotropism
Roots respond by moving downwards = positive geotropism

Question 6

What is the growth factor produced by plant in response

Answer 6

Auxin (IAA) is the plant hormone which acts as growth factor

Question 7

Describe the process of IAA synthesis and movement into shoot in plant response

Answer 7

1) IAA is synthesised in cells in shot tip (as stimuli detected by specific receptor proteins)
2) IAA diffuses down shoot equally on all sides

Question 8

Describe the effect of different concentrations of IAA on cells in plants in response to light stimuli

Answer 8

3) light on 1 side causes IAA to be transported to shaded side
4) concentration of IAA increases on shaded side causing elongation of cells
5) IAA activates proteins in plasma membrane H+ ion breaks H bond between cellulose microfibrils = easier for cell wall to expand. Elastin enzymes in cell wall break bonds between cellulose microfibrils allowing cell walls to stretch
6) on shaded side, there is greater elongation of cells, causing the shoot to bend towards light

Question 9

What type of response are taxes and kineses?

Answer 9

Simple innate responses that can maintain a Mobile organism in a favourable environment

Question 10

Def of taxis response

Answer 10

Movement of whole organism in response to direction of a stimulus
E.g
Some move directly towards (positive taxis) or away (negative taxis) to stimulus

Question 11

Def of kinesis response

Answer 11

Non-directional response in which rate of movement is related to the intensity of stimulus, not directional

Question 12

What are the 2 types of kinesis response

Answer 12

Orthokinesis - change in rate of movement
Klinokinesis - change in the rate of turning

Question 13

Outline the reflex arc

Answer 13

Stimuli, sensory receptor, sensory neurone, relay neurone, motor neurone, effector, response

Question 14

Why are reflexes important

Answer 14

1- involuntary as do not require decision making (adv of simple organisms)
2- brain is not overloaded with situations in which response is always the same
3- some responses are still sent to brain and can be over ridden if needed

They protect body from handful stimuli ^survival
They are effective from birth so don’t have to be learned
They are fast, because the neurone pathway is short with very few synapses

Question 15

2 parts of the nervous system

Answer 15

The central nervous system (CNS) and Peripheral nervous system (PMS)
(Brain and spinal cord). (All other peripheral nerves originating from brain and spinal cord)

Question 16

What are nerves

Answer 16

Nerves are organs - a group of neurones (tissue cells) as well as other tissues such as blood vessels and connective tissue

Question 17

Def of nerve impulse

Answer 17

A self-propagating wave of electrical disturbances which travels a long the surface of a neurone membrane

Question 18

What cells secrete myelin around axon

Answer 18

Myelin is secreted by Schwann Cells which surrounds the axon in a spiral structure

Question 19

How does myelin help axon
+ what is node of ranvier

Answer 19

It is an electrical insulator that prevents ions leaking out of axon and in a jointing cells
Node of ranvier = gaps between myelinated axon

Question 20

What is happening at resting potential

Answer 20

At resting potential = state of membrane when no impulse passed along it
Inside of axon is - ively charnged with respect to outside
There is a potential difference of -70mV
Membrane is said to be polarised

Question 21

How is resting potential established?

Answer 21

1) active transport of Na+ & K+ by Na/K pump
As 3 Na moved to 2K there is more + charge outside cell than inside

2) Facilitated diffusion of Na+ & K+ by channel protein molecules
Ions tend to diffuse back through channel proteins however membrane = more permeable to K+ so more K+ moves back out of axon than Na+ in

Question 22

What transport proteins do neurone membranes contain

Answer 22

• sodium potassium pumps
• voltage gated Na+ & K+ channels
  -carrier which allow facilitated diffusion of ions
• at synapses there are also Ligond gated and Ca2+ gated channels

Question 23

How is an action potential generated

Answer 23

Axon membrane contains Na/K voltage gated channels
At resting potential channels = closed
When potential difference reaches threshold value (-50mV)
Voltage gated Na+ channels open = Na+ moves into axon
Potential difference +40mV membrane is depolarised

