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Chapter 13 Answers
Evolution of Microbial Life
Visual Understanding
Figure 13.6
Viruses have dramatically different forms and shapes. What are the consistent features of all of
the viruses shown?
They all have a strand of nucleic acid, DNA or RNA, inside a protein shell.
Figure 13.9
Are the Volvox shown here multicellular organisms or numerous single-celled organisms
working together?
Volvox are colonial protists, which are single-celled organisms working together. The bodies of
all multicellular organisms exhibit two qualities: cell specialization, which is lacking in Volvox;
and intercellular coordination. Volvox are capable of some coordinated colonial activity, but
they don't exhibit a full level of intercellular coordination seen in multicellular organisms.
Challenge Questions
Origin of Life
Why can’t we prove how life began on earth?
The tests that we can do give indications of how life might have begun, but are not definitive.
Scientists think that they have a pretty good idea, but it is not proven. Since we have not
discovered life elsewhere yet, we have nothing to compare, either.
Prokaryotes
How do prokaryotes obtain the energy for life?
There are a variety of methods that prokaryotes use. The autotrophic prokaryotes use sunlight,
or chemicals such as sulfur or hydrogen sulfide. The heterotrophic prokaryotes use sunlight or
decompose dead tissue or attack living tissue.
Viruses
Why do we say that bacteria are alive but viruses are not?
All living organisms exhibit two basic characteristics that are not present in viruses: cellular
organization and the ability to grow and reproduce independently. Viruses are molecular
entities, DNA or RNA wrapped in a protein coat, but not cellular entities. Also, viruses can not
reproduce on their own; they require the cellular mechanisms of their host.
The Protists
Compare the methods of movement found in five major groups of protists.
There are heterotrophs that use pseudopodia – projections of the cytoplasm. There are
heterotrophs with flagella. The third heterotrophic group has some mobility; the slime molds
and water molds that can do certain types of streaming movements. The photosynthetic protists
include groups with flagella, and several nonmotile groups that either float freely in water or are
fixed in place.
The Ecology of Fungi
Describe three ways that fungi cooperate with other organisms.
Fungi form symbiotic relationships with photosynthesizers, typically plants, algae, and
cyanobacteria. One example is mycorrhizae which is an association between certain soil fungi
and the roots of many plants. Another example is a lichen composed of algae and fungi working
in harmony to live on rocks and other places where neither one could live alone. A third
example is another type of lichen composed on cyanobacteria and fungi that also lives on bare
rocks and other harsh environments.