Topic 3 - Task Answers

Task 1

Consider an investigation with the aim: “To investigate the effect of temperature on catalase activity”.

Identify the following:

• Independent variable - Temperature

• Dependent variable - Catalase activity

• Hypothesis - Temperature will affect catalase activity

• Null hypothesis - Temperature will have no effect on catalase activity

SQA Past Paper Question 1

Answer: A

The scientific cycle would begin with a hypothesis and an experiment would be designed to investigate this hypothesis. Data would be collected and anaylsed, resulting in conclusions related to the original hypothesis. This could then result in the formation of new hypotheses.

This solution does not emanate from the SQA.

Task 2

Consider the investigation "To investigate the effect of caffeine concentration on heart rate". This type of investigation would generally be done because we are interested in the effect caffeine has on the human heart - potentially investigating its impact on mental or physical wellbeing.

However, in light of government legislation, the Scottish Schools Education Research Centre (SSERC) published their document "Materials of Living Origin" and state that "Substances known to have a physiological effect (e.g. caffeine) should not be administered to pupils for the purposes of an investigation".

Suggest how this investigation could be carried out and what ethical considerations would need to be addressed prior to experimentation?

Consider the 3Rs: Replace (the organism), Reduce (the number of organisms required to the minimum required for a valid conclusion to be drawn) and Refine (refine methodology so no organism is harmed).

1. Replace - We cannot investigate this aim using human participants. However, this investigation is routinely carried out using the model organism Daphnia magna.

2. Reduce - Usually the data obtained using Daphnia in this investigation is fairly reproducible and 5 repeats should be sufficient - you will be able to evaluate this sample size during data collection by looking at the extent of variation in your data points.

3. Refine - Consider your methodology. Ensure each Daphnia is only held in the caffeine solution for the minimum time and then immediately replaced into the control solution (the solution provided by the aquarium retailer). Only use each Daphnia once.

Task 3

Wee Jonny couldn't wait to get to Biology on Wednesday. He burst in through Dr McRobbie's classroom door: "Miss, I have this mad wee experiment to do today, don't I?"

"Yes, Jonny, you do - You are going to investigate if aspirin inhibits catalase activity".

Jonny thought for a second: "Och, naw Miss, are we working with those tatties again?"

Dr McRobbie had some exciting news for wee Jonnie: "No Jonny, we are using liver as the source of catalase today".

Jonny was beyond delighted. He was feeling a little cautious so opted for the "height of foam" approach. He collected his apparatus and set up his control first - in this tube, he added hydrogen peroxide and detergent before enthusiastically lobbing in a 1g piece of liver. His smiled beamed from ear to ear as the foam, resulting from oxygen production, rose up the test tube. After a minute, he could cope no more and measured the height of foam using a ruler.

Wee Jonny repeated the experiment by placing hydrogen peroxide, detergent and 0.01% aspirin into the test tube before finally kicking things off with 1g liver.

The results are shown below.

Suggested responses:

1. Firstly, the approach to the pilot study was poor. The student needs to first check that the procedure used allows catalase activity to be observed. In this example, 1cm of foam in the absence of an inhibitor suggests the protocol is not working. The procedure needs to be refined by checking incubation time, concentration ranges of hydrogen peroxide, source of catalase and temperature (among other variables known to affect enzyme activity). This would be a negative control (absence of treatment/inhibitor).

2. Once catalase activity is clearly observed in the absence of an inhibitor, the student should attempt to prove that inhibition can be observed using a known (published) inhibitor, e.g. lead nitrate in this example. A suitable concentration of inhibitor can be determined using published articles, e.g. 2.5% lead nitrate. This would be a positive control (treatment known to inhibit the enzyme).

3. Once this has been determined, the same concentration of the hypothesised inhibitor can be tested. Simply guessing that 0.01% aspirin would result in observed inhibition is not a suitable approach.

Task 4

Consider the development of drugs against the parasite that causes malaria. Ultimately, researchers will need to develop a drug that can be given to humans that is effective against the parasite. However, to achieve this, many simple experiments must be carried out, e.g. investigating how particular metabolic enzymes work in the parasite and to establish if they could be a drug target. This might involve some fairly simple biochemistry assays to establish what a particular enzyme does in vitro. Why might the findings of these simple experiments not be "applicable to a wider setting"?

