topic 9 continued (9.2-9.7) Flashcards

Question

Flowering in long day plants | flower in summer

Answer 1

- Have long days + short nights = lots of light - high levels of **pfr stimulates flowering** - day = lots of pr →pfr - nights are short = little pfr converted back to pr - pfr levels maintained high = flowering occurs

Answer 2

photomorphogenesis is the process by which the form + development of a plant is controlled by the level of + type of light phytochrome Converts between 2 forms: ● Biologically inactive Pr absorbs red light ● Biologically active Pfr absorbs far-red light

Answer 3

Plants grown in the dark (all phytochrome is in form Pr) are etiolated : - Tall and thin - Fragile stems with long internodes - Small yellowed leaves - Little root growth - grow rapidly using food stores in attempt to reach light -changes that take place when plant becomes etiolated + the reverse of etiolation when germinating seeds break through soil are controlled by phytochrome | etiolated describes form of plants grown in dark

Answer 4

- phytochrome is synthesised as pr - when seedling emerges from seed underground it only contains pr as there's no light to produce pfr - = seedling shows characteristics of etiolation - no leaf growth, little root growth, stem lengthens but doesn't thicken, no chlorophyll (as useless in dark) - when shoot break through surface of soil - exposed to light = pr →pfr = - stem elongation slows down, first leaves open, chlorophyll forms + seedling starts to photosynthesise

Answer 5

- when the stem breaks through the soil, Pfr acts as a transcription factor - phytochrome could act as a transcription factor that is involved in switching genes on/off in the nucleus of plant cells

Answer 6

- pr is converted to pfr in presence of light - **pfr moves into nucleus** through pores in nucleur membrane - pfr **binds to** protein phytochrome-interacting factor (**PIF3**) in nucleus - PIF3 is a transcription factor which only binds to pfr - PIF3 **activates gene transcription** when it is bound to pfr - the genes activated by PIF3 control different aspects of growth + development in plants

Answer 7

Nervous system - 1. **CNS** (central nervous system) 2. **PNS** (peripheral nervous system) CNS - 1. **Brain** 2. **Spinal cord** PNS - 1. **somatic (Voluntary) system** 2. **Autonomic system** Autonomic nervous system - 1. **Sympathetic system** 2. **Parasympathetic system**

Answer 8

**CNS** - a specialised concentration of nerve cells that processes incoming information, sends impulses through motor neurons and carries impulses to effectors - processing of information **PNS** - consists of neurons not in the CNS that spread throughout the body, relays info between CNS + environment - has sensory input and motor output

Answer 9

**somatic (Voluntary) nervous system** - under conscious control - controls voluntary + conscious activity / actions **Autonomic nervous system** - Not under conscious control - involuntary control of eg heart rate, breathing

Answer 10

**Sympathetic system** - Usually stimulates effectors = coordinates fight-or-flight response - Neurotransmitter is noradrenaline - Ganglia are located near CNS **Parasympathetic system** - Usually inhibits effectors = coordinates rest/digest response + returns body to resting state after F/F - Neurotransmitter is acetylcholine. - Ganglia located far from CNS Sympathetic + parasympathetic nervous systems work **antagonistically**

Answer 11

- They act in opposite ways - The **sympathetic system** activates the “fight or flight” response - eg increases heart rate - while the **parasympathetic system** activates the “rest + digest” response - eg slows heart rate

Answer 12

Acts as a communication link between the brain + PNS + rest of body. CNS communicates with PNS through spinal cord - **Cylindrical bundle of nerve fibres** runs from brain stem to lower back - Surrounded by **spinal vertebrae** (protection) - Consists of nerve tissue (neurons, glia, blood vessels). - 31 pairs of **spinal nerves** branching out between vertebrae to the body - **Gray matter**: H-shaped region contains neurons - **White matter**: myelinated axons

Answer 13

**the medulla oblongata** – controls breathing + heart rate - controls autonomus functions **hypothalamus** – temperature regulation (thermoregulation) - osmoregulation - hormone secretion

Answer 14

**cerebellum** – controls balance + coordination of movement - Controls execution (not initiation) of movement - Possible role in cognition = attention & language. **cerebrum** – initiates movement - control for conscious thoughts - voluntary behaviour - personality

