Oxygen volumes collected from pondweed in three 5-minute repeats are 4.5, 5.0 and 5.5 cm³. A second student counts bubbles instead of collecting gas.
.1
Calculate the mean oxygen production rate.
[2 marks]
.2
Evaluate counting bubbles compared with collecting gas volume.
[2 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A potometer reservoir initially contains 24.0 cm³ of water. After 90 minutes it contains 17.7 cm³. A sealed control loses no water. The student claims that all 6.3 cm³ must have evaporated from the leaves.
.1
Calculate the shoot's mean uptake rate.
[2 marks]
.2
Evaluate the claim about evaporation.
[2 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Root cells absorb nitrate from a solution with a lower nitrate concentration than the cells. A poison stops respiration without damaging the cell membrane.
.1
Explain why nitrate uptake decreases.
[3 marks]
.2
Explain why water can still cross the membrane.
[2 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Eighteen approximately equal cells span a field diameter of 0.90 mm with no gaps.
.1
Estimate the mean cell width in micrometres.
[2 marks]
.2
Suggest why an individual cell may differ from this estimate.
[2 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A respirometer shows a germinating seed sample uses 2.4 cm³ oxygen in 8 minutes. Its mass is 3.0 g. An equal-mass boiled sample uses no measurable oxygen.
.1
Calculate oxygen uptake rate per gram in cm³ per minute per gram.
