21.2 Protist Structure and Function
How do protists move in the environment?- How do protists reproduce?
pseudopod • cilium • flagellum • spore • conjugation • alternation of generations • sporangium
Compare/Contrast Table As you read, make a table that compares and contrasts the different ways protists move.
BUILD Vocabulary
GREEK ROOTS The word pseudopod comes from the Greek roots pseudo, meaning “false,” and pod, meaning “foot.”
THINK ABOUT IT Our bodies are packed with specialized systems of every sort. Organ systems help us move, sense the environment, digest our food, and even reproduce. But protists have no such systems—they do it 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. The protists we see today are winners in that struggle.
How Protists Move
How do protists move in the environment?
Before they gave rise to multicellular eukaryotes, protists evolved just about every form of cellular movement known to exist. 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 known as pseudopods (SOO doh pahdz). The best-known protists with this form of movement are the amoebas. In Figure 21–4, you can see how 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 is found in many protists. 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.
FIGURE 21–4 Amoeboid Movement An amoeba moves by first extending a pseudopod away from its body. The organism's cytoplasm then streams into the pseudopod. Amoebas also use pseudopods to surround and ingest prey. Here, the prey is a cluster of green algal cells. (LM 220×)
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Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis