Topic 9

Question 1

Homeostasis definition?

Answer 1

the mainteance of a state of dynamic equilibrium in the body despite changes in the external or internal conditions

Question 2

negative Feedback and example?

Answer 2

in the control of any condition, changes are reverses and returned back to the set level. e.g negative feedback in enzymens

Question 3

positive feedback and example?

Answer 3

effectors work to increase the effect that has triggered a response. e.g oxytocin in stimulating contractions.

Question 4

Hormones definition? Types of hormones?

Answer 4

Hormone: a chemical messenger that travels through the blood to a target organ.
Steroid Hormones; cholesterol based and lipid soluble.
Protein Hormones; made from polypeptides.

Question 5

Endocrine vs exocrine glands?

Answer 5

Endocrine: glands that release hormones directly onto the blood. e.g pituitary, testes, pancreas.
Exocrine: glands that release enzymes/solutions into ducts. e.g tear ducts, salivary gland, pancreas

Question 6

how do steroid hormones work?

Answer 6

Hormone passes through the plasma membrane (as it is lipid soluble)
It binds to a receptor protein in the cytoplasm
The Hormone Receptor Complex acts as a transcription factor and binds to DNA.
It enters the nucleus through a pore.
Translation on protein.

e.g oestrogen, testosterone, progesterone

Question 7

How do protein hormones work?

Answer 7

The hormone binds to receptors within the plasma membrane.
This leads to a series of reactions and activates adenylyl cyclase.
This converts ATP into cyclic AMP
THis triggers a different type of chemical reaction on different cells as it activates specific enzymes in the cell.

e.g ADH, Insulin, FSH

Question 8

how does cell elongation in plants occur?

Answer 8

auxin binds to a receptor on the plasma membrane on plant cell.
This stimulates H+ ions to be pumped into cell wall space.
Hence reducing PH and therefore activating expansin enzymes in the cell wall.
Expansins loosen cellulose to make the wall more malleable, allowing water to enter the cell by osmosis to stretch the cell.

Question 9

how does positive phototropism in plants occurs?

Answer 9

The side of the shoot exposed to light contains less auxin as it diffuses across to the shady side. Hence more auxin diffuses down the dark side causing cell elongation on the dark side. Hence the shoot bends towards the light.

Question 10

What is Apical Dominance? How does it occur?

Answer 10

one lead shoot in young plants grows bigger than other lateral buds. This is because the other lateral buds are inhibited by the high auxin levels produced in the first shoot to emerge. The auxin acts antagonistically with cytokinin.
In natural growth as the first shoot grows away, the inhibition of auxin reduces so cytokinin become dominant hence lateral buds grow.

Question 11

What does gibberellin do?

Answer 11

a plant hormone that acts as growth regulators. It is involved in breaking dormancy in seeds and germination.
Seed absorbs water and swells activating embryo.
Embryo secretes gibberellin.
Gibberellin stimulates aleurone layer to produce amylase which diffuses to endosperm and breaks down food stores.
Enzymes produced in response to gibberellin digest the endosperm. Products released from endosperm are used by embryo to make new cells and germinate.

Question 12

Differences between plant and animal hormones?

Answer 12

1. plant hormones are made form simple organic molecules vs animal hormones which are complex proteins or steroids.
2. plant hormones are stimulates by environmental factors e.g light vs animal hormones which are usually homeostatic
3. Plant hormones transported in the phloem vs animal transported in the blood
4. plant hormones control growth vs animal hormones which have a range of functions.
5. plant hormones work slowly and are sustained vs animal hormones which act faster

Question 13

Photochrome?
Photomorphogenesis?
Pr?
Pfr?

Answer 13

Photochrome: plant pigment that affect the response to light.
Photomorphogenesis: plant growth and development influenced by light levels and types.
Pr: blue pigment that absorbs mostly red light. Synthesised in this form.
Pfr: blue green pigment that absorbs far red light. THis is the biologically active form that controls the onset of flowering. BUT only produced once the plant is exposed to light. It stimulates leaf and chlorophyll development.

Question 14

Long day plant?

