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1.1.7 Practice: Introduction to Metabolism and Homeostasis
Practice Assignment
AP Biology Sem 2 (S3796374)
Frankie Liang
Points possible: 25
Date: ____________
1. The hypothalamus in the human brain is involved in thermoregulation of the body. This organ
has been compared to a thermostat that uses a negative feedback mechanism to control the
heating and cooling in a house. Explain whether or not this comparison is accurate. Justify your
response. (3 points) 2. An enzyme was isolated from wild-type bacteria (WT). Three mutant forms of this same
enzyme were made using a mutagenesis technique, and then each mutant enzyme (1E8, 5F8,
D249G) was isolated. All four samples of purified enzymes were tested for thermal stability. To
do this, each enzyme was incubated at the temperatures indicated on the graph for 15 minutes
and then tested for the percentage of original catalytic activity that remained after the heat
treatment. Describe the effects of the mutations on the thermal stability of the wild-type enzyme.
Analyze the data to rank the four in order from least heat-stable to most heat-stable. (3 points) 3. A company that grows and sells fresh pears is concerned because workers notice that pears
placed in storage seem to ripen slowly at first, but then suddenly display extremely rapid
ripening. Perplexed, company officials call in two independent science teams to evaluate the
Team A makes the statement: “Your pears are under positive feedback control.”
Team B makes the statement: “Ethylene amplifies the fruit-ripening process by triggering both
its own production in fruit and the production of enzymes catalyzing the breakdown of cell
Both science teams made statements that help explain the observed acceleration of pear
ripening in storage. The pears are ripening because ethylene builds up, which signals an
increase in cell-wall breakdown, a reaction that is part of the ripening process. Ripening goes
slowly at first because there is little ethylene present, but because it is under positive feedback
control, a little ethylene induces more and more ethylene production as time goes on. This
means that ethylene concentrations amplify very quickly, with the result that ripening is also
amplified very quickly. A representative of the pear company explains that pears are typically stored in small, tightly
sealed storage bins just after harvesting. He asks whether the ripening process would be
different if the same number of pears were stored in a much larger room with better ventilation.
Predict whether these two scenarios can be expected to yield the same results, and explain
your reasoning. (2 points) 4. Bone is a dynamic tissue constantly undergoing change. As shown in the diagram below, two
sets of bone cells work in opposition to one another to maintain bone homeostasis. Osteoblasts
build bone, while osteoclasts break down bone. Blood calcium levels change in response to
these cell activities.
a. Calcitonin is a hormone produced by the thyroid gland. Calcitonin is released whenever blood
calcium levels go up. Calcitonin travels through the blood to bone, where it activates one of the
two types of bone cells and inhibits the other type. Predict the type of cells that will be activated
by calcitonin. Predict the type of cells that will be inhibited by calcitonin. Justify your responses.
(3 points) b. Refine the diagram to show the regulatory mechanism that triggers the changes in bone-cell
activity described in part a of the question. (4 points)
5. Sawflies are insects that lay eggs inside of plant tissue. The eggs hatch into larvae and feed
on the plant before pupating and transforming into adult flies. Sawflies target pine trees in
particular, and their larvae can destroy healthy trees in a short period of time. In defense, pine
trees produce volatile organic compounds that attract predatory wasps that feed on either eggs
or the larvae.
Researchers studied the induction of mRNA transcripts for a gene involved in synthesis of a
volatile organic compound by pine trees in response to egg-laying sawflies. The data below
show one control group and four experimental groups. The control (C) consisted of pine
branches with no eggs. E3 were branches laden with eggs tested 3 days after egg-laying. E14
were branches laden with eggs tested 14 days after egg-laying, just when larvae hatch. E+L
were branches laden with eggs that hatched and were fed on by larvae for two days.
a. Analyze the data in the graph to determine how the timing of the pine tree’s production of a
defensive volatile organic compound relates to the life cycle of the sawfly larvae. Explain the
mechanism of evolution of this process. (4 points) b. Draw a diagram to describe how information moves among the three organisms discussed in
this example. In your diagram, show the internal changes taking place in the pine-tree cells as
they receive information from one organism, respond to that information, and then transmit other
information to the second organism. (3 points)
6. The figure below shows the experimental setup used to test female cichlid fish's mating
preferences. The barriers separating the central tank from the end tanks are transparent in one
direction but opaque in the other, so that the female in the central tank can observe one male in
each of the tanks on the ends, but the males cannot observe the other male. In 16 out of 20
repeated trials, females preferentially produced eggs in the spawning nests nearer the larger
Describe how information moves between organisms in this example. Explain what the results
of this experiment suggest about differential reproductive success in cichlids and how it relates
to evolution. (3 points) Copyright © 2017 Apex Learning Inc. Use of this material is subject to Apex Learning's Terms of
Use . Any unauthorized copying, reuse, or redistribution is prohibited. Apex Learning ® and the
Apex Learning Logo are registered trademarks of Apex Learning Inc.


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