Topic 9 - Control Systems

Question 1

Homeostasis

Answer 1

The maintenance of a constant internal environment
e.g. temp, water, pH

Question 2

Negative feedback

Answer 2

Counteracts any change in internal conditions, restored to optimum

Question 3

Positive feeback

Answer 3

Acts in same direction as original disturbance therefore reinforcing original stimulus
e.g. blood clotting

Question 4

What are hormones and where do they come from?

Answer 4

They are signalling proteins secreted by endocrine glands directly into the bloodstream (specific)

Question 5

2 modes of hormone action

Answer 5

1) Hormones (e.g. adrenaline) bind to a receptor on target cell membrane. Triggers intracellular membrane-bound reactions and stimulates release of second messanger (e.g. cAMP). This activates enzymes to alter metabolism of cell.
2) Hormones (e.g. oestrogen) pass through cell membrane and bind to a receptor inside the cell. They form a hormone-receptor complex, passes into nucleus & acts as transcription factor to regulate gene expression.

Question 6

What do auxins do?

Answer 6

• Growth stimulants ~(e.g. IAA)
• Maintain apical dominance & suppress the growth of alteral buds
• Promote root growth
• Promote trophic responses to unilateral light (directional growth responses e.g. phototropism, geotropism)
• Functions; rooting powder, weed killers

Question 7

How do auxins work?

Answer 7

• Cause cell elongation via active transport of hydrogen ions into cell walls
• This lowers the pH of the walls
• This makes the walls mroe flexible to stretch to accommodate more water (enabling expansion and growth of cells)

Question 8

How does light influence auxins?

Answer 8

• When shoot is illuminated from all sides, auxins evenly distributed & move down shoot tip causing elongation of cells in zone of elongation
• When shoot is only illuminated from one side, auxins move to shaded part of shoot causing elongation of shaded side only (bends towards the light

Question 9

What do gibberellins do?

Answer 9

• Stimulate elongation at cell internodes
• Stimulate growth of fruit
• Stimulate germination
• Stimulate ‘bolting’ (rapid growth/flowering)

Question 10

How do gibberellins work?

Answer 10

• Seed absorbs water (activates the embryo)
• Activated embryo secretes gibberellins
• Gibberellins diffuse to aleurone layer
• Aleurone layer produces amylase
• Amylase diffuses to endosperm layer and breaks down starch into glucose

Question 11

What do cytokinins do?

Answer 11

• Promote cell division in apical meristems/lateral bud development
• Work synergistically with ethene to promote abcission of leaves

Question 12

What is phytochrome

Answer 12

Plant pigment (blue-green) that exists as 2 interconvertible forms;
- Pr = biologically inactive form, absorbs red light (like sunlight)
- Pfr = biologically active form, absorbs far red light

Question 13

When do the 2 forms of phytochrome interchange?

Answer 13

When phytochrome absorbs one of the two respective types of light, it is converted to the other form (or in darkness, converted to Pr) at a rate dependent on light intensity

Question 14

What happens in long/short day plants and neutral plants?

(in terms of Pfr)

Answer 14

• Long-day plants, Pfr stimulates flowering
• Short-day plants, Pfr inhibits flowering
• Day-neutral plants have different flowering triggers

Question 15

What are etiolated plants?
(& characteristics)

Answer 15

Plants grown in the dark (where phytochrome is in Pr);
- Tall and thin
- Fragile stems with long internodes
- Small yellowed leaves
- Little root growth

Question 16

What happens when an etiolated plants breaks through soil?

Answer 16

• Pfr acts as a transcription factor
• Moves through nuclear pores and binds to nuclear protein
• The complex activates transcription and controls aspects of growth and development

Question 17

Central nervous system

Answer 17

Specialised concentration of nerve cells that processes incoming information, sends impulses through motor neurons and carries impulses to effectors

Consists of brain and spinal cord

Question 18

Peripheral nervous system and consists of what 2 parts ?

Answer 18

Neurons not in the CNS that spread throughout the body

2 parts;
- Autonomic (not under conscious control)
- Voluntary (conscious control)

Question 19

Autonomic nervous system

Answer 19

• Sympathetic - ganglia close to CNS, neurotransmitter is noradrenaline, coordinates fight/flight response
• Parasympathetic - ganglia far from CNS, neurotransmitter is acetlcholine, coordinates rest/digest response

(Work antagonistically)

Question 20

Hypothalamus function

Answer 20

• Thermoregulation
• Osmoregulation
• Hormone secretions
• Basic drives

Question 21

Cerebellum function

Answer 21

• Smooth movements
• Balance/posture

Question 22

Cerebrum function

Answer 22

• Voluntary behaviour
• Personality

Question 23

Medulla oblongata function

Answer 23

• Reflex centres
• breathing
• heart rate
• peristalisis

Question 24

Types of neuron

Answer 24

• Sensory
• Relay
• Motor

Question 25

Sensory neuron function

Answer 25

Transmits impulses from receptors to the CNS

Question 26

Relay neuron function

Answer 26

Located in the CNS and are involved in transmitting the electrical impulses from sensory to motor neurons

