Practical Exam Questions

Question 1

Characteristics of a good biological drawing

Answer 1

Title
Scale bar
Large size - should cover at least 50% of paper
Ruled lines
No shading
Use a sharp pencil
Use plain paper
Continuous lines
Labels should not cross over each other

Question 2

Explain what is meant by a limiting factor?

Answer 2

A factor that will determine the rate when at sub-optimal level

Question 3

What to include in an evaluate the statement question?

Answer 3

For support - state trend + use data from graphs

For not support -
Correlational data does not show cause and effect
Problems with data presentation eg lack of units on graphs
No error bars or standard deviation bars overlap
Any issues with methodology - eg no control variables
Issues with validity
Lack of repeats
No stats tests conducted

Question 4

How to improve validity in experiments?

Answer 4

Fix any issues with the method
Give control variables
Use control group to compare results to
Use repeats to calculate mean
Do a stats test to prove significance

Question 5

Potential limitations for phototropism experiment

Answer 5

1) light intensity not specified, which could lead to variation in bending. Control distance and intensity

2) no method for selecting seedlings, which could lead to biased results. Should use random selection

3) degree of bending not considered, therefore a comparison is not possible. Should measure angle of bend

4) experiement was not repeated. Cannot calculate mean, identify anomalies or carry out stats tests. Should repeat at least twice.

Question 6

Plan an investigation into the rate of transpiration in two species of plant that would allow valid data to be collected.

Answer 6

1) measure transpiration using movement of bubble in Potometer.

2) time for 10 minutes, checking distance moved by bubble every 2 minutes.

3) repeat for both species of plant.

4) replication to gain repeats. Calculate mean and stats test.

5) control temperature, humidity, light, wind movement, surface area of leaves and state how each variable will be controlled.

Question 7

Explain how carrying out replicates improves an investigation?

Answer 7

1) can calculate mean
2) can identify anomalies
3) improves repeatability
4) allows statistical tests to be completed.

Question 8

Describe how a method that uses Benedict’s reagent and a colorimeter could be calibrated to measure the concentration of lactose in an unknown sample.

Answer 8

Add dilute HCl to sample and add to water bath that’s been brought to a boil. Then neutralise with sodium hydrogencarbonate. Then add Benedict’s solution and heat it in a water bath.

1) zero the colorimeter using blank.

2) use red filter

3) use known concentrations of lactose using serial dilutions.

4) construct calibration curve.

5) test unknown sample using same method and read from graph to determine unknown concentration.

Question 9

What does the Rf values from TLCs suggest about the chemical properties of the solutes?

Answer 9

Shows the adsorption/solubility in the stationary phase. Further it travels, the more soluble it it. This is usually dependant on the R groups of amino acids.

Question 10

A student investigated heart rates of smokers vs non-smokers. Suggest and explain improvements that the student could make to his experimental method and his presentation of data

Answer 10

Improvements to experimental data:
1) increase sample size to improve accuracy and repeatability of results
2) same number of smokers vs non smokers and males vs females to make comparison more valid
3) gender should be controlled seperately as heart rate may show difference between genders not smokers
4) diet, exercise history, health issues etc should be taken into account as they can affect heart rate.
5) more repeats before calculating mean heart rate to identify anomalies.

Presentation of data
1) units in title
2) same number of significant figures
3) present data graphically to make trends easier to spot
4) label heart rates as mean heart rates for clarity.