Pracicals

Question 1

Why does use of a colorimeter improve repeatability of results

Answer 1

It is quantitative and standardises the method

Question 2

What’s one way a student could ensure a sample is kept at the same temperature the whole way through the experiment

Answer 2

Measure the temperature at intervals and use appropriate corrective measure

Question 3

What’s the purpose of boiling the agar in the aseptic practical

Answer 3

So no contamination

Question 4

What’s the purpose of transferring the same volume of liquid culture onto each agar plate in the aseptic practical

Answer 4

So same number of bacteria transferred to allow comparison

Question 5

Describe how a student could make up a dilution series in bacteria practical

Answer 5

1. Add 1 part bacteria culture to 9 parts sterile liquid
2. Mix
3. Repeat using 9 parts fresh sterile liquid and 1 part of 10^-1 and 10^-2 dilutions to make 10^-3 dilutions

Question 6

Why does a student not use his preliminary dilution (aseptic practical)

Answer 6

• count is unlikely to be reliable
• because there’s too many cells

Question 7

Describe method for potato osmosis practical

Answer 7

1) put each cut cube in a test tube of sucrose and dilute water solution that you have made up

2) at room temperature

3) dry the cubes with paper towel before measuring

4) measure mass of cubes every 10 mins

Question 8

In chromatography why is pencil used to mark and not ink

Answer 8

The ink and leaf pigments would mix

Question 9

Describe the method to separate leaf pigments in chromatography

Answer 9

• level of solvent below line
• stop before solvent reaches the top

Question 10

What is the purpose of incubating the root tip with HCl

Answer 10

• stops cell division from occurring
• hydrolyses the middle of the lamella so that the cells can be separated easily

Question 11

How do you carry out a serial dilution?

Answer 11

1) Take original solution of known concentration
2) fill additional test tubes with the same volume of distilled water
3) transfer the same volume of solution from one test tube to the next and mix

Question 12

Describe how to produce a calibration curve eg for concentration of creatine in urine

Answer 12

• use water and your creatine solution to produce a dilution series
• add the creatine detecting solution
• use a known volume of a solution
• record absorbance of solutions using a colorimeter
• plot concentration of creatine solution against absorbance

Question 13

How could you use a calibration curve to find the concentration of something eg in urine

Answer 13

• use same volumes of solutions as used in producing the curve
• read of concentration again absorbance