Question 1
Paper 2Medium16 marksFigure 1 represents a water molecule. The positions of the electron pairs are shown.
A class investigated respiration in yeast cells with different water contents. The cultures were supplied with equal glucose and oxygen and kept at 25 °C. Table 1 gives the mean rate of carbon dioxide production.
| Water content of yeast cells / % | Mean rate of carbon dioxide production / μmol g⁻¹ dry yeast min⁻¹ |
|---|---|
| 20 | 0.4 |
| 35 | 1.2 |
| 50 | 2.4 |
| 65 | 3.6 |
| 80 | 4.0 |
In Figure 1, identify the type of bond represented by each solid line and state what is shared in this bond.
Using Figure 1, explain how water molecules can form hydrogen bonds with one another.
Draw two water molecules, showing the partial charges and one hydrogen bond between them. Use solid lines for covalent bonds and a dotted line for a hydrogen bond.
At 65% water content, calculate the amount of carbon dioxide produced in 30 min by 0.50 g of dry yeast. Assume that the rate remains constant.
Describe the relationship between water content and the rate of carbon dioxide production shown in Table 1.
Evaluate the conclusion that these results demonstrate that water is a medium for life and that the first cells originated in water. Use at least one value from Table 1 and your biological knowledge.