Question 24

How is depolarisation generated

Answer 24

Na+ voltage gated channels close at +30mV
K+ voltage gated channels open & K+ flow out of axon
Causing potential difference to be ^ negative
The Na/K pump begins again channels close resting potential restored
K+ channel remain open after repolarisation = more -time (hyperpolarised)

Question 25

Outline the change in charge produced by nerve cell in Resting potential , threshold, depolarisation, repolarisation

Answer 25

Resting potential -70mV Threshold -50 mV Depolarisation +40 mV Repolarisation -90mV

Question 26

What is refractory period

Answer 26

Period following action potential, the axon is not excitable

Question 27

Why is the refractory period important

Answer 27

Necessary as allows proteins on voltage sensitive ion channels to restore original polarity. Advantage: Nerve impulse flow in 1 direction Action potential separated, with no overlap > brain uses frequency of impulses to determine strength of stimulus More frequent impulse = strong stimulus

Question 28

Advantages of the refractory period

Answer 28

1) nerve impulses flow in 1 direction 2) action potential separated with no overlap

Question 29

In unmeyleinated neurones how are nerve impulses transmitted

Answer 29

Depolarisation of 1 area of membrane sets up **local current** which stimulates the next patch to open Na+ channels

Question 30

Speed of nerve impulse transmission through unmyleinated neurone compared to myelinated neurone

Answer 30

Speed = 1-3 ms-1 **unmyleinated** Speed = up to 120 ms-1 **myleinated**

Question 31

How are nerve impulses sent through myelinated neurones

Answer 31

In myelinated neurones, depolarisation occurs only at **node of ranvier** . Action potential jumps from 1 node to next ( known as **saltatory conduction** )

Question 32

How does saltatory conduction effect re polarisation

Answer 32

Metabolically increases efficient as less ions move across membrane so less energy expended restoring resting potential

Question 33

Factors that affect nerve impulse speeds

Answer 33

1) myelination 2) temperature 3) axon diameter

Question 34

How does myelination affect nerve impulse speeds

Answer 34

Myelinated axons shoe saltatoy conduction (jumps between nodes) = increases speed of transmission *not all organisms have this as size is dependent for example smaller organisms have less far for impulses to travel so don’t have myelination compared to larger ones*

Question 35

How does temperature affect nerve impulse speeds

Answer 35

Higher temps = fast the speeds Ions have more kinetic energy so diffusion rates increase However in excessive temps channel proteins can denature or membrane fluidity becomes disrupted *warm blooded animals have higher impulse speeds*

Question 36

How does axon diameter affect nerve impulse speeds

Answer 36

Larger diameter = faster the speed *Marine invertebrates who live in temps develop thick axons to increase speed of response*

Question 37

How is action potential started in receptor cells

Answer 37

1) nerve impulse created by altering permeability of membrane to Na+ ions 2) when gated Na+ channels open Na+ moves into cell 3) small influx of Na+ causes generator potential 4) if enough Na+ enters, threshold potential will be reached and an action potential generated

Question 38

What is generator potential

Answer 38

The small influx of Na+ caused by altered permeability of membrane to Na+ at receptor cells

Question 39

Examples of receptor cells

Answer 39

Pacinian corpuscles Baroreceports Chemoreceptors Photoreceptors

Question 40

Compare the rod and cone cells for - number of them in the eye - distribution of them

Answer 40

Rods - there are many more rods - highest density outside fovea and on perifory Cones - fewer cones - highest destiny around fovea

Question 41

What pigment is in rod cells

Answer 41

Rhodopsin

Question 42

What pigment is in cone cells

Answer 42

Iodopsin

Question 43

Compare rod and cone cells for - convergence (defining shapes) - visual acuity ( level of detail in image created)

