Question 1

What are some examples of protists?

Accepted Answer

Protists range from the microscopic, single-celled Acanthocystis turfacea and the ciliate Tetrahymena thermophila , which can be seen using light microscopy, to the enormous, multicellular kelps (Chromalveolata) that extend for hundreds of feet in underwater "forests".

Question 2

What is the origin of the term "protist"?

Accepted Answer

This name was first suggested by Ernst Haeckel in the late 19th century.

Question 3

What are some examples of protists with large, macroscopic cells?

Accepted Answer

Plasmodia (giant amoebae) of myxomycete slime molds, and marine green alga Caulerpa.

Question 4

What are some examples of multicellular protists?

Accepted Answer

Red, green, and brown seaweeds.

Question 5

What is endosymbiosis?

Accepted Answer

Engulfment of one cell within another such that the engulfed cell survives, and both cells benefit; the process responsible for the evolution of mitochondria and chloroplasts in eukaryotes.

Question 6

What is the endosymbiotic theory?

Accepted Answer

Theory that states that eukaryotes may have been a product of one cell engulfing another, one living within another, and evolving over time until the separate cells were no longer recognizable as such.

Question 7

What is a plastid?

Accepted Answer

One of a group of related organelles in plant cells that are involved in the storage of starches, fats, proteins, and pigments.

Question 8

In what kinds of environments are microscopic protists commonly found?

Accepted Answer

Soil, freshwater, brackish and marine environments, as well as the digestive tracts of animals and in the vascular tissues of plants. Others invade the cells of other protists, animals, and plants.

Question 9

What is the oldest fossils found?

Accepted Answer

The earliest fossils found appear to be Bacteria, most likely cyanobacteria. They are about 3.5 billion years old and are recognizable because of their relatively complex structure and, for prokaryotes, relatively large cells.

Question 10

When do the first eukaryotes appear in the fossil record?

Accepted Answer

Structures of size 10 micrometers and greater, which might be fossils, appear in the geological record about 2.1 billion years ago.

Question 11

Which characteristics must have been common in the most recent common ancestor of eukaryotic organisms?

Accepted Answer

1. Cells with nuclei surrounded by a nuclear envelope with nuclear pores. 2. Mitochondria. 3. A cytoskeleton containing the structural and motility components called actin microfilaments and microtubules. 4. Flagella and cilia. 5. Chromosomes, each consisting of a linear DNA molecule coiled around basic (alkaline) proteins called histones. 6. Mitosis. 7. Sex. 8. Cell walls.

Question 12

What is the prevalence of mitochondria in eukaryotes?

Accepted Answer

Some extant eukaryotes have very reduced remnants of mitochondria in their cells, whereas other members of their lineages have "typical" mitochondria.

Question 13

What is the prevalence of the cytoskeleton in eukaryotes?

Accepted Answer

All extant eukaryotes have actin microfilaments and microtubules.

Question 14

What is the prevalence of flagella and cilia in eukaryotes?

Accepted Answer

Some extant eukaryotes lack flagella and/or cilia, but they are descended from ancestors that possessed them.

Question 15

What is the prevalence of histones in eukaryotic chromosomes?

Accepted Answer

The few eukaryotes with chromosomes lacking histones clearly evolved from ancestors that had them.

Question 16

What is the prevalence of mitosis in eukaryotes?

Accepted Answer

Mitosis is universally present in eukaryotes.

Question 17

What is karyogamy?

Accepted Answer

A stage where two haploid nuclei fuse together to create a diploid zygote nucleus.

Question 18

What is the prevalence of cell walls in eukaryotes?

Accepted Answer

Members of all major lineages have cell walls, and it might be reasonable to conclude that the last common ancestor could make cell walls during some stage of its life cycle. However, not enough is known about eukaryotes' cell walls and their development to know how much homology exists among them. If the last common ancestor could make cell walls, it is clear that this ability must have been lost in many groups.

Question 19

What was likely the origin of eukaryotes?

Accepted Answer

All extant eukaryotes are descendants of a chimeric organism that was a composite of a host cell and the cell(s) of an alpha-proteobacterium that "took up residence" inside it.

