Topic 7 – Run for your life

Question 1

What is the term that describes the ability of the heart muscle to contract without external stimulation? (1)

Answer 1

-Myogenic.

Question 2

Explain why it is necessary for the cardiac output of marathon runners to increase during a race. (2)

Answer 2

-Increase supply of oxygenated blood to muscles.
-To allow aerobic respiration.
-To provide more energy to meet the increased demands.

Question 3

Deduce how adrenaline can cause a change in heart rate. (4)

Answer 3

-Adrenaline carried in the blood.
-Acts on SAN/Sinoatrial Node.
-Increasing frequency of impulses produced by SAN.
-Increasing rate at which heart contracts.

Question 4

Explain how starting to exercise causes an increase in breathing rate. (3)

Answer 4

-Exercises initiates impulses from motor cortex.
-Impulses sent to ventilation centre/medulla oblongata.
-Leading to increased impulses to intercostal muscles.

Question 5

The demand for oxygen changes during exercise.
The change in demand affects the breathing rate.

Explain the effect of exercise on the changes in oxygen consumption. (4)

Answer 5

-Exercise will increase oxygen consumption.
-Because there is increased aerobic respiration.
-Because more energy/ATP is needed by muscles.
-Oxygen required to convert lactic acid into glucose/pyruvate.
-Oxygen consumption begins to decrease after exercise.

Question 6

Describe how a spirometer trace can be used to calculate the respiratory minute ventilation. (2)

Answer 6

-Find difference in peak to trough volume to give tidal volume.
-Find ventilation rate.
-Multiple tidal volume by ventilation rate.

Question 7

Describe how a spirometer trace can be used to calculate the oxygen consumption per minute. (2)

Answer 7

-Difference in volume of one peak compared to a subsequent one.
-Divide by time between two peaks and multiply by 60.

Question 8

Describe how the sinoatrial node (SAN) is involved in bringing about a change in heart rate as the level of activity increases. (2)

Answer 8

-More stimulation/depolarisation of the SAN from sympathetic nervous system/more impulses to SAN.
-Causing more frequent waves of depolarisation from SAN to atria.
-Leading to more frequent contraction of atria/stimulation of SAN.

Question 9

Explain how a single gene can give rise to acetylcholinesterase molecules with different primary structures (2)

Answer 9

-Pre-mRNA splicing/post transcriptional modification.
-Different exons removed.
-Therefore producing different sequences of amino acids/mRNA sequences.

Question 10

Explain how the acetylcholinesterase gene can be expressed in some tissues but not others. (3)

Answer 10

-Chemical signals bind to receptors found only in some tissues/cells.
-Regulating a transcription factor/repressor molecules.
-Transcription factor/repressor molecule binds to promoter region of the acetylcholinesterase gene.
-Therefore switching on/off transcription.

Question 11

Beta cells in the pancreas produce insulin when there is an increase in glucose levels in the blood.

Explain how transcription factors could activate insulin gene expression in beta cells. (3)

Answer 11

-Interaction between transcription factors and promoter region on gene.
-RNA polymerase binds to promoter region.
-Transcription/mRNA produced for insulin gene.

Question 12

Explain how groups of cells can produce the same enzyme. (3)

Answer 12

-Genes can be activated or deactivated/switched on or off.
-These cells receive the same stimulus.
-All of these cells have the gene for the enzyme activated/switched on.
-Resulting in production of mRNA for enzyme.

Question 13

Describe how a tissue differs in structure from a system. (2)

Answer 13

-Tissue contains one type of cell.
-A system contains many different organs/tissues.

Question 14

Describe how mesenchymal stem cells can give rise to different types of cell. (4)

Answer 14

-Different stimuli activate different genes.
-Genes activated are transcribed/mRNA produced from active genes.
-mRNA translated to produce proteins.
-Proteins determine structure/function of cell.
-Different genes activated/proteins produced results in different types of cells being produced.

Question 15

Heat stress occurs when the core body temperature rises above 40 °C.

Describe how thermoregulatory mechanisms are controlled to help marathon runners avoid heat stress. (4)

Answer 15

-Thermoreceptors in hypothalamus or skin detect increase in temperature.
-Heat loss/thermoregulatory centre in hypothalamus stimulated.
-Hypothalamus sends impulses to sweat glands.
-Increased rate of blood flow to surface of skin by vasodilation of arterioles/vasoconstriction of shunt vessels.
-Decreased metabolic rate.

Question 16

Explain the role of the brain in reducing a persons heart rate after exercise. (2)

Answer 16

-Chemoreceptors detect change in pH/carbon dioxide.
-The cardiovascular control centre receives impulses from chemoreceptors/sends impulses to the heart.
-Therefore impulses transmitted along parasympathetic nervous system to the SAN reducing heart rate.

Question 17

Describe how the brain reduces the activity of the sweat glands after exercise. (2)

Answer 17

-Thermoreceptors detect a decrease in temperature.
-Hypothalamus/thermoregulatory centre sends fewer impulses to sweat glands.

Question 18

Explain why too much exercise could be harmful to the human body. (3)

Answer 18

-Increased exercise results in wear and tear of joints/cartilage/tendons/ligaments.
-Leading to joint damage.
-Suppression of immune system.
-Leading to increased risk of infection.

