APPLICATION/PRACTICALS

Question 1

an environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree. he was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside.

describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees (5)

Answer 1

1. use random sample of seeds from each population
2. use large enough sample to be representative of whole population
3. indication of what size wads measured eg. mass
4. calculate a mean and standard deviation for each population
5. use student’s t-test
6. analyse whether there is a significant difference between the means of the populations

Question 2

suggest two ways to improve a scientific drawing (2)

Answer 2

1. add scale bar
2. don’t use shading
3. add annotations
4. don’t cross label lines
5. only use single lines

Question 3

a student did not have access to a colorimeter. describe a method this student could use to prepare colour standards and use them to give data (3)

Answer 3

1. use known concentration of extract
2. prepare dilution series/serial dilution
3. compare results with these colour standards to give a value

Question 4

describe and explain three ways in which the scientists would ensure he used aseptic technique (3)

Answer 4

1. wash hands to kill microbes
2. bunsen burner close by to create upward current of air
3. disinfect bench to prevent contamination
4. flame equipment to sterilise
5. lift lid slightly to prevent entry of microbes

Question 5

explain the purpose of 1. boiling the agar and 2. transferring the same volume of liquid culture onto each agar plate (2)

Answer 5

1. so no contamination
2. so same number of bacteria transferred to allow comparison