Identify the independent variable and the dependent variable when comparing the strength of arteries and veins using the CTS test.

• Dependent variable: Mass required to break the blood vessel ring.
• Independent variable: Type of blood vessel (artery or vein).
• Independent variable: Mass required to break the blood vessel ring.

Describe how the CTS test could be used to determine and compare the mass needed to break rings cut from a large artery and a large vein. Assume standard lab apparatus… is available.

• Safety: Standard lab safety like wearing PPE when handling tissue and care with masses should be observed.
• Applying Mass: Masses should be added in standardized increments (e.g., 10g) until the vessel ring breaks, and the total breaking mass recorded accurately.
• Sample Preparation: Rings of standardized dimensions (e.g., width, thickness if possible) should be carefully cut from both artery and vein samples to ensure fair comparison.
• Replication and Comparison: The procedure must be repeated for several rings of each vessel type (e.g., at least 3-5 replicates) to calculate a reliable mean breaking mass for statistical comparison.
• Control Variables: Factors potentially affecting vessel strength or measurement (e.g., ring dimensions, source/age of tissue, temperature, hydration, measurement technique) should be kept as consistent as possible between samples.
• Procedure: Test all artery rings first, then immediately discard the setup and test all vein rings afterwards without necessarily re-checking calibration or control variables between the two batches.

A ring of vein had an initial length of 21 mm (0g mass). Calculate the percentage increase in length when the following masses were added: 10g (final length 36mm), 40g (final length 41mm), 50g (final length 41mm).

• Calculation for 10g: [(36 – 21) / 21] × 100 ≈ 71.4%
• Calculation for 40g & 50g: [(41 – 21) / 41] × 100 ≈ 48.8%
• Calculation for 40g: [(41 – 21) / 21] × 100 ≈ 95.2%
• Calculation for 50g: [(41 – 21) / 21] × 100 ≈ 95.2% (since length didn’t change from 40g)
• Formula used: % Increase = [(Final Length – Initial Length) / Initial Length] × 100

Explain why calculating the percentage increase in length is useful in such investigations.

• It allows direct comparison of the absolute amount of stretch (in mm) between different samples, regardless of their initial size.
• It standardizes the measure of stretch by expressing it relative to the original size (initial length) of the sample ring.
• It allows for a more valid comparison of the relative stretchiness (distensibility) between samples that may have started with slightly different initial lengths due to cutting variations.

Data for a vein ring: Mass added/g vs % increase in length: (0, 0), (10, 71), (20, 81), (30, 90), (40, 95), (50, 95). Describe how you would plot this data on a graph.

• Plotting: Plot each data point accurately using small, visible symbols like crosses (x) or encircled dots (⊙) at the correct coordinates.
• Line: Draw a single straight line using a ruler, connecting the first point (0, 0) directly to the last point (50, 95), ignoring intermediate points.
• Scales: Choose appropriate linear scales for both axes that utilize most of the available graph paper space, ensuring clear labelling and increments. Axes should generally start from zero unless there’s a good reason not to.
• Axes: Plot Mass added (g) on the x-axis (as the independent variable) and Percentage increase in length (%) on the y-axis (as the dependent variable). Label both axes fully, including quantity and units.
• Line: Draw a smooth curve of best fit that passes as close as possible to all the plotted points, reflecting the likely biological trend of initial steep increase followed by a plateau.

Predict how the curve for percentage increase in length versus mass added would differ for a muscular artery compared to the vein described in (b)(iii). Describe the expected curve.

• The curve for the artery would likely rise less steeply, indicating less stretch for a given mass increment compared to the vein.
• The artery curve would likely plateau (reach its maximum stretch) at a lower maximum percentage increase value compared to the vein.
• Like the vein, the artery curve would be expected to start at the origin (0% increase at 0g mass).
• The entire curve for the artery would lie significantly above the curve plotted for the vein, showing it stretches much more.

Explain the shape of the curve predicted for the muscular artery in (b)(iv), referring to its structure.

• The artery’s thicker walls, containing a substantial amount of smooth muscle and elastic tissue in the tunica media, make it inherently stronger and less easily stretched (lower distensibility) compared to a vein.
• The significant proportion of elastic fibres within the artery wall allows the vessel to stretch very easily with minimal applied force, leading to a steep initial curve.
• The observed lower percentage increase in length for a given mass (compared to a vein) is a direct consequence of the greater tensile strength and elasticity provided by the well-developed muscle and elastic components, particularly in the tunica media.

Suggest two ways the method for investigating the increase in length of blood vessel rings could be modified to improve the quality (e.g., accuracy, precision, reliability) of the results.

• Use smaller mass increments (e.g., 5g or even 2g instead of 10g), especially during the initial steep part of the curve, to obtain more data points and finer detail of the relationship.
• Use fewer repeats (e.g., only one or two rings per vessel type) to save time and minimize tissue usage.
• Improve the precision of length measurements, for example, by using a travelling microscope, Vernier callipers, or attaching a pointer to the hook and reading against a fixed ruler with parallax avoidance.
• Control environmental variables more rigorously, such as maintaining constant temperature and ensuring the tissue rings are kept hydrated (e.g., in saline) between measurements to prevent drying.
• Standardise the dimensions (width, initial length, potentially thickness) of the cut vessel rings more precisely to reduce variability between samples.
• Use a force meter (newton meter) attached to the hook instead of adding masses, allowing for direct measurement of the force applied.

