Chapter 28: Protists (1)

Question 1

Explain the structural diversity of protists.

Answer 1

• Protists are unicellular, although there
  are some colonial and multicellular species.
• The organelles that protists use are the nucleus, endoplasmic reticulum, Golgi apparatus, and lysosomes.
• Contractile vacuoles that pump excess water from the protistan cell

Question 2

Explain the nutritional diversity of protists.

Answer 2

• Some protists are photoautotrophs and contain chloroplasts.
• Some are heterotrophs, absorbing organic molecules or ingesting larger food particles. - Still other protists, called mixotrophs, combine photosynthesis and heterotrophic nutrition.

Question 3

Explain the reproduction diversity in protists

Answer 3

• Some protists are only known to reproduce asexually; others can also reproduce sexually or at least employ the sexual processes of meiosis and fertilization.
• All three basic types of sexual life cycles are represented among protists, along with some variations that do not quite fit any of these types.

Question 4

Amitochondriates (lacking conventional mitochondria) are the oldest lineage of
eukaryotes. True or false?

Answer 4

It is no longer thought that amitochondriates (lacking conventional mitochondria) are the oldest lineage of eukaryotes

– Many have been shown to have mitochondria and have been reclassified

Question 5

What are the 5 supergroups of protists?

Answer 5

1. Excavata
2. SAR
3. Archaeplastida
4. Unikonta
5. Chromaveolata

Question 6

Considerable evidence indicates that much of protist diversity has its origins in _________.

Answer 6

Considerable evidence indicates that much of protist diversity has its origins in
endosymbiosis.

Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then an organelle in the host cell

Question 7

How did mitochondria and plastid evolve?

Answer 7

– Mitochondria evolved by endosymbiosis of an aerobic prokaryote

– Plastids evolved later by endosymbiosis of a photosynthetic cyanobacterium

Question 8

The ancestral host of endosymbiosis may have been an _______ or a ________.

Answer 8

The ancestral host may have been an archaean or a “protoeukaryote”

Question 9

Explain the evolution of mitochondria and plastid.

Answer 9

• Mitochondria arose first through descent from a bacterium that was engulfed by a cell from an archaeal lineage
• The plastid lineage evolved later from a photosynthetic cyanobacterium that was engulfed by a heterotrophic eukaryote

Question 10

What did the plastid-bearing lineage of protists evolve into?

Answer 10

The plastid-bearing lineage of protists evolved into photosynthetic protists:
– red and green algae

Question 11

Define primary endosymbiosis and secondary symbiosis.

Answer 11

Primary endosymbiosis because it was the first transfer of photosynthesis from a prokaryote to a eukaryote.

Photosynthesis continued to be passed to diverse groups and across kingdoms in a process called secondary endosymbiosis

Question 12

Why would it be advantageous to the host to maintain a cyanobacterial endosymbiont?

Answer 12

It would have been advantageous to the host to maintain the cyanobacterial endosymbiont, as a source of sugar from photosynthesis.

Question 13

How does endosymbiont bacteria become an organelle?

Answer 13

Gene transfer tookplace from endosymbiont to the host nucleus made it dependent on the host
– transferred genes need to be expressed properly
– the translated proteins must be targeted back into the organelle,
where they function

Question 14

What are the characteristics of excavata?

Answer 14

• The clade Excavata is characterized by its cytoskeleton
• Some members have an “excavated” feeding groove
• This group includes diplomonads, parabasalids, and euglenozoans

Question 15

What are the characteristics of diplomonads and parabasalids?

Answer 15

Diplomonads and Parabasalids

• These groups
  – lack plastids,
  – have modified mitochondria
  – most live in anaerobic environments

MAP

Question 16

What are the characteristics of diplomonads?

Answer 16

Diplomonads

– Have modified mitochondria (mitosomes)
– Derive energy from anaerobic biochemical pathways
– Have two equal-sized nuclei and multiple flagella
– Are often parasites, for example, Giardia intestinalis

Question 17

What are the characteristics of Parabasalids?

Answer 17

Parabasalids

– Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically
(H2 gas released as a by-product)

– Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females

Question 18

What are the organisms that come under euglenozoa?

Answer 18

Euglenozoa is a diverse clade that includes :

– predatory heterotrophs
– photosynthetic autotrophs
– parasites

Question 19

What are the characteristics of Euglenozoa?

Answer 19

• The main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella
• Clade includes
  – kinetoplastids and
  – euglenids

Question 20

What are the characteristics of kinetoplastid?

Answer 20

• Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast
• They include free-living species that feed on prokaryotes
  in
  – freshwater,
  – marine, and
  – moist terrestrial ecosystems
• Some species are parasitic
  –(This group includes Trypanosoma, which causes sleeping sickness in humans)