Suggested responses: In such simple experiments, researchers typically work on purified enzymes - they add the enzyme and substrate to a tube and find out how much product is formed, for instance. They might then add a potential inhibitor to see if product formation is limited. However, in vivo, proteins rarely work alone - they often form larger complexes and interact in unexpected ways. This is magnified if an inhibitor is added into the mix - it becomes much less predictable. So, often would researchers might observe in vitro is not always what happens in vivo.

Task 5

For each of the examples that follow, establish whether it is an example of a simple, multifactorial or observational experiment. For an added bonus point, spot the deliberate mistake.

1.. A study took two groups of adults, one who engaged in regular exercise and a second that did not take part in any exercise in an average week. The researcher measured their blood pressure and concluded that regular exercise caused lower blood pressure.

2. A researcher wanted to investigate the optimal laser (pulse repetition frequency, pulse energy and exposure time ) and environmental (pH, NaCl concentration and wet or dry samples) parameters that should be employed to efficiently decontaminate bacterially-infected surfaces. The investigator found out that pH and salt concentration had minimal effect on all laser parameters but wet and dry surfaces with all laser parameters were significant.

3. An investigation was carried out to investigate the optimum pH for amylase activity. The researcher established that pH7 conditions led to higher rates of starch degradation by amylase.

Answers:

1: Observational study. Bonus point available for spotting that "regular exercise caused lower blood pressure" is inaccurate. It should have read "regular exercise is correlated with lower blood pressure". Observational studies cannot prove causation.

2. Multifactorial investigation

3. Simple experiment

Task 6

Use the information below to select the correct answer:

A. There is no correlation between mass of fertiliser and mass of algae.

B. There is a weak negative correlation between mass of fertiliser and mass of algae.

C. There is a strong positive correlation between mass of fertiliser and mass of algae.

Answer: C - the graph shows that an increase in the independent variable (mass of fertiliser) resulted in an increase in the dependent variable (mass of algae). This is regarded as a stong-ish correlation since the values lie fairly close to the imagined line of best fit.

Task 7

An investigator aimed to find the effect of enzyme type on the volume of juice extracted from apples. Pectinase, cellulase and amylase were individually incubated with apples for a period of time and the volume of juice released was measured.

Identify at least 4 confounding variables that would have to be kept constant so that they did not affect the dependent variable.

Suggested answers include:

• Concentration and volume of enzyme

• Incubating temperature (optimum for each enzyme to ensure valid comparison)

• pH (optimum for each enzyme)

• Incubation time (time that apples were incubated with enzyme)

• Type of apples

• Ripeness of apples

• Mass of apple incubated with enzyme

• Size of apple pieces incubated with enzyme

SQA Past Paper Question 2

Answer: A

A randomised block design is used to minimise the influence of confounding variables when it is difficult to control them.

This solution does not emanate from the SQA.

Task 8

Two different investigations will be presented below. For each, identify suitable control(s) that should be included during the experimental design.

Investigation 1: To investigate the antimicrobial effects of lavender oil on the growth of E. coli

Negative control - instead of lavender oil, an inert material with absolutely no antimicrobial properties should be used, e.g. phosphate-buffered saline (PBS).

Positive control - instead of lavender oil, a known antimicrobial agents should be used, e.g. iodine.

Investigation 2: To investigate the effect of temperature on pepsin activity.

No controls can be used in this investigation since temperature (the "treatment") cannot be removed. This is an investigation comparing different temperatures and no controls are appropriate here. However, this would have to be clearly explained in any formal report you produced.

Task 9

Consider the investigation introduced in Task 2 (Investigating the effect of caffeine concentration on Daphnia heart rate). This investigation involves recording the number of times the Daphnia heart beats in 1 minute. The problem is the resting heart rate of a typical Daphnia is about 200 beats/min (Ebert, 2005). Typical methodologies for this involve placing the Daphnia on a microscope slide and counting the number of heart beats in 20s (by looking down the microscope) and then multiplying this number by 3.

Question: How can you accurately record this number of heart beats?

In addition, if your treatment (caffeine) actually raises the heart rate, can you be confident in the accuracy of your measurements?

Suggest how you could adapt this simple methodology to improve the accuracy of your measurements. Remember, accuracy is all about recording data is reflects the true mean.

