BILD 2 Fall 2008 Dr. Towb Homework #1 10/13/08 1) Of the carbohydrates, fats, and proteins in a hamburger, what has been partially digested prior to entry into the small intestine? 2) Why are there multiple proteases during different stages of digestion? Won’t just one do the trick? 3) What does the acidic environment of the stomach do to ingested proteins? How does this aid protein digestion? 4) What causes the pH change in the “digestive broth” that is released from the stomach into the small intestine? Why is there a change in pH at this point in human digestion (what purpose does it serve)? 5) Cells must be bathed continuously in an aqueous medium to take in oxygen and nutrients and get rid of waste products via diffusion. Diffusion is efficient over only short distances. In fact, diffusion is efficient only for a distance of about three cell diameters maximum (approx. 200 to 300 µm). Note the following times required for oxygen to diffuse specific distances: Diffusion distance (µm) Time required for diffusion 1 0.5 msec 10 50 msec 100 5 sec 1000 (1 mm) 8.3 min 10,000 (1 cm) 14 hra. From the table calculate the mathematical relationship between the increase in distance and the corresponding increase in time required to diffuse that distance? b. How much time would be required for oxygen to diffuse 5 µm? 200 µm? 6) What happens to the surface area-to-volume (SA/V) ratio of a three-dimensional object (such as a cell) as its linear dimension increases? For example, how does the SA/V ratio of a sphere or cube change as the linear dimensions increase? (Hint: choose some sizes, like 1 mm in diameter, 1 cm, and 10 cm, and calculate the ratios.) Formulas for a sphere: surface area = 4r2; volume = 4/3 r3 7) Since heat is generated by all cells in an organism, but it is lost to the outside world only through the surface in contact with the outside, which of these two imaginary organisms would maintain their internal temperature with the least expenditure of energy – one that is a 1 cm in diameter ball of cells, or one that is 100 cm in diameter? Why? (Hint: see your results for #6) 8) Since oxygen and nutrients have to be absorbed from the outside world, would either of the above organisms be able to supply these materials effectively to all of their cells? Why or why
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