(a) A student investigated the concentration of lactic acid in the blood of an athlete during a 400 m race.
Fig. 5.1 shows the results of the investigation.
(i) Using the information in Fig. 5.1, state the time during the race when blood lactic acid concentration is 4.8 mmol per \( dm^{3}\).
(ii) Using the information in Fig. 5.1, calculate the increase in blood lactic acid concentration between 0 seconds and 20 seconds.
blood lactic acid concentration at 0 seconds ……………………………………… mmol per \( dm^{3}\)
blood lactic acid concentration at 20 seconds ……………………………………. mmol per \( dm^{3}\)
(iii) The list shows three statements about the data in Fig. 5.1.
Tick (✓) one correct statement.
(b) Complete the sentences about aerobic respiration.
During aerobic respiration, glucose reacts with …………………………………… .
Aerobic respiration takes place in the …………………………………… in cells.
Aerobic respiration releases …………………………………… energy than anaerobic respiration.
(c) Respiration releases energy.
State three uses of energy in living organisms.
▶️ Answer/Explanation
(a)(i) Ans: 15 s
From Fig. 5.1, the blood lactic acid concentration reaches 4.8 mmol per \( dm^{3} \) at 15 seconds.
(a)(ii) Ans: 0.8 mmol per \( dm^{3} \); 5.4 mmol per \( dm^{3} \); 4.6 mmol per \( dm^{3} \)
At 0 seconds, the concentration is 0.8 mmol per \( dm^{3} \), and at 20 seconds, it is 5.4 mmol per \( dm^{3} \). The increase is \( 5.4 – 0.8 = 4.6 \) mmol per \( dm^{3} \).
(a)(iii) Ans: The lactic acid concentration increased between 45 and 55 seconds (✓)
This is the only correct statement, as the graph shows a rise in lactic acid concentration during this interval.
(b) Ans: oxygen ; mitochondria ; more
Aerobic respiration requires oxygen, occurs in mitochondria, and releases more energy than anaerobic respiration.
(c) Ans: Any three from: muscle contraction, protein synthesis, cell division, active transport, growth, nerve impulses.
Energy is used for vital processes like muscle movement, building proteins, transporting substances, and cellular activities.
(a) Yeast can respire anaerobically.
The box on the left shows the beginning of a sentence. The boxes on the right show some sentence endings. Draw three straight lines from the box on the left to the boxes on the right to make three correct sentences.
(b) State two ways anaerobic respiration in yeast is used in biotechnology.
(c) A student investigated the effect of different glucose solution concentrations on the volume of gas produced by yeast. The results are shown in Table 8.1.
The rate of gas production can be calculated using the formula:
\( rate = \frac{1}{time} \)
Calculate the rate of gas production for the glucose solution concentration of 0.4 mol per dm3. Give your answer to two decimal places.
▶️ Answer/Explanation
(a) Anaerobic respiration in yeast is linked to:
- Breaks down nutrient molecules.
- Is a chemical reaction.
- Releases less energy than aerobic respiration.
(b) Two uses of anaerobic respiration in yeast (Biotechnology):
- Bread making (fermentation causes dough to rise).
- Production of ethanol/alcohol (used in biofuels and beverages).
(c) Calculation of gas production rate:
From Table 8.1, for 0.4 mol/dm3, time = 50 seconds.
Using the formula \( rate = \frac{1}{time} \),
\( rate = \frac{1}{50} = 0.02 \, cm^{3} \) per second.
Final Answer: 0.02 \( cm^{3} \) per s