Midterm #1

The first midterm will be Monday, February 3, 2014

The midterm will cover material presented in lecture and tutorial, up to and including the last lecture and tutorial before the midterm (i.e., lectures 1-12 and tutorial papers 1-4 will be covered).

The examples below are not intended to cover all of the topics that may be on the midterm – they are just to give you an idea of the type of questions, and how to answer them. Go through your lecture notes, identify what the main points are, and try to come up with your own questions for each lecture.

Example questions with answers (sample answers are highlighted yellow)

Imagine that you are a graduate student interested in studying how aquatic invertebrates cope with low oxygen environments.

• What are some of the considerations (apart from cost and availability) you would use in selecting a model species to study? Why would these factors be important? (3 marks)

• What are some of the types of responses you might look at? Include examples of these responses. (3 marks)

(6 marks total)

Good answer:

Selecting a model species:

· I’d identify a species that was relevant to my interests, e.g., if I was concerned about environmental issues, I’d pick an ecologically important species (or a close relative that was easy to study), if I was concerned about an economically important species, or a species that was a food item of an economically important species;

· I’d try to pick a species for which genomic resources were available so that I could measure gene expression or do population genetics

· I’d try to pick a species that was part of a family of species in which adaptation to low oxygen had occurred more than once so that I could be more confident that any physiological changes I saw between low and high oxygen environments were indeed adaptations. [you could expand this point to be worth 2 marks by discussing (A) the limits of studying extreme species and/or (B) why species are not necessarily independent observations and/or (C) what an adaptation is, compared to a phylogenetic effect. Example phylogenies might help]

· I’d try to pick a species which was feasible to bring into the lab so that I could compare populations from high and low oxygen habitats in a common environment to determine if differences between the populations had a genetic basis

· I’d try to pick a species with short generation times so that I could do selection experiments to establish causation between physiological changes and environmental tolerance

My example answer is longer than you’d need - you’d need to get 3 of these bullet points for full marks, and if you provided more detail, some of the bullet points above could be worth 2 marks.

Types of responses:

· I could study within individual responses such as acclimatization, e.g., what happens if they are placed in a low oxygen environment for a few weeks- how does the oxygen affinity of their respiratory pigment change? Does the total oxygen transport capacity of their circulatory fluid change (e.g., due to the production of more pigment)? [lots of other potential examples you could get into here]

· I could study evolutionary adaptations by comparing, e.g., the oxygen affinity of their respiratory pigment compared to that of related species that live in more oxygenated environments [lots of other potential examples you could get into here]

· [You could expand the points above by providing examples of different levels of response, e.g., molecular (affinity or gene expression) vs. physiological (e.g., control of respiration, structure/surface area of exchange surface) vs. behavioural]

Basically, you’d want to convey the idea that you can distinguish between within individual vs. evolutionary responses, and that a variety of different things (molecules, structures, behaviours) can be involved in each of these types of responses.

Bad answer:

· Relatedness to species of interest

· Availability of genomic resources

· Availability of phylogeny of related species

· Ability to do selection experiments

· Acclimatization

· Evolutionary adaptations

· Behavioural responses

This answer doesn’t include detail or examples, e.g., why is “availability of genomic resources” important? Also, there are actually two parts to the question, each worth 3 marks, whereas this answer has lumped together the answers to the two questions. In my example, it’s obvious which point relates to which question, but that isn’t always the case- make it easier for us to find your answers to each question!

Discuss the effects of increasing temperature on oxygen consumption in an aquatic ectotherm.

Good answer:

Increasing temperature will generally reduce the affinity of the respiratory pigment for oxygen, and so may facilitate the unloading of oxygen at the tissues (1 mark). However, the increasing temperature will also increase the metabolic rate of the animal (through Q10 effects on enzymes), increasing oxygen demand (1 mark), and will also reduce the solubility of oxygen in the water (1 mark). Increasing temperatures will increase the rate of diffusion of oxygen through water, but this effect will be small compared to the increase in metabolic rate and the reduced solubility (1 mark). Therefore, oxygen will likely become limiting at higher temperatures (1 mark).

In this example answer, I’ve made 5 points (worth one mark each). I would probably make a question like this worth 3 marks, in which case you would only have to mention 3 of the points to get full marks. The question will state how many marks it is worth so you know how many points to make. You could potentially draw out oxygen equilibrium curves at high and low temps to illustrate some of these effects if you found them difficult to explain with words, but you’ll only get one mark per ‘idea’.

