Responses to Changes in environment

Question 1

Caffeine affects the autonomic nervous system. Suggest how caffeine could account for the results of Group I in Figure 2 at 60 minutes

Answer 1

An increase in heart rate
More action potentials along sympathetic nervous system pathway
Sends more impulses to SAN increasing heart rate

Question 2

Exercise causes an increase in heart rate
Describe the role of receptors and of the nervous system in this process

Answer 2

Chemoreceptors detect a fall in blood pH due to increase in CO2
This sends action potentials to the cardiac centre in the medulla
This sends action potentials down the sympathetic nervous system pathway
These stimulate the SAN and cause an increase in heart rate

Question 3

When the heart beats, both ventricles contract at the same time.
Explain how this is coordinated in the heart after initiation of the heartbeat
by the SAN

Answer 3

Electrical impulse only from AVN and sends impulses down the bundle of his fibres
This wave of electrical activity passes through both ventricles at the same time

Question 4

Damage to the myelin sheath of neurones can cause muscular paralysis
(lines 2–4).
Explain how.

Answer 4

Without myelin there is no saltatory conduction
So nerve impulses are slowed
Neuromuscular junction does not receive enough impulses to stimulate contraction

Question 5

Sometimes Guillain–Barré syndrome causes heart rate irregularities (Unmyelinated neurons)
Suggest and explain why

Answer 5

Slower impulses along sympathetic/parasympathetic nervous system pathways
From the medulla/cardiac centre
To the SAN

Question 6

Suggest and explain how the interaction between the muscles labelled in
the diagram above could cause the pupil to constrict (narrow).

Answer 6

Circular muscle contracts
Radial muscle relaxes

Question 7

The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer

Answer 7

High visual acuity
As each cone is connected to its own single neuron
So they send separate sets of impulses to the brain

Question 8

The retina of an owl has a high density of rod cells. Explain how this enables an owl to hunt its prey at night. Do not refer to rhodopsin in your answer.

Answer 8

High visual sensitivity
Many rod cells are connected to a single neuron so it allows spatial summation
Enough neurotransmitters to reach threshold

Question 9

Explain how the resting potential of –70 mV is maintained in the sensory
neurone when no pressure is applied.

Answer 9

The Na+/K+ pump actively transports out 3 sodium for every 2 potassium in
Membrane more permeable to potassium than sodium

Question 10

Explain how applying pressure to the Pacinian corpuscle produces the
changes in membrane potential recorded by microelectrode P

Answer 10

Pressure causes lamellae to become deformed/stretched
Allows Na+ channels to open and sodium moves in
Greater pressure means more channels are open so more sodium enters

Question 11

The membrane potential at Q was the same whether medium or heavy
pressure was applied to the finger tip. Explain why

Answer 11

Threshold potential is reached
So causes maximal response/all or nothing principle

Question 12

Explain why the speed of transmission of impulses is faster along a
myelinated axon than along a non-myelinated axon.

Answer 12

Saltatory conduction
Myelin is impermeable to ions so action potential moves between nodes of ranvier
In non-myelinated axons depolarisation occurs along the whole length of the axon.

Question 13

A scientist investigated the effect of inhibitors on neurones. She added a
respiratory inhibitor to a neurone. The resting potential of the neurone
changed from –70 mV to 0 mV.
Explain why.

Answer 13

Inhibiting respiration means no ATP is produced
This means the Na+/K+ pump cannot actively transport sodium and potassium
This also means there is no electrochemical gradient for Na+ and K+ to move in or out of the axon

Question 14

Describe the sequence of events involved in transmission across a cholinergic
synapse.
Do not include details on the breakdown of acetylcholine in your answer.