Answer 14

Plant type: Long Day: only flower if the period of darkness is shorter than the critical length
Season flowering occurs: summer
Night length: short
Amount of Pfr at the end of the night: High (not much converted back to Pr overnight)
Pfr effect: Promotes flowering
Examples:
cabbages

Question 15

Short Day Plant

Answer 15

Plant type: Short day: only flower if the period of darkness is long er that the critical length.
Season Flowering occurs: spring/autumn
night length; long
Amount of Pfr at the end of the night; low (lots converted back to Or overnight)
pfr effect; inhibits flowering
Example; strawberries

Question 16

What is florigen?

Answer 16

a hypothetical plant hormone which is involved in the photoperiodic response. It is carried in the plant transport system to flower buds.
e.g if only one leaf is covered, the whole plant flowers because only one leaf is needed to be exposed to darkness longer than the critical period for florigen to diffuse to the other leaves causing flowering.

Question 17

What does the medulla oblongata do?

Answer 17

controls breathing and heart rate

Question 18

What does the cerebellum do?

Answer 18

controls balance and coordination of movement

Question 19

What does the cerebrum do?

Answer 19

Initiates movement

Question 20

what does the hypothalamus do?

Answer 20

temperature regulation and osmoregulation

Question 21

How is a resting potential achieved and what is it?

Answer 21

Membrane potential is -70mv
3 sodium ions are being actively pumped out of the axon, with only 2 potassium ions are being pumped in.
Sodium ions cannot diffuse back into the axon as the Na+ voltage gated channel is shut.
Hence inside of cell has a slight negative charge relative to the outside.

Question 22

What is depolarisation and how is it achieved?

Answer 22

Membrane potential is +40mv
VOltage gated sodium channels open, allowing rapid diffusion of sodium ions inside axon down their electrochemical gradient.
If this causes membrane potential to reach the threshold at -55mv an action potential results.

Question 23

What is repolarisation and how is it achieved?

Answer 23

Membrane potential is -90mv.
Voltage gated sodium channel shuts.
Voltage gated potassium open.
Hence k+ diffuse down their electrochemical gradient out of the axon.

Question 24

What is hyper polarisation and how is it achieved?

Answer 24

Membrane potential is returned to -70mv.
Both voltage gated channels are shut.
K+ ions diffuse down their electrical gradient.

Question 25

Why are axons myelinated?

Answer 25

the speed of transmission along myelinated axons greater due to saltatory conduction;

• Ions can only pass in and out of the axon freely at the node of ranvier.
• Hence action potential jumps between the nodes due to larger local currents.
• Hence speed of transmission is faster

Question 26

How are action potentials transferred across a synapse?

Answer 26

1. Action potential arrives at pre-synaptic bulb
2. Presynaptic membrane depolarises
3. Voltage gated Ca2+ channels open.
4. Calcium ions diffuse into the pre-synaptic bulb.
5. Vesicles containing neurotransmitters move towards and fuse with the pre-synaptic membrane.
6. Neurotransmitter released by exocytosis.
7. Neurotransmitter diffuses across the cleft.
8. Neurotransmitter binds to receptor in the post-synaptic membrane. This opens the NA+ channels.
9. Na+ diffuses into post-synaptic membrane. Excitatory post-synaptic potential (EPSP) is generated.
10. If threshold is met new action potential will fire.
11. Enzymes in the cleft break down the remaining neurotransmitter to stop overstimulation of the post-synaptic membrane.

Question 27

Effect of Nicotine on the nervous system?

Answer 27

Triggers release of dopamine which is associated with rewards and pleasure pathway.
Mimics the effect of acetylcholine and binds to specific ACH receptors called nicotine receptors. It triggers an action potential in the post-synaptic neuron which causes neural firing. It triggers the release of dopamine.

Question 28

Effect of Lidocaine on the nervous system?

Answer 28

Local Anaesthetic.
Blocks voltage gated sodium channels, preventing the production of an action potential in sensory nerves and so preventing you from feeling pain.
Also prevents some heart arrhythmias, block sodium channels raising depolarisation threshold.

Question 29

Effect of cobra venom on the nervous system?

