Name:______________________ Student ID #:_____________________ 1A) What are the three major forms in which animals excrete nitrogenous wastes? Ammonia (NH4) Urea Uric acid 1B) What is one advantage and one disadvantage each of using those compounds as an organisms’ nitrogenous waste molecule? #1 Ammonia Advantage: requires no additional metabolic energy cost to create Disadvantage: very toxic, have to dilute it and excrete it using a large amount of water #2 Urea Advantage: much less toxic than ammonia, requires less water to dilute and excrete Disadvantage: high metabolic energy cost to convert ammonia to urea #3 Uric acid Advantage: non-toxic, can be excreted with almost no associated water loss Disadvantage: very high metabolic energy cost to convert nitrogenous wastes to uric acid 2) Marine iguanas, unlike most lizards, get their body water from drinking seawater. What problem will drinking seawater cause for these creatures, and how might they solve the problem? (2-3 sentences) Drinking seawater, which is hyperosmotic to the body fluids of the iguana, causes the problem of getting rid of excess salt. The iguana could have a specialized salt concentrating and excreting organ so that it can excrete excess salt without a net loss of water. Another possibility is that the iguana could have body fluids isoosmotic to sea water - I’ll accept that answer even though real iguanas have salt glands. 3) Which of these mammals – Polar Bear, Housecat, Camel or Hippo - do you expect to have the longest descending loop of Henle, and why? (1-2 sentences) Camel, because it lives in an environment where water is very scarce, and the decending loop of Henle is the portion of the kidney where most water is recovered from the filtrate.Name:______________________ Student ID #:_____________________ 4) You have designed a compact heart / lung machine, but it does not sufficiently oxygenate the blood that passes through the machine. How might you improve your machine such that it better transfers oxygen from the air to circulating blood? (one solution, 1 – 2 sentences) Increase the surface area of the membrane in the machine that allows gas transfer to the blood. Or, you could say you could have a countercurrent mechanism between air flow through the machine and blood flow, to increase the efficiency of gas transfer. Finally, partial credit (50%) for supplying pure oxygen gas from gas cylinders (or something similar) to the machine. 5) Why do many physiological systems, such as the ones that control body temperature or blood osmolarity, contain negative feedback mechanisms? (Don’t assume I understand what “negative feedback” means.) (2 – 3 sentences) Most living creatures need to maintain these parameters within a fairly narrow range of permissible values (this is referred to as maintaining homeostasis). A negative feedback system ensures that if some biological parameter starts to deviate from optimal conditions, sensing systems will trigger a counteracting response that will restore the parameter to the proper range. 6) What role do vitamins serve in the body? (one sentence) Most are cofactors in enzymes (coenzymes). 7) What is a possible adaptive advantage to an animal (such as a human) to obtaining its vitamins through its diet? (one sentence) By not synthesizing vitamins in their own cells, humans avoid the metabolic costs of synthesizing these molecules. 8) List two essential minerals for humans, and state for each mineral where it is used in the body or why it is needed. (one example for each mineral) examples: Calcium needed as a structural material in bones and teeth Iron needed in blood (hemoglobin) for oxygen transport Sodium nerve functionName:______________________ Student ID #:_____________________ 9) Explain, with the aid of a diagram, where a counter-current exchange system might be found and what it does. (2 – 3 sentences) Can be found in fish gills to exchange oxygen from the water to blood, in flippers or other extremities to conserve heat, etc. The diagram should make it clear that the counter current system works to ensure a favorable diffusion gradient along the length of the exchanger. 10) Which chamber of the human heart is the most muscular, and why? (one sentence) The left ventricle is the most muscular, because it must supply enough pressure to pump blood through the entire systemic circulation. 11) Which cells (3 different types) are most responsible for the phenomenon that vaccinations protect against infectious agents? Memory B cells Memory Helper T cells Memory Cytotoxic T cells 12) If a person had defective MHC Class I molecules, which types of infectious challenge would his/her immune cells not be able to recognize? Explain. (2 – 3 sentences) Since the MHC Class I molecule displays peptides from virus infected or cancerous cells, and presents them to T cell receptors, the immune system cells (notably helper T cells and cytotoxic T cells) of that person’s immune system would be unable to recognize those threats.Name:______________________ Student ID #:_____________________ 13) What allows a person’s immune system to contain some B and T cells that recognize a novel microorganism; one that has never before infected the person? (2 – 3 sentences) The genes for the B cell and T cell receptors are rearranged randomly in individual lymphocytes, and they produce proteins that recognize random epitopes. Millions of lymphocytes are present in the body, so most microorganisms contain an epitope that is recognized by at least one of the lymphocytes. 14) A person with insulin-dependent diabetes needs to continuously monitor his/her blood sugar levels. Explain why this is so, and explain what might happen, and why, if insulin is administered to such a patient at an incorrect time. (3 – 4 sentences) Insulin-dependent diabetes results from the loss of the insulin-producing beta cells in the pancreas. Without them, a person cannot secrete insulin into the blood in response to elevated blood sugar levels. If a person with this condition had low blood sugar when he/she received an injection of insulin, his/her blood sugar levels would decline drastically, and this might result in unconsciousness or worse.
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