Biology 2025 · Oct/Nov

The plantain lily , Hosta plantaginea, as shown in Fig. 1.1, is a flowering plant found in Asia. leaf with stomata on the lower epidermis The hydrostatic pressure increases inside guard cells when water enters the guard cells down a water potential gradient. This affects the width of the stomata. Fig. 1.2 shows 1 open stoma from the plantain lily surrounded by 2 guard cells. stoma guard cells Fig. 1.2 * 0000800000002 * A student investigated the ef fect of dif ferent sucrose solutions on the width of stomata in the leaves of plantain lily. The student: Table 1.1 microscope slide number liquid added to microscope slide 1 large drop of distilled water

large drop of 2.5% sucrose solution

large drop of 5.0% sucrose solution

large drop of 10.0% sucrose solution

large drop of 20.0% sucrose solution

(i) State the independent and dependent variables in the investigation. independent dependent

The student prepared 20 cm of 2.5%, 5.0% and 10.0% sucrose solutions from a 20.0% w/v stock solution. Complete the description of the student' s dilution method for the 2.5% and 5.0% sucrose solutions by writing the correct volumes in the following sentences. The student mixed cm of 20.0% sucrose stock solution with cm of distilled water to produce a 2.5% sucrose solution. The student mixed cm of 20.0% sucrose stock solution with cm of distilled water to produce a 5.0% sucrose solution. [2] * 0000800000003 * lens. Outline a method the student could use to investigate the ef fect of the sucrose solutions in Table 1.1 on the width of stomata in the leaves of plantain lily. 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 prepare the microscope slides should not be included.

Predict the ef fect of increasing the sucrose concentration from 0.0% to 20.0% on the width of stomata in the leaves of plantain lily. Explain your prediction. prediction explanation [2] * 0000800000005 *

Another piece of lower epidermis from a leaf of plantain lily was immersed in a large drop of distilled water on a microscope slide. The student determined the stomatal density on the lower epidermis using Fig. 1.3 only . stomata 40 μm

Use Fig. 1.3 to calculate the stomatal density on the lower epidermis. Use the equation: area = πr and π = 3.14 Give your answer to the nearest whole number and show your working. stomatal density = mm

Suggest how this investigation could be improved to increase confidence in your answer in (b)(i).

A different plant species had a lower stomatal density than the value calculated for plantain lily in (b)(i). Suggest how the environmental conditions of the dif ferent plant species may vary from those of the plantain lily. Explain your answer. [Total: 18] * 0000800000007 * 2 Scientists investigated the ef fect of abscisic acid (ABA) on reducing water loss in plants. The scientists predicted that ABA, as well as stimulating stomatal closure, also reduces water loss in plants in other ways. The scientists used a mutant variety of thale cress, Arabidopsis thaliana, that has stomata that do not respond to ABA. When ABA is present, the stomata of the mutant variety remain open. The scientists sprayed dif ferent concentrations of ABA on the leaves of the mutant variety and measured the transpiration rates of the plants. The results are shown in Fig. 2.1. 0.0 01050 ABA concentration / μmol dm Error bars show ± 1 standard error (SE). 0 μmol dm ABA = distilled water 100400 0.5 1.0 1.5 mean transpiration rate / mmol m 2.0 2.5

Calculate the percentage decrease in transpiration rate from 0 to 400 µmol dm of ABA for the mutant variety. Show your working. percentage decrease = [2] * 0000800000008 *

With reference to Fig. 2.1, suggest conclusions that can be made about the ef fect of dif ferent concentrations of ABA on the transpiration rates of the mutant variety. State the evidence that supports your conclusions.

The scientists used a mutant variety of thale cress that has stomata that do not respond to ABA. The scientists concluded that ABA reduces water loss in thale cress by ways other than stomatal closure. Suggest additional information that is required to increase the confidence in this conclusion. [Total: 7] * 0000800000009 * The awn is an extension on the E. cicutarium seed. The seed uses the awn to push the seed head into the soil to allow the seed to germinate. The awn changes shape when the humidity changes. Humidity is the concentration of water vapour in the air . The higher the humidity , the higher the concentration of water vapour in the air. awn in high humidity seed heads awn in low humidity A student investigated the effect of humidity on the appearance of the awn. The student set up the apparatus as shown in Fig. 3.2. Water can be added to the filter paper to change the humidity in the beaker surrounding the seed. Increasing the volume of water added to the filter paper increases the humidity.awn filter paper seed head 250 cm beaker material to hold seed in place Petri dish Fig. 3.2 * 0000800000010 * [ b

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 ef fect of dif ferent levels of humidity on the appearance of the awn, using the apparatus in Fig. 3.2. Do not include standardised variables from

or a risk assessment. [Total: 5] * 0000800000011 * [[b The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country , territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries. reasonable ef fort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Local Examinations Syndicate (UCLES), which is a department of the University of Cambridge. BLANK PAGE * 0000800000012 * [Tb