Question 20

Which metabolic processes are found in prokaryotes, and in eukaryotes?

Accepted Answer

Many important metabolic processes arose in prokaryotes, and some of these, such as nitrogen fixation, are never found in eukaryotes. The process of aerobic respiration is found in all major lineages of eukaryotes, and it is localized in the mitochondria. Aerobic respiration is also found in many lineages of prokaryotes, but it is not present in all of them, and many forms of evidence suggest that such anaerobic prokaryotes never carried out aerobic respiration nor did their ancestors.

Question 21

What is the history of atmospheric oxygenation?

Accepted Answer

Various metabolic processes evolved that protected organisms from oxygen, one of which, aerobic respiration, also generated high levels of ATP. It became widely present among prokaryotes, including in a group we now call alpha-proteobacteria. Organisms that did not acquire aerobic respiration had to remain in oxygen-free environments. Originally, oxygen-rich environments were likely localized around places where cyanobacteria were active, but by about 2 billion years ago, geological evidence shows that oxygen was building up to higher concentrations in the atmosphere. Oxygen levels similar to today's levels only arose within the last 700 million years.

Question 22

When were the first organelles observed?

Accepted Answer

Mitochondria were first observed by light microscopists in the late 1800s, where they appeared to be somewhat worm-shaped structures that seemed to be moving around in the cell.

Question 23

What is the history of the endosymbiotic theory?

Accepted Answer

In the 1960s, American biologist Lynn Margulis developed endosymbiotic theory. In 1967, Margulis introduced new work on the theory and substantiated her findings through microbiological evidence. Although Margulis' work initially was met with resistance, the once-revolutionary hypothesis is now widely (but not completely) accepted, with work progressing on uncovering the steps involved in this evolutionary process and the key players involved.

Question 24

What are some features of mitochondria?

Accepted Answer

Mitochondria arise from the division of existing mitochondria; they may fuse together; and they may be moved around inside the cell by interactions with the cytoskeleton. However, mitochondria cannot survive outside the cell.

Question 25

How are mitochondria created?

Accepted Answer

Mitochondria divide independently by a process that resembles binary fission in prokaryotes. Specifically, mitochondria are not formed from scratch (de novo) by the eukaryotic cell; they reproduce within it and are distributed with the cytoplasm when a cell divides or two cells fuse. Their reproduction is synchronized with the activity and division of the cell.

Question 26

Where are genes for respiratory proteins found?

Accepted Answer

Many of the genes for respiratory proteins are located in the nucleus, but in some eukaryotic groups, they are found in mitochondria.

Question 27

What is some evidence from respiratory protein genes for the endosymbiont theory?

Accepted Answer

The genes of respiratory proteins in eukaryotes, when compared to those of other organisms, appear to be of alpha-proteobacterial origin. The fact that in many eukaryotes they are found in the nucleus and not mitochondria has been interpreted as evidence that the genes have been transferred from the endosymbiont chromosome to the host genome. This loss of genes by the endosymbiont is probably one explanation why mitochondria cannot live without a host.

Question 28

Are mitochondria found in anaerobic eukaryotes?

Accepted Answer

Some anaerobic eukaryotes appear to lack organelles that could be recognized as mitochondria. Findings suggest that reduced organelles are found in most, if not all, anaerobic eukaryotes, and that all eukaryotes appear to carry some genes in their nuclei that are of mitochondrial origin.

Question 29

What are some functions associated with the reduced mitochondrion-derived organelles of anaerobic eukaryotes?

Accepted Answer

The generation of clusters of iron and sulfur for use as cofactors.

Question 30

Which type of molecule is found in plastids that is involved in the light-harvesting chemical reactions of photosynthesis?

Accepted Answer

Plastids are rich in the pigment chlorophyll a and a range of other pigments, called accessory pigments, which are involved in harvesting energy from light.

Question 31

What is the primary endosymbiotic origin of plastids?

Accepted Answer

Plastids are derived from cyanobacteria that lived inside the cells of an ancestral, aerobic, heterotrophic eukaryote. Plastids of primary origin are surrounded by two membranes.

Question 32

Why is it suggested that primary endosymbiosis has occurred twice in the history of photosynthetic eukaryotes?