Answer 15

**Sensory neurons** - transmit impulses / info from sensory receptors to the CNS - long dendrons - short axons

Answer 16

**Relay neurons** - transmit electrical impulses from sensory neurons to motor neurons - short axons - short dendrites

Answer 17

**Motor neurons** - transmit electrical signals from the CNS to effectors like muscles or glands - short dendrites - long axons - myelin sheath (made by Schwann cells)

Answer 18

- **rapid responses** which take place with **no conscious thoughts** involved - nervous communication **via spinal cord** - controlled by simplest type of nerve pathway in body = reflex arc - crucial for survival as they enable quick responses to potentially harmful stimuli 2 types of reflexes: 1. **spinal reflexes** (hand moves from hot object) 2. **Cranial reflexes** (blinking, pupil reflexes)

Answer 19

Stimulus received by sensory receptors→ action potential travels along sensory neurone into spinal cord → synapse with relay neurone in grey matter → synapse with motor neurone in grey matter → action potential in motor neurone leaves spinal cord → reaches motor end plate in muscle → stimulates contraction of muscle = move hand away eg

Answer 20

- conc of sodium ions (Na+) + potassium ions (K+) outside axon is different than conc inside axon = basis of nerve impulse - potential difference measures the difference in charge across a membrane (inside v outside axon)

Answer 21

- = The potential difference across the cell membrane of a neuron at rest which is around -70 millivolts (mV) Nerve cells are polarised in their resting state = As a result there is a difference in the voltage across the neuron membrane, with a value of -70mV known as the resting potential

Answer 22

When the inside of the cell is slightly negative in charge relative to the outside (outside is more positive) inside of cell is more negative compared to outside = value of charge difference is resting potential

Answer 23

- Due to the sodium - potassium pump which moves sodium ions out of the neuron + potassium ions into the neuron - Requires energy, so ATP broken into ADP + P (Dephosphyraltion) - in order to pump out 3 NA+ and pump in 2 K+ (actively transported) - Because for every 3 NA+ pumped out, only 2 K+ pumped in = number of positive ions outside membrane is higher than inside - Ion channels allow ions to move down electrochemical gradient through facilitated diffusion - Sodium ion channels are mostly closed = low rate of diffusion of NA+ back into axon = membrane relatively impermeable to sodium ions - potassium ion channels are mainly opened = high rate of diffusion of K+ back out of axon - = makes inside of axon more negative compared to outside (which is positive)

Answer 24

1. Sodium potassium pump transfers 3 NA+ out of axon for every 2 K+ in 2. The outwards movement of potassium ions down electrochemical gradient via facilitated diffusion through ion channels = these 2 factors mean there's more positive ions on outside of axon than inside = produces membrane potential

Answer 25

**Action potential:** - The temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse **Stages in generating an action potential:** 1. Depolarisation 2. Repolarization 3. Hyperpolarization 4. Return to resting potential

Answer 26

- voltage-gated ion channels only open when the membrane potential reaches a certain value - voltage gated sodium + pottasium ion channels

Answer 27

when impulse travels along axon due to stimulus, making membrane more permeable to sodium ions - Neurone **stimulated** (receives signal from stimulus) - = excitation of a neuron cell triggered - = causes the voltage-gated **sodium channels** / gates to **open** - = making it more permeable to sodium ions NA+ - = **NA+** rapidly **diffuse** down electrochemical gradient **into** the **neuron** - = making the **inside less negative** / more positive - potential difference across membrane is briefly reversed - potential difference is now **+40 mV** - depolarisation lasts around 1 millisecond

Answer 28

- pd reaches +40 mV = triggers.. - Voltage-gated **Na+ channels** to **close** - +voltage-gated **K+ channels** to **open** = - Facilitated diffusion of **K+ ions out** of axon down electrochemical gradient - **inside** of axon becomes more **negative** relative to outside - p.d. across membrane becomes more negative

Answer 29

- Large amount of pottasium ions diffuse out the axon - = inside of axon becomes more negative than the resting potential

Answer 30

- Voltage-gated **K+ channels close** - **sodium-potassium pump** re-establishes resting potential by pumping **NA+ out** and **K+ in** - K+ attracted back into axon by negative charge when the membrane is hyperpolarised - = causes PD to rise - **resting potential** equilibrium **restored**

