Midterm 1 Study Guide

Brian McCauley's Bio 6A, Fall 2019

This study guide is complete for Fall 2019.

Midterm 1 will be Monday, October 14. You’ll have the whole lecture period. The format will be mixed, including multiple-choice questions and one long-answer question. You don't need a Scantron; there will be a Zipgrade form on the test. On the multiple choice questions, there might be more than one correct answer; you have to mark all the correct answers and none of the incorrect answers to get credit. There will be no partial credit. Be sure to read the directions on the exam before answering the questions.

The exam will be based on the material I cover in lecture. I will assume that you have read the sections of the textbook that I covered in lecture. If I skipped a section in the book, I won’t ask any questions on that. The exam won’t include material that was covered only in lab (plants, for example), but it will include questions on systematics and gas exchange, which were covered in lab as well as lecture.

This study guide is intended as a guide. It isn’t guaranteed to cover every question that will be on the midterm.

The best strategy for doing well on the midterm:

Work on the long-answer questions first. If you can provide good answers to all those questions, you will be well-prepared for most of the multiple-choice questions. You're welcome to collaborate as you work on your answers, but if you simply read someone else's answer, you won't learn very much. Doing the work of creating your own answer will lead you to a genuine understanding.

Don't spend time reading the chapter first, or watching videos on YouTube. Just start on your long answers. As you work, you should  find that there are things that you don't fully understand, and then go back and review the lecture, read the book, or use other sources. Reading the book with specific questions in mind will put you in a more active frame of mind.

After you've worked on all the long-answer questions, look at the "Important Concepts" section of this study guide and at the lecture PowerPoint to see what topics you still need to study.

Long-Answer Questions

One of the following questions will be on the midterm (you won’t get to choose). There will be space on the midterm to write your answer; you won’t need any extra paper. Your answer should be no more than three pages long, but you don't get points for length. Include as many diagrams or graphs as is appropriate. If the question says, “Diagram and describe,” you must include a diagram; otherwise, diagrams are optional. Use paragraphs and headings; don’t write a long, unbroken stream of text. If your answer is a single long paragraph, you will automatically lose points, no matter how good the answer is. Your answer will be graded on clarity and completeness. Base your answer on the material that was covered in lecture.

Use your own words. That's how you learn.

I will use a random number generator (http://www.random.org/integers/) to randomly choose the question for the test. I highly recommend that you write out detailed answers to all the questions before the exam. You may discuss your answers with me or with your fellow students. The subject matter of the three questions that aren’t on the test will be emphasized for the multiple-choice questions; the time you spend on these questions won’t be wasted.

  1. Compare and contrast the gas exchange systems of fish and mammals in relation to their environments. (Hint: fish have a system that works well in water; mammals have a system that works well in air. Explain why each system works in its particular environment. Your answer should include a discussion of countercurrent exchange.)
  2. Diagram & describe how the oxygen-carrying pigments in mammals help ensure that tissues will get enough oxygen. [Hints: your answer should include adult & fetal hemoglobin, myoglobin, CO2, and rest vs. exercise situations.]
  3. Compare and contrast the structure and function of the circulatory systems in insects and in mammals. [Hints: explain why each animal’s system works for that animal. Don’t ignore gas exchange; it’s connected with circulation.]
  4. Compare and contrast diving in humans (both free diving and SCUBA) and in marine mammals. Include the gas-related problems that can arise due to diving, and how marine mammals avoid these problems. What makes marine mammals better divers than humans?

Important Concepts

Systematics & History of Life

  • Phylogeny, systematics, taxonomy.
  • Taxonomic hierarchy (domain, kingdom, phylum, class, order, family, genus, species)
  • Monophyletic groups vs. groups that aren’t monophyletic. (I might ask you if a group is monophyletic; I won’t ask you to distinguish between paraphyletic and polyphyletic.)
  • Cladistics, cladogram, clade. How is cladistics different from traditional Linnaean systematics? Identify a clade on a cladogram. Explain what the branching points mean.
  • What does the length of the branches represent on a phylogenetic tree?
  • Why are the branching points on a cladogram supposed to be 2-way splits?
  • What is horizontal gene transfer? How is it connected to the gecko? Why is this a challenge for cladistics?
  • What does the web of life say?
  • Homology & analogy. Give examples; relate this to a cladogram. Remember that these terms apply to traits, not whole organisms. Why is the 4-chambered heart of birds considered to be analogous to the 4-chambered heart of mammals?
  • DNA and cladistics: how is DNA data different from other sorts of data for cladistics?
  • Evolutionary milestones/history of life on earth: you don’t need to remember exactly when they occurred, but you should know the order in which they occurred:
    • Origin of life
    • Formation of O2
    • First eukaryotes
    • Domains: Bacteria, Archaea, Eukarya. List the key characteristics of each, and know what sorts of organisms are in each domain. How are Archaea different from bacteria?
    • Eukaryotes: how they originated by membrane infolding and endosymbiosis (two different events!)

