Exam Questions Jan Exam

Question 1

The muscle fibre is relaxed. When the muscle contracts what happens to the appearance of:

• A band
• I band
• H zone

Answer 1

A: no change
I: shorter
H: shorter/disappears

Question 2

Describe the role of calcium ions in muscle contraction (2)

Answer 2

Binds tropomyosin filaments

Revealing binding sites on actin activating ATPase

Question 3

Skeletal muscle is made of bundles of fibres.

a) Describe the roles of calcium ions, ATP and phosphocreatine in producing contraction of a muscle fibre. (4

Answer 3

Calcium ions bind to troponin;
Remove blocking action of tropomyosin / exposes actin binding sites;
ATP allows myosin to join / bind to actin / form cross-bridge;
‘Re-cocks’ myosin cross bridge / allows detachment from actin;
Enables calcium ions to be pumped back in;
Phosphocreatine allows regeneration of ATP without respiration;
Phosphocreatine releases Pi to join ADP;

Question 4

Endurance athletes, such as marathon runners, nearly always have a high proportion of slow fibres in their muscles. Explain the benefit of this.

Answer 4

Endurance athletes exercise for long periods of time;
Respire / release energy aerobically;
Or too much lactate would accumulate;
Slow twitch fibres adapted to aerobic metabolism;
As have many mitochondria;
Site of Krebs’ cycle;
And electron transport chain;
Much ATP formed;
Also are resistant to fatigue;

Question 5

Both slow and fast fibres contain ATPase. Explain why (2)

Answer 5

Splitting / breakdown / hydrolysis of ATP; (Muscle) contraction requires energy / ATP;

Use of ATP by myosin.

Question 6

The muscle in the diagram had been stained for viewing with a microscope.
What is the evidence that it had been stained for viewing with an optical microscope? (2)

Answer 6

1. 2.
   3.
   Accept either approach as some texts refer to ATPase as the enzyme at the end of the ETC in mitochondria.
   Need light to see colour / brown / yellow;
   Requires reference to light.
   Cannot see colour / brown / yellow with electrons / an electron microscope;
   Requires reference to electrons / electron microscope.
   Accept ‘see black and white with electrons / electron microscope’.
   No organelles are visible.
   Accept appropriate named examples of organelles.

Question 7

One form of muscle disease is caused by a mutated allele of a gene. This leads to production of myosin molecules that are unable to bind to other myosin molecules.
If myosin molecules are unable to bind to other myosin molecules, this prevents muscle contraction.
Use the diagram and your knowledge of how muscles contract to suggest why. (3)

Answer 7

Can’t form myosin / thick filaments;
Neutral: prevents actin and myosin sliding filament action
Can’t pull / can’t move actin / slide actin past / (myosin) have to be joined / fixed to pull actin;
Accept: myosin can’t pull on each other
Myosin moves / if attached doesn’t move;
Can’t move actin towards each other / middle of sarcomere / between myosin / can’t shorten sarcomere / can’t pull Z lines together.

Question 8

Describe the roles of calcium ions in the contraction of a myofibril (5)

Answer 8

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 9

What’s the role of phosphocreatine in providing energy during muscle contraction? (2)

Answer 9

To make ATP;
Accept:
ADP + CP → ATP + C Neutral – provides ATP

Question 10

People who have McArdle’s disease produce less ATP than healthy people. As a result, they are not able to maintain strong muscle contraction during exercise. Use your knowledge of the sliding filament theory to suggest why. (3)

Answer 10

(Idea ATP is needed for:)
1. Attachment / cross bridges between actin and myosin;
Accept the role of ADP in attachment
2. ‘Power stroke’ / movement of myosin heads / pulling of actin;
Not just ‘filaments slide’ as given in the question stem
3. Detachment of myosin heads;
4. Myosin heads move back / to original position / ‘recovery stroke’

Question 11

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

Answer 11

The nembrane is less permeable to sodium ions but more permeable to potassium ions. This means that sodium ions are pumped out whilst potassium ions are pumped in.

Question 12

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

Answer 12

Pressure causes the membrane to become stretched, so.sodium.ion channels in the membrane open and sodium ions move in. More channels open when the pressure is greater.

Question 13

Both slow and fast muscle fibres contain ATPase.
Explain why (2)

Answer 13

Splitting / breakdown / hydrolysis of ATP;

(Muscle) contraction requires energy / ATP;

Question 14

The tissue in the diagram came from muscle with a high proportion of brown-staining fibres. Was the tissue removed from slow or fast skeletal muscle?
Explain your answer. (1)

Answer 14

Fast because (lots of) ATPase allows rapid hydrolysis of ATP OR
Slow because (lots of) ATPase allows rapid synthesis of ATP.

Question 15

Damage to the myelin sheaths of neurones can lead to problems controlling the contraction of muscles.
Suggest one reason why.

