The body cells of a species of fish contain 30 chromosomes, in 15 pairs.
.1
Give the number of chromosomes in one of this fish's gametes.
[1 mark]
.2
Give the number of chromosomes in a fertilised egg cell of this fish.
[1 mark]
.3
Describe what happens to the chromosomes when a cell divides by meiosis to form gametes.
[3 marks]
3 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Evolution is a change in the inherited characteristics of a population over time through natural selection.
.1
Put the stages of natural selection in order, starting with the first.
[2 marks]
.2
Define the term species.
[1 mark]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
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]
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
Tobacco mosaic virus (TMV) infects tomato and tobacco plants. HIV infects humans.
.1
TMV causes a mosaic pattern of discoloured patches on the leaves.
Explain why an infected plant grows more slowly.
[3 marks]
.2
Explain how viruses make people ill.
[2 marks]
.3
How is HIV controlled in a person who is infected?