Answer 29

Death by paralysis.
Binds reversibly to ACH receptors in post-synaptic membranes and neuromuscular junctions. Prevents the transmission of impulses across synapses. So muscles are not stimulated to contract eventually causing paralysis.

Question 30

Eye exposed to bright light?

Answer 30

Pupil constricts = circular muscles contract, radial muscles relax.

Question 31

Structure of retina?

Answer 31

Light => ganglion cells => bipolar cells => photoreceptors (rods and cones) => pigment epithelium => choroid.
Inverted structure
Many rod cells synapse with one bipolar cell whereas only one cone for one bipolar cell. Hence Cones have better visual acuity but rods operate in lower light levels.
Rods are evenly distributed, but none in fovea or blindspot. Cones have highest concentration in fovea and none in blindspot.

Question 32

How do rod cells detect light?

Answer 32

1. A photon of light is absorbed by rhodopsin, embedded in the membrane discs of rod cells.
2. This causes cis retinal to be converted to trans retinal. Hence causing bleaching of the rhodopsin, because the opsin and retinal separate.
3. The trans retinal interacts with the membrane proteins in the rod cell, to close the sodium ion channels.
4. This causes the rod cell to become hyperpolarized because sodium ions can still be pumped out, but are now unable to diffuse back in down their electrochemical gradient. Hence the inside of the rod cell becomes more negative.
5. This causes less of the inhibitory neurotransmitter glutamate to be secreted into the synaptic cleft with the bipolar cell.
6. Hence without the constant inhibition, the bipolar cell is able to depolarise, because the Na+ channels in the post synaptic cleft open to allow Na+ in.
7. If the depolarisation reaches threshold an action potential fires. This could be achieved through convergence in which many rod cells attached to one bipolar cell, summate to let the bipolar cell reach threshold.
8. The action potential travels along the ganglion cells, along the optic nerve to the brain.

Question 33

What are baroreceptors and chemoreceptors?

Answer 33

Baroreceptors are cells with sensory neurons that detect pressure changes. They are found in the aorta and carotid arteries.
Chemoreceptors are sensitive to PH. They are found in the aorta and carotid arteries.

Question 34

How is an increase in blood pressure controlled?

Answer 34

1. Detected by baroreceptors.
2. Sensory neurones fire to cardiac control centre in medulla.
3. Increase in Parasympathetic stimulation. Decrease in sympathetic stimulation.
4. Decrease in heart rate, stroke volume, peripheral resistance.
5. Normal blood pressure.

Question 35

What is the response to exercise?

Answer 35

1. exercise = increase in respiration = increase in CO2 and lactate = decreased blood PH.
2. Detected by chemoreceptors. Sensory neurones to brain.
3. CCC in medulla initiates response.
4. increases sympathetic stimulation.
5. noradrenaline released at SAN
6. increased heart rate

Question 36

Functions of the kidney?

Answer 36

Osmoregulation
Excretion
Erythropoietin (hormone that makes red blood cells)

Question 37

How is urea produced?

Answer 37

Proteins are broken down in digestion to form amino acids. Some of these are used for growth, repair, enzymes… The excess amino acids can not be stored in the LIVER. Hence the amino acids are broken down to keto acid plus ammonia. Keto acid is used in cellular respiration or converted or fat. Ammonia is too toxic. Therefore during the Ornithine cycle deamination occurs to turn ammonia into less toxic urea.

Question 38

What is ultrafiltration?

Answer 38

There is high blood/hydrostatic pressure in the glomerulus.
This is because the afferent arteriole is wider than the efferent arteriole.
This causes small molecules; water, glucose, urea, ions, hormones, amino acids, antibodies to be pushed out of the pores in the endothelium (capillary walls)
The second filter is the pores in the basement membrane. This is a glycoprotein matrix which acts as a molecular sieve. Which ensure only small molecules in size and charge can pass through.
The final filter is the fthe podocyte cells and the filtration slits between the pedicels.

Question 39

What is selective reabsorption?

Answer 39

This is where all glucose, most amino acids, most water, most ions and some urea is reabsorbed in the Proximal convoluted tubule. This means that useful products are kept in the blood.
The PCT is adapted for reabsorption because:
It has protein pumps and channels for facilitated diffusion
Contains many mitochondria for ATP production via respiration
Microvilli surface on apical membrane = large SA for diffusion
Very close and dense network of capillaries = steep concentration gradient
Wall of PCT is 1 cell thick = short diffusion distance.

