IB Biology Paper 3 Question Bank

1.) Describe the structure of striated muscle fibres.
Cells joined with no dividing membranes. Plasma membrane called sarcolemma. Multinucleate cytoplasm. Large numbers of mitochondria. Sarcoplasmic reticulum. Bundles of protein filaments/myofibrils. Myofibrils made of actin and myosin produce banding patterns that have light and dark bands.

2.) Explain how a skeletal muscle contracts.
The sarcolemma is depolarised by a nerve impulse. The sarcoplasmic reticulum releases calcium ions and these bind to thin / actin filaments. The binding sites are exposed. Hence myosin head binds and a cross-bridge forms. The head bends and pulls thin / actin filament. Sarcomere shortens / distance between Z lines shortens. ATP binds to the myosin head. This breaks the cross-bridge and the head swings back to the start position.

3.) Explain the need for increases in tidal volume and ventilation rate during exercise.
More significant muscle activity/increase in respiration requires more oxygen and glucose. Greater muscle activity/increase in respiration produces more carbon dioxide. Tidal volume is air breathed in / out with each breath. Ventilation rate is the number of breaths per minute. Increase in both is required to maintain high/steep concentration gradients between blood and air in alveoli for both oxygen and carbon dioxide. A high concentration gradient holds a high concentration of oxygen and a low concentration of carbon dioxide in the blood

4.) Explain the changes in cardiac output and venous return during exercise.
Fall in blood pH (due to carbon dioxide from muscle respiration) detected by chemoreceptors in carotid arteries. Impulses are sent to the sinoatrial node/pacemaker. This increase in cardiac output causes muscle contractions which squeeze veins. Increase in venous return to the heart.

5.) Evaluate the risks and benefits to an athlete of using erythropoietin (EPO).
EPO is produced naturally by the body to stimulate the formation of red blood cells. Using EPO will increase the red cell count. More oxygen supplied to muscles could improve performance, especially useful for endurance events. Blood is thickened which can cause blood clots/strain on the heart. This causes an increased risk of heart attack/stroke and increased risk of dehydration in endurance events.

6.) Outline the method of ATP production used by muscle fibres during the exercise of varying intensity and duration.
ATP is produced from aerobic respiration and anaerobic respiration and from creatine phosphate. Creatine phosphate is used for brief periods / few seconds of intense activity – e.g. 100 m sprint / similar. Anaerobic respiration is used for short periods/seconds to 2 minutes of intense activity – e.g. 200 m sprint / similar. Aerobic respiration is used for extended periods / several minutes to hours of low-level activity – e.g. long run /
cross country run/marathon / aerobic exercises.

7.) Outline how the oxygen debt is formed and repaid.
Anaerobic respiration in muscle produces lactate. Lactate is transferred to the liver via blood. The liver converts lactate back to pyruvate. Pyruvate oxidised to carbon dioxide and water/enters the Krebs cycle. For this oxygen is required. Deep breathing continues (for a short time) after exercise has ended to supply oxygen to repay debt

8.) Distinguish between fast-twitch and slow-twitch muscle fibres.

9.) Distinguish between a sprain, a tear and a dislocation.

10.) A reliable method of estimating cardiovascular fitness is by measuring the body’s oxygen consumption when the rate of heartbeat is at its maximum (Vmax) during intense exercise. This test was used to measure fitness among 71 volunteers. Two weeks later, the same individuals were asked to run for 2.1 km at two different speeds (V70 and V90) and the power they developed during these runs was measured.

• V70 in which they ran at a speed where their rate of the heartbeat was 70% Vmax.
• V90 in which they ran at a speed where their rate of the heartbeat was 90% Vmax.

A. State the maximum power developed by a runner at V70.
335 (±5) W

B. Outline the relationship between running velocity and power developed at V90.
as velocity increases power increases

C. Compare the data for V70 and V90.
Both have the same/similar maximum power. Both show increased power at greater velocities.

D. Suggest why measurements of Vmax are dangerous for older people.
Risk of heart attack

11.) During the muscular activity, the heart must deliver more blood to the tissues due to increased oxygen demand. Graph 1 shows the distribution of total blood flow (cardiac output) between muscles (grey-shaded bars) and all other parts of the body (black-shaded bars) in resting men and in both average men and top athletes doing heavy exercise. Graph 2 shows oxygen consumption by the muscles and all other parts of the body in the three groups. The value given for each bar represents the total body values.

A. Describe the relationship between exercise and total cardiac output.
Directly proportional

(i) Calculate the percentage of cardiac output to the muscles for an average man during heavy exercise as compared to the total body value.
82.5 (±3)%

(ii) Calculate the increase in total oxygen consumption (ml min−1) for a top athlete during heavy exercise as compared to a resting man.

C. Using the data, explain how training affects an athlete’s body with respect to cardiac output and oxygen consumption.
Cardiac output to muscles / overall cardiac output increases. More in top athletes / with training. Training / top athlete decreases cardiac output to the rest of the body. Training increases oxygen consumption in muscles/ overall oxygen consumption during heavy exercise.