Topic 9

Question 1

homeostasis

Answer 1

maintenance of a state of dynamic equilibrium, despite changes in the external or internal conditions

Question 2

negative feedback

Answer 2

maintains a condition within a narrow range so when something deviates from the norm, changes occur to bring it back to norm

Question 3

positive feedback

Answer 3

when something deviates from the norm and this results in an even greater deviation from the norm

Question 4

endocrine glands

Answer 4

produce hormones and release them into the blood to target organs via transport systems so have a rich blood supply

Question 5

exocrine glands

Answer 5

release chemicals along ducts/ small tubes

Question 6

hormone action: non-lipid soluble hormones

Answer 6

E.g. adrenaline

o bind to receptors on target organ specific to hormone
o attachment causes a series of membrane-bound reactions resulting in formation of second chemical messenger e.g. cyclic AMP which activates several enzymes in the cell to alter metabolism
o cyclic AMP triggers several responses in a cell including increased respiration, increased contraction of muscle cells, relaxation of smooth muscle

Question 7

hormone action: lipid soluble hormones

Answer 7

E.g. oestrogen and testosterone

o passes through the membrane and binds to a receptor inside the cell forming hormone-receptor complex
o passes through the nuclear membrane pores to the nucleus and acts as a transcription factor
o regulating gene expression, switching sections of DNA on and off

Question 8

tropism

Answer 8

directional growth response to specific environmental cues

Question 9

auxins

Answer 9

synthesised in the meristems

o auxins diffuse away from tip to site of cell elongation and bind to receptor sites which activates hydrogen ion pumps in CSM to lower pH in cell wall in the dark side

o pH 5 is optimum pH for enzymes to break down bonds between cellulose microfibrils in cell wall

o cell wall is more flexible and stretch allowing cell to expand when absorbing water by osmosis

o stimulates elongation and therefore more growth in the dark side resulting in shoot bending towards the light

Question 10

synergism of plant hormones

Answer 10

e.g. auxins and gibberellins have a greater effect together in the growth of stems

Question 11

antagonism of plant hormones

Answer 11

auxins and cytokinins maintain apical dominance of the lead shoot grows bigger than others (auxins inhibit growth of lateral buds, cytokinins stimulate)

removing meristem/ absence of auxins results in lateral root growth
auxins inhibit cytokinin action

Question 12

photomorphogenesis

Answer 12

process by which the form and development of a plant is controlled by the levels and type of light

Question 13

how light affects germination

Answer 13

red light stimulates germination by converting Pr to Pfr
farred light inhibits germination by converting Pfr to Pr
last wavelength received determines form of phytochrome present as it is a reversible reaction

Question 14

cerebrum

Answer 14

at the front of the brain made up of two cerebral hemispheres, thinking, seeing, conscious movement

Question 15

cerebellum

Answer 15

at the back of the brain, controls balance and coordination of movement

Question 16

hypothalamus

Answer 16

controls secretion of the pituitary gland, coordinates autonomic nervous system, thermoregulation and osmoregulation

Question 17

medulla oblongata

Answer 17

in the brain stem, contains reflex centres that control breathing rate, heart rate, peristalsis, swallowing

Question 18

spinal cord

Answer 18

column of nervous motor and relay tissue (grey matter) protected by long nerve fibres (white matter) and pairs of nerves emerge at intervals

impulses from sensory receptors enter via dorsal root and leave from motor neurons via ventral root effectors

Question 19

autonomic system

Answer 19

carries nerve impulses to areas controlling breathing rate, heart rate, iris, glands sub-divided into two systems which are antagonistic

split into the sympathetic and parasympathetic system

Question 20

sympathetic system

Answer 20

fight or flight system rapidly stimulates organs to cope with imposed stress by producing noradrenaline

long unmyelinated postganglionic fibre, short myelinated preganglionic fibre

Question 21

parasympathetic system

Answer 21

slow inhibitory effect, maintains normal functioning of the body, restoring after a stressful situation by producing acetylcholine

short unmyelinated postganglionic fibre, long myelinated preganglionic fibre

Question 22

voluntary system

Answer 22

carries nerve impulses by motor neurons to body muscles under conscious control involving cerebrum

