1(a)(i) Preparing Ethanol Dilutions

You need to prepare 20 cm³ of a 20% ethanol solution using a 50% ethanol stock solution (E) and distilled water (W). Which step below describes an incorrect action or calculation for this specific task?

• Identify the target concentration (C2 = 20%) and target volume (V2 = 20 cm³).
• Identify the stock concentration (C1 = 50%).
• Calculate the required volume of 50% stock solution (V1) using C1V1 = C2V2: V1 = (20% × 20 cm³) / 50% = 8.0 cm³.
• Calculate the required volume of distilled water (W): V2 – V1 = 20 cm³ – 8.0 cm³ = 12.0 cm³.
• Carefully measure 8.0 cm³ of distilled water (W) and 12.0 cm³ of 50% ethanol (E) and mix them thoroughly.

1(a)(ii) & (iii) Table Setup and Expected Trend

You are investigating the effect of ethanol concentration (0% to 50%) on pigment release from 10 beetroot discs soaked for 10 minutes, assessing the colour intensity using symbols (+ to ++++++). Which statement describes an incorrect way to set up the results table or describe the expected trend?

• Set up a table with ‘Percentage concentration of ethanol (%)’ as the independent variable.
• Use ‘Intensity of colour (Symbol)’ as the heading for the dependent variable column.
• Record the results for each concentration using the qualitative symbols provided (+, ++, etc.).
• The expected trend is that as the percentage concentration of ethanol increases, the intensity of the red colour decreases.
• Predict that the 0% ethanol solution (control) will show the least colour (+) and the 50% ethanol solution will show the most intense colour (++++++).

1(a)(iv) Explaining the Effect of Ethanol on Membranes

Explain why increasing ethanol concentration leads to greater release of red pigment from beetroot cells, referring to its effect on cell membranes. Which statement provides an incorrect part of the biochemical explanation?

• Ethanol acts as an organic solvent that physically interacts with and disrupts the lipid bilayer structure of cell membranes.
• Ethanol affects both the cell surface membrane (plasmalemma) and the membrane surrounding the vacuole (tonoplast), where the betalain pigment is stored.
• Ethanol can cause the denaturation (loss of functional three-dimensional shape) of important proteins embedded within the cell membranes, affecting their function (e.g., transport proteins).
• By dissolving membrane lipids and denaturing proteins, ethanol significantly decreases the overall permeability of the membranes, effectively trapping the pigment inside the cell.
• The increased membrane damage and disruption caused by higher ethanol concentrations compromises membrane integrity, allowing more red pigment (betalain) to leak out of the vacuole and subsequently the cell.

1(a)(v) Identifying the Dependent Variable

In the experiment investigating how different concentrations of ethanol affect the release of pigment from beetroot tissue, what is the dependent variable? Which statement below incorrectly identifies a variable or its role?

• The independent variable, which is deliberately changed or selected by the investigator, is the percentage concentration of ethanol used.
• The dependent variable, which is measured or observed as the result of changing the independent variable, is the intensity of the red colour in the surrounding solution (representing pigment leakage).
• A key controlled variable (a factor kept constant) is the number and approximate size of beetroot discs used in each test tube (e.g., 10 discs of similar dimensions).
• The dependent variable is the duration for which the beetroot discs are left soaking in the ethanol solution (e.g., 10 minutes).
• A factor that must be standardised (controlled variable) is the volume of the ethanol solution used for soaking each set of discs (e.g., 10 cm³).

1(a)(vi) Standardising a Variable

Besides ethanol concentration, soaking volume, and beetroot source, you need to standardise other factors in the beetroot permeability experiment. Which option describes a relevant variable but proposes an ineffective or inappropriate method for its standardisation?

• Variable: Temperature. Method: Place all test tubes containing the samples in a thermostatically controlled water bath set to a specific, constant temperature (e.g., 30°C) throughout the soaking period.
• Variable: Soaking time. Method: Use an accurate timer (e.g., stopwatch) to start and stop the soaking period for all samples simultaneously or ensure each soaks for precisely the same duration (e.g., exactly 10 minutes).
• Variable: Surface area of discs. Method: Use the same diameter cork borer for cutting all discs and then visually estimate the thickness to ensure all discs are roughly the same thickness.
• Variable: Temperature. Method: Ensure all test tubes are left undisturbed on the same laboratory bench, away from direct sunlight, drafts, or heat sources, for the entire duration of the experiment.
• Variable: Surface area of discs. Method: Use a specific diameter cork borer for cutting all discs and then use a ruler or digital callipers to measure and select discs of a standard thickness (e.g., all discs 2mm thick).