Answer 14

Action potential reaches the synaptic knob of presynaptic membrane which stimulates Ca2+ channels to open and causes calcium to flow in.
This causes vesicles containing acetylcholine to bind to the presynaptic membrane and release acetylcholine
Acetylcholine diffuses across the synaptic cleft
Acetylcholine attaches to receptors on postsynaptic membrane
This causes sodium channels to open and sodium ions enter and cause depolarisation

Question 15

Dopamine has a role in numerous processes in the brain including pain relief. The release of dopamine can be stimulated by chemicals called endorphins produced in the brain. Endorphins attach to opioid receptors on
presynaptic neurones that release dopamine. Morphine is a drug that has a similar structure to endorphins and can
provide pain relief.
Explain how

Answer 15

Morphine attaches to opioid receptors
More dopamine is released causing pain relief

Question 16

GABA is a neurotransmitter released in some inhibitory synapses in the
brain. GABA causes negatively charged chloride ions to enter postsynaptic
neurones.
Explain how this inhibits postsynaptic neurones.

Answer 16

This lowers the charge within the postsynaptic neuron
This means more sodium ions must flow in to reach threshold potential
And cause depolarisation

Question 17

Use your knowledge of how myosin and actin interact to suggest how the
myosin molecule moves the mitochondrion towards the presynaptic
membrane.
Do not include the roles of calcium ions and tropomyosin in your answer.

Answer 17

Myosin attaches to actin and bends causing powerstroke
This pulls mitochondria along actin filament
Next myosin head attaches and performs another powerstroke

Question 18

This movement of mitochondria happens when nerve impulses arrive at the
synapse.
Suggest and explain one advantage of the movement of mitochondria
towards the presynaptic membrane when nerve impulses arrive at the
synapse.

Answer 18

Mitochondria supply ATP
For movement of vesicles

Question 19

Explain how a decrease in the concentration of calcium ions within muscle
tissues could cause a decrease in the force of muscle contraction

Answer 19

No tropomyosin moved from binding site
No actomyosin bridges formed
Myosin does not contract and pull actin

Question 20

The scientists then compared the length of time that the control mice and
the trained mice could carry out prolonged exercise. The trained mice were
able to exercise for a longer time period than control mice.
Explain why.

Answer 20

Aerobic respiration produces more ATP
Anaerobic is delayed
Less or no lactate is produced

Question 21

he image shows glycogen granules present in skeletal muscle.
Explain their role in skeletal muscle

Answer 21

As a store of glucose for respiration
To release ATP for muscle contraction

Question 22

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in
pH leads to a reduction in the ability of calcium ions to stimulate muscle
contraction.
Suggest how.

Answer 22

Low pH changes calcium ion channel structure
Fewer calcium ions bind to troponin
Fewer tropomyosin move
Fewer binding sites on actin are revealed
Fewer cross bridges form

Question 23

Describe the roles of calcium ions and ATP in the contraction of a
myofibril.

Answer 23

Calcium diffuses into myofibril from sarcoplasmic reticulum
Calcium binds to troponin and causes tropomyosin to change structure and
reveal binding sites on actin filament.
Myosin heads bind and form cross bridges
hydrolysis of ATP causes myosin heads to contracts in powerstroke and
pull on actin filament
then ATP binds to myosin head causing it to detach

Question 24

Neonatal diabetes is a disease that affects newly born children. The disease is caused by a change in the amino acid sequence of insulin.
This change prevents insulin binding to its receptor. Explain why this change prevents insulin binding to its receptor

Answer 24

Changes tertiary structure
No longer complementary (to receptor)

Question 25

Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes.

Answer 25

High concentration of glucose in blood/filtrate
Not all glucose is reabsorbed in the proximal convoluted tubule
Carrier/co-transport proteins are saturated/working at their maximum rate

Question 26

Describe the role of glucagon in gluconeogenesis.
Do not include in your answer details on the second messenger model of glucagon action.