Accepted Answer

In one case, the common ancestor of the major lineage/supergroup Archaeplastida took on a cyanobacterial endosymbiont; in the other, the ancestor of the small amoeboid rhizarian taxon, Paulinella , took on a different cyanobacterial endosymbiont. Almost all photosynthetic eukaryotes are descended from the first event, and only a couple of species are derived from the other.

Question 33

What is one of the differences between cyanobacteria and most other prokaryotes?

Accepted Answer

Cyanobacteria have extensive, internal membrane-bound sacs called thylakoids.

Question 34

What are some similarities between chloroplasts and cyanobacteria?

Accepted Answer

Chloroplasts of primary origin have thylakoids, a circular DNA chromosome, and ribosomes similar to those of cyanobacteria.

Question 35

Which plastids have a relictual cyanobacterial wall?

Accepted Answer

Each chloroplast is surrounded by two membranes. In the group of Archaeplastida called the glaucophytes and in Paulinella , a thin peptidoglycan layer is present between the outer and inner plastid membranes. All other plastids lack this relictual cyanobacterial wall.

Question 36

What are the origins of the two plasma membranes of plastids?

Accepted Answer

The outer membrane surrounding the plastid is thought to be derived from the vacuole in the host, and the inner membrane is thought to be derived from the plasma membrane of the symbiont.

Question 37

What are some endosymbiotic characteristics of plastids?

Accepted Answer

There is, as with the case of mitochondria, strong evidence that many of the genes of the endosymbiont were transferred to the nucleus. Plastids, like mitochondria, cannot live independently outside the host. In addition, like mitochondria, plastids are derived from the division of other plastids and never built from scratch.

Question 38

When did the endosymbiotic event that led to Archaeplastida occur?

Accepted Answer

Researchers have suggested that the endosymbiotic event that led to Archaeplastida occurred 1 to 1.5 billion years ago, at least five hundred million years after the fossil record suggests that eukaryotes were present.

Question 39

What is secondary endosymbiosis?

Accepted Answer

A cell containing an endosymbiont to itself became engulfed.

Question 40

What are some characteristics of secondary plastids?

Accepted Answer

Secondary plastids are surrounded by three or more membranes, and some secondary plastids even have clear remnants of the nucleus of the endosymbiotic alga. Others have not "kept" any remnants.

Question 41

Are all plastids in eukaryotes derived from primary endosymbiosis?

Accepted Answer

Not all plastids in eukaryotes are derived directly from primary endosymbiosis. There are cases where tertiary or higher-order endosymbiotic events are the best explanations for plastids in some eukaryotes.

Question 42

What is a chlorarachniophyte?

Accepted Answer

Chlorarachniophytes are rare algae indigenous to tropical seas and sand that can be classified into the rhizarian supergroup. Chlorarachniophytes extend thin cytoplasmic strands, interconnecting themselves with other chlorarachniophytes, in a cytoplasmic network. Molecular and morphological evidence suggest that the chlorarachniophyte protists are derived from a secondary endosymbiotic event, where a eukaryote engulfed a green alga, the latter of which had already established an endosymbiotic relationship with a photosynthetic cyanobacterium.

Question 43

What is the evidence that chlorarachniophytes evolved from secondary endosymbiosis?

Accepted Answer

The chloroplasts contained within the green algal endosymbionts are still capable of photosynthesis, making chlorarachniophytes photosynthetic. The green algal endosymbiont also exhibits a stunted vestigial nucleus. Additionally, the plastids of chlorarachniophytes are surrounded by four membranes.

Question 44

Why is it suggested that chlorarachniophytes are the products of an evolutionary recent secondary endosymbiotic event?

Accepted Answer

Their plastids are surrounded by four membranes, whereas in other lineages that involved secondary endosymbiosis, only three membranes can be identified around plastids, which is explained as a sequential loss of a membrane during the course of evolution.

Question 45

How are the four membranes of chlorarachniophytes explained?

Accepted Answer

The first two correspond to the inner and outer membranes of the photosynthetic cyanobacterium, the third corresponds to the green alga, and the fourth corresponds to the vacuole that surrounded the green alga when it was engulfed by the chlorarachniophyte ancestor.