Suggestion: This methodology could be adapted by using a camera, carefully positioned over the microscope eyepiece, to record the Daphnia for several minutes. The film could be uploaded to a computer and slowed down to ensure accurate counting of the number of heart beats in 20s (which could be multiplied by 3 for beats/minute).

SQA Past Paper Question 3

Answer: D

The same banana extract was used for all 5 repeats of the same assay. While each individual assay has given reliable results across the three measurements, there is considerable variability in the absorbance achieved between assays - and therefore the data is not reliable. Since we do not know the true mean, we cannot say the data is necessarily accurate.

This solution does not emanate from the SQA.

Task 10

Read the following enviornmental investigation examples and identify whether they used a random, systematic or stratified sampling methodology.

1. A habitat was to be sampled for vegetation using a quadrat. A 10m x 10m square was marked out on the group using tape. A number generator was used to select a pair of numbers between 1 and 10. This pair of numbers formed an X and Y coordinate within this 10x10m square section, e.g. if numbers 5 and 7 were revealed on the generator, a quadrat would be placed 5m up and 7m along the marked out square. The vegetation found within the quadrat was recorded. This process was repeated 10 times within the area.

2. A member of the Woodland Trust visited a site and needed to take a proportionate number of observations from each part of the population. She divided the habitat into zones based on the knowledge that 60% of the area was heathland and 40% gorse. As a consequence, 60% of samples were taken within the heathland and 40% of the sample were taken from the gorse area.

3. The number of barnacles found from the seashore inland was measured using a quadrat. A transect was used to sample every 10m along from the seashore to the sand dune system.

Answers:

1: Random sampling

2: Stratified sampling

3: Systematic sampling

Task 11

An investigation was carried out by one of my AH Biology students, Rob: "To investigate the effect of age on memory". The student was interested in comparing 2 different age groups (Age 10-18 and Age 60-70), with 10 participants from each age range. However, the student was keen to maintain a gender balance and even distribution of individual participants from the age ranges, i.e. they were keen to avoid 10 boys who were 11 years old from the first group.

To achieve this, the student constructed an excel spreadsheet with all available participants. He selected 5 males and 5 females from each group, selecting 2x 10 year olds, 2x11 year olds, 2x 14 year old, 2x 16 year olds, 2x 18 years. He did a similar procedure in the older age group.

What type of sampling procedure was applied and why?

Answer: A stratified sampling approach was used where the original population was sub-divided into gender and smaller age divisions. This was done to gain a more representative understanding of the impact of age on memory from the groups chosen.

Task 12

Sylvie, a student in the AH Biology class, carried out an investigation into the effect of caffeine concentration on Daphnia heart rate (that old favourite back again!). She chose 5 bathing solutions (ranging from 0-4 units of cafffeine). For each caffeine concentration, 5 different Daphnia were used. Because she was a particularly excellent student, she remembered that a Randomised Block Design would be important here.

Her data is shown below:

Task 13

Raymond has been investigating the effect of alcohol concentration on cell membrane permeability. He performed 3 repeats at each alcohol concentration and collected his data. He was so happy when he was finished! Dr McRobbie ruined his day when she reminded him of the "independent replication" rule. "What, I have to do the whole thing again?" - "Why, yes indeed you do, Raymond", she replied in her knowing way.

Raymond, downtrodden, went back to the fridge and collected his scabby old beetroot - again, Dr McRobbie approached him and asked what he was doing. He replied, "I'm doing my independent replicate Miss".

Question: What did Dr McRobbie say next?

Suggested reply:

"Raymondo, you cannot use that scabby, old beetroot for an INDEPENDENT replicate! You must buy it fresh, with a similar "ripeness", as your first run through! This also applies to all those test tubes of ethanol you have left on my windowsill for the past week - it all needs to be made up fresh!"

Raymond muttered something under his breath. Dr McRobbie didn't hear it.

Task 14

1. First task - calculate the average values for the missing cells in Avaz's table.

2. Second task - generate a table that shows Avaz's "overall results calculated and presented".

Task 15

You begin your final AH Biology Project with a title of "Investigation into the effect of alcohol on Daphnia heart rate". Write a bullet-point list of information you will want to include in your "Introduction" section.

• Aim - To investigate the effect of alcohol concentration on Daphnia heart rate.

