Download Inquiry 12/e Critical Thinking Questions (Chapter 1)

Answers to Thinking Critically Questions
Mader: Inquiry into Life, Twelfth Edition
Chapter 1
1. How can evolution explain both the unity and diversity of life?
Explanation/Answer: Evolution explains the unity of life because all organisms
share a common ancestor, the first cell or cells that existed almost 4 billion years ago.
Evolution also explains life’s diversity because the environment is always changing.
Through time, different organisms have responded differently to environmental
change. That is, some individuals have had adaptations or features to make them
more suited to the new environment than other features and these individuals tend to
produce more offspring than less suited individuals (without the features). Changes
in frequencies of traits in populations is called evolution. Because there is variation
among individuals, populations, and species, there is variation in responses to
environmental change. Thus, evolution has contributed to the great diversity of
species because of variation and the changing environment over the past 4 billion
years since life began.
2. Viruses are infectious particles. Outside a living cell, some viruses can be stored in
the environment, while others cannot survive. Viruses can reproduce, but only inside
a living (host) cell. Viruses do contain genetic material and can evolve, thereby
evading destruction by the host’s immune system. Should a virus be considered
alive? Explain the criteria upon which you base your answer.
Explanation/Answer: Most scientists do not consider viruses alive because they
cannot reproduce on their own. That is, they need host cells in order to reproduce.
One of the criteria for life, as mentioned earlier in the chapter, is reproduction.
Viruses are considered by many as quasi-species, however, because they exhibit
many of the other characteristics of life. Viruses are organized—they have molecules
organized into a genetic material that is packaged inside proteins. Viruses “hijack”
host cells to acquire materials and energy. Viruses can respond to stimuli—moving
to host cells to which they are best suited to take over so that they can copy
themselves. Viruses also have the capacity to adapt to a changing environment and
are considered to be in an evolutionary arms race with their hosts. That is, as hosts
develop better and better defenses against viruses, viruses must evolve better and
better ways to evade those host defenses.
3. You are a scientist working at a pharmaceutical company and have developed a
new cancer medication that has the potential for use in humans. Outline a series of
experiments, including use of a model, to test whether the cancer medication works.
Explanation/Answer: First, the experimental chemical should probably be studied
in a model species, such as mice or rats. This is commonly done for most new drugs.
The experiment using the model should have both a control group (which receives no
drug, or the inert ingredients used in the drug’s formulation) and a treatment group
(which receives the drug’s active ingredient). Both groups should be under identical
conditions and should therefore have the same type of cancer that is trying to be
eliminated. Usually the dosage for mice is corrected for their body weight, since they
weigh much less than humans. Then, data will be collected on tumor development in
the treatment group relative to the control group. If the treatment group shows, on
average, much greater tumor reduction than the control group, the drug may then be
approved for human trials. In humans, the experiment should follow the same basic
protocol. To control the experiment, groups should be separated by age, gender and
tumor type. In each experiment—that is within each age group, gender and tumor
type—some subjects should receive a placebo while others receive the actual drug.
4. One of the biggest bioethical issues that we face in the twenty-first century is the
loss of biodiversity; much is due to human activities, such as development and
agriculture. These activities benefit human society by providing shelter, food and
other necessities of life, yet they also threaten many of the world’s species with
extinction. Given the benefits of development to humans, why should we conserve
biodiversity?
Explanation/Answer: Life is interconnected in biological communities and
ecosystems. Ecosystems are characterized by chemical cycling and energy flow. The
loss of species disrupts this energy flow and could cause a reduction in the amount of
energy in an ecosystem. This, in turn, could affect other species. Many species
depend on the existence of other species for their survival. For example, if you
removed the food source for hawks (e.g., rabbits and rodents), they could not survive.
The loss of many species could affect humans in several ways. First, we may lose
species that we rely on directly for food, shelter, or other products. We may also lose
species that we enjoy to look at, such as fish in coral reefs. As another example, we
may lose species that have the potential for development of new products or
medicines, such as species of bacteria that have proven useful for cleaning up oil
spills or for development of new drugs.
5. Technology can be considered a “double-edged sword.” That is, many
technological inventions, such as medicines, have provided great benefits to society.
Other technological innovations, such as pesticides and fertilizers can be considered
both—advances, because they increase crop yields, and drawbacks because they can
have adverse effects for humans and wildlife. Using the Internet or other resources,
come up with your own example of a technological invention that has both
advantages and drawbacks. Discuss the pros and cons of this invention.
Explanation/Answer: Students could come up with just about any example, just as
long as they discuss the pros and cons. They could discuss the DDT example as
mentioned in the chapter. A student could do more research on the use of malathion
for mosquito control to help control West Nile Virus in the United States (a pro) and
come up with cons such as adverse effects on amphibians, fish and other wildlife.
Another example could be bioengineered organisms – students could argue their
benefits to society (increased crop yields), but also that they have unknown side
effects (possible adverse health effects or bioengineered crops that could hybridize
with non-native species, making “superweeds.”