1(a)(vii) Error Source in Visual Colour Assessment

When assessing the results of the beetroot experiment by visually comparing the redness of the solutions against standards or a scale, what is a potential source of error? Which of the following is least likely to be a significant source of error specifically related to the visual judgement of colour intensity?

• The inherent subjectivity in interpreting colour hues and intensities; different observers may rank or describe the same solution slightly differently.
• The difficulty for the human eye in accurately distinguishing between solutions that have very similar, but not identical, colour intensities, especially at the extremes of the scale.
• Using sample containers (e.g., test tubes) made of slightly different types or thicknesses of glass, which might subtly affect the perceived colour or light transmission.
• Forgetting to zero or calibrate the colorimeter properly before taking absorbance readings for each of the coloured solutions.
• Natural biological variation in the initial pigment concentration between the individual beetroot discs used, leading to real differences in leakage even at the same ethanol concentration.

1(a)(viii) Modifying Experiment for Temperature Effects

How should the procedure be modified to investigate the effect of temperature (independent variable) on beetroot membrane permeability (measured by pigment leakage), rather than the effect of ethanol concentration?

• Prepare multiple, identical beetroot samples (e.g., same number of discs, same size, from the same beetroot if possible).
• Prepare a single, standard soaking solution to be used for all temperature treatments (e.g., use only distilled water, or perhaps a fixed, low concentration of ethanol like 10% if investigating combined effects, but keep it constant).
• Set up thermostatically controlled water baths to maintain at least five different, constant temperatures covering a physiologically relevant range (e.g., 10°C, 20°C, 30°C, 40°C, 50°C).
• Place one beetroot sample into the standard soaking solution within each pre-equilibrated water bath for a fixed, identical soaking time (e.g., exactly 15 minutes for all temperatures).
• Adjust the soaking time for each temperature being tested, using shorter soaking times for the higher temperatures and longer soaking times for the lower temperatures, before assessing the pigment release.

1(b)(i) Plotting Blood Pressure Data

You need to plot a graph of the difference in mean blood pressure (BP) compared to a control group (y-axis, kPa) against time after drinking beetroot juice (x-axis, minutes). The data includes time points up to 220 minutes and negative values for the BP difference (reaching -1.33 kPa). Which instruction below describes an incorrect procedure for drawing this graph?

• Label the horizontal axis (x-axis) clearly as “Time after drinking beetroot juice / minutes”.
• Label the vertical axis (y-axis) clearly as “Difference in mean blood pressure compared to control group / kPa”.
• Choose linear scales for both axes. The x-axis scale must extend from 0 to at least 220 minutes. The y-axis scale must appropriately include the range from 0.0 down to at least -1.33 kPa (e.g., starting slightly above 0 and extending below -1.4).
• Plot each data point accurately using small, neat symbols such as crosses (‘x’) or encircled dots (‘☉’).
• Draw a calculated mathematical curve of best fit (e.g., using polynomial regression) that represents the trend but may pass significantly distant from some individual data points.

1(b)(ii) Interpolation and Calculation

Using the blood pressure data points (Time = 80 min, Difference = -0.57 kPa) and (Time = 125 min, Difference = -0.92 kPa), you need to estimate the difference in BP at 100 minutes. The control group’s mean BP at 100 minutes was 15.79 kPa. Which step describes an incorrect method for this estimation or subsequent calculation?

• Recognise that the target time (100 minutes) falls between the two given data points (80 min and 125 min), so interpolation is required.
• Estimate the value at 100 min by extrapolating the trend observed between the 0 min and 80 min data points, assuming the rate of change continued linearly.
• Assume a linear change between 80 min and 125 min. Calculate the rate of change: (-0.92 – (-0.57)) kPa / (125 – 80) min = -0.35 kPa / 45 min. Estimate the value at 100 min (20 min after 80 min): -0.57 kPa + (20/45) * (-0.35 kPa) ≈ -0.73 kPa.
• Use the interpolated difference at 100 min (e.g., approximately -0.73 kPa) and the control group’s BP at 100 min (15.79 kPa) to calculate the beetroot group’s estimated BP: Estimated BP = Control BP + Difference.
• Calculate the final estimated blood pressure for the beetroot group at 100 minutes: 15.79 kPa + (-0.73 kPa) ≈ 15.06 kPa.