Answer 43

Rods - have higher convergence, as multiple rods per bipolar cell and multiple bipolar per ganglion - lower visual activity Cones - lower convergence as 1 cone per bipolar cell-polar cell and ganglion - higher visual activity due to this individual cells

Question 44

Label the structure of the eye

Question 45

Label the rod and cone cells diagram

Question 46

Compare rods and cone cells for -sensitivity to light - wavelengths of light they detect

Answer 46

Rods - very sensitive to light and stimulated in low light conditions - detect in black and white Cones - not sensitive to light so required bright light to work - colour spectrum

Question 47

The role of receptors

Answer 47

-detect change in internal/external environment - energy transducers ( covert 1 from of energy to another) - adapted to detect changes in particular forms of energy - transfer energy of stimulus into electrical energy for impulse

Question 48

How are receptors classified by

Answer 48

1) the stimulus they detect 2) their structure (simple primary or complex secondary) 3) source of stimulation (external or internal)

Question 49

How do receptor cells generate an action potential

Answer 49

1)Receptor cells are the same as other neurones when in their resting potential and how it is generated 2) when stimulus detected, the cell surface membrane becomes more permeable to Na+ (and other ions)allowing more ions to move into cell 3) this change in potential difference due to stimulus = generator potential *bigger stimulus = more channels open = more ion movement in* 4) if generator potential is enough to reach threshold then action potential is formed

Question 50

What are the layers of connective tissue around Pacinian corpuscles called + label the Pacinian corpuscle

Answer 50

Lamellae

Question 51

How do Pacinian corpuscles in the skin work to generate an action potential when detect pressure change

Answer 51

When Pacinian corpuscles are stimulated the lamellae deforms and presses on the sensory nerve ending. This causes the sensory- neurone’s cells membrane to stretch, deforming the stretch-mediated sodium channels . Na + channels open and Na+ diffuses in creating a generator potential. If generator potential reaches the threshold it triggers and action potential

Question 52

Label the structure of the eye

Answer 52

Sclera Fovea Retina Optic nerve Blind spot Vitreous humour Suspensory ligament Lense Pupil Iris Ciliary muscle Cornea

Question 53

How does the iris change size of the pupil 1) in bright light 2) in dim light

Answer 53

1) in bright light -circular muscles contract - radial muscles relax - pupil constricts 2) in dim light - circular muscles relax - radial muscles contract - pupils dilate

Question 54

Where are photoreceptors found in the eye

Answer 54

Both photoreceptors are found embedded into the retina and fovea Higher conc. of cones in the fovea Higher conc. of rods in the retina

Question 55

How do photoreceptors work to generate an action potential

Answer 55

Light enters the eye, hit the photoreceptors and is absorbed by light sensitive optic pigment 1) light bleaches the pigment, causing chemical change and altering the membrane permeability to Na+ 2) a generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone. (Bipolar neurone connects photoreceptors to the optic nerve which then take impulse to the brain)

Question 56

Label the structure of the synapse

Answer 56

Pre-synaptic membrane Mitochondria Synaptic vesicle Synaptic cleft Neurotransmitter (acetylcholine) Post synaptic membrane Synaptic knob Voltage gated Na+ and Ca+ channels Liganded gated Na+ channels Acetyl choline Esterase

Question 57

Process of transmission across cholinergic synapse

Answer 57

1) action potential arrives in synaptic knob (presynaptic membrane) 2) Ca2+ enter pre-synaptic cell from synaptic cleft by facilitated diffusion 3) Ca2+ causes vesicle of acetylcholine fuse with pre-s membrane 4) acetylcholine released by exocytosis and diffuses across cleft 5) acetylcholine binds to receptor proteins on post-s membrane 6) Na+ channel open leading to depolarisation of post-s membrane 7) if sufficient Na+ diffuses in = threshold reached action potential is induced in post-s neurone 8) acetylcholine is hydrolyses by enzyme acetylcholinesterase to choline and ethanoic acid