Question 19

What structure joins bones to bones in an elbow joint? (1)

Answer 19

-Ligaments.

Question 20

Describe the changes caused when calcium ions bind to troponin. (3)

Answer 20

-Troponin changes shape
-Tropomyosin is moved by troponin
-Myosin binding sites on actin are exposed.

Question 21

Explain how the changes caused by calcium ions binding to troponin causes muscles to contract. (4)

Answer 21

-Myosin heads can bind to binding sites.
-Myosin changes shape.
-Actin filaments slide over myosin.
-Therefore muscle fibres/sarcomeres/myofibril shorten.
-ATP hydrolysed/ADP and inorganic phosphate released.

Question 22

Describe the interaction between troponin and tropomyosin that allows muscle contraction. (2)

Answer 22

-Troponin changes shape.
-Causing tropomyosin to move away from myosin binding sites on actin.

Question 23

The thick filament in a myofibril contains myosin. The myosin head contains the enzyme ATPase.

Explain the importance of the primary structure for the functioning of this enzyme. (3)

Answer 23

-Primary structure determines interaction between amino acids/R groups.
-Primary structure determines folding/tertiary structure.
-Therefore affecting shape of active site.
-Active site is complementary to ATP.

Question 24

Describe how the concentration of calcium ions around the myofibrils is controlled. (3)

Answer 24

-Calcium ions released from sarcoplasmic reticulum.
-In response to depolarisation/action potential/nerve impulse.
-Calcium channels open to allow calcium ions to cross the membrane/enter sarcoplasm.
-Calcium ions taken back up into sarcoplasmic reticulum by active transport.

Question 25

Describe the role of calcium ions in the contraction of muscle fibres. (3)

Answer 25

-Calcium ions bind to troponin/changes shape of troponin.
-Causing tropomyosin shape to be altered/tropomyosin moved.
-Exposing myosin binding sites on actin.

Question 26

Where is the myosin binding site found? (1)

Answer 26

-Actin.

Question 27

Describe two structural differences between fast twitch muscle fibres and slow twitch muscle fibres. (2)

Answer 27

-Fast twitch fibres have few/no mitochondria present/Slow twitch fibres have many mitochondria.
-Fast twitch fibres have few/no capillaries present/Slow twitch fibres have many capillaries present.

Question 28

Explain how the structure of a muscle fibre is related to its specialised function. (3)

Answer 28

-Cell surface membrane/sarcolemma contains voltage gated channels to allow depolarisation of muscle cells.
-Many mitochondria for aerobic respiration.
-Presence of myofibrils/myosin and actin.
-Myofibrils allow contraction of muscle.

Question 29

Describe how tertiary structure of myosin is related to its function. (3)

Answer 29

-Folded into a specific shape with a globular head.
-That can bind to actin.
-Myosin has a site that can bind with actin.
-Straight to form a bundle with other myosin molecules.

Question 30

Name two molecules needed for aerobic respiration that can move into the mitochondria. (2)

Answer 30

-Pyruvate.
-Oxygen/ADP/Reduced NAD.

Question 31

The outer mitochondrial membrane is not permeable to hydrogen ions (H+).

Explain the importance of this feature of the membrane. (4)

Answer 31

-To stop H+ diffusing out of mitochondrion/into cytoplasm.
-Therefore maintaining a high concentration of H+ in the intermembrane space.
-So H+ can move down concentration/electrochemical gradient.
-By chemiosmosis.
-To synthesise ATP.

Question 32

State the name of the site where the Krebs cycle occurs. (1)

Answer 32

-Matrix.

Question 33

State the name of the site where Oxidative phosphorylation occurs. (1)

Answer 33

-Crista.

Question 34

Explain why some ATP is broken down during glycolysis. (2)

Answer 34

-Breakdown of ATP donates phosphate to the glucose/phosphorylates the glucose.
-ATP supplies energy to break down glucose.
-To produce phosphorylated 3 carbon compound.

Question 35

The electron transport chain occurs in the cristae of mitochondria. The electron transport chain involves a number of carrier molecules.

Explain the role of these carrier molecules in the electron transport chain. (3)

Answer 35

-Receive hydrogen from reduced NAD/FAD.
-Breaks hydrogen into H+ and electrons.
-Electrons transferred by a series of redox reactions.
-Energy released is used to pump H+ into intermembranal space.

Question 36

Cells produce lactate during anaerobic respiration. Lactate travels in the blood to the liver. Liver cells can absorb lactate from the blood.

Deduce what happens to the lactate in these cells. (2)

Answer 36

-Lactate is oxidized to form pyruvate.
-Pyruvate converted to glucose.
-Pyruvate/Glucose used in respiration.

Question 37

Devise an investigation, using a respirometer, to find the optimum temperature for respiration in maggots. (5)

Answer 37

-Suitable range of temperatures used.
-Age, species, mass or size of maggots controlled.
-Record distance bubble travels in a set time/record time taken to travel a set distance.
-Note first temperature where distance bubble moves is less, so previous highest temperature to this is the optimum.
-Details of respirometer set up: use water baths, soda lime, time for
organisms to acclimatise etc.
-Repeats at each temperature to calculate a mean value.