1. Section 1: Characteristics of Protists

2. Key Ideas What types of organisms are classified as protists?
What methods of reproduction do protists use?
Why is the classification of protists likely to change in the future?

3. What Are Protists?
Protists are eukaryotic organisms that cannot be classified as fungi, plants, or animals.
Several important characteristics evolved in protists. Those characteristics are:
membrane-bound organelles
complex cilia and flagella
sexual reproduction with gametes
multicellularity

4. Visual Concept: Characteristics of Protists

5. Visual Concept: Origin of Eukaryotic Cells

6. Reproduction
Asexual reproduction results in offspring that are genetically identical to the parent.
Sexual reproduction results in offspring that are genetically different from either parent.

7. Reproduction, continued
Asexual Reproduction
Binary fission
unicellular organism reproduces by splitting in half after replicating its DNA.
Multicellular organisms do not undergo binary fission.
Budding
part of the parent organism pinches off and forms a new organism.
can occur in unicellular and multicellular organisms.
offspring is smaller than the parent.

8. Reproduction, continued
Asexual Reproduction
Fragmentation
part of a multicellular organism breaks off and starts a new organism.
budding is an action that is performed by the organism itself.
Fragmentation is the result of an action that is done to an organism.

9. Reproduction, continued
Unicellular Sexual Reproduction
response to environmental stress.
Zygospore
Protective structure that contains a zygote
can survive freezing, drying, and UV radiation.

10. Reproduction, continued
Unicellular Sexual Reproduction
Most mature unicellular protists are haploid
divides by binary fission to produce haploid gametes
Two gametes fuse to form a diploid zygote and a zygospore.
When environmental conditions improve
Meiosis occurs
Haploid cells break out
Grow to mature cells

11. Visual Concept: Sexual Reproduction in Unicellular Protists

12. Reproduction, continued
Multicellular Sexual Reproduction
Many multicellular protists can reproduce both sexually and asexually.
This process is called alternation of generations
Two or more different methods of reproduction

13. Reproduction, continued
Multicellular Sexual Reproduction
sporophyte generation
diploid, spore-producing phase
The adult sporophyte has sporangia
reproductive cells that produce haploid spores by meiosis
spores grow into multicellular haploid organisms
gametophyte generation
haploid, gamete-producing phase
mature gametophyte produces haploid gametes by mitosis.

14. Reproduction, continued
Multicellular Sexual Reproduction
Two gametes fuse to form a diploid zygote.
The zygote divides to form a multicellular diploid organism.
This step begins the first stage of a new sporophyte generation.

15. Visual Concept: Reproduction in Ulva

16. Classifying Protists
Some protists share characteristics of plants or animals, while others are more like fungi.
Classified by
DNA, RNA, protein
Likely to change as scientists learn more
could be classified into up to 20 kingdoms!
characteristics that protists share with plants, animals, and fungi provide information about the evolution of these organisms.

17. Summary
Protists are eukaryotic organisms that cannot be classified as fungi, plants, or animals.
Protists can reproduce asexually by binary fission, budding, and fragmentation. Protists can also reproduce sexually by fusion of gametes.
The classification of organisms currently grouped in the kingdom Protista is likely to change as scientists learn more about how these organisms are related to each other and to members of other kingdoms.