Question 58

Adaptions of the synapse and synaptic membranes

Answer 58

Mitochondria - makes/regenerates neurotransmitters - makes vesicles -Na+/k+ pump to generate resting potential Synaptic cleft -short diameter gap = short diffusion pathway Vesicles of neurotransmitters - acetylcholine, noradrenaline, dopamine, adrenaline

Question 59

How is neurotransmitters released to synaptic cleft

Answer 59

1) Action potential arrives at synaptic knob in presynaptic membrane opening Ca2+ channels 2) Ca2+ enters pre-synaptic by facilitated diffusion 3) Ca2+ causes vesicles of acetylcholine to fuse with pre-synaptic membrane 4) this releases acetylcholine by exocytosis to synaptic cleft

Question 60

How does acetylcholine cause action potential in the post-synaptic cleft

Answer 60

1) Acetylcholine binds to receptor proteins on post-synaptic membrane 2) Na+ channels open = depolarisation of membrane 3) if threshold reached action potential induced and membrane changes permeability to Na+ causing influx making membrane positive

Question 61

How is a synapse adapted to prevent acetylcholine to keep biding to receptors

Answer 61

Post-synaptic membrane contains the enzyme acetylcholinesterase This hydrolyses acetylcholine after impulse into choline ad ethanoic acid These products re-enter the pre-synaptic cell and are re-synthesised back into acetylcholine (This process requires ATP)

Question 62

Def of summation

Answer 62

Rapid build-up of neurotransmitters in the synapse to help generate an action potential

Question 63

What are the types of summation

Answer 63

Temporal summation - one neurone releases more than 1 nerve impulse so neurotransmitter repeatable releases until threshold reached Spatial summation - multiple presynaptic neurones release their neurotransmitters to the same postsynaptic combining to reach threshold

Question 64

What is temporal summation

Answer 64

Two or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely because more neurotransmitter released into the synaptic cleft.

Question 65

What is spatial summation

Answer 65

Two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone. The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach threshold

Question 66

Is it true that neurotransmitters can be both excitatory and inhibitory

Answer 66

It is true Neurotransmitters can be excitatory, inhibitory or both.

Question 67

How do excitatory neurotransmitters work + give an example

Answer 67

Excitatory neurotransmitters depolarise the postsynaptic membrane, making it fire and action potential if the threshold is reached + E.g acetylcholine is an excitatory neurotransmitter at cholinergic synapses in the CNS and at neuromuscular junctions

Question 68

How do inhibitory neurotransmitters work + give an example

Answer 68

Inhibitory neurotransmitters hyperpolarise the postsynaptic membrane (making the potential difference more negative preventing it from firing an action potential + E.g GABA is an inhibitory neurotransmitter that bind to receptors it causes k+ channels to open on the postsynaptic membrane, hyperpolarising the neurone Acetylcholine is an inhibitory neurotransmitter at cholinergic synapse in the heart. When it binds to receptors here it also causes K+ channels to open ..

Question 69

What is a synapse called where inhibitory neurotransmitters released by pre-synaptic membrane

Answer 69

Inhibitory synapses

Question 70

What is a neuromuscular junction

Answer 70

Specialised cholinergic synapse between motor neurone and muscle cell.

Question 71

Label the structure of neuromuscular junction

Answer 71

Include: - motor neurone - presynaptic membrane - vesicles containing ACh - ACh (acetylcholine) - AchE (breaks down ACh - post synaptic membrane (also called motor end plate) - nicotine cholinergic receptors - AChE stored in clefts - muscle fibre

Question 72

How does action potential extend at a neuromuscular junction

Answer 72

Basically in the same way as cholinergic synapse 1) ACh released from vesicle in presynaptic membrane diffuses across synaptic cleft Binds to cholinergic receptors on post synaptic membrane Triggers Na+ move in until threshold reaches ACh is broken down by enzyme acetylcholinesterase (AChE)