Question 27

Motor neurons function

Answer 27

Involved in transmitting electrical signals from CNS to muscles and glands in the body

Question 28

Resting potential

Answer 28

When the inside of the axon is negatively charged compared to outside of the axon (axon is polarised) Typically resting potential = -70mV

Question 29

How resting potential happens

Answer 29

1) Na ions are actively transported OUT of the axon by the Na-K pump 2) K ions are actively transported INTO the axon by the Na-K pump 3) The active transport of Na ions is greater than that of the K ions, 3 Na move out OUT for every 2 K ions that move in 4) Na will naturally diffuse back into the axon & K out of the axon 5) However, most Na channels are closed (less leaky) and most K channels are open (more leaky) 6) This means the electrochemical gradient is maintained

Question 30

Action potential

Answer 30

- An explosion of electrical activity - Occurs when a neurone sends info from it's cell body down it's axon - Also known as A SPIKE or FIRING of a neurone

Question 31

Depolarisation (action potential)

Answer 31

Movement of sodium ions into the neurone reduces the potential difference across the membrane When stimulus received by a receptor/nerve endings, its energy causes a temporary reversal of the charge on the axon membrane e.g. inside becomes less negative/more positive

Question 32

Repolarisation (action potential)

Answer 32

Movement of potassium ions out of the neurone reverses the depolarisation

Question 33

Hyperpolarisation (action potential)

Answer 33

Potassium channels stay open a bit too long Gradually ion concentrations go back to resting levels

Question 34

Events at the synapse

Answer 34

1) Action potential depolarises the presynaptic neuron 2) Calcium channels open and calcium diffuses in 3) Synaptic vesicles move to and fuse with the presynaptic membrane 4) The neurotransmitter is released into synaptic gap 5) Neurtotransmitter moves across cleft by diffusion 6) Neurotransmitter binds to specific protein receptors on the sodium channel on the post synpatic membrane 7) Sodium channels open and sodium diffuses in 8) This causes a change in the potential difference of the membrane and an excitatory post-synaptic potential (EPSP) to be set up

Question 35

Inhibitory post-synpatic potential (IPSP)

Answer 35

- Kind of synpatic potential that makes a postsynaptic neurone less likely to generate an action potential - Here, different ion channels open in the membrane allowing inward movement of negative ions - This makes post-synpatic cells more negative than normal resting potential - This means an action potential is less likely to occur

Question 36

How are neurotransmitters broken down and what happens after?

Answer 36

- Broken down by hydrolic enzymes - They then move back across the cleft, back into synaptic knob and are recycled

Question 37

2 main types of synapses, where they are found and what neurotransmitter they release

Answer 37

1) Adrenergic , sympathetic NS, noradrenaline & adrenaline 2) Chlinergic, parasympathetic NS, acetylcholine

Question 38

Salactory conduction

Answer 38

- Process where action potentials are transmitted from one node of ranvier to next myelinated nerve - Speeds up transmission as ionic movements associated with action potential occur less frequency

Question 39

How does depolarisation occur

Answer 39

1) The excitation of a neuron cell triggered by a stimulus causes the sodium channels to open, making it more permeable to sodium ions which diffuse into the neuron down the electrochemical gradient, making the inside less negative 2) When its reached the threshold, more sodium channels open, eventually giving a potential difference which is the end if the depolarisation and start of repolarisation

Question 40

Generally how do drugs increase the response of the synpase

Answer 40

- Increases amount of neurotransmitter synthesised - Increases release of neurotransmotter from vesicles at presynaptic membrane - Binds to post-synaptic receptors and activates them/ increases effect of the normal neurotransmitter - Prevents degradation of neurotransmitter by enzymes or prevents reuptake into presynaptic knob

Question 41

Generally how can drugs decrease the synaptic response

Answer 41

- Block synthesis of neurotransmitters - Causes neurotransmitters to leak from vesicles and be destroyed by enzymes - Prevents release of neurotransmitters from vesicles - Blocks receptors and prevents neurotransmitter binding

Question 42

What affect does nicotine have on the synapse

Answer 42

- Mimics effect of acetylcholine - Triggers action potential in post-synaptic neuron but then the receptor remains unresponsive for some time - At low doses = nicotine has stimulating effects - At high doses = can be lethal - Triggers release of dopamine which can be associated with pleasure sensations

Question 43

What affect does lidocaine have on the synapse

Answer 43

- Used as local anaesthetic by dentists - Blocks voltage-gated Na channels preventing action potential in sensory neurons - Used to prevent some heart arrhythmias as it blocks Na channels raises depolarisation threshold so prevents early or extra action potentials in the pacemaker

Question 44

What affect does cobra venom have on the synpase

Answer 44

- Toxic and often lethal - Binds reversibly to acetylcholine receptors and so prevents transmission of impulses across synapses - Means muscles are not stimulated to contract so person becomes paralysed - Low doses = can be used to relax trachea muscles in asthma patients to save lives - High doses = stop breathing altogether and cause death