Question 46

What are some examples of secondary endosymbiosis, excluding chlorarachniophytes?

Accepted Answer

Secondary endosymbiosis of green algae led to euglenid protists, whereas secondary endosymbiosis of red algae led to the evolution of dinoflagellates, apicomplexans, and stramenopiles.

Question 47

What evidence is there that mitochondria were incorporated into the ancestral eukaryotic cell before chloroplasts?

Accepted Answer

All eukaryotic cells have mitochondria, but not all eukaryotic cells have chloroplasts.

Question 48

What is a mixotroph?

Accepted Answer

Organism that can obtain nutrition by autotrophic or heterotrophic means, usually facultatively.

Question 49

What is a pellicle?

Accepted Answer

Outer cell covering composed of interlocking protein strips that function like a flexible coat of armor, preventing cells from being torn or pierced without compromising their range of motion.

Question 50

What is a phagolysosome?

Accepted Answer

Cellular body formed by the union of a phagosome containing the ingested particle with a lysosome that contains hydrolytic enzymes.

Question 51

How diverse are protists?

Accepted Answer

There are over 100,000 described living species of protists, and it is unclear how many undescribed species may exist. Since many protists live as commensals or parasites in other organisms and these relationships are often species-specific, there is a huge potential for protist diversity that matches the diversity of the hosts. As the catchall term for eukaryotic organisms that are not animal, plant, or fungi, it is not surprising that very few characteristics are common to all protists.

Question 52

What are some characteristics of protist cell structure?

Accepted Answer

The cells of protists are among the most elaborate of all cells. Most protists are microscopic and unicellular, but some true multicellular forms exist. A few protists live as colonies that behave in some ways as a group of free-living cells, and in other ways as a multicellular organism. Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, like ferns. In fact, many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function.

Question 53

What is the size and protective features of protists?

Accepted Answer

Single protist cells range in size from less than a micrometer to three meters in length to hectares. Protist cells may be enveloped by animal-like cell membranes or plant-like cell walls. Others are encased in glassy silica-based shells or wound with pellicles of interlocking protein strips.

Question 54

What are the stages of phagocytosis?

Accepted Answer

The engulfment of a food particle, the digestion of the particle using hydrolytic enzymes contained within a lysosome, and the expulsion of undigested materials from the cell.

Question 55

What is a saprobe?

Accepted Answer

A subtype of heterotrophs, which absorb nutrients from dead organisms or their organic wastes.

Question 56

What modes of movement have protists evolved for motility?

Accepted Answer

The majority of protists are motile, but different types of protists have evolved varied modes of movement. Some protists have one or more flagella, which they rotate or whip. Others are covered in rows or tufts of tiny cilia that they coordinately beat to swim. Others form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a substrate, and pull themselves forward.

Question 57

What is taxis?

Accepted Answer

The movement toward or away from a stimulus.

Question 58

What is phototaxis?

Accepted Answer

Movement toward light, which is accomplished by coupling a locomotion strategy with a light-sensing organ.

Question 59

What are examples of protists which use different transportation methods?

Accepted Answer

Paramecia waves hair-like appendages called cilia to propel itself; amoebas use lobe-like pseudopodia to anchor itself to a solid surface and pull itself forward; Euglena use a whip-like tail called a flagellum to propel itself.

Question 60

What are the two modes of binary fission in protists?

Accepted Answer

Transverse or longitudinal, depending on the axis of orientation.

Question 61

What is an example of a protist which exhibits binary fission?

Accepted Answer

Paramecium .

Question 62

What is an example of a protist which exhibits multiple fission?

Accepted Answer

True slime molds.

Question 63

What are some different modes of replication among protists?

Accepted Answer

Asexual reproduction, such as binary fission, multiple fission, or budding which divide and grow to the size of the parental protist; or sexual reproduction involving meiosis and fertilization.

23: Protists Flashcards

Eukaryotic Origins, Characteristics of Protists, Groups of Protists, Ecology of Protists

Brainscape's Knowledge GenomeTM

23: Protists Flashcards

Eukaryotic Origins, Characteristics of Protists, Groups of Protists, Ecology of Protists

Brainscape's Knowledge Genome^TM