Question 73

Differences between neuromuscular junction and cholinergic synapse

Answer 73

**Neuromuscular** Only excitatory Connects motor neurone to muscle End point for the action potential Acetylcholine binds to receptors on muscle fibre Postsynaptic membrane folded to from clefts that store AChE More receptors than other synapses **Cholinergic** Inhibitory and excitatory Connects two neurones which could be sensory, relay or motor New action potential generated in the next neurone Acetylcholine binds to receptors on postsynaptic No folds and clefts in the postsynaptic membrane Less receptors than neuromuscular junctions

Question 74

What are the 3 types of muscle

Answer 74

**smooth muscle** - contract without conscious control **cardiac muscle** - contracts without conscious control but only found in the heart **skeletal muscle** - type of muscle that you use to move (*can also be called striated, striped or voluntary muscle*)

Question 75

What are skeletal muscles attached to to allow use to move

Answer 75

Skeletal muscles are attached to bones by tendons. Ligaments attach bone to bone. This allows arm to move

Question 76

What does it mean if muscles act in antagonistic pairs

Answer 76

When one muscle in the pair contracts that other muscle in the pair relaxes.

Question 77

Label the structure of skeletal muscle fibre

Question 78

Ways in which toxins can distrust the synapse transmission

Answer 78

Inhibition of Na+ channels (poison dart frog) Block Ca2+ channels. (Pufferfish) Cause massive release of acetylcholine (black widow spider) Block acetylcholine release (botulinum toxin) Bind to acetylcholine receptors (snakes) Inhibit acetylcholinesterase (nerve gases)

Question 79

How can excitatory drugs work on. The synapse + give example of a drug for each mechanism

Answer 79

Mimic the neurotransmitter - amphetamines mimic noradrenaline - nicotine mimics acetylcholine Stimulate release of neurotransmitters - canine stimulates more Ca2+ ions to be uptakes Slows/stop enzyme action to break down neurotransmitter - nerve gases

Question 80

How do inhibitory drugs work on the synapse +. Give example of drug for each mechanism

Answer 80

Prevent the release of neurotransmitters - botulinum toxin Block action of transmitter at receptor sites - snake venoms

Question 81

What are the types of synapses

Answer 81

Excitatory - induce an action potential Inhibitory - makes action potential less likely Neuromuscular junctions - between motor neurone and muscle cells

Question 82

Function of synapses

Answer 82

- allow single impulse along one neurone to be transmitted to number of different neurones at a synapse - a stimulus Crete multiple simultaneous response - number of different impulse can combine at the synapse (spatial summation) - multiple stimuli from different receptors to interact to produce 1 response

Question 83

The 2 types of effector junctions

Answer 83

1- neuromuscular junction (motor effector) 2- neuroglandular junction ( secretory effector)

Question 84

What is neuromuscular junction

Answer 84

Specialised synapse between motor neurone and a skeletal muscle fibre

Question 85

What are synaptic boutons in neuromuscular junctions

Answer 85

Synaptic boutons are extensions of the motor neurone that release neurotransmitter ACh, for role in muscle contraction

Question 86

What separates the synaptic boutons from the end plate in a neuromuscular junction

Answer 86

The synaptic cleft

Question 87

What does the end plate of neuromuscular junction contain

Answer 87

The end-plate constrains junction all folds with numerous ligand-gated ion channel receptors for neurotransmitters like acetylcholine

Question 88

Describe the significance of acetylcholine in the neuromuscular junction

Answer 88

Acetylcholine is released when an action potential travels down the motor neurone binds to receptors in the muscle membrane’s junction all folds causing muscle depolarisation = muscle contraction

Question 89

How does the neuromuscular junction lead to muscle contraction?

Answer 89

Released of ACh triggers opening of ion channels = depolarisation leading to opening of V-gated Na+ channels = action potential