Planning

State two variables the student would need to standardise for the investigation using the apparatus shown in Fig. 3.2.

Outline a method the student could use to measure the effect of different levels of humidity on the appearance of the awn, using the apparatus in Fig. 3.2.

Do not include standardised variables from (a) or a risk assessment.

State the independent variable and the dependent variable in this investigation.

independent variable = ______

dependent variable = ______

Explain why the students stirred the mixture of yeast and glucose before adding it to the tube in the apparatus in Fig. 1.2.

Describe a method using the apparatus, set up as shown in Fig. 1.2, that the students could use to find the temperature at which yeast carries out fermentation at its maximum rate.

Your method should be set out in a logical order and be detailed enough for another person to follow.

You should not include details of how to make the yeast suspension or how to set up the apparatus.

Complete the sketch graph to predict the results that you would expect from the method that you have given in part (iii). Include axes labels with units in your answer.

Scientists have discovered that some other species of yeast show the Crabtree effect.

The Crabtree effect means that in high concentrations of glucose and with oxygen present, pyruvate is not metabolised in mitochondria so aerobic respiration does not occur.

Yeast species that are able to maintain their levels of ATP production when conditions suddenly change and no oxygen is available show the Crabtree effect.

An investigation compared S. cerevisiae with the yeast Candida tropicalis to see if this other species also shows the Crabtree effect.

Three flasks containing suspensions of S. cerevisiae in a growth medium were initially kept in different conditions (conditions for growth).

After a set time, the yeast in each flask was transferred to a flask containing a fresh medium with high glucose concentration and no oxygen (experimental conditions). All other conditions were standardised.

The same procedure was repeated for C. tropicalis.

The conditions for growth and the experimental conditions in the flasks are summarised in Table 1.1.

Table 1.1

Samples taken from the flasks kept in the experimental conditions were put into the apparatus shown in Fig. 1.2 to measure the volume of carbon dioxide produced by the two yeast species.

The results are shown in Fig. 1.3.

The final volume of carbon dioxide produced by the sample of yeast from flask 1 at 30 minutes is shown as a maximum volume of 100% in Fig. 1.3. All other volumes were calculated as a proportion of this maximum. This allows a direct comparison to be made between the two species.

State and explain the evidence in Fig. 1.3 that supports the idea that C. tropicalis does not show the Crabtree effect.

State three variables which were standardised in this technique.

1 ______
2 ______
3 ______

Suggest one reason why it is important that the semen sample is not spun at a very high speed.

The semen is analysed by technicians to determine its quality before it is sexed.

Technicians use microscopy to look at the appearance and motility of the sperm cells and to estimate the sperm count.

Fig. 2.2 shows the surface view of a haemocytometer used to estimate the number of sperm cells in a sample.

The depth of the haemocytometer is $0.1\ \text{mm}$.

Suggest how this apparatus could be used to estimate the number of sperm cells per $\text{cm}^3$ of semen and describe how the technician decided which sperm cells to include in the count.

Outline how a colorimeter is set up so that a test cuvette can be placed in the slot to obtain a correct measurement of intensity of a coloured solution.

The range of concentrations that can be measured using a colorimeter in a biuret assay is 0.1 – 1.0% w/v.

A stock solution of 1.0% w/v protein can be diluted using distilled water to prepare the standard solutions of protein.

Describe how the student could prepare a 0.1% solution of protein using the stock solution.

Construct a table to show how the dilution is made for the 0.1% solution and for other concentrations the student could use to produce a calibration curve for the biuret assay.

Space for table.

Identify the independent variable and dependent variable for the preparation of the calibration curve.

independent variable ______
dependent variable ______

The biuret assay assumes that if the same intensity of colour in the biuret test is obtained with the test sample and a protein standard, then the protein concentration is the same, even though they are different proteins. This is summarised in Fig. 1.3.

Use the information on the biuret test given on page 2 to explain why different proteins of the same concentration will result in the same intensity of purple colour in the biuret test.

Describe how the student would:

• use the standard protein concentrations prepared in (b)(i) to obtain a calibration curve
• determine the concentration of protein in the egg albumen from eggs of chickens fed on the new chicken feed.

Do not repeat any detail given in (a) of how to use the colorimeter or in (b)(i) of how the standard protein solutions would be prepared.

Your method should be set out in a logical way and be detailed enough to let another person follow it.

Suggest a suitable control for this investigation.

Describe a method, using the apparatus shown in Fig. 1.1, that the students could use to investigate the effect of light intensity on the rate of photosynthesis of E. densa.

Your method should be set out in a logical order and be detailed enough to allow another person to follow it.

The steps carried out to set up the apparatus shown in Fig. 1.1 should not be included.

Complete the sketch graph to predict the results that you would expect from the method you have given in (b)(i).

Include axis labels with units in your answer.

Identify the independent variable in this investigation.

Identify three variables, other than the chromatography solvent and the specific dye, that the student has standardised in their investigation.

Describe how the student might have standardised two of these variables.

Suggest a control that the students could use for this investigation.

Describe a method that the student could use to prepare and use chromatograms to compare the changes in the products of hydrolysis of starch by the three different amylases over time.

Your method should be detailed enough for another person to follow.

The grey dune ecosystem is a habitat for the grey bush cricket, Platycleis albopunctata.

Fig. 1.2 shows a grey bush cricket.

The biologist wanted to estimate the population size of the grey bush cricket in the grey dune ecosystem.

The biologist used a sweep net to catch grey bush crickets. The biologist moved the sweep net through the plants growing in the grey dune ecosystem. Any grey bush crickets on the plants were caught in the net.

Fig. 1.3 shows a biologist using a sweep net.

Describe the mark-release-recapture method that the biologist could use to estimate the population size of the grey bush cricket.