• Hypothesis - As alcohol concentration increases, Daphnia heart rate will decrease.

• Basic features of a Daphnia - What is Daphnia? Describe their habitat; general variations in the population with regards to size, gender, average heart rate.

• Circulatory system of a Daphnia in more detail and compare to the human circulatory system. Are there known factors that influence Daphnia heart rate?

• Why use Daphnia as a model organism? Ethical issues that might arise with their use.

• Consider the procedure you intend to use and discuss why it is appropriate.

• Why investigate the effect of alcohol? What alcohol are you using in the investigation? What impact does alcohol have in society? Why is this an important area to investigate?

• Is there any controversy in the field? Do some sources claim alcohol is beneficial to health whereas others claim the opposite?

Task 16

Read the following Procedures section, written by Candidate X. How many marks (out of 9) would you award Candidate X?

5 test tubes were collected and 20vol hydrogen peroxide was added to each. 2 drops of washing up liquid (Fairy) was added to each test tube. The test tubes were placed at room temperature. A small block of liver was added to test tube 1; a small block of potato to test tube 2; a small block of carrot to test tube 3; a small block of apple to test tube 4 ; test tube 5 had no source of catalase as this was the negative control (without treatment). Test tube 5 would show how much foam would be produced in the absence of catalase activity - any measured value here would have to be subtracted from all other measurements.

Confounding variables included the concentration of hydrogen peroxide (kept constant by using a bottle given to me by the technician) and the amount of detergent (2 drops added with a pipette).

The experiment was repeated 3 times, which is appropriate for a simple in vitro experiment. My pilot study was previously carried out and, across the 3 repeats per tissue type, there was a low level of variation.

Marker Commentary:

• Procedure appropriate to aim - Yes - the procedure chosen by the candidate should allow him to determine the effect of tissue type on catalase activity - 1 mark

• Procedures described in sufficient detail - No - This basic level of information is here so you can visualise what the candidate is doing, however:

  • • • there is no information about how solutions were prepared (a technician should not be providing an AH candidate with pre-made solutions unless a Risk Assessment makes that essential)

      • lack of information about volumes of solutions added

      • the temperature of the room and whether this was monitored

      • what apparatus was used to make measurements

      • how was a "small block of [tissue]" measured?

      • How was height of foam recorded?

0 marks

• Controls identified - the candidate has correctly identified the negative control - 1 mark

• Confounding variables - poor level of information here both in terms of an exhaustive list of confounding variables and a clear understanding of how these were being controlled throughout the investigation - 0 marks.

• Sample size - 3 repeats in this type of experiment, especially in light of their comments about the pilot study, is appropriate - 1 mark

• Independent replicate - as discussed previously, results are only deemed reliable if they can be independently replicated. This candidate has not stated this was done - 0 marks.

• Justification of how the pilot study informed the final procedure(s) - no - 0 marks

• Shows complexity, creativity or accuracy - No - this is a standard protocol the candidate will potentially have performed from S1-S3. The candidate should be doing wider reading to investigate an alternative approach to study this aim that would give a greater level of accuracy in their results - 0 marks.

Overall mark - 3/9

Task 17

Holly carried out an investigation into the temperature on respiration in yeast, using the displacement of water protocol. Her results are shown below.

For Question 2, you should produce a line graph as the independent variable is continuous. The graph should look like this. If yours does not, please contact me for additional help.

Task 18

Corinna performed an investigation into the effect of tea-tree oil on the growth of bacteria. She incubated one culture of bacteria in an appropriate culture media and a second with culture media containing tea-tree oil. After 1 day, Corinna monitored the turbidity of the culture by measuring the transmission of light through the culture using a colorimeter. She repeat her investigation 5 times. Her data is shown below.

Using R, perform a t-test to test the null hypothesis, i.e. that tea-tree oil has no effect on bacterial growth.

Answer: The R code used to input the data is shown below. This is always important to do because you must always establish whether your data is "normally distributed" first - this does effect the type of statistical analyses you can perform. In this case, the median and mean values are very similar so we can conclude the data is approximately "normal".

The t-test reports a p-value of 0.0000000032. Since this value is <0.05, we can reject the null hypothesis and conclude there is a evidence that tea-tree oil has a statistically significant effect on the growth of bacteria.