Gas Exchange

  • How gas exchange relates to respiration & photosynthesis
  • What is VO2 max?
  • Diffusion: importance in gas exchange
  • Surface area to volume ratio
  • What does a random walk say about diffusion?
  • Why flatworms & jellyfish don’t need gills
  • Fick’s law of diffusion: know what all the variables are, and how they affect gas exchange rate in organisms. Give examples of how these variables relate to real organisms. Which variables can change quickly, in response to exercise? Which ones can change through evolution?
  • Air composition, partial pressure, & solubility. How do these affect the amount of oxygen available to an animal?
  • Partial pressure vs. molar concentration or ml O2 per liter of water or air. Why do we use these different ways of expressing concentration? What does it mean if a gas and a liquid are at equilibrium?
  • Diving bell spider: would O2 be diffusing into the spider’s bubble from the water or out of it?
  • Why is O2 level always lower in the organism than in its environment? Explain the bar graph shown in lecture.
  • Bigger fish have bigger gills…but not relative to their body size.
  • Mackerel vs. toadfish: what do these numbers mean? What information would you need to know in order to predict the gill surface area of a fish?
  • Opercular pumping & ram ventilation. What part of Fick’s equation is affected by these? When would ram ventilation be better, and when would opercular pumping be better?
  • Fish gills: countercurrent exchange mechanism. Why is this so important? Why wouldn’t concurrent work as well? Why don’t mammals have this?
  • Why is water flow across fish gills 1-way, while air flow in mammalian lungs is 2-way? How does this relate to the problems of gas exchange and to the physical properties of air vs. water?
  • Breathing air vs. breathing water: what are the important physical differences and how must animals adapt to them?
  • Gills are used for gas exchange in water, while lungs are used for gas exchange in air. Why not the other way around?
  • Slugs: compare & contrast with mammals
  • Insects: exoskeleton, tracheae, spiracles. Compare & contrast with mammals, slugs.
  • Why were some paleozoic insects able to become much larger than modern insects? How is gas exchange related to maximum size for insects?
  • Why are frogs able to eliminate all their CO2 through their skin, while they must rely on their lungs to take up O2?
  • Amphibians: why are some salamanders lungless?
  • Why do lizards do gas exchange differently from salamanders?
  • Positive pressure breathing in frogs.
  • Mammals: lung structure, alveoli, dead space, tidal volume, negative pressure breathing.
  • Avoiding water loss in breathing. Which vertebrates have turbinates or similar structures, and why? Explain how metabolic rate, body temperature, and water loss are connected. Compare crocodiles, birds, and mammals.
  • Birds:
    • 1-way flow through lungs.
    • Air sacs: How does this help?
    • Do birds still have dead space?
    • How does the lung structure of birds improve gas exchange compared to mammals? (In addition to air flow, consider flexible vs. rigid lung structures and diffusion distance.)
    • What is the significance of having nuclei in red blood cells?
  • Which is better at gas exchange – a mammal or a fish?

Animal Circulatory Systems

  • Diffusion & convection: what role do they play in oxygen uptake for mammals and for other animals? Where do they occur?
  • Functions of circulatory systems
  • Gastrovascular cavity. How is it like a circulatory system? How is it different?
  • Open circulatory systems. Why is the fluid called hemolymph instead of blood? Why this system works well for insects. Why is it important that insects have an exoskeleton?
  • Closed circulatory systems
  • Vertebrates: 2, 3, 4-chambered hearts. Which animals have which one? Why does it matter? How many times does the blood get pumped to make one circuit around the body?
  • Pulmonary & systemic circulation
  • Arteries, capillaries, veins
  • Blood flow velocity, cross-sectional area, and blood pressure: study the diagrams from the PowerPoint & textbook
  • Blood pressure & osmotic pressure: why fluid leaks out of capillaries and then leaks back in.
  • Lymphatic system: function & structure. How lymphatic system interacts with blood system.

Respiratory pigments

  • Gases diffuse down gradients: how does this relate to partial pressures at different points in our gas exchange & circulation system? Study the graph carefully; you should be able to predict where partial pressure will be higher or lower.
  • Where is hemoglobin located? Where is myoglobin located?
  • How are mammalian erythrocytes different from those of other vertebrates?
  • Binding affinity: graph and explain. Why is the sigmoidal curve important? What if it was a straight line? How does the behavior of hemoglobin create a sigmoidal curve of binding affinity?
  • Partial pressure and saturation
  • Fetal hemoglobin. Why is its oxygen-binding affinity curve different from that of adult hemoglobin?
  • Myoglobin. Why is its oxygen-binding affinity curve different from that of hemoglobin?
  • Globin gene evolution: are all those globins homologous? How can there be a cladogram of genes that exist within one species?
  • Bohr effect: graph and explain.
  • How does 2,3-DPG affect oxygen binding? How does it affect oxygen delivery to a fetus?
  • CO2 transport in blood


  • Regulation of breathing by CO2 level
  • Hyperventilation & Shallow-water blackout. Explain what happens to O2 & CO2 partial pressures.
  • Decompression sickness & pulmonary barotrauma: compare & contrast.
  • Marine mammals: How can seals dive so long & deep? Why don’t they get shallow-water blackout, air embolism or decompression sickness?
  • Would marine mammals be better off if they had gills?
  • Do humans have a diving reflex like seals do?


  • What short-term and long-term changes occur in humans in response to the increased oxygen demand of exercise?
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