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Lesson Overview
Protist Structure and Function
Lesson Overview
21.2 Protist Structure
and Function
Lesson Overview
Protist Structure and Function
THINK ABOUT IT
Protists move, sense the environment,
digest food, and even reproduce—all
within the confines of a single cell.
Imagine what such cells would have to
be like to succeed in the never-ending
struggle for life on Earth. Protists are
winners in that struggle.
Lesson Overview
Protist Structure and Function
How Protists Move
How do protists move in the environment?
Lesson Overview
Protist Structure and Function
How Protists Move
How do protists move in the environment?
Some protists move by changing their cell shape, and
some move by means of specialized organelles. Other
protists do not move actively but are carried by wind,
water, or other organisms.
Lesson Overview
Protist Structure and Function
Amoeboid Movement
(Blendspace videos #22-23)
Many unicellular protists move by changing
their shape, a process that makes use of
cytoplasmic projections known as
pseudopods. The cytoplasm of the amoeba,
for example, streams into the pseudopod and
the rest of the cell follows.
This type of locomotion is called amoeboid
and is found in many protists.
movement
Amoeboid movement is powered by a cytoskeletal protein called
actin. Actin also plays a role in the muscle contractions of animals.
Lesson Overview
Protist Structure and Function
Cilia and Flagella
(Blendspace videos #24-25)
Many protists move by means of cilia and flagella, structures supported
by microtubules. Cilia are short and numerous, and they move
somewhat like oars on a boat.
Flagella are relatively long and usually number only one or two per cell.
Some flagella spin like tiny propellers, but most produce a wavelike
motion from base to tip.
Lesson Overview
Protist Structure and Function
Cilia and Flagella
Protists that move using cilia are
known as ciliates, and those that
move with flagella are called
flagellates.
Lesson Overview
Protist Structure and Function
Passive Movement
Some protists are nonmotile—they depend on air or
water currents and other organisms to carry them
around.
These protists form reproductive cells called spores
that can enter the cells of other organisms and live
as parasites.
Spore-forming protists include Plasmodium, which is carried by
mosquitoes and causes malaria, and Cryptosporidium, which spreads
through contaminated drinking water and causes severe intestinal
disease.
Lesson Overview
Protist Structure and Function
Protist Reproduction
How do protists reproduce?
Lesson Overview
Protist Structure and Function
Protist Reproduction
How do protists reproduce?
Some protists reproduce asexually by
mitosis. Others have life cycles that
combine asexual and sexual forms of
reproduction.
Lesson Overview
Protist Structure and Function
Cell Division
Amoebas, and many other protists, reproduce
by mitosis: They duplicate their genetic
material and then divide into two genetically
identical cells.
Mitosis enables protists to reproduce rapidly,
especially under ideal conditions, but it
produces cells that are genetically identical to
the parent cell, and thus limits the
development of genetic diversity.
Lesson Overview
Protist Structure and Function
Conjugation
Paramecia and most ciliates reproduce asexually by mitotic cell division.
However, under stress, paramecia can remake
themselves through conjugation—a process in which
two organisms exchange genetic material.
After conjugating, the cells then reproduce by mitosis.
Lesson Overview
Protist Structure and Function
Conjugation
Paramecium has two types of nuclei:
a macronucleus and one or more
smaller micronuclei.
The micronucleus holds a “reserve
copy” of every gene in the cell.
The macronucleus has multiple
copies of the genes the cell uses in
its day-to-day activities.
Lesson Overview
Protist Structure and Function
Conjugation
Conjugation is not a type of reproduction
because no new individuals are formed.
Conjugation is, however, a sexual process
because new combinations of genetic
information are produced.
In a large population, conjugation helps
produce and maintain genetic diversity.
Lesson Overview
Protist Structure and Function
Sexual Reproduction
Many protists have complex sexual life cycles in which they alternate
between a diploid and a haploid phase, a process known as alternation
of generations.
Lesson Overview
Protist Structure and Function
Sexual Reproduction
A water mold is an example of a protist that undergoes alternation of
generations.
Lesson Overview
Protist Structure and Function
Sexual Reproduction
Water molds grow into long branching filaments consisting of many cells
formed by mitotic cell division.
Lesson Overview
Protist Structure and Function
Asexual Reproduction
Water molds reproduce asexually by producing spores in a structure
called a sporangium.
In water molds the spores are flagellated.
Lesson Overview
Protist Structure and Function
Sexual Reproduction
Water molds also reproduce sexually by undergoing meiosis and
forming male and female structures.
Lesson Overview
Protist Structure and Function
Sexual Reproduction
The male and female structures produce haploid nuclei that fuse during
fertilization, forming a zygote that begins a new life cycle.