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Protists part 2
- 1. Protist Structure and Function
- 2. Learning Objectives  Describe the various methods of protist locomotion.  Describe how protists reproduce.
- 3. Protists Motion: Amoeboid Movement • Move by changing shape • Use cytoplasmic projections called pseudopods Pseudopod
- 4. Protist Motion: Cilia Motion by cilia is like oars propelling a large rowboat forward. Cilia
- 5. Protist Motion: Flagella Motion by some flagella is like the back-and-forth movement of a single long oar at the back of a boat, propelling it forward. Flagellum
- 6. Protist Motion: Passive • Nonmotile • Form reproductive structures called spores
- 7. Protists Reproduction: Cell Division Amoebas and many other protists produce new individuals through mitosis.
- 8. Protist Reproduction: Conjugation Macronucleus Micronucleus Micronucleus undergoes meiosis. Three micronuclei disintegrate. Remaining micronucleus undergoes mitosis.
- 9. Protist Reproduction: Conjugation, cont. Cells exchange one micronucleus. Micronuclei fuse; macronucleus disintegrates. New macronucleus forms from micronucleus. Diploid
- 10. Alternation of Generations: Overview Fertilization Meiosis Asexual reproduction Sexual reproduction
- 11. Alternation of Generations: Asexual Stage Sporangium Flagellated spores Spores undergo mitosis. 2N
- 12. Alternation of Generations: Sexual Stage Male reproductive structure Female reproductive structure Zygotes Fertilization Meiosis Egg cell Male nuclei 2N
- 13. Overview: Locomotion and Reproduction Locomotion 1. 2. 3. 4. Reproduction Many protists undergo to produce genetically identical offspring. In alternation of generations, an organism goes through a and an stage. mitosis asexual sexual Amoeboid movement Passive movement Use of cilia Use of flagella
Hinweis der Redaktion
- Read title aloud to students.
- Click to reveal each learning objective in turn. Read each objective aloud or ask a volunteer to do so. Ask students to recall the ways prokaryotes move and reproduce. Answer: They move in different ways, such as using flagella and gliding. Some do not move. They reproduce in different ways, such as simple cell division, conjugation, and spore formation. Tell students that protists move and reproduce in many of the same ways as prokaryotes and, like prokaryotes, protists are diverse in how they carry out these functions.
- Tell students that the name for this kind of motion comes from the protists known as amoebas, shown here. An amoeba moves by first extending a pseudopod away from its body. The organism’s cytoplasm then streams into the pseudopod. Explain that amoebas also use pseudopods to surround and ingest prey. In this set of photos, the prey is a cluster of green algal cells. Ask for a volunteer to go to the screen to point to a pseudopod. Click to reveal the label and leader lines. Point out that amoeboid motion is powered by a protein in the cytoskeleton called actin. Actin is also found in the muscle cells of animals, where it plays an important role in muscle contraction.
- Explain that cilia (singular: cilium) are short and numerous, and they move somewhat like oars on a boat. Point out that cilia are evenly spaced and beat in a regular, efficient pattern. Tell students that protists that move by way of cilia are called “ciliates.”
- Explain that flagella (singular: flagellum) 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, whipping back and forth in a pattern that propels the organism through water. Tell students that protists that move using flagella are called “flagellates.” Point out that both cilia and flagella are supported by microtubules and have similar internal structures. The microtubules use energy from ATP to slide against one another. Each stroke of a cilium or flagellum involves thousands of chemical reactions. Ask students to make an inference about the kinds of environments that ciliates and flagellates live in. Ask: Based on their structure and type of locomotion, in what kind of environments would you expect to find ciliates and flagellates? Answer: aquatic environments Be sure students understand that, for tiny organisms such as these, an aquatic environment could be large like a pond or even as small as a few drops of water or moist soil or in the fluids of another organism’s body!
- Explain that some of the most important protists are nonmotile, that is, they cannot move under their own power. But being nonmotile does not mean they stay in one place. One example of a nonmotile protist is Plasmodium (left), which is carried by mosquitoes and causes malaria. Another example is Cryptosporidium (right), which is spread through contaminated water and causes intestinal disease. Protists such as these form reproductive structures called spores that can enter the cells of other organisms and live as parasites.
- Distribute the lesson worksheet and instruct students to make a three-circle Venn diagram to compare forms of reproduction and nonreproductive sexual processes in protists: Cell Division, Conjugation, Alternation of Generations. Explain that amoebas reproduce by mitosis; that is, they duplicate their genetic material and then simply divide into two genetically identical cells. Most other protists have phases in their life cycle in which they also produce new individuals by mitosis. Ask students to consider what advantages and disadvantages of this form of reproduction are. Guide them to conclude that mitosis enables protists to reproduce rapidly, especially under ideal conditions, but that it produces cells that are genetically identical to the parent cell, and thus limits the development of genetic diversity.
