A student investigated the effect of pH on the time taken for amylase to break down starch.
She mixed amylase, starch and a buffer solution in a water bath at 35 °C. Every 30 seconds she put a drop of the mixture onto iodine solution on a spotting tile. She recorded the time when the iodine no longer turned blue-black.
Time for starch to be broken down: pH 5, 150 s; pH 6, 90 s; pH 7, 60 s; pH 8, 120 s; pH 9, 240 s.
pH
Time for starch to be broken down (s)
5
150
6
90
7
60
8
120
9
240
.1
The rate of reaction can be found with:
rate =time1000
Calculate the rate of reaction at pH 7.
[1 mark]
.2
Explain why the starch took much longer to break down at pH 9.
[2 marks]
.3
Suggest how the student could find the optimum pH of amylase more precisely.
[1 mark]
.4
Sampling every 30 seconds limits the accuracy of the times.
Explain why.
[1 mark]
8 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A student models a small organism as a cube with sides 3 cm long.
.1
Calculate the total surface area of the cube.
[2 marks]
.2
Calculate the volume of the cube.
[1 mark]
.3
Calculate the surface area to volume ratio of the cube.
[1 mark]
.4
A larger organism has a smaller surface area to volume ratio.
Explain why a large multicellular organism needs exchange surfaces and a transport system.
[2 marks]
.5
Explain why root hair cells need energy to take in mineral ions from the soil.
[2 marks]
3 marksFoundation
Spec and skills
Original practice question
Answer and supported method checks
A student put some pondweed in a beaker of water under a lamp. She collected the oxygen given off in an upturned 25 cm³ measuring cylinder that was full of water at the start.
The measuring cylinder's scale starts at 0 cm³ at its closed end, which is now at the top. As oxygen collects at the top, it pushes the water down.
After 10 minutes, the boundary between the oxygen and the water was at the 4.0 cm³ mark.
.1
What volume of oxygen did the student collect?
[1 mark]
.2
Calculate the rate of oxygen production in cm³ per minute.
[1 mark]
.3
Another student counted the bubbles of oxygen instead.
Suggest why measuring the volume of gas gives more accurate results than counting bubbles.
[1 mark]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A student measured his reaction time. His partner held a ruler with the 0 cm mark level with the top of the student's thumb, then dropped it without warning. The student caught it as quickly as possible, and the partner read the distance fallen.
Conversion table from distance fallen to reaction time: 10 cm, 0.143 s; 11 cm, 0.150 s; 12 cm, 0.156 s; 13 cm, 0.163 s; 14 cm, 0.169 s; 15 cm, 0.175 s.
Distance fallen (cm)
10
11
12
13
14
15
Reaction time (s)
0.143
0.150
0.156
0.163
0.169
0.175
.1
In five trials the ruler fell 15 cm, 12 cm, 14 cm, 11 cm and 13 cm.
Calculate the mean distance.
[2 marks]
.2
Use the conversion table to give the student's mean reaction time.
[1 mark]
.3
Give two variables the student should control to make his results valid.
[2 marks]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A student used a potometer to measure the rate of water uptake by a leafy shoot. An air bubble moved along a scale as the shoot took up water.
In still air the bubble moved 45 mm in 5 minutes. With a fan blowing on the shoot, the bubble moved 72 mm in 5 minutes.
.1
Calculate the rate of water uptake in still air, in mm per minute.
[1 mark]
.2
Calculate the percentage increase in the rate when the fan was on.
[2 marks]
.3
Explain why the rate of water uptake increased when the fan was on.
[2 marks]
.4
Give one variable the student should keep the same when comparing still air with moving air.
