Germinating seeds respire aerobically to release the energy needed for growth. In an investigation, 100 germinating mung bean seeds were placed in a respiro...
Question 1 Report
Germinating seeds respire aerobically to release the energy needed for growth. In an investigation, 100 germinating mung bean seeds were placed in a respirometer and the volume of oxygen they consumed each hour was measured once a day for five days. Throughout the investigation the seeds were kept at a constant temperature of 25 °C. The graph shows how the oxygen consumed per hour changed over the five days, and the table gives the same readings in cubic centimetres for each day. Mung beans are commonly used in class experiments because they germinate quickly and respire steadily.
| Day | Oxygen consumed per hour (cm3) |
|---|---|
| 1 | 0.5 |
| 2 | 1.2 |
| 3 | 2.8 |
| 4 | 4.0 |
| 5 | 5.1 |
(a) State the word equation for aerobic respiration in the germinating seeds. [2]
(b) Using the graph, describe how the rate of oxygen consumption changes between day 1 and day 5. [3]
(c) Using the table, calculate the increase in oxygen consumption per hour between day 2 and day 4. Show your working. [2]
(d) The seedlings consume more oxygen each day as they continue to grow. Explain why. [3]
Answer Details
This question tests aerobic respiration and reading a rate from a graph and table.
(a) Word equation. [2] \[\text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water}\] One mark for the correct reactants (glucose + oxygen) and one for the correct products (carbon dioxide + water) [2]. Energy is released but is not written as a product in the word equation.
(b) Change from day 1 to day 5. [3] Describe the trend using figures: oxygen consumption increases throughout, from day 1 to day 5 [1]; the rise is small/slow at first (0.5 to 1.2 cm3 per hour between day 1 and day 2) [1]; then it becomes steeper/faster, reaching 5.1 cm3 per hour by day 5 [1]. Quoting values from the graph earns the data-handling marks.
(c) Increase from day 2 to day 4. [2] \(4.0-1.2=\mathbf{2.8\ cm^{3}}\) per hour [2: working 1, answer with unit 1].
(d) Why more oxygen is used each day. [3] As the seedling grows it has more cells / a larger body [1]; growth and cell division create a greater demand for energy [1]; so the rate of respiration rises and more oxygen is required [1]. Exam tip: link "more growth" to "more respiration" through the idea of energy demand, do not just restate the graph.
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