1. molecular processes of life are sensitive to ambient conditions
1. examples include temperature, pH, solute concentration
1. homeostasis is the collection of mechanisms maintaining appropriate conditions
1. physiological, such as hunger and thirst
2. behavioral, such as moving into or out of sun
2. feedback is the process of monitoring and correcting ambient conditions
1. large organisms will have low surface area:volume ratio
1. there are advantages and disadvantages to large (or small) size
1. small organisms will more rapidly change chemistry, temperature in response to ambient changes
2. Hunger and satiation as an example
1. There are several feedback loops involved
1. insulin regulation of blood glucose levels
2. leptin regulation of fat deposition
3. other hormones and pathways are still being explored
2. failure of regulation
1. obesity
2. diabetes

1.  Scaling influences maintenance of internal body temperature.  Monitor lizards and anolis lizards are both reptiles, close to opposite ends of the size range in extant lizards.  They are both "cold" blooded.  Speculate on the amount of monitoring and rapidity of response required by each.

2.  Which of the following are not examples of feedback in a biological system?

1. you feel warm, so you take off your sweater
2. when a plant's cells start to become flacid, the pores in the leaves (stomata) close to prevent further water loss
3. following meoisis, the daughter cells have half as many chromasomes as the parent cell
4. spiders that capture few or no prey will build a larger web the next day
5. geese need water in order to swallow their food

3.  What role does homeostasis play in the increased complexity of the Protista compared to the Bacteria?

4.  What is one advantage of ectothermy (cold-bloodedness) compared to endothermy (warm-bloodedness)?  What is an example of an advantage of endothermy compared to ectothermy?

5.  Studies have shown that many obese individuals actually have higher than normal levels of leptin in their blood.  Given this information, how would you respond to a pharmacological company's plan to market leptin as a weight-control medication?

6.  Currently (and far into the past) there are arguments about diet and health:  some people advocate diets high in protein, others call for diets high in complex carbohydrates.  Others in the medical community call for decreased total calory intake.  Which of these makes the most sense in terms of your understanding of  the feedback loops in blood glucose and fat homeostasis?

See also:  pages 744-745 "content" #5, 6;  "concept review" #2, 4
pages 784-785 "concept review" #5, "applying ideas" #7
pages 538-539 "content" #1;  "concept review" #1

Answers