Mock Exam Set 1 - Paper 2

[Maximum mark: 15]

Appetite regulating genes expressed in the brain are understood to have an important role in feeding behaviour and the study of this is important in order to understand the underlying causes of feeding disorders. However, other areas, outside the brain, such as the gastrointestinal tract, are receiving attention for their potential influence in the regulation of appetite.

In a study, scientists investigated the expression of appetite-regulating genes in the gut, using zebrafish (Danio rerio) as a model organism.

In their first experiment, a variety of feeding conditions were applied to wild type zebrafish and the expression of different genes, known to have a role in appetite regulation, were measured.

[Source: Adapted from Ahi EP, Brunel M, Tsakoumis E, Chen J, Schmitz M (2022). Appetite regulating genes in zebrafish gut; a gene expression study. PLoS ONE 17(7): e0255201. Retrieved December 01, 2022, from https ://journals.plos.org/plosone/article?id=10.1371/journal.pone.0255201. Copyright-free]

1. Identify the gene and feeding condition which show the greatest difference in relative fold change in expression compared to the control. [2]
   

2. Describe the effect of feeding conditions on the expression of the galr2a gene. [3]
   

3. Calculate the increase, as a percentage, in the relative fold change in expression between the control feeding condition and the fasted feeding condition for the gene cnr1. [1]
   

4. State the name of the gene which had the greatest increase in expression when zebrafish were fed every 2 hours. [1]
   

In a second experiment, scientists used a zebrafish mutant, which, unlike the wild type, had impaired leptin receptors, due to a mutant gene lepr. The same feeding conditions were then applied and the expression of the same genes were measured.

[Source: Adapted from Ahi EP, Brunel M, Tsakoumis E, Chen J, Schmitz M (2022). Appetite regulating genes in zebrafish gut; a gene expression study. PLoS ONE 17(7): e0255201. Retrieved December 01, 2022, from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0255201. Copyright-free]

5. 1. Compare and contrast the effect of feeding conditions on the expression of the apln gene in wild type and mutant zebrafish. [2]
      

   2. State which feeding condition, other than the control, had the most similar results for wild-type and lepr-mutant zebrafish for the gene scg2a. [1]
      

A final experiment was conducted to test the effect of a variety of known appetite suppressing agents on the feeding volume of zebrafish, as a precursor to studying their effect on gene expression.

In the experiment, paramecia were fluorescently labelled and fed to zebrafish, with transparent body cavities, which were treated using an appetite suppressing agent. Using a 96-well microplate reader, scientists were able to measure the intensity of fluorescence in zebrafish as a measure of the volume of paramecia they consumed. The experiment and its results are outlined below.

[Source: Adapted from Shimada Y, Hirano M, Nishimura Y, Tanaka T (2012) A High-Throughput Fluorescence-Based Assay System for Appetite-Regulating Gene and Drug Screening. PLoS ONE 7(12): e52549. Retrieved December 01, 2022 from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052549. Copyright-free.]

[Source: Adapted from Shimada Y, Hirano M, Nishimura Y, Tanaka T (2012) A High-Throughput Fluorescence-Based Assay System for Appetite-Regulating Gene and Drug Screening. PLoS ONE 7(12): e52549. Retrieved December 01, 2022 from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052549. Copyright-free.]

6. 1. State the name of the agent which, at a concentration of 3.3µM, resulted in zebrafish having the poorest appetite. [1]
      

   2. Suggest why there are no results for Mazindol at a concentration of 10µM. [1]
      

7. Approximately 70% of the coding genes of zebrafish are related to humans, and about 84% of human genes associated with disease are related to zebrafish. Evaluate the use of zebrafish in the study of obesity in humans. [3]
   

[Maximum mark: 6]

The micrograph below shows the xylem vessels in a developing shoot taken at 400$\times$ magnification.

[Source: Adapted from Berkshire Community College Bioscience Image Library, (2019, October). File vessels in developing Coleus shoot (35105390750).jpg. Wikimedia commons. Retrieved June 20, 2022, from https:// commons.wikimedia.org/wiki/File:Xylem_vessels_in_developing_Coleus_shoot_%2835105390750%29.jpg. Copyright under CC-Zero]

1. Draw and label the structure of a primary xylem vessel in a developing shoot using the micrograph above. [2]
   

2. Describe the features of xylem vessels which enable them to withstand changes in pressure. [2]
   

3. Explain why the active uptake of mineral ions in roots leads to the absorption of water. [2]
   

[Maximum mark: 7]

In Mongolian horses (Equus przewalskii), fur colour is determined by a number of genes. Brown colour (B) is dominant to sandy colour (b) and an ombre (two tone) colour (P) is dominant to one tone (p).

