Estimate the solute concentration of the zucchini cells.

If a zucchini is allowed to dry in the open air, predict how the osmolarity of the zucchini cells would change.

Explain one reason for calculating the percentage changes in mass.

Predict what would happen to a red blood cell placed in distilled water.

0.36 mol dm^-3/M ✔

Units required
Allow a range of 0.35–0.37 mol dm^-3/M.

osmolarity will increase «because the cells become dehydrated»
OR
the cells become hypertonic ✔

Accept water potential of the tissue decreases.
Do not accept "change" instead of "increase".

a. the change in mass indicates whether the tissue has gained/lost water ✔

b. the pieces of tissue will not all be the same mass «at the beginning of the experiment» ✔

c. to compare the relative changes in mass ✔

a. water would move into the red blood cells ✔

b. it would lyse
OR
swell
OR
burst ✔

Concerns have been raised about the effect of rising pollution levels on sperm production in men. To investigate the possible effects of pollution on spermatogenesis, sperm samples from men of similar ages were collected in Kolkata in the 1980s and 2000s. The box plot represents the mean and range of sperm counts in the 1980s and 2000s.

[Source: Republished with permission of Elsevier Science and Technology Journals, from ‘Semen quality and age-specific changes: A study between two decades on 3729 male partners of couples with normal sperm count and attending an andrology laboratory for infertility-related problems in an Indian city’, Dyutiman Mukhopadhyay, Alex C. Varghese, Manisha Pal, Sudip K. Banerjee, Asok K. Bhattacharyya, Rakesh K. Sharma, and Ashok Agarwal, Fertility and Sterility, 93 (7), 2009; permission conveyed through Copyright Clearance Center, Inc]

A hypothesis has been suggested that pollution may have a negative effect on spermatogenesis. Evaluate whether the data support this hypothesis.

Calculate the actual size of the seminiferous tubule in the area indicated by the line across it, giving the units.

Identify the type of cell labelled Z.

a. hypothesis not supported as there is a «slight» increase/not much difference in sperm count between the 1980s and the 2000s

    OR

    hypothesis not supported as similar means/values for both groups

b. no information on sample size

c. no information/data provided on pollution levels/types of pollution

d. other factors affecting sperm count not considered

    OR

    other elements than sperm count could be affected

e. data limited to Kolkata/one country/one city

    OR

    pollution may affect spermatogenesis elsewhere

[Max 3 Marks]

62 mm Υ400 = 0.155 mm/155 μm/micrometers/10^-6 m

OR

61 mm Υ400 = 0.153 mm/153 μm/micrometers/10^–6 m

Calculation and units required. Accept correct answers expressed in cm

spermatogonium

OR

primary spermatocyte

Data was collected on rabbit red blood cells that were exposed to sodium chloride (NaCl) and scorpion venom. Under some osmotic conditions red blood cells swell and burst, releasing hemoglobin (hemolysis). The graph shows the response of red blood cells to different concentrations of sodium chloride, with and without scorpion venom.

[Source: Adapted from Mirakabadi A Z, et al., (2006), J. Venom. Anim. Toxins incl. Trop. Dis., 12 (1), pages 67–77 (London: BioMed Central)]

Outline the effect of the venom on the hemolysis of red blood cells.

Describe how the variables would be controlled in an experiment to estimate the osmolarity of plant tissue.

a. in NaCl concentrations between 0.3 to 0.5 % venom increases the percentage of hemolysis/more cells lyse 

b. venom has no effect below 0.3% and above 0.55% NaCl
OR
Venom has no effect at very low or very high NaCl concentrations

a. weigh all pieces to ensure same amount of plant material/allow comparisons 

b. control surface area by having same shape/ size 

c. carry out experiment at same temperature e.g. using a water bath or constant room temperature 

d. all samples in solution for same length of time 

e. all samples from same plant (to minimize variability) 

f. use a range of solutions of the same solute 

g. constant method of removing excess fluid before weigh tissue samples

Do not accept just a list of controlled variables.

Describe briefly how scientists obtained leaf phloem sap from the potato plants.

Suggest reasons for different amounts of sucrose in the leaf phloem sap of the potato plants.

a. aphids insert stylet in «potato» plants/feed from «potato» plants

“Aphids” is essential for the mark.

b. phloem exudates/sap obtained from severed stylets

“Stylets” is essential for the mark.

a. sucrose produced by leaves during photosynthesis

b. sucrose moves/translocates from source/leaves to sink/roots/tubers
OR
sucrose carried by phloem to tuber

c. «wk 5» high sucrose with increased leaf growth/photosynthesis / OWTTE

d. «wk 5-7» more sucrose used for general plant growth / OWTTE

e. «wk 7-11» concentration sucrose increases due to greater production/photosynthesis «than usage/storage» / OWTTE

f. sucrose transformed into starch in tuber «from week 9»

g. contribution of amino acids unknown so difficult to know about different amounts of sucrose / OWTTE

Award the mark for realizing that amino acids play a role in the ratio

h. «abiotic» conditions in greenhouse may vary over time / OWTTE

Accept abiotic factors only if variation through time is explicit.

Calculate the magnification of the image, showing your working.

. . . . . . . . . . . . . . . . . . . . x

The mean stomatal density for the lower epidermis of P. decandrum was around 600 per mm². Predict how the stomatal density for the upper epidermis would compare.

Calculation: size of bar ÷ 15 μm (1.5 cm ÷ 15 μm or 15 000 μm ÷ 15 μm);

Answer: 1000 x;

First marking point is for division by 15 μm;

Second marking point is for the correct answer; accept 930 and 1070 x.

(upper surface/epidermis usually has) fewer stomata/lower stomatal density/no stomata/OWTTE

Do not accept a numerical value only.

Most candidates managed to calculate the magnification correctly by dividing their scale bar measurement by the provided scale, others inverted the division or displayed incomprehensible calculations; some calculations were difficult to follow, with no apparent methodology or structure; there were too many unit conversion errors, sometimes because candidates did not use units within their calculation (e.g. measuring in centimetres, but calculating as millimetres); a limited number measured the complete image width but didn't adjust the scale bar proportionally.

Most predicted that the upper epidermis would have a lower density, although some stated the reverse.

One of the functions of this organ is absorption. On the micrograph, draw an arrow showing the direction of absorption.

Label tissues X and Y.

Calculate the actual width along line A-B of the parenchyma cell shown.

Describe the distribution of vascular tissues in the stem of dicotyledonous plants.

a. X: phloem ✔

b. Y: xylem ✔

A-B = $\frac{7\text{mm}}{400}$

OR

17.5 μm ✔

Accept answers in the range of 17 to 19 μm

a. stem vascular tissue is in bundles ✔

b. «bundles» form a ring

c. phloem is towards outside «of bundle»
OR
xylem is towards centre «of bundle» ✔

Allow answers in an annotated drawing