Question 1

Which of these observations gives the most support to the endosymbiotic theory for the origin of eukaryotic cells?
A) the existence of structural and molecular differences between the plasma membranes of prokaryotes and the internal membranes of mitochondria and chloroplasts
B) the similarity in size between the cytosolic ribosomes of prokaryotes and the ribosomes within mitochondria and chloroplasts
C) the size disparity between most prokaryotic cells and most eukaryotic cells
D) the observation that some eukaryotic cells lack mitochondria

Accepted Answer

The similarity in size between the cytosolic ribosomes of prokaryotes and the ribosomes within mitochondria and chloroplasts provides support for the endosymbiotic theory because it suggests that these organelles were once free-living prokaryotes that were engulfed by another cell and began to live inside the host cell in a mutually beneficial relationship. This is an important piece of evidence because it supports the idea that the origin of eukaryotic cells involved the incorporation of one or more prokaryotic cells into another cell, leading to the formation of a new type of organism with a combination of characteristics from both cells.

Question 2

Which of the following was derived from an ancestral cyanobacterium?
A) chloroplast
B) mitochondrion
C) hydrogenosome
D) mitosome

Accepted Answer

Chloroplasts are believed to have originated from an ancestral cyanobacterium through endosymbiosis.

Question 3

Why can eukaryotes be considered "combination" organisms?
A) Some of their genes and cellular characteristics were derived from archaea, and others from bacteria.
B) They eventually developed flagella.
C) Their diversity outnumbers prokaryotes by over 1 million species.
D) They eventually developed cellulose plates.

Accepted Answer

Eukaryotes are considered "combination" organisms because some of their genes and cellular characteristics were derived from archaea (such as the presence of a nucleus) and others from bacteria (such as the presence of mitochondria).

Question 4

The chloroplasts of all of the following are thought to be derived from ancestral red algae, except those of
A) diatoms.
B) dinoflagellates.
C) green algae.
D) brown algae.

Accepted Answer

Green algae chloroplasts are believed to be derived from a different lineage, specifically from primary endosymbiosis involving cyanobacteria, rather than from red algae.

Question 5

Which of the following is the most likely sequence of events, from earliest to most recent, in the evolution of sponges (organisms with many cells that have different functions)?
1) single-celled eukaryote
2) single-celled prokaryote
3) multicellular eukaryote
4) colonial eukaryote
A) 2, 1, 4, 3
B) 2, 1, 3, 4
C) 1, 2, 3, 4
D) 1, 2, 4, 3

Accepted Answer

The correct sequence starts with single-celled prokaryotes (2), which are the earliest and most primitive forms of life. Next, single-celled eukaryotes (1) evolved, which have a more complex cell structure. Colonial eukaryotes (4) represent a stage where eukaryotic cells started living together in colonies, which eventually led to the evolution of true multicellular organisms (3), like sponges, where cells have different functions.

Question 6

Multicellular colonies of plant cells adhere to each other primarily by ________, whereas multicellular colonies of animal cells are typically held together by ________.
A) fusion of cellular membranes; cell walls
B) cell walls; fused cellular membranes
C) cell walls; proteins
D) interlocking chloroplasts; interlocking mitochondria
E) interlocking cellular shapes; large, calcified capsules

Accepted Answer

Multicellular colonies of plant cells are held together by cell walls made of cellulose, whereas multicellular colonies of animal cells are held together by proteins such as cadherins and integrins. Therefore, choice C, which states that plant cells are held together by cell walls and animal cells are held together by proteins, is the most accurate answer.

Question 7

Diatoms are mostly asexual members of the phytoplankton. They obtain their nutrition from functional chloroplasts, and each diatom is encased within two porous, glasslike valves. Which question would be most important for one interested in the day-to-day survival of individual diatoms?
A) How does carbon dioxide get into these protists with their glasslike valves?
B) How do diatoms get transported from one location on the water's surface layers to another location on the surface?
C) How do diatoms with their glasslike valves keep from sinking into poorly lit waters?
D) How do diatoms with their glasslike valves avoid being shattered by the action of waves?
E) How do diatom sperm cells locate diatom egg cells?

Accepted Answer

This question focuses on the day-to-day survival of individual diatoms, and the ability to stay within well-lit surface waters is crucial for their survival. A, B, D, and E are not as directly related to the day-to-day survival of individual diatoms.

Question 8

The last common ancestor of fungi and animals was most likely a
A) multicellular photosynthetic eukaryote.
B) colonial photosynthetic prokaryote.
C) multicellular photosynthetic prokaryote.
D) single-celled eukaryote.

Accepted Answer

The last common ancestor of fungi and animals was most likely a single-celled eukaryote because both fungi and animals are members of the eukaryotic domain and their common ancestor would also have been a eukaryotic organism.

