The Dirt on Black-Market Plants ■ 299Leveling Up
(^12) Life choices If fungi are more closely related to animals than to
plants, should vegetarians and vegans refrain from eating fungi?
Why or why not?
(^13) Write Now biology: is a mass extinction under way? The
International Union for Conservation of Nature maintains what it
calls its Red List, which identifies the world’s threatened species.
To be defined as such, a species must face a high to extremely
high risk of extinction in the wild. The 2016 Red List contains
almost 25,000 species threatened with extinction out of the
approximately 79,000 species assessed.
Because this assessment accounts for only a small percentage
of the world’s 1.7 million described species, the total number of
species threatened with extinction worldwide may actually be much
larger. For example, only 6,051 of 1 million described insect species
have been assessed in terms of their survival risk.
The Red List is based on an easy-to-understand system for
categorizing extinction risk. It is also objective, yielding consistent
results when used by different people. These two attributes have
earned the Red List international recognition as an effective tool
for assessing extinction risk.
a. If the threatened species listed by the IUCN do become extinct
and the percentages of species under threat in other taxonomic
groups turn out to be similar to those listed, then the percentages
of species that will go extinct will approach the proportions
lost in some of the previous mass extinctions. Does this mean
that a mass extinction is under way? Why or why not? Explain
your reasoning, using information about mass extinctions from
Chapter 14 (in particular, Figure 14.15) to support your argument.
b. What are the causes of the current high extinction rates?
Compare the causes of the current situation with those of
previous mass extinction events. In what ways are they similar,
and in what ways do they differ?
c. Why are some groups in more danger of extinction than others?
Choose one group that has a large proportion of species
threatened with extinction, and find out more about it (you can
begin at http://www.iucnredlist.org)::)
● (^) What kinds of habitat are they found in?
● (^) Does a particular aspect of their ecology—for example, feeding
or reproduction—make them more vulnerable to extinction?
● (^) Is anything being done to protect them and/or their habitat?
● (^) Has there been an increase or decrease in the number
of species within the group that have been identified as
vulnerable to extinction?
Challenge Yourself
(^6) Place the following adaptations in the correct order from
earliest to most recent by numbering them from 1 to 5.
a. vascular tissue
b. flowers
c. seeds
d. multicellularity
e. movement to land
(^7) Which of the following groups contains only multicellular
species?
(a) algae
(b) protists
(c) eukaryotes
(d) fungi
(e) angiosperms
(^8) Of the kingdoms covered in this chapter, which, if any, are
composed of only autotrophic species? Which, if any, have only
heterotrophs?
Tr y Something New
(^9) Symbiosis is a long-term and intimate association between
two different types of organisms. A symbiotic organism may live
on or inside another species. For each of the following symbiotic
relationships, (1) define the relationship in one to three sentences,
(2) identify the domain—and for Eukarya, the kingdom—of
each partner in the relationship, and (3) discuss whether the
relationship evolved as a mutualism (both benefit), commensalism
(one benefits, while the other is not affected), or parasitism (one
benefits to the detriment of the other). You may need to read more
than your textbook to answer this question.
a. mycorrhizae
b. lichens
c. hermit crabs/shells
d. malaria
(^10) Which plant groups produce pollen, and what is the adaptive
value of pollen?
(^11) Plants are not the only organisms susceptible to fungal
infections. Give an example of a fungal infection to which humans
are susceptible. For more, visit digital.wwnorton.com/bionow2 for access to:
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