Name
Class
Date
Protists
and Fungi
Interdependence in Nature
Q: How do protists and fungi affect the homeostasis of other organisms and
ecosystems?
WHAT I KNOW
21.1 Why are
“protists” difficult to
classify?
21.2 How do
protists move and
reproduce?
21.3 What roles
do protists play in
the environment?
21.4 What are
fungi, and what
roles do they play
in the environment?
WHAT I LEARNED
SAMPLE ANSWER:
Protists have
many different body forms
and ways of living.
SAMPLE ANSWER:
SAMPLE ANSWER:
Protists move
and reproduce in a similar
way to bacteria.
SAMPLE ANSWER:
SAMPLE ANSWER:
Protists are at
or near the bottom of many
food chains.
SAMPLE ANSWER:
SAMPLE ANSWER:
SAMPLE ANSWER:
Fungi include
mushrooms and molds. They
are decomposers.
Protists display
a great degree of diversity.
Many protists are far more
closely related to members of
other eukaryotic kingdoms
than they are to other protists.
Some protists
move by changing their
cell shape. Some move by
specialized organelles. Other
protists do not move actively.
Some protists reproduce
asexually by mitosis, and some
undergo conjugation. Other
protists combine asexual and
sexual reproduction.
Some protists
are autotrophs, and others
are heterotrophs. Many
protists engage in symbiotic
relationships.
Fungi are
heterotrophic eukaryotes with
cell walls that contain chitin.
Many fungi help ecosystems
maintain homeostasis
by breaking down dead
organisms. Many fungi carry
on symbiotic relationships
with other organisms.
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325
Name
Class
Date
21.1 Protist Classification—The Saga
Continues
Lesson Objectives
Explain what a “protist” is.
Describe how protists are related to other eukaryotes.
Lesson Summary
The First Eukaryotes Protists are eukaryotes that are not members of the plant, animal, or
fungi kingdoms. The first eukaryotes were protists.
▶ Most protists are unicellular.
▶ Protists are a very diverse group of species.
▶ Many species of protists are more closely related to plants, fungi, or animals than they
are to other protists. Because of this, some scientists think the members of the kingdom
Protista should be reclassified.
Protists—Ancestors and Descendants All eukaryotes are descended from early protists,
but modern protists are very different from their ancestors. Like other eukaryotes, they have
been evolving over the last 2.5 billion years.
The First Eukaryotes
1. What is a protist?
It is any organism that is not a plant, an animal, a fungus, or a prokaryote.
2. Why are brown algae considered protists even though they are multicellular?
They are more closely related to some unicellular protists than any other kingdom.
3. Why do scientists no longer use the categories of animal-like, plantlike, and funguslike
protists to classify protists?
These categories do not reflect the evolutionary history of protists.
For Questions 4–7, complete each statement by writing the correct word or words.
4. Most single-celled eukaryotes are currently classified as
protists
5. Genetic analyses of protists indicate that they belong in six different
6. Protists were the first
eukaryotes
.
clades
.
7. Unlike most protists, which are unicellular, kelp has differentiated
tissues.
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326
.
Name
Class
Date
For Questions 8–11, use the diagram and legend below.
Six Major Groups
Excavates
Plants
Fungi
Animals
Chromalveolates
Cercozoa,
Foraminifera,
and Radiolaria
Rhodophyta
(red algae)
Amoebozoa
Choanozoa
C
8. Plants are most closely related to which of the following groups?
A. Amoebozoa
B. Cercozoa
C. Rhodophyta
D. Choanozoa
D
9. Brown algae is a member of the clade Chromalveolates. Which of the following
is its closest relative?
A. slime mold, an Amoebozoan
C. Giardia, an Excavate
B. red algae, a Rhodophytan
D. Globigerina, a Foraminiferan
A
10. Which clade is most primitive?
A. Excavates
B. Choanozoa
C. Cercozoa
D. Chromalveolates
A
11. Which statement is true?
A. Plants, fungi, and animals all emerged from a common protist ancestor.
B. Only fungi and animals emerged from a common protist ancestor.
C. Only animals and plants emerged from a common protist ancestor.
D. Plants, fungi, and animals all emerged from different protist ancestors.
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Protists—Ancestors and Descendants
For Questions 12–19, write True or False on the line provided.
False
12. The first eukaryotes were Archaea.
False
13. It is possible to find the earliest fungi by looking at modern protists.
False
14. Modern protists have evolved very little from their ancestral forms.
True
15. Today, there are as many as 300,000 known species of protists.
True
16. The oldest known eukaryotic fossils are around 1.5 billion years old.
False
17. The first protists most likely evolved 3.6 billion years ago.
True
18. Plants, animals, and fungi most likely evolved from multicellular protists.
True
19. The protists are more diverse than any other eukaryotic kingdom.
20. Complete the concept map below.
Certain ancient
species of
Archaea
evolved into
Ancestral
protists
which evolved into
Many different
modern groups
of protists
Plants
Animals
Fungi
21. Euglena are photosynthetic protists that live in fresh water. How would their
photosynthetic properties help stabilize a pond ecosystem? Suppose they and all the other
photosynthetic organisms disappeared from the pond. How might their disappearance
affect other organisms that lived in the pond?
