t6 test

Question 1

Describe the myogenic stimulation of the heart and how the regular contraction of the atria and ventricles is coordinated

Answer 1

SAN releases wave of electrical activity

Atria contract at the same time

AVN passes electrical activity after a short delay

Via Purkyne tissue and bundle of His;

So ventricles contract at the same time from bottom upwards

Question 2

Describe how stimulation of a Pacinian corpuscle produces a generator potential

Answer 2

There are stretch-mediated sodium ion channels in the
membrane

Increased pressure deforms sodium ion channels

Sodium ion channels open

Sodium ions diffuse in

Depolarisation leading to generator potential

Question 3

Following the release of acetylcholine into a neuromuscular junction, a muscle contraction occurs

Describe the sequence of events, following the release of acetylcholine, that leads to stimulation of this contraction

Answer 3

Acetylcholine diffuses across synaptic cleft

Acetylcholine attaches to receptors on the sarcolemma

Sodium ions enter leading to depolarisation

Calcium ions released by sarcoplasmic reticulum

Question 4

Inhibitory synapses cause hyperpolarisation in postsynaptic neurones

Explain how this inhibits synaptic transmission

Answer 4

Axon potential is below resting potential

More sodium ions required to enter for action potential

Question 5

Fast muscle fibres have a higher concentration of glycogen than slow muscle fibres

Explain how the difference in glycogen concentration is related to the different properties of these muscle fibres

Answer 5

Fast fibres contract quickly whereas slow fibres contract slowly

Fast fibres mainly use anaerobic respiration

Fast fibres produce ATP quickly

Glycogen hydrolysed to glucose

Question 6

Describe the roles of ATP in muscle contraction

Answer 6

To break actinomyosin bridges

To move the myosin head

For active transport of calcium ions into sarcoplasmic reticulum

Question 7

What does creatine do

Answer 7

Creatine used to form phosphocreatine

Phosphocreatine combines with ADP to form ATP

Question 8

How does an increase in muscle activity causes an increase in heart rate

Answer 8

Increase in CO2 detected by chemoreceptors

Send more impulses to the medulla

More impulses from medulla along sympathetic pathway

To SAN

Question 9

Give reasons why a weight-loss programme could be used to treat type II diabetes but not type I diabetes

Answer 9

Type l do not produce insulin

In type II receptors less responsive to insulin

Weight not linked to type l diabetes

Question 10

Describe and explain how features of the cells in the proximal convoluted tubule allow the rapid reabsorption of glucose into the blood

Answer 10

Microvilli provide a large surface area

Many channel proteins for facilitated diffusion

Many carrier proteins for active transport

Many mitochondria produce ATP

Many ribosomes to produce carrier proteins

Question 11

Describe the effect of ADH on the collecting ducts in kidneys

Answer 11

Stimulates addition of aquaporins into membrane

More water reabsorbed

By osmosis

Question 12

Explain how the fovea enables an eagle to see its prey in detail

Answer 12

High visual acuity

Each cone is connected to a single neurone

Cones send separate sets of impulses to brain

Question 13

Explain how a resting potential is maintained across the axon membrane in a neurone

Answer 13

Potassium ions diffuse out

Membrane more permeable to potassium ions

Sodium ions actively transported out and potassium ions in

Question 14

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

Answer 14

Myelination provides electrical insulation

In myelinated saltatory conduction

In non-myelinated depolarisation occurs along whole length of axon

Question 15

Describe the sequence of events involved in transmission across a cholinergic synapse

Answer 15

Depolarisation of presynaptic membrane

Calcium channels open and calcium ions enter synaptic knob

Calcium ions cause synaptic vesicles fuse with
presynaptic membrane and release acetylcholine

Acetylcholine diffuses across synaptic cleft

Acetylcholine attaches to receptors on the postsynaptic membrane

Sodium ions enter postsynaptic neurone leading to depolarisation

Question 16

Role of glycogen in skeletal muscle

Answer 16

To be hydrolysed to glucose

For respiration

Question 17

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

Answer 17

Calcium ions diffuse into myofibrils from sarcoplasmic reticulum

Calcium ions cause movement of tropomyosin on actin

This movement causes exposure of the binding sites on the actin

Myosin heads attach to binding sites on actin

Hydrolysis of ATP on myosin heads causes myosin heads to bend

Bending pulling actin molecules

Attachment of a new ATP molecule to each myosin head causes myosin heads to detach from actin sites

Question 18

Give ways in which ATP is a suitable energy source for cells to use

Answer 18

Releases relatively small amount of energy

Releases energy instantaneously

Phosphorylates other compounds, making them more reactive

Can be rapidly re-synthesised

Does not leave cells

Question 19

What is the role of ATP in myofibril contraction

Answer 19

Reaction with ATP allows binding of myosin to actin

Provides energy to move myosin head

Question 20

Explain why glucose is found in the urine of a person with untreated diabetes

Answer 20

High concentration of glucose in blood

Not all the glucose is reabsorbed at the proximal convoluted tubule

Carrier proteins are saturated

Question 21

Describe the role of glucagon in gluconeogenesis

Answer 21

Attaches to receptors on target cells and activates enzymes

Glycerol into glucose

Question 22

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

Answer 22

Treat with insulin injection

Control diet

Question 23

Describe how ultrafiltration occurs in a glomerulus

Answer 23

High hydrostatic pressure

Ions and urea pass out

Through small gaps in capillary endothelium

And through basement membrane

Question 24

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

Explain why

Answer 24

Water potential of blood will decrease

Water moves from osmoreceptor into blood by osmosis

Question 25

Describe and explain how the secretion of ADH affects urine produced by the kidneys

Answer 25

Permeability of membrane to water is increased More water absorbed from collecting duct Smaller volume of urine Urine becomes more concentrated