Answer 31

- The time it takes for ionic movements to repolarise an area of the membrane + restore the resting potential after an action potential - depends on sodium/pottasium pump and on membrane permeability to pottasium ions

Answer 32

**Absolute refractory period** - for the 1st millisecond after action potential, it is impossible for another action potential to be generated - as sodium ion channels are completely blocked - +resting potential has not been restored **Relative refractory period** - After this, for several milliseconds, the axon may be restimulated - but it will only respons to much bigger threshold than before = the threshold has been raised - sodium ion channels are not blocked, butvoltage-depending potassium ion channels are still open - its not until they're closed that normal resting potential can be fully restored

Answer 33

- limits rate at which impulses may flow along a fibre - ensures impulse flow is only in 1 direction along nerve - (until resting potential is restored, the part of nerve fibre that impulse had just left cannot conduct another impulse = impulse can only continue travelling in same direction)

Answer 34

- Threshold = the point when sufficient sodium ions channels open for the rush of sodium ions into the axon to be greater thanthe outflow of pottasium ions = resulting in an action potential - The size of the action potential is always the same = all-or-nothing response - Any generator potential which reaches or exceeds the threshold potential will produce an action potential of equal magnitude = all or nothing response | threshold = -55 V

Answer 35

~myelin sheath serves as an insulator of axons + dendrites ~it's produced by Schwann cells - The mechanism by which the speed is increased is known as **saltatory conduction** - In myelinated neurones, ions can only pass in/out of axon at **nodes of Ranvier** (where there's no myelin sheath) - = action potential can only occur at nodes = **action potential 'jumps'** from one to the next - because the myelin sheath is impermeable - transmission is sped up as ionic movement associated with action potential occurs less frequently, taking less time - impulse doesn't travel along whole axon + depolarisation of one node causes depolarisation of next node = faster conduction along nerve tissue

Answer 36

**Synapse** - The junction between 2 neurons that nerve impulses cross via neurotransmitters **Synaptic cleft** - the gap between the pre + post synaptic membranes in synapse **Synaptic knobs** - bulges at end of presynaptic neurone where neurotransmitters are made (contains vesicles filled with neurotransmitters)

Answer 37

- **Action potential** arrives at presynaptic knob - = presynaptic membrane depolarises - causing the **calcium channels** to open - = **calcium ions** diffuse into neurone - causes **synaptic vesicles** filled with a neurotransmitter (eg acetylcholine) to **fuse with** the **presynapc membrane** - = causing **release** of **neurotransmitters** (exocytosis) - they **diffuse** across the **synaptic cleft** - neurotransmitter binds to the **receptors** on **postsynaptic membrane** - this can have 2 effects (excitation / inhibition)

Answer 38

- neurotransmitters bind to specific protein **receptors** on sodium channels of **post-synaptic membrane** = Stimulates opening of cation channels - This **opens sodium ion channels** in the membrane - Lots of **NA+ enter** nerve fibre - reduced **PD raises** membrane to threshold potential - causing an **action potential** - =travels along post-synaptic neurone

Answer 39

- When neurotransmitters bind to specific protein **receptors** on **post-synaptic membrane** = neurotransmitter has opposite effect = Stimulates opening of anion channels - different **negative (anion) ion channels open** in membrane (anion) - allowing **inwards movement** of negative ions (eg chloride ions Cl-) - makes **inside more negative** than normal resting potential - less likely that action potential will occur - (p.d. becomes more negative - **hyperpolarisation**)

Answer 40

- synthesised in synaptic knob using ATP produced from many mitochondria present - found in all nerves in voluntary + parasympathetic autonomic system - nerves using ACh = knows as cholinergic nerves - once ACh has done its job = its broken down / hydrolised by enzyme **acetylcholinesterase** into acetate + choline (which diffuse back to presynaptic membrane) - **ACh usually results in excitation at post-synaptic membrane** | INSERT INTO EPSP / IPSP EVENTS BUT SUB ACh FOR 'neurotransmitter'

Answer 41

- found in nerves of the sympathetic autonomic nervous sytem - nerves using this = adrenergic nerves - binding of it to receptors in post-synaptic membrane depends on conc of it in synaptic cleft - as release of it from presynaptic knob stops = levels in synaptic cleft fall - = noradrenaline released from post-synaptic receptors back to synaptic cleft - +most is reabsorbed y presynaptic knob = repackaged + reused when another action potential comes | INSERT INTO EPSP/IPSP EVENTS BUT SUB noradrenaline FOR 'neurotransmitter