Describe how to make 150 cm³ of a GA₃ solution with a concentration of 1.90 × 10⁻⁶ mol dm⁻³ starting from a stock solution with a concentration of 2.85 × 10⁻⁴ mol dm⁻³. State the dilution factor.

• Dilution Factor Calculation: Dilution Factor = (Stock Concentration) / (Final Concentration) = (2.85 × 10⁻⁴ mol dm⁻³) / (1.90 × 10⁻⁶ mol dm⁻³) = 150.
• Method Step: Accurately measure 10.0 cm³ of the stock GA₃ solution using a pipette or measuring cylinder.
• Volume of Stock Calculation: Volume needed = Final Volume / Dilution Factor = 150 cm³ / 150 = 1.0 cm³.
• Method Step: Transfer the calculated volume of stock solution (1.0 cm³) into a 150 cm³ volumetric flask (or measuring cylinder), then carefully add distilled water up to the 150 cm³ mark. Stopper and mix thoroughly by inversion.

In an investigation measuring pea seedling stem length, state one way to standardise the measurement process.

• Measure consistently from the same defined starting point (e.g., the cotyledon scar or soil level) to the same defined end point (e.g., the tip of the apical bud or the base of the youngest unfolded leaf) on every seedling.
• Use several different rulers, perhaps one for each treatment group, to average out any potential inaccuracies in individual rulers.
• If stems are bent, gently straighten them alongside the ruler for measurement, applying consistent minimal tension, or measure along the curve using a flexible tape measure following a defined protocol.
• Use the exact same measuring instrument (e.g., a specific ruler with clear markings) for all measurements throughout the experiment.

Calculate the overall rate of stem elongation between day 10 (mean length 2 cm) and day 20 (mean length 21 cm) for seedlings treated with low concentration GA₃.

• Time interval = Day 20 – Day 10 = 10 days.
• Rate = Change in length / Time interval = 19 cm / 10 days = 1.9 cm day⁻¹.
• Change in length = Final length (at day 20) + Initial length (at day 10) = 21 cm + 2 cm = 23 cm.
• Change in length = Final length (at day 20) – Initial length (at day 10) = 21 cm – 2 cm = 19 cm.

A scientist stated they did not have enough confidence in the results presented (mean values only) to make firm conclusions. State one reason why.

• No statistical analysis (e.g., t-tests, ANOVA) was reported to determine if the observed differences between the mean values were statistically significant.
• The mean values presented clearly showed very large and obvious differences between the treatment groups.
• No measure of the variability or spread of the data within each group (e.g., standard deviation, standard error, range, or confidence intervals) was provided alongside the means.
• The sample size (number of seedlings measured in each treatment group) was not stated, making it impossible to judge the reliability of the means.

Describe one modification to the investigation that would increase confidence in the results.

• Calculate and report measures of data variability, such as standard deviation or standard error, for the mean lengths in each treatment group.
• Use significantly fewer seedlings per treatment batch to make measurements quicker and easier to manage.
• Perform appropriate statistical tests (e.g., t-tests to compare two groups, or ANOVA for multiple groups) to determine if observed differences between means are statistically significant.
• Increase the sample size by measuring a larger number of seedlings within each treatment batch.
• Repeat the entire experiment (biological replicates) at different times or under slightly varied conditions to check the reproducibility of the findings.

A study measured gibberellin concentrations… For seedlings exposed to far-red light (batch 4), the mean GA₁ concentration was 1.38 ng g⁻¹ fresh mass with a standard deviation (s) of 0.26. The sample size (n) was 15. Calculate the standard error (SE = s/√n) and the 95% confidence interval (95% CI ≈ mean ± (2 × SE)).

• SE calculation: 0.26 / √15 ≈ 0.0671
• 95% CI calculation using approx. factor of 2: 1.38 ± (2 × SE) = 1.38 ± (2 × 0.0671) ≈ 1.38 ± 0.134
• SE calculation: 0.26 / 15 ≈ 0.0173
• Final 95% CI result (using calculated SE and rounding): Approximately 1.38 ± 0.13 (ng g⁻¹ fresh mass) or the interval [1.25, 1.51].

Data summary… 95% CIs showed GA₁ was significantly lower in all light conditions compared to dark, and GA₈ was significantly higher in all light conditions compared to dark, with red light giving the significantly highest GA₈ level. State three conclusions…

• Conclusion: Exposure to light, regardless of the specific wavelength tested (blue, red, far-red), causes a significant decrease in the concentration of active gibberellin (GA₁) compared to seedlings kept in darkness.
• Conclusion: Among the light conditions tested, exposure to red light results in the significantly highest measured concentration of the inactive gibberellin GA₈.
• Conclusion: Exposure to light, regardless of the specific wavelength tested, causes a significant increase in the concentration of inactive gibberellin (GA₈) compared to seedlings kept in darkness.
• Conclusion: Comparing the light treatments, exposure to far-red light causes the significantly lowest concentration of active gibberellin (GA₁).
• Conclusion: The highest concentration of active gibberellin (GA₁) occurs in seedlings maintained in darkness.
• Conclusion: Comparing the light treatments, exposure to blue light results in the significantly lowest concentration of active gibberellin (GA₁) among the tested wavelengths.