Ch 27: Protists First Group

A(n) __________ is environmentally friendly because it possesses the ability to break down decaying matter and to help recycle nutrients.

A plasmodial slime mold is environmentally friendly because it possesses the ability to break down decaying matter to help recycle nutrients. Like the cellular slime mold, the plasmodial slime mold influences nutrient cycling by feeding on microorganisms.

Which of the following characteristics are common to protists, bacteria, and archaea, as well as many other eukaryote lineages?

A range of habitats is common among protists, bacteria, and archaea, as well as many other eukaryote lineages. Most plants, fungi, and animals are terrestrial, but protists are found in wet soils and aquatic habitats or inside the bodies of other organisms—including humans. Compared to bacteria and archaea, most eukaryotic cells are large, have many more organelles, and have a much more extensive system of structural proteins called the cytoskeleton. Many diverse species of protists are less than 0.2 μm in diameter. These cells overlap in size with bacteria, which typically range from 0.5 μm to 2 μm in diameter. Some protists ingest food as well as performing photosynthesis—meaning that they use a combination of feeding strategies. Many protists have cell walls outside their plasma membrane; others have hard external structures (shells); others have rigid structures inside the plasma membrane. In many cases, these novel structures represent synapomorphies that identify monophyletic groups among protists.

Which mode of locomotion is characteristic of amoebozoa?

Amoebozoa species lack cell walls and take in food by engulfing it. They move via amoeboid motion and produce large, lobe-like pseudopodia. Ciliates may be filter feeders, predators, or parasites. They use cilia to swim and have a mouth area where food is ingested. About half of the dinoflagellates are photosynthetic. They are distinguished by the arrangement of their two flagella, which allows them to swim in a spinning motion: One flagellum projects out from the cell while the other runs around the cell.

Which of the following is an advantage of sexual reproduction?

An advantage of sexual reproduction is that diverse offspring are more likely to survive changing environmental conditions. The evolution of sexual reproduction ranks among the most significant evolutionary innovations observed in eukaryotes. The leading hypothesis to explain why meiosis evolved states that genetically variable offspring may be able to thrive if the environment changes.

Which group belongs to the alveolate lineage?

Apicomplexans belong to the alveolate lineage. Members of the lineage Alveolata comprise three subgroups of single-celled species that are diverse in morphology and nutrition. Ciliates are named for the cilia that cover them. Some 12,000 species are known to live in freshwater, marine, and wet soil environments. Most of the 4,000 known species of dinoflagellates are marine or freshwater plankton. All of the 5,000 known species of apicomplexans are parasitic.

__________ and __________ reproduce asexually by fission.

Bacteria and archaea reproduce asexually by fission. Asexual reproduction is based on mitosis and cell division in eukaryotic organisms and on fission in bacteria and archaea. It results in daughter cells that are genetically identical to the parent.

What subgroup of stramenopiles is the most abundant primary producer in freshwater and saltwater and has glassy cell walls that are used as an ingredient in cosmetics?

Diatoms are considered the most important primary producers in freshwater and saltwater. Their glassy cell walls settle into massive accumulations that are mined and sold as diatomaceous earth, which is used in filtering applications and as an ingredient in polishes, paints, cosmetics, and other products.

Why are dinoflagellate blooms harmful to humans?

Dinoflagellate blooms are harmful to humans because dinoflagellates produce toxins as a defense mechanism. Certain dinoflagellates synthesize toxins to protect themselves from predation by small animals called copepods. Algal blooms can be harmful to people because clams and other shellfish filter photosynthetic protists out of the water as food. During a bloom, high levels of toxins can build up in the flesh of these shellfish, which are then consumed by humans.

The diameter of an average eukaryotic cell is 10 times larger than that of an average bacterial cell. How do eukaryotic cells carry out their cellular processes efficiently?

Eukaryotes divide their volume into compartments, which allows them to carry out their cellular processes efficiently. Biologists hypothesize that the earliest eukaryotes were probably single-celled organisms with mitochondria, a nucleus and endomembrane system, which allowed these cells to divide their volume into subcellular compartments.

Which protist taxon lacks mitochondria and chloroplasts?

Excavata (which include diplomonads) mostly have cells with a pronounced "feeding groove" where prey or organic debris is ingested. Most species lack typical mitochondria, although genes derived from mitochondria are found in the nucleus.

For protists to be considered a monophyletic group, what taxa other than protists would need to be included?

For protists to be considered a monophyletic group, land plants, fungi, and animals would have to be included. The term protist refers to all eukaryotes that are not land plants, fungi, or animals. Protist lineages are colored orange in the figure. Protists do not make up a monophyletic group. Instead, they refer to a paraphyletic group—they represent some, but not all, of the descendants of a single common ancestor. No synapomorphies define the protists. Protists have no trait that is found only in protists and in no other organisms.

What is necessary for symbiosis to occur?

For symbiosis to occur, two organisms must live in regular physical contact with each other. Many protists ingest their food—they eat bacteria, archaea, or even other protists whole. This process is called phagocytosis. Two organisms competing for the same resources is called competition. When one organism must live with another organism to survive, this is an obligate symbiosis. While some symbioses are obligate, others are able to live with or without their symbiont.

Which characteristic distinguishes members of the group Stramenopila from other protists?

Hairy flagella distinguish members of the group Stramenopila from other protists. Stramenopiles are sometimes called heterokonts, which translates as "different hairs." At some stage of their life cycle, all stramenopiles have flagella that are covered with distinctive hollow "hairs." The structure of these flagella is unique to the stramenopiles. Stramenopiles are a large and morphologically diverse group of eukaryotes. They include parasitic, saprophytic, and photosynthetic species, and they range in size from tiny, single-celled members to some of the largest multicellular organisms in the oceans.