Question 9

Which of the following organism pairs is/are an example of secondary endosymbiosis?
I. red algae-heterotrophic eukaryote
II. green algae-heterotrophic eukaryote
III. E. coli bacteria-photosynthetic cyanobacterium
IV. Chlamydomonas and Gonium
A) I only
B) III and IV
C) I and II
D) II and III

Accepted Answer

Secondary endosymbiosis occurs when a eukaryotic host cell engulfs another eukaryotic cell that has already undergone primary endosymbiosis. This is seen in cases where a heterotrophic eukaryote engulfs a photosynthetic eukaryote, such as red or green algae, leading to a complex relationship where the engulfed cell functions within the host. Options I and II (red algae-heterotrophic eukaryote and green algae-heterotrophic eukaryote) are examples of this process. E.coli and cyanobacteria, as well as Chlamydomonas and Gonium, do not fit the criteria for secondary endosymbiosis.

Question 10

Which of the following pairs of protists and their characteristics are mismatched?
A) apicomplexans-internal parasites
B) mixotrophs-combine photosynthesis and heterotrophic nutrition
C) euglenozoans-unicellular flagellates
D) ciliates-red tide organisms

Accepted Answer

Ciliates are not red tide organisms. Red tides are caused by dinoflagellates.

Question 11

The evolution of multicellularity in animals has primarily occurred by
A) changing how existing genes are used.
B) deleting many old genes.
C) producing many new genes.
D) deleting many old chromosomes.

Accepted Answer

The evolution of multicellularity in animals mainly occurred by changing how existing genes are used. This process involved the development of new regulatory mechanisms that allowed for the coordination of cell differentiation and specialization, leading to the formation of organs and tissues. It did not require the deletion of many old genes or chromosomes nor the production of many new genes.

Question 12

All protists are
A) unicellular.
B) eukaryotic.
C) symbionts.
D) monophyletic.
E) mixotrophic.

Accepted Answer

All protists are eukaryotic, meaning they have a true nucleus and membrane-bound organelles. The other choices are not true of all protists.

Question 13

A large seaweed that floats freely on the surface of deep bodies of water would be expected to lack which of the following?
A) alveoli
B) bladders
C) holdfasts
D) flagella

Accepted Answer

Holdfasts are specialized structures that attach seaweed to the ocean floor. A seaweed that floats freely on the surface of deep bodies of water would not need holdfasts since it is not attached to the bottom. Alveoli are small air sacs found in the lungs of mammals and have no relevance to seaweed. Bladders are structures found in some species of seaweed that help them float, but not all seaweed have bladders. Flagella are whip-like structures used for movement and are found in some types of single-celled organisms, but not in seaweed.

Question 14

In a sample of pond water, a new organism is identified with the following characteristics: It consists of 70 cells surrounded by rigid cell walls that join the cells together. Inside each of these identical cells are mitochondria and chloroplasts. Such an organism would most likely be classified as a
A) colonial photosynthetic eukaryote.
B) fungal photosynthetic eukaryote.
C) colonial photosynthetic prokaryote.
D) multicellular photosynthetic prokaryote.
E) colonial eukaryotic fungus.

Accepted Answer

The presence of mitochondria and chloroplasts indicates that the organism is a eukaryote, as these organelles are not found in prokaryotes. The fact that the cells are joined together by rigid cell walls and are identical suggests a colonial organism rather than a truly multicellular one. The presence of chloroplasts indicates that the organism is capable of photosynthesis. Therefore, it is best classified as a colonial photosynthetic eukaryote.

Question 15

What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth?
1) origin of mitochondria
2) origin of multicellular eukaryotes
3) origin of chloroplasts
4) origin of cyanobacteria
5) origin of fungal-plant symbioses
A) 4, 3, 2, 1, 5
B) 4, 1, 2, 3, 5
C) 4, 1, 3, 2, 5
D) 4, 3, 1, 5, 2
E) 4, 3, 1, 2, 5

Accepted Answer

The correct sequence starts with the origin of cyanobacteria, which are among the earliest forms of life on Earth. Following this, the origin of mitochondria and chloroplasts through endosymbiotic events occurred, leading to the development of complex eukaryotic cells. Multicellular eukaryotes then evolved, and finally, symbiotic relationships such as fungal-plant symbioses developed.

Question 16

Why is the filamentous morphology of the slime molds considered a case of convergent evolution with fungi?
A) Water molds evolved from filamentous fungi.
B) Body shape reflects ancestor-descendant relationships among organisms.
C) DNA sequence analyses indicate that slime molds descended from different unicellular ancestors than did fungi.
D) Filamentous body shape is evolutionarily ancestral for all eukaryotes.