Ions are actively transported by protein pumps and carrier proteins across the apical membrane before diffusing into the capillaries
Glucose and amino acids are co-transported across the apical membrane with Sodium which acts as the symport. They then diffuse into the capillaries.
The removal of these soluble substances results in an osmotic gradient between the fluid in the tubule and the cells which line it. Hence water travels by osmosis and into the capillaries.

Question 40

What is osmoregulation and the countercurrent multiplier?

Answer 40

Na+ and Cl- ions are actively pumped out of the ascending limb. The ions accumulate in the interstitial fluid. This lowers the water potential of the interstitial fluid. (water wants to osmotically follow the ions but can not as the ascending limb is impermeable to water.)
But water can be drawn out of the descending limb into the interstitial fluid by osmosis. Hence the fluid in the descending limb become more concentrated.
Hence the fluid in the bottom of the loop is very concentrated. As is the interstitial fluid surrounding the bottom of the loop - in the medulla- due to the accumulation of ions.
The fluid moves up the ascending limb, where ions are actively pumped out.
Hence the fluid at the top of the ascending limb is very dilute again.
The fluid then enters the Collecting Duct, which passes through the very concentrated medullary region.
Under the influence of the hormone ADH, the wall of the CD becomes permeable to water. Hence H2O is osmotically drawn out of the CD and into the blood capillaries in the region.
Hence a very concentrated urine can be produced.

Question 41

How does ADH increase permeability of the collecting duct?

Answer 41

ADH binds to a receptor in the plasma membrane of the CD wall cell.
Activation of adenylyl cyclase enzyme which converts ATP to cyclic AMP
THis causes vesicles containing aquaporins, to move towards and fuse with the membrane.
More aquaporins in plasma membrane = increase in permeability of CD wall = more H2O reabsorbed.

Question 42

What is the response to drinking lots of water?

Answer 42

1. dilute blood
2. detected by osmorecptors in the hypothalamus.
3. In the posterior pituitary; no ADH secreted from vesicles in neurosecretory cell terminal
4. In the collecting Duct; no ADH binds to receptors = decrease in cAMP = decrease in number of water channels
5. CD less permeable = less water reabsorbed from filtrate into blood. Large volume of dilute urine.

Question 43

how are kangaroo rats adapted for water conservation?

Answer 43

Produce very concentrated urine
Many juxtamedullary nephrons (nephrons with longer loop of henle vs cortical = shorter LOH)
Long loops of henle
Very folded membrane of epithelial cells lining tubule
High numbers of mitochondria
Also live in burrows = cooler and more stable = less resources needed for thermoregulation
Generate water from oxidative reactions which involve condensation reaction in which water is a by product. Gain the rest of the water they need form water in food.

Question 44

What happens when an endotherm is too hot?

Answer 44

Hair erector muscles relax = hair lie flat = no insulating layer of air
Sweat glands produce sweat = evaporates from skin = increases heat loss
Vasodilation = blood vessels open up allowing more blood to flow through capillaries = more heat loss by radiation
Decrease in metabolic rate
Panting

Question 45

What happens when an endotherm is too cold?

Answer 45

Hair erector muscles contract = hair pulled upright = insulating layer of air trapped above skin
No sweat production
Vasoconstriction = blood vessels contract so less blood flows to capillaries = less heat loss by radiation
Increase in metabolic rate e.g adrenaline
Shivering and involuntary contractions of skeletal muscles

Question 46

Adaptations for animals living in warm environments?

Answer 46

large, thin extremities e.g ears wiht rich blood supply. Thin layer of subcutaneous fat
Behaviour; burrowing

Question 47

Adaptations for animals living in cold environments?

Answer 47

larger animals = smaller SA:V. THick layer of fat. Small extremities. Countercurrent exchange systems to conserve body temperature.
Behaviour; hibernation (the slowing of metabolic rate for a very deep sleep), eatng more before hibernation to gain fat.