SAMPLE ANSWER:
The photosynthetic properties of Euglena would help stabilize the
ecosystem because they would utilize the carbon dioxide excreted by some organisms and provide oxygen for use by the same organisms. If Euglena and all the
other photosynthetic organisms disappeared from the pond, all the other organisms would eventually die, since the bases of all of the food chains would be gone.
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21.2 Protist Structure and Function
Lesson Objectives
Describe the various methods of protist locomotion.
Describe how protists reproduce.
Lesson Summary
How Protists Move Protists move in a wide variety of ways.
▶ Some protists move by extending temporary projections of cytoplasm known as
pseudopods. These protists, such as amoebas, also use pseudopods for getting prey.
▶ Some protists swim using cilia, numerous short hairlike projections. Others swim using
flagella, which are similar to cilia, but are longer and fewer in number.
▶ Some protists do not move on their own. They depend on wind, water, or another
organism to move them. They reproduce by means of spores.
Protist Reproduction Protists reproduce in a wide variety of ways.
▶ Some protists reproduce asexually by mitosis.
▶ Some protists can undergo conjugation—a sexual process in which two organisms
exchange genetic material. Conjugation helps produce genetic diversity.
▶ The life cycles of many protists include switching between a diploid and a haploid
generation, a cycle called alternation of generations.
▶ Some protist species reproduce asexually by producing spores in a structure called a
sporangium.
How Protists Move
1. What are pseudopods? How do protists use them? They are temporary projections of
cytoplasm used for feeding and movement.
2. How do amoebas capture and ingest food? They use their pseudopods to surround a
food particle or cell and take it inside themselves, ingesting it.
3. What are cilia? How are they used by protists? They are short hairlike projections used
for movement.
4.
In the three boxes below, draw pictures of three organisms—one
with a pseudopod, one with a flagellum, and one with cilia.
Students’ drawings
should resemble the
amoeba shown in the
textbook.
Pseudopod
Students’ drawings
should resemble the
flagellate shown in the
textbook.
Flagellum
Students’ drawings
should resemble the
ciliate shown in the
textbook.
Cilia
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329
Name
5.
Class
Date
The visual analogy compares structures used by cells for movement
to boat oars. Explain why a series of oars is compared to cilia, and why only one oar is
used to represent flagella.
Motion by cilia is analogous to oars
propelling a large rowboat forward
through the water.
Motion by a flagellum is analogous to
the back-and-forth movement of a
single long oar at the back of a boat,
propelling it forward.
Flagella and cilia are used to move through liquids, such as water. Cilia move rather
like oars on a boat, and they are numerous on a protist. Protists with flagella usually
only have one or two.
Protist Reproduction
6. How do amoebas reproduce?
They reproduce asexually by means of mitosis.
7. What is conjugation?
It is a process that allows ciliates to exchange genetic information with other
individuals.
8. Within a large population, how does conjugation benefit protists?
The process helps to create and maintain genetic diversity.
9. What occurs in the process known as alternation of generations?
Alternation of generations is a means of sexual reproduction in which the reproductive cycle switches back and forth between haploid and diploid stages during an
organism’s life cycle.
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10. Complete the flowchart to show the process of conjugation between two paramecia.
Conjugation begins when two paramecia attach to each other.
Meiosis of their diploid micronuclei produces four haploid micronuclei.
In each cell, three of the micronuclei disintegrate.
The remaining micronucleus in each cell divides by mitosis.
The two cells exchange one haploid micronucleus from each pair.
In each cell, the micronuclei fuse to form a single diploid micronucleus, and the macronuclei
disintegrate.
Each cell forms a new macronucleus from its micronucleus.
11. Plasmodium is the protist that causes malaria in humans. It is carried by mosquitoes,
which transmit the parasite when they bite humans. In the human body, Plasmodia
cause red blood cells to break and release spores in the evening. The spores can then
travel through the bloodstream. How would this mechanism help spread the parasite
throughout an ecosystem? What methods might help prevent its spread?
SAMPLE ANSWER:
Mosquitoes bite in the evening. By releasing spores at that time, the parasite
increases its chances of being ingested by the mosquito and carried to another host. Preventative methods may include staying inside in the evening, wearing bug spray or clothes
with total coverage, sleeping under nets, and keeping windows and doors screened.
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