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

Q1. Kingdom Protista is considered “polyphyletic” now – what does this mean?

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 and Concepts:

• 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 consists of a common ancestor and all its descendants.

• Paraphyletic: A group that includes a common ancestor but not all its descendants.

Step-by-Step Guidance

1. Recall that biological classification aims to group organisms based on shared ancestry.

2. Think about what it means for a group to have multiple evolutionary origins (i.e., not all members share a recent common ancestor).

3. Consider why Protista does not fit the definition of a monophyletic group.

4. Try to explain, in your own words, what “polyphyletic” means and why Protista is considered polyphyletic.

Try solving on your own before revealing the answer!

Final Answer:

"Polyphyletic" means that the group called Protista includes organisms that do not all share a single common ancestor unique to them. Instead, they have multiple evolutionary origins. This is why Protista is considered "polyphyletic"—the group is made up of organisms from different evolutionary lineages, not a single ancestor and all its descendants.

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

Background

Topic: Cellular Organization in Protists

This question tests your understanding of the diversity of protists in terms of their cellular structure and examples of each type.

Key Terms:

• Unicellular: Organisms made up of a single cell.

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

• Protist Examples: Amoeba (unicellular), Kelp (multicellular).

Step-by-Step Guidance

1. Recall the general characteristics of protists and their diversity.

2. Think about whether most protists are made of one cell or many cells.

3. Identify a common unicellular protist and a common multicellular protist.

4. Explain your reasoning for each example.

Try solving on your own before revealing the answer!

Final Answer:

Most protists are unicellular, meaning they consist of a single cell. For example, Amoeba is a unicellular protist. However, some protists are multicellular, such as certain types of algae like kelp (a brown alga). This shows the diversity within the group.

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 timeline of prokaryotes and eukaryotes.

Key Terms and Concepts:

• Endosymbiotic Theory: The idea that certain organelles (like mitochondria and chloroplasts) originated as free-living bacteria 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 idea of the endosymbiotic theory in your own words.

2. Identify which organelles are thought to have originated through endosymbiosis.

3. Consider the evolutionary timeline: which cell type appeared first, and what evidence supports this?

4. Think about why prokaryotes are believed to have evolved before eukaryotes.

Try solving on your own before revealing the answer!

Final Answer:

The endosymbiotic theory proposes that mitochondria and chloroplasts in eukaryotic cells originated from free-living prokaryotes that were engulfed by a host cell. Prokaryotes are believed to have evolved first because they are simpler, fossil evidence shows they appeared earlier, and eukaryotes likely evolved from prokaryotic ancestors through endosymbiosis.

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 sunlight (e.g., phytoplankton).

• 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 producers).

2. Consider how protists can form beneficial relationships with other organisms (e.g., in digestion or mutualism).

3. List two specific examples of how protists are helpful.

Try solving on your own before revealing the answer!

Final Answer:

Protists are beneficial because (1) many, like phytoplankton, are primary producers in aquatic ecosystems, forming the base of the food web, and (2) some live in symbiotic relationships, such as helping termites digest cellulose or corals obtain nutrients through photosynthetic protists (zooxanthellae).

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.

• Pathogen: An organism that causes disease.

Step-by-Step Guidance

1. Recall that some protists are parasitic and can cause diseases in humans, animals, or plants.

2. Think of a well-known disease caused by a protist.

3. Describe how this protist harms its host.

Try solving on your own before revealing the answer!

Final Answer:

Some protists are harmful because they are parasites. For example, Plasmodium causes malaria in humans by infecting red blood cells, leading to illness and sometimes death.

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 Producers in Different Ecosystems

This question is about the similarities and differences in the types of organisms that serve as primary producers on land versus in water.

Key Terms:

• Primary Producer: An organism that can produce its own food from inorganic substances (usually through photosynthesis).

• Phytoplankton: Microscopic, photosynthetic protists in aquatic environments.

Step-by-Step Guidance

1. Recall that on land, plants are the main photosynthetic organisms.

2. Think about what organisms fill this role in aquatic ecosystems.

3. Compare the main producers in both environments and explain the difference.

Try solving on your own before revealing the answer!

Final Answer:

In terrestrial ecosystems, plants are the main primary producers. In aquatic ecosystems, most primary producers are protists, especially phytoplankton, which perform photosynthesis and form the base of aquatic food webs.

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. Consider the role of protists as primary producers in aquatic food webs.

2. Think about how a decrease in protists would affect organisms that rely on them for food.

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

Try solving on your own before revealing the answer!

Final Answer:

If there were fewer protists in aquatic biomes, food webs would collapse because many organisms depend on them as a primary food source. Additionally, global oxygen production would decrease, and nutrient cycling in aquatic environments would be disrupted.

Be able to define:

• Photoautotroph

• Heterotroph

• Mixotroph

• Endosymbiosis

• Producer

• Consumer

• Symbiont (which are symbiotic)

• Parasites (which are parasitic)

Background

Topic: Key Terms in Protist Biology

These definitions are foundational for understanding protist diversity and ecological roles.

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. Review your definitions and compare them to textbook or lecture notes for accuracy.

Try solving on your own before revealing the answer!

Final Answer:

• Photoautotroph: An organism that uses light energy to make its own food from inorganic substances (e.g., plants, algae).

• Heterotroph: An organism that obtains food by consuming other organisms (e.g., animals, many protists).

• Mixotroph: An organism that can use both autotrophic and heterotrophic modes of nutrition (e.g., Euglena).

• Endosymbiosis: A relationship where one organism lives inside another, often leading to mutual benefit (e.g., origin of mitochondria).

• Producer: An organism that makes its own food, usually through photosynthesis.

• Consumer: An organism that eats other organisms for energy.

• Symbiont: An organism that lives in close association with another, often with mutual benefit.

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