Exercises: Biology in Practice Investigation: research, experiment and report

A classmate says: "The Biology in Practice Investigation is just a practical we do in class. The teacher marks it and it is a small part of the grade." Correct this statement by answering the following in short sentences.

1. a) What share of the Leaving Certificate Biology certification does the Biology in Practice Investigation carry? What share does the written examination carry?

1. b) Who publishes the Investigation Brief, and in which term of which year of the course is it published?

1. c) Name the two kinds of work that students carry out to complete the investigation.

1. d) When is the report submitted, who marks it, and in whose format must it be written?

1. e) What does the specification say is the approximate time the component is envisaged to take?

1. f) Give two things you should check in the current brief or in the Guidelines for the Biology in Practice Investigation rather than assume from a textbook.

Ciara lives near the N7 in Co. Kildare. She notices that grass at the roadside looks brown in spring, after the council has spread rock salt in winter. Her first idea for an investigation is: "Salt is bad for plants." She plans to use cress seeds (Lepidium sativum) grown on cotton wool in Petri dishes.

1. a) Explain why "Salt is bad for plants" is not yet a testable hypothesis. Give two reasons.

1. b) Rewrite it as a testable hypothesis and also as a null hypothesis.

1. c) Identify the independent variable and the dependent variable. For the dependent variable, say exactly what you would measure and in what unit.

1. d) State three variables that must be controlled. For each, say how you would control it.

1. e) Give one piece of biological theory that supports your hypothesis. Use the terms osmosis and water potential in your answer.

The research part of the investigation involves gathering, processing and evaluating information from secondary sources. A student investigating "nutrient runoff and algal growth in Irish lakes" finds four sources. These are practice sources invented for this exercise.

Source	Description
A	A 2023 report by a national environmental agency. It has a methods section, data tables for 40 named lakes and a reference list.
B	A social media post by a garden-products company. It says "nitrates are harmless to lakes" and gives no data.
C	A 2021 article in a peer-reviewed journal by university researchers. It reports a three-year study of nutrient levels and has 35 references.
D	An online encyclopaedia page with no date of last edit shown. It has some references, but the author is anonymous.

1. a) Rank the sources from most to least trustworthy. Give two reasons for each placement.

1. b) Which source would you least want to rely on, and why?

1. c) The student reads that algal blooms are linked to high phosphate levels. Write one sentence describing how this finding could shape the student's own experiment (for example, the variable chosen or the range of values).

1. d) The specification says students may develop an investigative log. Suggest four details you would record about each source so that you can find it again and credit it.

Practice context (not an SEC brief). A student plans to test this hypothesis: "As the concentration of sucrose solution increases, potato cylinders gain less mass, and eventually lose mass, because water moves out of the cells by osmosis." The independent variable is sucrose concentration (0.0, 0.2, 0.4, 0.6 and 0.8 mol dm⁻³). A stock solution of 1.0 mol dm⁻³ sucrose is available.

1. a) Calculate the volume of stock solution and the volume of distilled water needed to make 50 cm³ of each of the 0.2, 0.4, 0.6 and 0.8 mol dm⁻³ solutions. Show your method for one of them.

1. b) Write a numbered method of 8 to 10 steps. Your plan must include: how the cylinders are cut and made equal, the number of cylinders per concentration, the soaking time, how surface water is removed, how mass is measured and what is recorded.

1. c) State the number of replicates you would use and explain why.

1. d) Copy and complete a risk assessment table with at least two hazards.

Hazard	Risk	Control measure

1. e) The specification stresses that students should give an authentic account of how their work unfolds. Write one sentence about a decision you made in this plan, and the reason for it.

A student carried out the potato experiment above. Each cylinder had a starting mass of 2.00 g. Final masses after 24 hours are shown.

Sucrose (mol dm⁻³)	Final mass, cylinder 1 (g)	Final mass, cylinder 2 (g)	Final mass, cylinder 3 (g)
0.0	2.31	2.29	2.30
0.2	2.14	2.16	2.15
0.4	1.99	2.01	2.00
0.6	1.81	1.79	1.95
0.8	1.62	1.60	1.64

1. a) Copy the table and add columns for the mean final mass (g) and the percentage change in mass, using $\text{percentage change} = \dfrac{\text{final} - \text{initial}}{\text{initial}} \times 100$.

1. b) One value looks anomalous. Identify it. Explain what the student should do about it (deleting it silently is not an option). Then recalculate the mean and percentage change for 0.6 mol dm⁻³ with it left out, and report both versions.

1. c) Describe the graph you would draw. Say which variable goes on each axis and why. State the type of graph and what unit appears on each axis.

1. d) From the data, estimate the sucrose concentration at which there is no net change in mass. Say what this tells you about the cells.

1. e) Describe the trend, quoting at least two numbers from your table.

1. f) Name a digital tool you could use to process the data and draw the graph. Give one advantage over doing it by hand.

A student wrote this conclusion about the potato experiment (mean percentage change in mass: +15.0, +7.5, 0.0, −10.0, −19.0 for 0.0, 0.2, 0.4, 0.6 and 0.8 mol dm⁻³):

"My experiment proves that sucrose makes potatoes shrink. It was a perfect experiment, and the results were good so there is no need to change anything."

Use the rubric below, which is based on the descriptors of quality for analysis and conclusions.