In comparing protists, bacteria, and archaea, which method of obtaining energy is unique to protists?

In comparing protists, bacteria, and archaea, the method of obtaining energy unique to protists is ingesting other organisms, such as bacteria, archaea, and other protists. Many protists ingest their food—they eat bacteria, archaea, or even other protists whole. This process is called phagocytosis. When phagocytosis occurs, an individual takes in packets of food much larger than individual molecules. Thus, protists feed by either (1) ingesting packets of food, (2) absorbing organic molecules directly from the environment, or (3) performing photosynthesis.

What statement best defines multicellularity?

In the simplest multicellular species, certain cells are specialized for producing or obtaining food while other cells are specialized for reproduction. The key point about multicellularity is that not all cells in a multicellular organism express the same genes.

Why are protists ecologically important?

Protists are ecologically important because organic molecules produced by protists are the basis of food chains in both freshwater and marine environments. Food chain is a term used to describe nutritional relationships among organisms, and thus how chemical energy flows within ecosystems. In this case, photosynthetic protists and other primary producers are eaten by primary consumers, many of which are protists. Primary consumers are eaten by fish, shellfish, and other secondary consumers, which in turn are eaten by tertiary consumers—whales, squid, and large fish (such as tuna). Many of the species at the base of food chains in aquatic environments are protists. Several lineages of protists have shells made of calcium carbonate (CaCO3). When these shells sink from the ocean surface and settle in layers at the bottom, the deposits that result are compacted by the weight of the water and by sediments accumulating above them. Eventually, the deposits turn into rock.

Which statement accurately describes alternation of generations in protists?

Protists displaying alternation of generations are multicellular in both the haploid and diploid phases of the life cycle. In contrast to the relatively simple life cycles of single-celled protists, many multicellular protists have a multicellular haploid form in one phase of their life cycle alternating with a multicellular diploid form in another phase. This alternation of multicellular haploid and diploid forms is known as alternation of generations.

Which of the following statements about characteristics shared by all protists is correct?

Protists live in wet environments. By definition, protists are a diverse lot. The common feature among protists is that they tend to live in environments where they are surrounded by water most of the time.

The symbiotic α-proteobacteria that took up residence in an early eukaryote had a genome that coded many more proteins than are present in the mitochondrial DNA of living eukaryotes. What happened to the other bacterial genes?

Some genes moved from the mitochondrial genome to the nuclear genome. One intriguing feature of mitochondrial genomes is that they typically encode fewer than 50 genes, whereas the genomes of their bacterial cousins encode about 1,500 genes. Most of the genes from the endosymbiotic bacterium moved into the nuclear genome in what was one of the most spectacular lateral gene transfer events in the history of life. Some unnecessary genes were lost, but many still encode proteins that are synthesized by cytosolic ribosomes and imported into mitochondria.

Why do some scientists believe that increasing populations of protists could help reduce global warming?

Some scientists believe that increasing populations of protists could help reduce global warming because the calcium carbonate shells found in some protist lineages act as a long-term carbon sink. Protists are often tremendously abundant in marine and freshwater plankton and other habitats. Protists provide food for many organisms in aquatic ecosystems and fix so much carbon that they have a large impact on the global carbon budget. Several lineages of protists have shells made of calcium carbonate (CaCO3). When these shells sink from the ocean surface and settle in layers at the bottom, the deposits that result are compacted by the weight of the water and by sediments accumulating above them. Eventually the deposits turn into rock. Releasing carbon dioxide into the ocean would increase global warming if that CO2 were released into the atmosphere. The calcium carbonate (CaCo3) of some protists would have the opposite effect, reducing CO2, a greenhouse gas that contributes to global warming, and thereby slowing global warming.

Which finding about the structure and function of mitochondria provides the best support for the endosymbiotic origin of this organelle?

The best support for the endosymbiotic origin of mitochondria is the finding that mitochondrial gene sequences are more closely related to DNA sequences from bacteria than to eukaryotic gene sequences.

Select the correct description of the earliest eukaryotes.

The earliest eukaryotes had mitochondria but lacked cell walls. Based on the distribution of cell walls in living eukaryotes—some have cell walls and some do not—it is likely that the first eukaryotes lacked this feature. Virtually all bacteria and all archaea are unicellular. Given that most subgroups of the major lineages of eukaryotes are also unicellular, it is logical to conclude that the first eukaryote was a single-celled organism. Further, all eukaryotes alive today have (1) either mitochondria or genes that are normally found in mitochondria, (2) a nucleus and an endomembrane system, and (3) a cytoskeleton.

The filamentous extensions formed by some water molds are called __________.

The filamentous extensions formed by some water mold are called hyphae.

Which statement explains how endosymbiosis has played a role in runners winning marathons, cheetahs sprinting to catch prey, and birds migrating great distances?

Through endosymbiosis, eukaryotes evolved structures that allow them to produce a high yield of ATP. This explains how endosymbiosis has played a role in runners winning marathons, cheetahs sprinting to catch prey, and birds migrating great distances. The relationship between the archaeal host and the engulfed bacterial cell was presumed to be stable because a mutual advantage existed between them: The host cell supplied the bacterium with protection and carbon compounds, while the bacterium supplied the host cell with ATP.

According to the endosymbiotic theory, mitochondria are believed to have initially been free-living bacteria which were engulfed by other bacteria. The majority of mitochondrial genes are believed to have been transferred into the nuclear DNA of eukaryotic cells by the process of __________.

lateral gene transfer Lateral gene transfer is the physical transfer of a gene or genes from one species to another.