Human Biology, Spring 2000
First Quiz: 1 February 2000
Answer Key

1. (b). The rest mass of the electron is 1/1836th of that of the neutron, so it is not close.
   incorrect answers: The electron is the carrier of negative charge in ordinary matter. It is the subatomic particle responsible for most chemical reactivity. Its behavior is governed by quantum mechanics.

2. (d) tubulin and actin are the proteins involved in cytoskeletal structures. Tubulin is the building block for microtubules and centrioles. Actin is the building blocks of actin filaments, used in microvilli and other structures.
   incorrect answers: Myosin is a protein that is hugely important (along with actin) in muscle contraction, but it's not part of the cytoskeleton. Gamma globulin is a protein carried in the blood; it is also called immunoglobulin G, and it is the protein responsible for humoral immune response. Elastin is a structural protein that makes up some kinds of cartilage, but is not involved in cytoskeletons. Pepsin and trypsin are both proteases, i.e. enzymes that break down other proteins.

3. (b) trypsin is a protease and does not have any hormonal activity.
   incorrect answers: Gastrin is the hormone responsible for turning on the churning response of the stomach to food. Insulin is the hormone produced in the islet cells of the pancreas; it stimulates the conversion by the liver of glucose to glycogen, thereby regulating glucose concentration in the blood. Gastric inhibitory peptide is a hormone that shuts down the gastric gland secretion.

4. (a) iodine, selenium, and molybdenum are all microminerals; iodine and selenium appear in table 4.8, and molybdenum is mentioned in the text.
   incorrect answers: Nobelium has no stable isotopes, so it's a dead giveaway for answer (b); as far as I know astatine (which is very poisonous) and rubidium are not microminerals. Arsenic and zinc are microminerals, but francium has no stable isotopes. Sodium is a macromineral, not a micromineral. Manganese is a micromineral, but tungsten has no biological role of which I'm aware.

5. (c) lactose is a disaccharide built from a linkage between galactose and glucose.
   incorrect answers: Maltose is another disaccharide, formed from a pair of glucose molecules; when you hydrolyze lactose, water will be a reactant, not a product. Lactase is the enzyme that catalyzes the hydrolysis of lactose to galactose and glucose. Carbonic acid, H₂CO₃, is the hydrated form of carbon dioxide. Glucuronic acid is a compound fairly similar to glucose except that it has an exposed carboxylate (COO^-) group on it; ribose is a five-carbon sugar.

6. (c) pepsin is the protease that operates in the stomach at low pH.
   incorrect answers: Pancreatic amylase is an enzyme that breaks down starches to sugars, and it operates at near-neutral pH. Glucagon is a hormone secreted by the pancreas to stimulate the reconversion of glycogen back to glucose. Trypsin is a protease, but it is produced in the pancreas and operates in the small intestine at near-neutral pH.

7. Hydrophobic means "water-shunning", i.e. with a tendency to repel water.
   Scoring: 0.5 points if repulsion is mentioned; 0.2-0.3 if "insolubility" is mentioned without mentioning repulsion.

8. The Integumentary System is the skin and associated structures, e.g. nails, sweat and oil glands, and hair.
   Scoring: 0.5 points, i.e. full credit, for "skin").

9. A fetal skeleton composed of cartilage will be strong and yet flexible, which is required for the cramped surroundings in which the fetus grows and for maneuvering through the birth canal without injury.
   Scoring: at least 0.7 points if strength and flexibility are both mentioned. Either the growth or the birth-canal stuff is sufficient.

10. Dietary intake of fiber tends to prevent cancer of the colon in two ways: insoluble fiber speeds passage of feces through the colon, thereby reducing the exposure of the colon tissue to potential carcinogens.
    Scoring: 0.5 for getting the organ right; 0.3 more for mentioning reduction of exposure to carcinogens; full credit if speeding things up is mentioned.

11. Negative feedback is the process whereby a change in one bodily parameter, such as core body temperature, blood pressure, or blood pH, is counteracted by some response of the body that tends to restore the optimal value of that parameter. This contributes to homeostasis since it is a mechanism for maintaining the internal environment within normal limits. An example is the insulin-based control of blood glucose levels. In this system, an increase in glucose in blood triggers a release of insulin, which signals the liver to store glucose as glycogen, thereby lowering the blood sugar concentration. Once the blood sugar level falls to normal, insulin secretion ends, and the liver stops converting glucose to glycogen.
    Scoring: Definition of negative feedback is worth 1-1.5 points; the connection to homeostasis (including an implied definition for homeostasis) is worth 0.5-1 point. The remaining 2 points come from an adequate exposition of an example. The glucose example is not the only feasible one; blood pressure control via nervous-system feedback and temperature regulation are other examples.

12. The small intestine receives food as a mashed-up mixture called chyme and completes the hydrolysis of the complex biological molecules (proteins, lipids, carbohydrates, nucleic acids, and other substances) in it into their component building blocks (amino acids, glycerol and fatty acids, bases and sugars, and simple sugars, respectively). It also acts as a site where these simple substances are taken up into the blood (for amino acids, sugars, and nucleotide bases) and lymph (for fats, which are reconstituted before transport). The breakdown of proteins into amino acids is accomplished with proteases like trypsin, derived from the pancreas, and other peptidases arising within the small intestine itself. The breakdown of carbohydrates into simple sugars is accomplished with pancreatic amylase, derived from the pancreas, and maltase, derived from the small intestine itself. Nucleic acids are broken down by nucleases secreted from the pancreas and nucleosidases secreted within the small intestine. Fats are broken down by lipases secreted from the pancreas.
    Scoring: 1 point for articulating the fact that the small intestine is the site of hydrolysis of complex molecules into building blocks. 1 point for mentioning uptake of the building blocks into the blood and lymph. Fractional credit will be lost from these if the three major categories -- protein, lipid, and carbohydrate--are not all mentioned; nucleic acids can be skipped without penalty. 1 point for naming several categories of the enzymes involved in hydrolysis and clarifying that some are produced in the pancreas and secreted into the small intestine. The final point comes from naming specific enzymes. Not all the enzymes need to be named for full credit.