Answer 26

Glucagon binds to receptor on target cells and activates/stimulates enzymes
Conversion of glycerol/fatty acids/amino acids into glucose

Question 27

Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration

Answer 27

More insulin binds to receptors
Stimulates uptake of glucose by channel/transport proteins
OR
Activates enzymes involved in conversion of glucose to glycogen

Question 28

Explain how inhibiting adenyl cyclase will lower the blood glucose concentration

Answer 28

Less/no ATP converted into cAMP
Less Protein Kinase A activated
Less glycogenolysis

Question 29

Give two reasons why pancreas transplants are not used for the treatment of type II diabetes

Answer 29

Type II produce insulin
Receptors are less sensitive to insulin
Treated by exercise/diet

Question 30

Give two ways in which people with type 1 diabetes control their blood
glucose concentration

Answer 30

Treat with insulin injections
Control diet/glucose intake

Question 31

Diabetes can damage the nervous system. The response of the rats with diabetes is different from the response of the healthy rats. Use your knowledge of the control of heart rate by the nervous system to suggest an explanation for these results.

Answer 31

Damage to autonomic nervous system
Damage to baroreceptors in carotid body so they don’t work as well
Change in number of impulses sent to/from medulla
When pressure drops damage to sympathetic nervous system pathway means heart rate doesn’t speed up enough
When pressure rises damage to parasympathetic pathway means heart rate doesn’t slow down enough

Question 32

Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of both men and women. Affected individuals have proteinuria (high quantities of protein in their urine). Explain why.

Answer 32

Affects basement membrane
More protein channel/carriers in basement membrane
Protein can pass into glomerular filtrate

Question 33

Describe how ultrafiltration occurs in a glomerulus

Answer 33

High blood/hydrostatic pressure in afferent arteriole
Water, glucose, AA, urea, ions move out
Through pores/fenestrations in capillary endothelium
And through the basement membrane

Question 34

Scientists investigated the relationship between the thickness of the kidney medulla of different species of mammals and the concentration of their urine. Explain why a thicker medulla results in more concentrated urine.

Answer 34

Thicker medulla means longer loop of Henle
Therefore sodium ion concentration gradient is maintained for longer
Therefore water potential gradient maintained for longer so more water reabsorbed from loop of Henle/collecting duct

Question 35

Furosemide inhibits the absorption of sodium and chloride ions from the filtrate produced in the nephrons. Explain how furosemide causes an increase in the volume of urine produced

Answer 35

Water potential in the filtrate is lowered
Less water is reabsorbed by osmosis
In the collecting duct

Question 36

More than 99% of biological molecules are reabsorbed from the filtrate in
the proximal convoluted tubule.
Despite this, the concentration of fluid in this tubule remains constant.
Explain why

Answer 36

Water is also reabsorbed

Question 37

Explain why concentration of filtrate increases and then decreases in the loop of Henle

Answer 37

Increases in descending limb as water leaves by osmosis and ions enter
Concentration falls in the ascending limb as sodium and chloride ions are actively transported out
But water remains in as its walls are impermeable to water

Question 38

Give the location of osmoreceptors in the body of a mammal.

Answer 38

Hypothalamus

Question 39

When a person is dehydrated, the cell volume of an osmoreceptor decreases.
Explain why.

Answer 39

Water potential in the blood is lower than osmoreceptor
So water moves from osmoreceptor to blood by osmosis

Question 40

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys.

Answer 40

Permeability of membranes is increasing
More water absorbed from the distal convoluted tubule/collecting duct
Smaller volume of urine
Urine becomes more concentrated

Question 41

Creatinine is a breakdown product of creatine found in muscle tissues.
Apart from age and gender, give two factors that could affect the
concentration of creatinine in the blood

Answer 41

Muscle/body mass
Ethnicity
Exercise
Kidney disease

Question 42

The acidic pH conditions created by osteoclasts cause the inactive form of
the protein osteocalcin to change into the active form of osteocalcin.
Suggest how

Answer 42

Fall in pH changes hydrogen bonding so tertiary structure of osteocalcin changes

Question 43

Binding of insulin leads to an increase in the rate of respiration in cells such
as osteoblasts.
Explain how

Answer 43

Insulin leads to more GLUT4/channel/carrier proteins for glucose
More glucose enters cell for respiration