Question 23

at resting potential

Answer 23

the inside of an axon is negatively charged compared to the outside

• Na+ are actively transported out of the axon (via the sodium-potassium pump)
• K+ are actively transported into the axon (via the sodium-potassium pump)
3Na+ out for every 2K+ in
More positive outside than inside
• Na+ diffuse back in and K+ diffuse back out but there are more K+ gates open than Na+

Question 24

action potential

Answer 24

when a big enough stimulus is detected by a receptor, the energy of the stimulus causes a temporary reversal of charges inside and outside of the axon (depolarised)

• Depolarising stage: energy of the stimulus causes the Na+ voltage-gated channels to open allowing Na+ to diffuse into the axon causing inside to be more positive (positive feedback cause more Na+ channels to open so more Na+ to move in)
stimulates opening of Na+ channels further along the axon causing further depolarisation

• Repolarising stage: at a certain difference Na+ channels close and K+ channels open so more K+ diffuse out
• Hyperpolarisation: movement of K+ out causes a temporary undershoot where inside is more negative than usual

Question 25

refractory period

Answer 25

time for ionic movements to repolarise a membrane and restore resting potential after an action potential = absolute refractory period + relative refractory period Absolute refractory period: after action potential when it is impossible to re-stimulate as Na+ channels are blocked and resting potential not restored Relative refractory period: after action potential and absolute rp when axon can be re-stimulated but only with a stronger stimulus than before

Question 26

sensory neuron

Answer 26

cell body in the middle, longer myelinated dendrons, shorter axons, no motor end plates, axon terminal (attaches to another neuron)

Question 27

motor neuron

Answer 27

cell body at one end, shorter unmyelinated dendrons, longer axons, has motor end plates (attaches to effector e.g. muscle, gland)

Question 28

salutatory conduction

Answer 28

presence of myelin sheath (formed by Schwann cells covering axon) increases conduction as action potential jumps from node to node o Depolarisation at node of Ranvier o Local currents occur over a longer distance o Myelin sheath provides insulation

Question 29

spatial summation

Answer 29

several presynaptic neurons release enough neurotransmitter to stimulate action potential in one postsynaptic neuron

Question 30

temporal summation

Answer 30

one presynaptic neuron releases enough neurotransmitter to stimulate action potential in one postsynaptic neuron

Question 31

synaptic transmission

Answer 31

1. Action potential arrives at knob causing Ca2+ channels to open allowing Ca2+ to enter by facilitated diffusion 2. Causes synaptic vesicles containing neurotransmitter to move towards and fuse with the CSM and release neurotransmitters into the synaptic cleft by exocytosis 3. Neurotransmitters e.g. acetylcholine diffuse across the synaptic cleft and bind with specific complementary receptor sites in the postsynaptic membrane 4. Na+ channels open allowing Na+ in, causing a depolarisation 5. If enough is present, a new action potential is generated in the postsynaptic neuron in one direction 6. Acetylcholinesterase hydrolyses acetylcholine into acetyl and choline which diffuse back across the synaptic cleft so receptors are available again 7. Neurotransmitter is resynthesised so acetyl and choline combine to form acetylcholine to be used again using ATP from many mitochondria

Question 32

noradrenaline

Answer 32

neurotransmitter in sympathetic nervous system and adrenergic synapses

Question 33

acetylcholine

Answer 33

neurotransmitter in parasympathetic nervous system and cholinergic synapses

Question 34

EPSP

Answer 34

Excitatory postsynaptic potential (EPSP): when neurotransmitter attachment causes Na+ channels open allowing Na+ to enter resulting in a change in potential difference Sufficient EPSP causes positive charge in postsynaptic neuron to exceed the threshold level generating an action potential