[Adapted from: Source Ksuryawanshi. (2015, October 15). Category: Mongolian horse. Wikimedia Commons. Retrieved July 31, 2022, from https ://commons.wikimedia.org/wiki/File: Mongolian_horses.jpg Copyright under CC BY 4.0]

1. A homozygous sandy ombre male horse is crossed with a heterozygous horse for both traits. Draw a Punnett square to show the potential results of this cross. [3]
   

2. Identify the possible genotype recombinations, after fertilisation, from the cross in part (a). [1]
   

3. In pigs, the curly tail is dominant to the straight tail, and pink skin is dominant to black skin. On a pig farm, the resulting phenotypes from double-heteroygous genotype breeding were recorded. The chi-square value for the phenotypes of the offspring was calculated and the result was 340.6.
   The table below shows the degrees of freedom (D.f.) and critical values at a significance level (p) of 0.05 (5%) for a chi-squared test.
   Discuss whether the genes for skin colour and tail shape in pigs are linked or unlinked. [3]
   
   

$\hspace{1.5em}$D.f. $\hspace{1.5em}$	$\hspace{1.5em}$p=0.1 $\hspace{1.5em}$	$\hspace{1.5em}$ p=0.05 $\hspace{1.5em}$	$\hspace{1.5em}$ p=0.01 $\hspace{1.5em}$
1	2.706	3.841	6.635
2	4.605	5.991	9.210
3	6.251	7.815	11.345
4	7.779	9.488	13.277
5	9.236	11.070	15.086

[Maximum mark: 6]

The cladogram below shows three possible evolutionary origins of the platypus (Platypus X, Y, and Z), an egg-laying mammal with webbed feet. The italicised taxa are extinct.

[Sources: adapted from Celik, M.A. and Phillips, M.J. (2020). Conflict Resolution for Mesozoic Mammals: Reconciling Phylogenetic Incongruence Among Anatomical Regions. Front. Genet. 11:0651. Retrieved January 4, 2023 from https://pubmed.ncbi.nlm.nih.gov/32774343/. Copyright under CC BY 4.0]

1. State the taxa most closely related to marsupials. [1]
   

2. 1. The cladogram shown is based on morphological traits. Describe one other type of evidence that can be used to deduce evolutionary relationships. [2]
      

   2. Suggest one type of morphological evidence that could be used to provide support for Platypus Z over Platypus X as the origin of the platypus. [1]
      

3. Taxonomists classify organisms according to their evolutionary origins using a hierarchical classification system.

   Outline the principal taxonomic ranks in the modern classification system. [2]
   

[Maximum mark: 6]

The diagram below shows an animal-pollinated flower.

[ © Revision Village 2022. Created with BioRender.com]

1. Identify the processes that occur in locations I and II. [2]
   

2. Sexual reproduction in flowers produces seeds. Seeds contain structures that are essential for germination and early growth of the plant. Draw a labelled diagram to show the different parts found within seeds. [4]
   

[Maximum mark: 16]

Cells are typically categorized as eukaryotic (for example, a liver cell) or prokaryotic (for example, a bacterium cell).

1. Outline Cairns’ technique for measuring the length of prokaryotic DNA. [3]
   

2. Outline the advantages of compartmentalization in eukaryotes. [4]
   

3. Explain how the misuse of antibiotics can lead to the development of antibiotic resistance in bacteria. [8]
   

[Maximum mark: 16]

DNA is the code of life and is expressed in all living organisms. This code is passed through generations in cell nuclei and mitochondria.

1. Outline the role of gene expression in stem growth. [3]
   

2. Outline how mitochondrial DNA can be used to construct a cladogram. [4]
   

3. Describe the Hershey and Chase experiment, which demonstrated that genetic information is carried in DNA.[8]
   

[Maximum mark: 16]

Muscle atrophy is the loss of muscle tissue and may be caused by genetic factors or other medical conditions. Enzyme inhibitors may prevent the atrophy of muscles.

1. Distinguish between anaerobic respiration in muscle and yeast cells. [3]
   

2. Enzymes are regulated by inhibitors that are classified as competitive and non-competitive. Distinguish between these two types of inhibitors. [4]
   

3. Describe the process of muscle contraction. [8]