Question 21M.2.SL.TZ1.1f
| Date | May 2021 | Marks available | [Maximum mark: 3] | Reference code | 21M.2.SL.TZ1.1f |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Evaluate | Question number | f | Adapted from | N/A |
Antiretroviral drugs are used to treat Human Immunodeficiency Virus (HIV) infections. Zidovudine (ZDV) and nevirapine (NVP) are examples of antiretroviral drugs. There are concerns that these drugs may be toxic to body cells in mitosis. In a study using Allium cepa, root tips were exposed to the drugs for 96 hours at a range of concentrations. The control treatment was a drug concentration of 0μmol. In the graph, root lengths after the 96-hour treatment period are expressed as a percentage of the length of the control.
[Source: Onwuamah CK, Ekama SO, Audu RA, Ezechi OC, Poirier MC, Odeigah PGC (2014) Exposure of Allium cepa Root Cells to Zidovudine or Nevirapine Induces Cytogenotoxic Changes. PLOS ONE 9(3): e90296. https://doi.org/10.1371/journal.pone.0090296 (CC0 1.0 - https://creativecommons.org/publicdomain/zero/1.0/).]
Both ZDV and NVP are believed to have a damaging effect on the process of mitosis but ZDV in particular is believed to block the formation of the spindle.
[Source: Medical Images / Carolina Biological.]
Mitosis plays an important role in tissue regeneration and can be an important factor in recovery from surgery. The hormone leptin has been shown to promote mitosis in certain circumstances. The bar chart shows the mitotic indices of liver tissue exposed to leptin and control tissue during 72 hours after surgery.
[Source: Adapted from Cilekar M, Uysal O, Bal C, Turel S, Yılmaz S. Leptin increases mitotic index and regeneration ratio in hepatectomized rats. Med Sci Monit Basic Res. 2013 Nov 13;19:279-84. doi: 10.12659/MSMBR.889591]
Based on the data, evaluate the evidence for leptin promoting regeneration of liver tissue.
[3]
a. mitotic index in treatment greater than in control/leptin appears to promote mitosis ✔
b. mitotic index increases with time suggests ongoing regeneration/growth
OR
positive correlation between exposure to leptin and increased mitotic index ✔
c. but experiment limited to 72 hours/regeneration/recovery may take longer than 72 hours ✔
d. no error bars shown/no information on significance/sample size ✔
Acknowledge WTTE.
Many students were able to extract conclusions from the data but did not take the evaluation into discussion of shortcomings of the design or error bars in the data.