- Explain that paramecia and most ciliates also reproduce asexually by mitotic cell division. However, under stress, such as during a change in environmental conditions, paramecia can remake themselves through conjugation—a process in which two organisms exchange genetic material. Ask: Why would an exchange of genetic information be beneficial under stressful conditions? Sample Answer: Exchanging genetic material increases genetic diversity, which could allow for new combinations of traits potentially favorable to new environmental conditions. Explain that paramecium has two types of nuclei: a macronucleus and one or more smaller micronuclei. The micronucleus is a bit like a reference library where books don’t circulate—it holds a “reserve copy” of every gene in the cell. The macronucleus is more like a lending library—it has multiple copies of the genes the cell uses in its day-to-day activities. Have a volunteer go to the board to write on the labels for macronucleus and micronucleus on the far left portion of the diagram. Click to reveal the correct answers. First, two paramecia attach to each other, as shown at far left. The diploid micronuclei of each paramecium undergo meiosis. Click to reveal the label for meiosis. Ask: Are the four micronuclei in each cell haploid or diploid? Answer: haploid 3. In each cell, three of the haploid micronuclei disintegrate. Click to reveal the label for disintegration. 4. The remaining micronucleus in each cell undergoes mitosis. Click to reveal the label for mitosis. Ask: Is the remaining micronucleus haploid or diploid? Will its daughter cells following mitosis be haploid or diploid? Answer: haploid; haploid
- Click to reveal callout for cells exchanging micronucleus. 5. The two cells exchange one haploid micronucleus from each pair. Click to reveal callout for micronuclei fusing and macronucleus disintegrating. 6. In each cell, the micronuclei fuse to form a single diploid micronucleus, and the macronuclei disintegrate. Click to reveal callout for new macronucleus forming from micronucleus. 7. Each cell forms a new macronucleus from its micronucleus. Ask: Is the final macronucleus haploid or diploid? How do you know? Answer: Diploid; the macronucleus formed from a micronucleus formed through joining of two haploid nuclei. Click to reveal the diploid label at far right. Ask: How is conjugation similar to mitosis? Answer: A cell that has the same number of chromosomes as the parent cell results—in this case a diploid cell. Ask: How is conjugation similar to meiosis and fertilization? Answer: The end result is a diploid cell with recombined genes. Ask: What is the advantage of conjugation for a paramecium species? Answer: Conjugation provides new combinations of genes. Be sure to emphasize that conjugation is NOT a type of reproduction because no new individuals are formed. It is, however, a sexual process, using meiosis to produce new combinations of genetic information. In a large population, conjugation helps produce and maintain genetic diversity, the raw material for evolution.
- Explain that 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. An example is the life cycle of a type of protist known as a water mold. Water molds, or oomycetes, thrive on dead and decaying organic matter in water or as parasites of plants on land. Ask for a volunteer to go the board to label the portions of the cycles in the diagram where you would expect to find haploid calls and where you would expect to find diploid cells. Click to reveal the key at bottom left which identifies haploid and diploid color-coding. Tell students that in the next two slides they will look more closely at each cycle.
- Explain that water molds grow into long branching filaments consisting of many cells formed by mitotic cell division. Water molds—and many other protists—reproduce asexually by producing spores in a structure called a sporangium. Click to reveal the sporangium and the label. Point out that in water molds the spores are flagellated. Click to reveal the label, leader line, and circle for spores. Explain that spores are disbursed through moisture, and when conditions are favorable, spores undergo mitosis. Click to reveal mitosis label. Ask for a volunteer to label in the blank space whether the structure that develops from the spore is 1N or 2N. Click to reveal the correct answer. Ask: How does the organism developing from the spore grow? Answer: through mitosis
- Explain using the diagram that 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. Ask: Are the egg cells and male reproductive cells 1N or 2N? Answer: 1N Ask for a volunteer to label in the blank space whether each zygote that forms is 1N or 2N. Click to reveal the correct answer. Ask: How does the organism developing from the zygote grow? Answer: through mitosis Ask: Which form of reproduction results in a greater variety of offspring? Answer: sexual reproduction
- Ask for volunteers to go to the board and list four methods of protist locomotion. (Answers: amoeboid movement, passive movement, use of cilia, use of flagella) Click to reveal answers. Ask for other volunteers to answer verbally with the terms that correctly complete the sentences about protist reproduction. (Answers: mitosis; sexual, asexual) Click to reveal answers Ask: What do paramecia exchange during conjugation? Answer: haploid nuclei Ask: Why is conjugation not considered a form of reproduction, even though genetic material is exchanged? Answer: No new individuals are formed.
- Allow students a few minutes following the presentation to complete their Venn diagrams. Then draw a three-ring Venn diagram on the board and ask for student volunteers to fill in the different segments. Worksheet Answers: Alternation of Generations (AG) and Cell Division (CD): new individuals form Conjugation (C): no new individuals form AG and C: exchanges of genetic material CD: offspring cells are genetically identical to parent AG and C: increase genetic variety AG and C: involve both meiosis and mitosis CD: mitosis only AG: multicellular (at least at some stage) protists CD and C: unicellular protists