Lauren Ward and Amelia Ault
Period 2
Chapter 21
Protist Classification
**** What are protists? = Protists are single celled eukaryotes that are not member of
the plant, animal, or fungal kingdoms.
● Recently biologist discovered that the “protists” display a far greater degree of
diversity than any other eukaryotic kingdom.
● Many of these organisms are far more closely related to members of other
eukaryotic kingdoms that they are to other “protist”
The “protist” Dilemma:
● Members of a living kingdom, such as plants or animals, should be more like
another than like members of other kingdoms than they are to other protists. This
is not true of protists, which means that reclassification is necessary. Biologists
continues to debate the best way to do this.
● In the past scientists sorted protists into three groups: Plantlike, protists, animal like protists, and fungus like protists. This began to fail as biologist realized that
many protists do not fit into any of these groups.
Multiple Kingdoms:
● Protists were the first eukaryotes, and evolution has had far more time to develop
differences among protists than among more recently evolved eukaryotes like
plants and animals.
● “Protists” are not a single kingdom but a collection of organisms that include
several distinct clades
Protists – Ancestors and Descendants:
**** How are protists related to other eukaryotes? = Today’s protists include groups
whose ancestors were among the very last to split from the organisms that gave rise to
plants, animals, and fungi.
● The roots of all eukaryotic diversity, from plants to animals to fungi, are found
among the ancestors of protist.
● Protists were the first eukaryotes
● Genetic fossil evidence indicates that eukaryotes evolved from prokaryotes and
are more closely related to present-day Archaea than to Bacteria.
● Protists have diversified into as many as 300,000 species found in every corner
of the planet.
● Most of the major protists groups are unicellular, but have produced organisms
that developed true multicellularity.
Protist Structure and function
**** 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.
Amoeboid Movement ● Many unicellular protists move by changing their shape, a process that makes
use of cytoplasmic projections know as Pseudopods
○ The cytoplasm of the amoeba streams into the pseudopod and the rest of
the cell follows. This type of locomotion is called amoeboid movement and
it is found in many protist.
○ It is powered by a cytoskeletal protein called actin. Actin is also found in
the muscle cells of animals, where it plays an important role in muscle
contraction.
Cilia and Flagella
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 (Ciliates)
Flagella are relatively long and usually number only one or two per cell. (Flagellates)
Passive Movement:
● Some of the most important 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.
● ex. Spore forming protists include Plasmodium, which is carried by mosquitoes
and causes malaria and Cryptosporidium, which spread through contaminated
drinking water and cause severe intestinal disease.
Protists Reproduction
**** How do protists reproduce? = Some protists reproduce asexually by mitosis. Others
have life cycles that combine asexual and sexual forms of reproduction.
● Conjugation: A process in which two organism exchange genetic material.
● Conjugation is not a type of reproduction because no new individuals are formed.
It is a sexual process using meiosis to produce new combinations of genetic
genetic information.
● In large population, conjugation helps produce and maintain genetic diversity, the
material for evolution.
● Water molds grow into long branching filaments consisting of many cells formed
by mitotic cell division. Water molds– and many other protist– reproduce
asexually by producing spores in a structure called a sporangium.
● In water molds the spores are flagellated
● Water molds also reproduce sexually by undergoing meiosis and forming male
and female structures. These structures produce Haploid nuclei that fuse during
fertilization, forming a zygote that begins a new life cycle.
Autotrophic Protists
**** What is the ecological significance of photosynthetic protists? = The position of
photosynthetic protists at the base of the food chain makes much of the diversity of
aquatic life possible.
● Diversity
○ Photosynthetic protists include many phytoplankton species and the red
and brown algae, as well as euglenas and dinoflagellates.
○ These protists share an autotrophic lifestyle
■ Autotrophic Lifestyle = this kind of lifestyle is marked by the ability
to use the energy from light to make a carbohydrate food source.
○ Photosynthetic protists are not closely related to plants, they are closer to
the nonphotosynthetic protists.
■ Red algae are the photosynthetic protist that is the closest relative
to plants of them all.
● Ecological Roles
○ Feeding Fish and Whales
■ Phytoplankton makes a direct source of nourishment for
organisms as diverse as shrimp and baleen whales.
■ Phytoplankton makes an indirect source of nourishment for
humans.
■ When you eat tuna fish you are eating a fish that fed on a smaller
fish that fed on a still smaller fish that fed on photosynthetic protists.
○ Supporting Coral Reefs
■ coral reefs are found in warm ocean waters throughout the ocean.
■ their purpose is to provide food and shelter for other fish and
organisms.
■ Most of the coral’s energy is provided by zooxanthellae, which is a
type of protist algae, by photosynthesis.
■ This type of algae helps preserve equilibrium in the coral’s
ecosystem.
■ Coralline red algae provide calcium carbonate to stabilize the
growing coral reefs.
○ Providing Shelter
■ The protist kelp is the largest protist. It is made of brown algae that
can grow to 60 meters in length!
■ It provides shelter for other marine species and is a source of food
for sea urchins.
■ sargassum is another type of brown algae that forms huge floating
mats on the bottom of the Atlantic Ocean floor.
○ Recycling wastes
■ Euglena can grow to enormous numbers resulting in an algal bloom.
● Algal blooms can disrupt an ecosystem’s homeostasis.
● In a pond or lake it depletes nutrients from the water, and
decomposition of the dead protists can rob water of its
oxygen leaving the fish to die.
● Red tides are build ups of toxins in the water
Heterotrophic Protists
****how do heterotrophic protists obtain food? = Some heterotrophic protists engulf and
digest their food, while others live absorbing molecules from the environment.
● Amoebas
○ They can capture and digest their food surrounding a cell or particle and
then taking it inside themselves to form a food vacuole.
■ a food vacuole is a small cavity inside the cytoplasm that
temporarily stores food
● Ciliates
○ They sweep food particles into the gullet
■ a gullet is an indentation in one side of the organism
○ Food vacuoles pinch off the cytoplasm
● Slime Molds
○ Thrives on decaying or dying organisms.
○ Found in rich piles of organic matter
○ Plasmodium is a parasitic protozoa
Symbiotic Protists
***What types of symbiotic relationships involve protists? = mutualistic
relationships where both they and the host benefit.
● Mutualists
○ Trichonympha is flagellated protist that lives within the digestive
system of various species of termites that makes it easy to digest
wood.
○ Termites are not able to digest the cellulose in the wood alone.
They do not digest the cellulose though.
● Parasites and Diseases
○ *** Parasitic protists are responsible for some of the world’s most
deadly diseases.
○ Intestinal diseases
■ Some water borne protists can cause major harm to humans
in rivers and lakes
○ african sleeping sickness
■ Caused by the flagellated protists in the genus trypanosome.
■ Transferred from person to person by a bit of a tsetse fly.
■ They destroy blood cells and deteriorate nerve cells.
■ Causes people to fade into a fatal sleep hence the name
sleeping sickness.