Accepted Answer

DNA sequence analyses indicate that slime molds descended from different unicellular ancestors than did fungi, suggesting that their similar filamentous morphology is a case of convergent evolution rather than reflecting a shared ancestral trait.

Question 17

Which of the following statements about dinoflagellates is true?
A) They possess two flagella.
B) All known varieties are autotrophic.
C) Their walls are usually composed of silica plates.
D) Many types lack mitochondria.
E) Their dead cells accumulate on the seafloor and are mined to serve as a filtering material.

Accepted Answer

Dinoflagellates possess two flagella, which are used for locomotion.

Question 18

An individual mixotroph loses its plastids, yet continues to survive. Which of the following most likely accounts for its continued survival?
A) It relies on photosystems that float freely in its cytosol.
B) It must have gained extra mitochondria when it lost its plastids.
C) It engulfs organic material by phagocytosis or by absorption.
D) It has an endospore.
E) It has multiple alveoli.

Accepted Answer

Since the mixotroph has lost its plastids, it can no longer photosynthesize to produce its own organic material. Therefore, it must rely on other methods to obtain nutrients, and the most likely method is to engulf organic material by phagocytosis or absorption.

Question 19

According to the endosymbiotic theory of the origin of eukaryotic cells, how did mitochondria originate?
A) from infoldings of the plasma membrane, coupled with mutations of genes for proteins in energy-transfer reactions
B) from engulfed, originally free-living proteobacteria
C) by secondary endosymbiosis
D) from the nuclear envelope folding outward and forming mitochondrial membranes
E) when a protoeukaryote engaged in a symbiotic relationship with a protocell

Accepted Answer

The endosymbiotic theory proposes that mitochondria originated from the engulfment of free-living proteobacteria by ancestral eukaryotic cells. The proteobacteria were not digested, but instead formed a symbiotic relationship with the host cell, eventually becoming an organelle within it. This theory is supported by evidence such as the presence of a double membrane surrounding mitochondria, the similarity between mitochondrial and bacterial ribosomes, and the fact that mitochondria have their own circular DNA.

Question 20

The evolution of multicellularity in animals required adaptations that promoted
A) cellular migration and intercellular communication.
B) cellular migration and cellular adhesion.
C) cellular adhesion and intercellular communication.
D) photosynthesis and cellular migration.
E) cellular fusion and regeneration.

Accepted Answer

The evolution of multicellularity in animals required adaptations that promoted cellular adhesion and intercellular communication. Cellular adhesion allows cells to stick together and form tissues, while intercellular communication allows cells to coordinate and work together as a larger organism. Cellular migration and fusion are not necessarily required for multicellularity in animals, and photosynthesis is a process that is primarily used by autotrophic organisms.

Quiz 25: The Origin and Diversification of Eukaryotes

Which of these observations gives the most support to the endosymbiotic theory for the origin of eukaryotic cells?

Which of the following was derived from an ancestral cyanobacterium?

Why can eukaryotes be considered "combination" organisms?

The chloroplasts of all of the following are thought to be derived from ancestral red algae, except those of

Which of the following is the most likely sequence of events, from earliest to most recent, in the evolution of sponges (organisms with many cells that have different functions) ? 1) single-celled eukaryote 2) single-celled prokaryote 3) multicellular eukaryote 4) colonial eukaryote

Multicellular colonies of plant cells adhere to each other primarily by , whereas multicellular colonies of animal cells are typically held together by .

Diatoms are mostly asexual members of the phytoplankton. They obtain their nutrition from functional chloroplasts, and each diatom is encased within two porous, glasslike valves. Which question would be most important for one interested in the day-to-day survival of individual diatoms?

The last common ancestor of fungi and animals was most likely a

Which of the following organism pairs is/are an example of secondary endosymbiosis? I. red algae-heterotrophic eukaryote II. green algae-heterotrophic eukaryote III. E. coli bacteria-photosynthetic cyanobacterium IV. Chlamydomonas and Gonium

Which of the following pairs of protists and their characteristics are mismatched?

The evolution of multicellularity in animals has primarily occurred by

All protists are

A large seaweed that floats freely on the surface of deep bodies of water would be expected to lack which of the following?

What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth? 1) origin of mitochondria 2) origin of multicellular eukaryotes 3) origin of chloroplasts 4) origin of cyanobacteria 5) origin of fungal-plant symbioses

Why is the filamentous morphology of the slime molds considered a case of convergent evolution with fungi?

Which of the following statements about dinoflagellates is true?

An individual mixotroph loses its plastids, yet continues to survive. Which of the following most likely accounts for its continued survival?

According to the endosymbiotic theory of the origin of eukaryotic cells, how did mitochondria originate?

The evolution of multicellularity in animals required adaptations that promoted