Chapter 28 Study Guide: Protists – Step-by-Step Guidance

Q1. What does it mean that Kingdom Protista is considered “polyphyletic” now?

Background

Topic: Evolutionary Relationships & Classification

This question is testing your understanding of how organisms are grouped based on evolutionary history, and what it means for a group to be polyphyletic.

Key Terms:

• Polyphyletic: A group of organisms derived from more than one common evolutionary ancestor or ancestral group, and therefore not suitable to be placed in the same taxon.

• Monophyletic: A group that includes an ancestor and all of its descendants.

• Paraphyletic: A group that includes an ancestor and some, but not all, of its descendants.

Step-by-Step Guidance

1. Recall the definitions of monophyletic, paraphyletic, and polyphyletic groups in evolutionary biology.

2. Think about how organisms in Kingdom Protista are related to each other—do they all share a single common ancestor, or do they come from multiple evolutionary lines?

3. Consider why scientists might have reclassified Protista as polyphyletic based on genetic and evolutionary evidence.

4. Reflect on what this means for the classification of protists and how it affects our understanding of their evolutionary history.

Try explaining what 'polyphyletic' means in your own words before checking the answer!

Q2. Are most protists multicellular or unicellular? Explain, and provide an example of each.

Background

Topic: Cellular Organization in Protists

This question tests your knowledge of the diversity of protists in terms of their cellular structure and ability to exist as single cells or as multicellular organisms.

Key Terms:

• Unicellular: Organisms made up of a single cell.

• Multicellular: Organisms made up of more than one cell, often with specialized functions.

• Example: Think of specific protists that fit each category.

Step-by-Step Guidance

1. Recall the general characteristics of protists regarding their cellular organization.

2. Identify whether most protists are unicellular or multicellular.

3. Think of a common example of a unicellular protist (e.g., Amoeba or Paramecium).

4. Think of a common example of a multicellular protist (e.g., certain types of algae).

5. Explain why being unicellular or multicellular might be advantageous for protists in different environments.

Try to recall examples before checking the answer!

Q3. Describe the endosymbiotic theory. Then, state what are believed to have evolved first, prokaryotes, (and why)?

Background

Topic: Evolution of Eukaryotic Cells

This question is about the origin of complex cells and the evolutionary relationship between prokaryotes and eukaryotes.

Key Terms and Concepts:

• Endosymbiotic Theory: The idea that certain organelles (like mitochondria and chloroplasts) originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells.

• Prokaryotes: Simple cells without a nucleus (e.g., bacteria, archaea).

• Eukaryotes: Cells with a nucleus and membrane-bound organelles.

Step-by-Step Guidance

1. Summarize the main points of the endosymbiotic theory—what does it propose about the origin of mitochondria and chloroplasts?

2. List the evidence supporting the endosymbiotic theory (e.g., double membranes, their own DNA, similarities to bacteria).

3. Consider the timeline of evolution: which cell type (prokaryote or eukaryote) is believed to have appeared first, and why?

4. Think about the characteristics of early Earth and which cell type would be better suited to those conditions.

Try outlining the theory and reasoning before checking the answer!

Q4. State two ways that protists are beneficial to our ecosystems or our bodies.

Background

Topic: Ecological Roles of Protists

This question is about the positive impacts protists have on the environment and human health.

Key Terms:

• Primary Producers: Organisms that produce organic compounds from inorganic substances (e.g., photosynthetic protists).

• Symbionts: Organisms that live in close association with another species, often benefiting both.

Step-by-Step Guidance

1. Think about the role of protists in aquatic food chains (e.g., as phytoplankton).

2. Consider how protists contribute to nutrient cycling or oxygen production.

3. Recall any examples of protists that have beneficial relationships with other organisms (e.g., in the human gut or with corals).

4. List at least two specific benefits, explaining each briefly.

Try to list two benefits before checking the answer!

Q5. State a way that protists can be harmful to an organism (provide an example).

Background

Topic: Harmful Effects of Protists

This question is about the negative impacts protists can have, such as causing disease.

Key Terms:

• Parasite: An organism that lives on or in a host and causes harm to the host.

• Pathogen: An organism that causes disease.

Step-by-Step Guidance

1. Recall examples of protists that are known to cause diseases in humans, animals, or plants.

2. Think about how these protists harm their hosts (e.g., by destroying cells, causing illness).

3. Choose one example and briefly describe the harm it causes.

Try to recall a harmful protist and its effects before checking the answer!

Q6. In most terrestrial (land-based) ecosystems, plants are the primary producers – meaning they perform photosynthesis to convert energy from the sun to chemical energy that can be consumed by organisms (glucose). How do terrestrial ecosystems compare to aquatic ecosystems regarding producers?

Background

Topic: Primary Production in Ecosystems

This question is about the similarities and differences in the main producers in land versus water ecosystems.

Key Terms:

• Primary Producer: An organism that can produce its own food from inorganic substances.

• Photosynthesis: The process by which light energy is converted to chemical energy.

Step-by-Step Guidance

1. Recall that plants are the main producers on land.

2. Think about what types of organisms perform photosynthesis in aquatic environments (e.g., algae, phytoplankton).

3. Compare the roles of these aquatic producers to those of terrestrial plants.

4. Consider the ecological importance of aquatic protists as producers.

Try to compare the two ecosystems before checking the answer!

Q7. What would be some negative consequences to not having as many protists in aquatic biomes globally?

Background

Topic: Ecological Importance of Protists

This question is about the potential impacts on ecosystems if protist populations decline.

Key Terms:

• Food Web: The interconnected feeding relationships in an ecosystem.

• Oxygen Production: Many protists contribute significantly to global oxygen levels.

Step-by-Step Guidance

1. Think about the role of protists as primary producers in aquatic food webs.

2. Consider how a decrease in protist populations would affect organisms that rely on them for food.

3. Reflect on the impact on global oxygen production and nutrient cycling.

4. List at least two negative consequences of reduced protist abundance.

Try to list possible consequences before checking the answer!

Be able to define the following terms:

• Photoautotroph

• Heterotroph

• Mixotroph

• Endosymbiosis

• Producer

• Consumer

• Symbiont (which are symbiotic)

• Parasites (which are parasitic)

Background

Topic: Key Biological Terms

These definitions are foundational for understanding protist biology and ecology.

Step-by-Step Guidance

1. For each term, try to write a concise definition in your own words.

2. Think of an example organism or context for each term.

3. Consider how these terms relate to the roles of protists in ecosystems.

Try defining each term before checking the answer!