Answer 42

- some drugs can affect the function of synapses + cause changes to synaptic transmission These drugs include - nicotine - lidocaine - cobra venom

Answer 43

1. Increases the amount of neuritransmitter synthesised 2. Increases the release of neurotransmitter from the vesicles at the presynaptic membrane 3. Binds to post-synaptic receptors + activates them or increases the effect of the normal neurotransmitter 4. Prevents the degradation of neurotransmitter by enzyms OR prevents reuptake into presynaptic knob

Answer 44

1. blocks the synthesis of neurotransmitter 2. causes neurotransmitter to leak from vesicles + be destroyed by enzymes 3. prevents the release of neurotransmitter from vesicles 4. blocks the receptors + prevents neurotransmitter binding

Answer 45

- mimicks effects of acetylcholine - component of cigarette smoke which affects synapses in brain + in the PNS - these synapses have nicotinic acetylcholine (ACh) receptors = which are normally stimulated by neurotransmitter ACh but also respond when nicotine binds - this can increase heart rate + blood pressure due to nerves being stimulated - triggers release of dopamine in brain = feeling of hapiness - at low dose nicotine has stimulating effects - at high dose nicotine blocks acetylcholine receptors + can kill **Action on postsynaptic neuron: excitatory**

Answer 46

- Used as local anaesthetic - block voltage gated Na+ channels in postsynaptic membrane - Na+ ions cannot enter neurone when neurotransmitter binds - action potential cannot form in the postsynaptic neurone - = prevents impulses from being conducted along nerve fibres responsible for causing pain sensations **Action on postsynaptic neuron: Inhibitory**

Answer 47

- binds + blocks acetylcholine receptors in postsynaptic membrane - prevents transmission of impulses across synapse - When nerves that stimulate breathing are affectes = muscles not stimulated to contract = eventually become paralysed - when toxins reach muscles involved in breathing = causes death **Action on postsynaptic neuron: Inhibitory**

Answer 48

- **ganglion cell** (from optic nerve fibre) - **bipolar neurones** - **photoreceptors** - = light-sensitive cells - **rods + cones** (which provide info needed for brain to produce images) - Rods + cones respond to different intensities of light = giving effective vision in different conditions DIRECTION OF LIGHT PASSING THROUGH RETINA: ganglion neurone --> bipolar neurones --> cones + rods

Answer 49

- Electrical **signals** are sent from photoreceptors → bipolar cells → ganglion cells → along the optic nerve → to the visual cortex of the brain - The brain interprets these signals, allowing us to perceive attributes of light such as colour + intensity

Answer 50

**Cones** ``` - provide colour vision - responsible for vision in bright light - 3 types: red, green + blue cones = each sensitive to a different wavelength of light ``` **Rods** ``` - provide greyscale vision - responsible for vision during night / low intensity light - very sensitive to light - contain a light-sensitive pigment called rhodopsin ```

Answer 51

**Rod**: - evenly distributed around periphery but NOT in central fovea **Cone**: - mainly central fovea `No photoreceptors at blind spot where ganglion axon fibres form optic nerve`

Answer 52

- absorbs light energy - and as a result splits into retinal + opsin

Answer 53

- when rhodopsin (in rod cells) absorb light = it splits into retinal + opsin = this is called bleaching - opsin causes Na+ channels to close - Na+ ions stop moving into the cell - sodium/potassium pump continues = Na+ still move out - inside the cell becomes more more negative as there's less positive ions inside - = hyperpolarisation occurs - = stops inhibitory neurotransmitter release (glutamate) - allows depolarisation / action potential in bipolar / ganglion cell [ as it allows the bipolar neurone to stimulate the sensory nerve fibre to depolarise + cause action potential = AP transmitted to the brain via the opc nerve + subsequently processed by the brain]

Answer 54

- Na+ ions diffuse into rod through open channels - Na+ ions actively pumped out of rod cell - inside of the cell only slightly more negave compared to the outside = causing membrane to be slightly depolarised - = stimulates secretion of a neurotransmitter glutamate, which inhibits depolarisation of bipolar neurone - = no information is transmitted to the brain