HL Paper 3
An experiment was carried out to study osmosis in plant cells. Small cylinders of zucchini (Cucurbita pepo) were cut and placed in different sucrose solutions at 25 °C. The figure shows the percentage changes in mass after 24 hours.
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.
The light micrograph shows a cross section of seminiferous tubules.
[Source: Micrograph of a seminiferous tubule with sperm by Nephron (https://commons.wikimedia.org/wiki/File:Seminiferous_tubule_and_sperm_low_mag.jpg)]
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.
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.
The diagram shows the development of potato plants (Solanum tuberosum) over 14 weeks. New tubers start growing from week 9. These are modified underground stems serving as a starch reserve and bearing buds from which new plants arise.
Scientists planted several potato plants in a greenhouse. The sucrose and amino acids in potato plant phloem exudates were measured during several weeks.
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.
The stomatal density is the number of stomata per area of leaf epidermis. A study was done on the stomatal density of the lower epidermis of leaves from Protium decandrum, a tree found in the Amazon forest.
The image shows the epidermis stripped from the lower surface of a leaf.
[Source: Camargo, M.A.B. and Marenco, R.A., 2011. Density, size and distribution of stomata in 35
rainforest tree species in Central Amazonia. Acta Amazonica, 41(2), pp.205–212. Image courtesy of Miguel from
Camargo & Marenco (2011).]
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.
The micrograph shows a section of an organ in the human body.
One of the functions of this organ is absorption. On the micrograph, draw an arrow showing the direction of absorption.
The micrograph shows a section through the root of a dicotyledonous plant (× 400).
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.