The biologist monitored the light intensity and temperature in the grey dune ecosystem.

Suggest two other abiotic factors the biologist could monitor during the ten-year period.

Describe a method the biologist could use to investigate changes in the species diversity of the plants in the grey dune ecosystem during the ten-year period after the conservation practices were introduced.

Your method should be set out in a logical order and be detailed enough to allow another person to follow it.

Details of how to calculate Simpson’s index of diversity should not be included.

Identify the independent variable in this investigation.

The student carried out the investigation in a laboratory with standard laboratory apparatus.

Describe a method, using the apparatus shown in Fig. 1.1, that the student could use to investigate the effect of wind speed on the rate of transpiration by Japanese spiraea.

Your method should be set out in a logical order and be detailed enough to allow another person to follow it.

Details of how to set up the apparatus shown in Fig. 1.1 should not be included.

Predict the effect of wind speed on the results of the investigation using the method you have given in (a)(ii).

State one variable that should be standardised in the procedure to obtain the liquid carrot extract, other than the carrot tissue, fine sand and apparatus used.

The student carried out these steps to investigate the activity of catalase in the different samples of carrot root tissue.

• A disc of filter paper of $5\ \text{mm}$ diameter was dipped into the liquid carrot extract using forceps.
• The filter paper disc was placed at the bottom of a beaker of $1\%$ hydrogen peroxide solution using forceps.
• The time taken for the filter paper disc to rise to the surface of the hydrogen peroxide solution was measured.

Fig. 1.4 shows the apparatus used to measure the time taken for the filter paper disc to rise.

State the relationship between the time taken for the filter paper disc to rise to the surface of the hydrogen peroxide solution and the catalase activity of the liquid carrot extract.

The student made the prediction:

As the distance from the base of the shoot increases, the catalase activity of carrot root tissue increases.

Identify the independent variable in this investigation.

Describe a method that the student could use to test the prediction that:

As the distance from the base of the shoot increases, the catalase activity of carrot root tissue increases.

Your method should be set out in a logical order and be detailed enough to allow another person to follow it.

Details of how to use the centrifuge to prepare the liquid carrot extract should not be included.

Identify the dependent variable in this investigation.

To investigate the effect of hydrogen peroxide concentration on the activity of catalase in yeast, the student first prepared a range of known concentrations of hydrogen peroxide.

The student was given a $6.0\%$ stock solution of hydrogen peroxide. The student decided to use the stock solution to make hydrogen peroxide solutions with concentrations of $3.0\%$, $3.6\%$, $4.8\%$ and $5.4\%$.

The student made $50\ \text{cm}^3$ of each solution.

Complete Table 1.1 to show how these solutions could be made by proportional dilution of the $6.0\%$ stock solution of hydrogen peroxide.

Table 1.1

Use this space for your working.

A sterile cotton wool bung was used in the top of the flask containing the fresh broth culture of B. subtilis to protect the culture from contamination.

Explain why it is better to use a sterile cotton wool bung in a flask containing broth culture of B. subtilis, rather than using a sterile rubber bung.

Before comparing the two antibacterial substances, the student carried out a trial experiment.

The student transferred a sample of fresh broth culture to a culture tube and incubated the tube at $25^\circ\text{C}$ for 24 hours.

Fig. 1.2 summarises the results of the trial experiment.

The student decided that turbidity of the broth culture is a measure of bacterial population growth (bacterial growth).

Explain how this concept can be used in an investigation to measure the extent of bacterial growth.

The student decided to test the antibiotic solution before testing the Manuka honey.

In addition to normal laboratory apparatus and materials, the student was provided with:

• a fresh broth culture of B. subtilis
• a clear antibiotic stock solution
• nutrient solution to dilute the antibiotic stock solution
• $15\ \text{cm}^3$ flat-bottomed glass culture tubes with sterile cotton wool bungs
• a choice of graduated pipettes to measure volumes accurately: $0.2\ \text{cm}^3$, $2.0\ \text{cm}^3$, $10.0\ \text{cm}^3$, $25.0\ \text{cm}^3$.

The student:

• prepared dilutions of the antibiotic stock solution and added a volume of each to different culture tubes
• added a volume of fresh broth culture of B. subtilis to each culture tube
• incubated the culture tubes in an incubator
• allowed time for bacterial growth to occur and then checked each culture tube
• recorded and analysed the results
• decided on the lowest concentration of antibiotic solution that appeared to kill or inhibit the growth of B. subtilis.

Outline a control for this part of the investigation.

In the next part of the investigation, the student used a stock solution of Manuka honey. The student remembered that hydrogen peroxide could be present but could not think of a way to break down the hydrogen peroxide to remove it from the solution.

Describe how the student can improve the investigation by removing hydrogen peroxide from the Manuka honey solution and explain why this improvement makes the results more valid.

The student was provided with a stock solution of Manuka honey containing an MGO concentration of $600\ \mu\text{g cm}^{-3}$. This was a clear solution, labelled '100% honey'.

The same apparatus and materials were available.

Describe how the student could prepare a 10% solution of honey using the stock solution.

Construct a table to show how the dilution is made for the 10% solution and the other concentrations that the student could use.

Space for table.

State the independent variable and dependent variable for the part of the investigation involving Manuka honey solution.

independent variable = ______

dependent variable = ______

Predict the results the student would expect when investigating the effect of Manuka honey on B. subtilis.

Explain the reasoning behind the prediction.

Describe how the student could determine the lowest concentration of Manuka honey solution that would kill or inhibit the growth of B. subtilis.

• Do not repeat any detail given in (d) of how to prepare the different concentrations of Manuka honey solution
• Do not give details of using aseptic technique (techniques to prevent contamination of the student, the environment or other people).

Your method should be set out in a logical way and be detailed enough to let another person follow it.