Criterion	High	Moderate	Low
Conclusion	Valid, justified by the data and linked to the hypothesis	Relates to the hypothesis	Limited conclusion
Sources of error	Sources of error in the design are thoroughly evaluated	Potential sources of error are identified	No sources of error identified

1. a) List three weaknesses in the student's paragraph.

1. b) Rewrite the conclusion in 80 to 120 words. Refer to the hypothesis, quote at least two data values, use cautious language such as "supports" rather than "proves", and mention at least two sources of error.

1. c) Give the draft paragraph and your rewrite a level for each criterion. Add a one-line reason for each of your four ratings.

A group investigated the effect of temperature on yeast fermentation. Each tube contained 5 g of yeast in 100 cm³ of 5% glucose solution, with a delivery tube leading to water. Bubbles of CO₂ per minute were counted by eye.

Temperature of water bath (°C)	Trial 1	Trial 2	Trial 3
10	2	3	2
20	7	8	6
30	18	20	19
40	31	29	33
50	12	14	13
60	0	1	0

Notes from the group's log:

1. Bath temperatures were checked only at the start. The baths cooled by about 3 °C during the 10 minutes.

2. Bubbles were counted by eye, and their size varied.

3. The yeast suspension was added without being warmed or cooled to bath temperature first.

4. One thermometer was used for all baths. It was never checked and was later found to read 1.5 °C too high.

1. a) Calculate the mean and the range for each temperature.

1. b) State the temperature that gave the highest rate. Explain what the data allow you to say about the optimum temperature, and what they do not allow you to say.

1. c) For each of the four notes, classify the weakness as random error, systematic error or a limitation of design. Explain the likely effect on the results.

1. d) Suggest one improvement for each note.

1. e) Write three sentences beginning "If I repeated this investigation I would…". They should show an authentic account of how the work might be revised, not a claim that the experiment was perfect.

One of the descriptors of quality asks students to relate their investigative work to the work of scientists in society. Choose one of these (practice scenarios):

• Soil scientists advising farmers in Co. Wexford after coastal flooding has put sea water on fields.

• Food technologists at an Irish vegetable-processing company in Co. Meath who use salt solutions when preparing produce.

Write a reflection of 120 to 160 words that covers:

• what the scientists do that relates to your potato or cress investigation

• one way their methods are similar to yours

• one way their work goes beyond a school investigation

• one benefit and one concern or issue for society.

Rubric:

Criterion	High	Moderate	Low
Links to a scientist's work or to science and society	A considered reflection that places the investigation within broader issues in the work of a scientist or in science and society	Reflects on how the outcomes relate to the work of a scientist or to science and society	Limited links between the outcomes and the work of a scientist or science and society

Then rate these three sample statements High, Moderate or Low and explain each rating in one sentence.

• S1: "Scientists do experiments like me."

• S2: "Soil scientists measure salt in flooded fields using samples, as I did with cress. Their results help farmers decide what to plant."

• S3: "Soil scientists test fields much more widely than my 15 dishes, so their results can guide advice to farmers. They have to weigh the cost of draining and re-seeding against the risk to food supply, and my small, controlled experiment shows only one part of that picture."

Finally, rate your own reflection against the rubric, with a one-line reason.

Maya drafted her investigation report. Summary of the draft:

• Research: she used her textbook and one website, with no sources listed. She explains osmosis accurately in terms of water potential. She does not state the purpose of the investigation.

• Hypothesis: "If sucrose concentration increases, potato cylinders will lose more mass, because water moves out by osmosis from a higher to a lower water potential."

• Design and method: five concentrations and three cylinders each, all from one potato. Room temperature was not recorded. The data table has no units in its headings. She plotted a bar chart of mean masses and did not calculate the mean for the anomaly she noticed.

• Results (mean % change in mass): +14, +6, −1, −9, −17.

• Conclusion: "The results support my hypothesis" (she quotes the data). She identifies two sources of error (inconsistent drying of cylinders and limited balance precision) but suggests no improvements.

• Society: "Scientists also study osmosis."

Rubric (levels from the descriptors of quality):

Strand	High	Moderate	Low
Knowledge and understanding	Thorough, clear, accurate; testable hypothesis underpinned by theory; clear purpose	Good engagement; describes the phenomena; testable hypothesis; outlines purpose	Limited engagement; outlines phenomena; given a hypothesis
Investigative skills (design and method)	Clear, thorough, appropriate design; high quality data, presentation and analysis	Clear and appropriate design; good quality data, presentation and analysis	Unclear design; limited data, presentation and analysis
Investigative skills (analysis and conclusions)	Valid conclusions justified by data; thorough evaluation of error	Conclusions relate to hypothesis; errors identified	Limited conclusions; errors not identified
Work of scientists in society	Considered reflection placing outcomes in broader issues	Reflects on how outcomes relate to a scientist's work or to science and society	Limited links

1. a) Give Maya's draft a level (High, Moderate or Low) for each of the four strands. Quote or refer to evidence from the summary for each rating.

1. b) List three prioritised improvements. Say which strand each would raise and why you placed them in that order.

1. c) Write a 100-word evidence-based argument responding to this practice question (not an SEC brief): "To what extent can a simple experiment help explain why sea-water flooding harms crops?" Use Maya's results, state one limit on what the experiment shows and finish with a clear claim.

1. d) The specification says the report must follow a format prescribed by the SEC and that the brief is published annually. Say what Maya should check before finalising her report, and who she should ask.