Bad answer:

O2 affinity of pigments

Metabolic rate

O2 content of water

Diffusion

With this kind of answer, I see where you are coming from, but it is not clear that you understand the effect of temperature on each of these things, and the consequences for the animal. Complete sentences are not absolutely required, but will probably help to make sure that I know that you understand what’s going on.

In what sense are respiratory surfaces a compromise? Consider both water and air-breathing animals. (2 marks)

Good answer:

For both air and water breathing animals, increased respiratory surface area would increase gas transfer, but in the case of air-breathers, a large surface area would also increase evaporative water loss, whereas in water-breathers, a large surface area would increase the exchange of ions with the environment.

Answer worth one mark:

A large surface area would increase evaporative water loss or increase the exchange of ions with the environment.

What’s wrong? (A) The answer doesn’t specify which problem occurs for water vs. air-breathing animals; (B) A compromise is when something that you do for one function conflicts with something you do for another function, so it is necessary to describe both the costs AND the benefits of increasing SA, i.e., increasing SA improves gas transfer.

Example tutorial question

For either of the papers about phylogenetic analyses (birds or butterflies)….

• Explain why it is necessary to consider information about phylogeny when comparing physiological traits between different species.  (2 marks)  
• What were the main traits examined in the paper? (1 mark)
• Were these traits phylogenetically clustered? (1 mark) 

You only have to answer these questions for ONE of the papers.

(4 marks total)

Sample questions without answers

The following questions are from Chapter 9, Moyes and Schulte, 2^nd edition. At the end of each chapter, Moyes and Schulte have “Review questions” and “Synthesis questions”. Review questions can be answered by relying on memorization (more or less). Synthesis questions require thought to put things together in ways that were not necessarily presented in lecture. I attempt to compose exams of both “review” questions and “synthesis” questions, in roughly equal amounts.

Review questions

1. Why is diffusion an inefficient respiratory strategy for organisms that are more than a few millimeters thick?

2. Compare and contrast the lungs of birds, the lungs of mammals, and the tracheal systems of insects.

3. Explain how countercurrent flow arrangements can lead to more efficient gas exchange across a respiratory surface.

8. Outline how chemoreceptors influence ventilation in mammals.

Synthesis questions

1. Very few animals that use water as the respiratory medium have lungs. Instead, most water breathers use gills for gas exchange. What functional disadvantages do lungs have in water.

6. What effects might you expect in a mammal whose major hemoglobin is mutated such that it lacks a Bohr effect?

7. Metabolic rate can increase as much as 40-fold above resting values as a result of feeding in some species of reptiles. In addition, during digestion, a large amount of H+ is secreted into the stomach, which results in the so-called alkaline tide, a large metabolic alkalosis in which blood pH increases. Outline the likely response of the respiratory system to this increased oxygen demand and pH disturbance.

8. In fish, there is a positive correlation between whole animal metabolic rate and the surface area of the gill. What might explain this relationship?

10. Hemoglobin is typically saturated with oxygen when the blood leaves the lungs. In a person who is doing pull-ups, will hemoglobin release more of the bound oxygen in the quadriceps (leg muscles) or biceps (arm muscles)? Describe at least two factors that could cause a difference, if any, in oxygen release between your biceps and quadriceps.

11. Imagine that you take hemoglobin molecules from both a sheep fetus and its mother. You mix equal amounts of these two hemoglobins in an aqueous solution in the presence of oxygen, at a PO2 that is not sufficient to saturate all the hemoglobin sites on the molecules you have added. Given what you know about maternal and fetal hemoglobins, where would you expect to find most of this oxygen bound? How would this compare to the amount of oxygen dissolved in your solution and not bound to hemoglobin? Why? [Hint: fetal hemoglobin has higher oxygen affinity than adult hemoglobin]

12. Anxiety can cause a person to hyperventilate (rapid deep breathing). This can cause a variety of symptoms, including dizziness and fainting. What changes would you expect in systemic arterial O2 and CO2 concentration and pH during an episode of hyperventilation? Breathing into a paper bag is often suggested as a treatment for hyperventilation. Do you think that this would work? Why or why not?