Answer 15

Action potentials travel more slowly/don’t travel
So delay in muscle contraction/ muscle don’t contract
ORRR
Action potential/depolarisation leaks to adjacent neurones
So wrong muscle fibres contract

Question 16

Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction.

Answer 16

Prevents influx of calcium ions (into pre-synaptic membrane);

(Synaptic) vesicles don’t fuse with membrane / vesicles don’t release neurotransmitter (acetylcholine)

Neurotransmitter does not diffuse across synapse / does not bind to receptors (on post-synaptic membrane);

No action potential / depolarisation (of post-synaptic membrane) / sodium (ion) channels do not open / prevents influx of sodium ions.

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

ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.

Answer 18

Releases relatively small amount of energy / little energy lost as heat;

Releases energy instantaneously;

Phosphorylates other compounds, making them more reactive;

Can be rapidly re-synthesised;

Is not lost from / does not leave cells.

Question 19

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

Answer 19

Membrane more permeable to potassium ions and less permeable to sodium ions

Sodium ions are actively transported/pumped out and potassium ions are pumped in

Question 20

Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential.

Answer 20

(Pressure causes) membrane / lamellae to become deformed / stretched;

Sodium ion channels in membrane open and sodium ions move in;

Greater pressure more channels open / sodium ions enter.

Question 21

One reason that reaction time is slower when body temperature falls is because nerve impulse conduction is slower. Explain how a lower temperature leads to slower nerve impulse conduction

Answer 21

Slower diffusion;

(Of) ions / Na+ / K+;

Question 22

Other than temperature, give two factors that affect the speed of nerve impulse conduction.

Answer 22

Myelination

Axon diameter

Question 23

Give one similarity and one difference between taxis and tropism

Answer 23

Similarity − directional response (to a stimulus) / movement towards / away from a stimulus;
Difference − taxis (whole) organism moves and tropism a growth (response).

Question 24

Explain how this distribution of IAA causes the root to bend

Answer 24

IAA) at bottom of root / where IAA concentration high inhibits expansion / elongation (of cells);

(IAA) at top of root / where IAA concentration low leads to expansion / elongation (of cells);

Question 25

People who have McArdle’s disease produce less ATP than healthy people. As a result, they are not able to maintain strong muscle contraction during exercise. Use your knowledge of the sliding filament theory to suggest why.

Answer 25

(Idea ATP is needed for:)
1. Attachment / cross bridges between actin and myosin;
Accept the role of ADP in attachment
2. ‘Power stroke’ / movement of myosin heads / pulling of actin;
Not just ‘filaments slide’ as given in the question stem
3. Detachment of myosin heads;
4. Myosin heads move back / to original position / ‘recovery stroke

Question 26

When the sarcomeres contract, what happens to the length of (i)
the I-band?
the A-band?

Answer 26

I band: decreases

A band: nothing

Question 27

What is the role of phosphocreatine (PC) in providing energy during muscle contraction?

Answer 27

Provides phosphate

Makes ATP

Question 28

Describe how acetylcoenzyme A is formed in the link reaction.

Answer 28

Oxidation of/hydrogen removed from pyruvate and CO2 is released

Addition of co enzyme A

Question 29

i) Oxaloacetate is the first substrate to bind with the enzyme citrate synthase.
This induces a change in the enzyme, which enables the acetylcoenzyme A to bind.
Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme

Answer 29

Change (in shape) of active site / active site moulds around the substrate;

(Substrate / active site) now complementary.

Question 30

Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration.

Answer 30

Regenerates / produces NAD / oxidises reduced NAD;

(NAD used) in glycolysis.

Question 31

In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this.

Answer 31

(Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic / harmful / causes cramp / (muscle) fatigue.

Question 32

During the experiment, the coloured liquid in the tubing moved towards tube B.

Explain what caused this.

Answer 32

Oxygen taken up / used by seeds;

CO2 given out is absorbed by KOH (solution);

Volume / pressure (in B) decreases.

Question 33

Respiration produces more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent. Explain why.
(2)

Answer 33

Oxygen is final / terminal (electron) acceptor / oxygen combines with electrons and protons;

Oxidative phosphorylation / electron transport chain provides (most) ATP / only glycolysis occurs without oxygen / no Krebs / no link reaction;

Question 34

The stomata close when the light is turned off.

Explain the advantage of this to the plant.

Answer 34

Water is lost through stomata

Closure prevents water loss

Maintains the water content of cells

Question 35

Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil.

Answer 35

(Fertility increased as) more nitrate formed / less nitrate removed / broken down;

Less / no denitrification / process P is decreased / fewer denitrifying bacteria.

Question 36

Suggest two ways in which crop rotation may lead to high crop yields.

Answer 36

Grow crops / plants with nitrogen-fixing (bacteria);

(Different crops use) different minerals / salts / nutrients / ions (from the soil);

(Different crops have) different pests / pathogens / diseases.