Question 35

IPSP

Answer 35

Inhibitory postsynaptic potential (IPSP): when neurotransmitter attachment causes in the inward movement of negative ions so inside is more negative so less likely for an action potential to be generated

Question 36

effect of drugs on nervous system (5)

Answer 36

- block synthesis of neurotransmitter - increase/ decrease release of neurotransmitter from vesicles - cause neurotransmitter to leak out of vesicles and be destroyed by enzymes - block receptors - inhibit enzymes breaking down neurotransmitter in receptor

Question 37

rods

Answer 37

spread evenly across the retina and not in the fovea used for vision in low light intensity and does not detect colour Retinal convergence - several rods synapse with one sensory neuron (bipolar cell) so are very sensitive but do not provide a clear picture

Question 38

cones

Answer 38

highly packed in the fovea used for vision in high light intensity and can detect colour each cone synapses with one bipolar cell providing high visual acuity

Question 39

how the heck do you see

Answer 39

rods contain visual pigment rhodopsin made up of opsin and retinal bleaching: when light hits cis retinal it converts into trans retinal causing opsin and retinal to break causes sodium channels to close so fewer Na+ diffuse in but sodium pump continues pumping Na+ out of cell so cell more negative (hyperpolarisation) generator potential is set up Inhibitory post synaptic potential: if threshold is reached, it stops glutamate neurotransmitter to be released into the synapse Bipolar cell sets up an action potential by opening Na+ channels which leave the eye via the optic nerve

Question 40

if myelinated neurons in retina, no clear image

Answer 40

myelin absorbs light less light passes through to light sensitive cells rods not bleached/ stimulated

Question 41

controlling blood pressure at the start of exercise

Answer 41

* At the start of exercise blood pressure drops as blood vessels dilate (vasodilation) in response to adrenaline * Reduces stretch on baroreceptors which reduces stimulation from baroreceptor to cardiac centre * Cardiac centre in medulla oblongata sends signals along sympathetic nerve to increase heart rate and increase blood pressure by vasoconstriction

Question 42

controlling blood pressure at the end of exercise

Answer 42

* At the end of exercise blood pressure continues to increase * Baroreceptors are stretched so send more impulses to cardiac centre * Cardiac centre sends signals along parasympathetic system to decrease heart rate and lower blood pressure by widening blood vessels by vasodilation

Question 43

controlling heart rate during exercise

Answer 43

(More muscle contraction requires more energy from ATP produced from more respiration) • Produces more CO2 • Lowered pH detected by chemoreceptors in the carotid arteries increases frequency of impulses to medulla oblongata • Releases noradrenaline to SAN via sympathetic nervous system • Heart rate increases to supply more of oxygen and glucose to the muscles

Question 44

producing urea

Answer 44

in the liver, urea is produced from excess amino acids by deamination remove amino group to form ammonia ammonia + CO2 ornithine cycle is a series of enzyme-controlled reactions that converts ammonia into less toxic urea Co(NH3)2

Question 45

how does ADH regulate water potential in blood | e.g. decrease in water potential

Answer 45

* Osmoregulators in hypothalamus detect water potential of blood decrease so sends impulses to posterior gland to release ADH in the blood * Binds to receptors on membrane of tubule cells * Triggers formation of cAMP as secondary messenger which sets up a series of reactions that cause vesicles to move and fuse with cell surface membrane * Vesicles contain water channels which are inserted in the membrane, making it more permeable to water * More water out of tubules by osmosis forming more concentrated urine and increases water potential in blood

Question 46

muscles in the skin when cold

Answer 46

sphincter muscles contract (vasoconstriction) so arteriovenous shunt vessels open to divert blood away from capillaries on the surface erector pili muscles contract so pulls hair upright traps layer of air to insulate