2(a)(i) Plan Diagram of a Dicot Leaf

When drawing a plan diagram showing the distribution of tissues in a transverse section of a typical dicot leaf lamina, which feature or instruction below is incorrect?

• Represent the upper epidermis and lower epidermis as single, continuous lines forming the top and bottom boundaries of the section.
• Show the palisade mesophyll tissue as a distinct region containing clearly drawn, individual, elongated cells packed tightly below the upper epidermis.
• Indicate the spongy mesophyll tissue region located below the palisade layer, potentially showing some unshaded areas within its outline to represent intercellular air spaces.
• Draw outlines representing several vascular bundles (veins), containing xylem and phloem, embedded within the mesophyll layers, showing their position and relative size.
• Ensure that no individual cells are drawn within any tissue region; tissues should be represented solely by outlined areas with appropriate labels identifying the tissue type.

2(a)(ii) High Power Drawing of a Stoma

You are making a high-power drawing of two guard cells forming a stoma, along with two adjacent lower epidermal cells from a dicot leaf transverse section or peel. Which instruction describes an incorrect representation or technique for a standard biological drawing?

• Draw the two guard cells accurately showing their characteristic kidney or bean shape, positioned to enclose the central stomatal pore.
• Draw the two adjacent epidermal cells accurately, typically showing them with irregular, interlocking shapes, like pieces of a jigsaw puzzle.
• Use sharp, clear, continuous single lines to represent the cell walls separating the guard cells from each other, the guard cells from the epidermal cells, and the outer boundary of the epidermal cells.
• Ensure the adjacent epidermal pavement cells are generally drawn larger in size than the specialized guard cells.
• Add a clear label line, drawn with a ruler and not crossing other label lines, pointing accurately to the wall of one of the guard cells, with the label ‘Cell wall’ written horizontally.

2(b)(i) Identifying Structural Differences Between Leaf Sections

You are comparing Micrograph 1 (representing slide N1, assumed to be a typical mesophytic dicot leaf) with Micrograph 2 (Fig. 2.1, showing structural variations potentially related to adaptation) to identify three observable structural differences in transverse view. Which of the following comparisons is least useful or irrelevant for identifying inherent structural differences between the two leaf sections themselves?

• Comparing the differentiation and relative thickness of palisade versus spongy mesophyll layers (e.g., clear distinction vs. less differentiated isobilateral).
• Comparing the location (e.g., embedded vs. near surface), size, and structure (e.g., bundle sheath presence) of the vascular bundles (veins).
• Comparing the specific colour (e.g., pink vs. blue) imparted by the histological stains used in preparing each slide.
• Comparing the thickness of the epidermal layers (upper and lower) or the thickness and prominence of the cuticle covering the epidermis.
• Comparing the overall shape or cross-sectional profile of the leaf section (e.g., flat vs. curved, presence of grooves or ridges).

2(b)(ii) Calculating Actual Leaf Thickness from Scale Bar

A photomicrograph shows a leaf section (Fig. 2.1). A scale bar printed on the image is labeled ‘100 µm’ and measures 20 mm long when measured with a ruler on the image. A line A-B drawn across the leaf’s thickness on the same image measures 80 mm long with the ruler. Which step below shows an incorrect calculation or value used in determining the actual thickness A-B?

• Measurement on Image: Length of the scale bar = 20 mm.
• Actual Length represented by the scale bar = 100 µm.
• Measurement on Image: Length of the feature A-B (leaf thickness) = 80 mm.
• Calculate Ratio: Feature image length / Scale bar image length = 80 mm / 20 mm = 4. (The feature A-B is 4 times longer on the image than the scale bar).
• Calculate Actual Thickness = Ratio × Image length of scale bar = 4 × 20 mm = 80 mm.

2(b)(iii) Calculating Magnification

Using the image measurement for leaf thickness (line A-B = 80 mm) and the correctly calculated actual thickness (400 µm from Q2bii), calculate the magnification of the photomicrograph, giving the answer to two significant figures. Which step describes an incorrect procedure or result?

• Recall or state the formula for magnification: Magnification = Image size / Actual size.
• Convert Image size and Actual size to the same units before division. E.g., Image size = 80 mm = 80,000 µm; Actual size = 400 µm.
• Substitute the values (in consistent units) into the formula: Magnification = 80,000 µm / 400 µm.
• Perform the calculation: Magnification = 80,000 / 400 = 200.
• Express the answer to the required two significant figures as x20.