Chapter 23

Describe the hypothesized steps in the origin of eukaryotic cells.

Eukaryotic cells arose through endosymbiotic events that gave rise to the energy-producing organelles within the eukaryotic cells such as mitochondria and chloroplasts. The nuclear genome of eukaryotes is related most closely to the Archaea, so it may have been an early archaean that engulfed a bacterial cell that evolved into a mitochondrion. Mitochondria appear to have originated from an alpha-proteobacterium, whereas chloroplasts originated as a cyanobacterium. There is also evidence of secondary endosymbiotic events. Other cell components may also have resulted from endosymbiotic events.

Plasmodium Species

Members of the genus Plasmodium must colonize both a mosquito and a vertebrate to complete their life cycle.

Bioluminescence

generation and emission of light by an organism, as in dinoflagellates

Kinetoplast

mass of DNA carried within the single, oversized mitochondrion, characteristic of kinetoplastids (phylum: Euglenozoa)

Mitosomes

nonfunctional organelle carried in the cells of diplomonads (Excavata) that likely evolved from a mitochondrion

Mitochondria

o Eukaryotic cells may contain anywhere from one to several thousand mitochondria, depending on the cell's level of energy consumption. o Several lines of evidence support that mitochondria are derived from this endosymbiotic event. Most mitochondria are shaped like alpha-proteobacteria and are surrounded by two membranes. o

Metabolism

o Protists that store energy by photosynthesis belong to a group of photoautotrophs and are characterized by the presence of chloroplasts. o Other protists are heterotrophic and consume organic materials (such as other organisms) to obtain nutrition. o Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis, in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole o Subtypes of heterotrophs, called saprobes, absorb nutrients from dead organisms or their organic wastes o some mixotrophs

Which parasitic protist evades the host immune system by altering its surface proteins with each generation? a. Paramecium caudatum b. Trypanosoma brucei c. Plasmodium falciparum d. Phytophthora infestans

Trypanosoma brucei

Human Pathogens

A significant number of protists are pathogenic parasites that must infect other organisms to survive and propagate.

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

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

Giardia lamblia is a cyst-forming protist parasite that causes diarrhea if ingested. Given this information, against what type(s) of environments might G. lamblia cysts be particularly resistant?

As an intestinal parasite, Giardia cysts would be exposed to low pH in the stomach acids of its host. To survive this environment and reach the intestine, the cysts would have to be resistant to acidic conditions.

Protists with the capabilities to perform photosynthesis and to absorb nutrients from dead organisms are called ______________. a. photoautotrophs b. mixotrophs c. saprobes d. heterotrophs

B. mixotrophs

Why might a light-sensing eyespot be ineffective for an obligate saprobe? Suggest an alternative organ for a saprobic protist.

By definition, an obligate saprobe lacks the ability to perform photosynthesis, so it cannot directly obtain nutrition by searching for light. Instead, a chemotactic mechanism that senses the odors released during decay might be a more effective sensing organ for a saprobe.

Motility

Cilia, flagella, pseudopod

Diplomonads

Have mitosomes, exist in anaerobic environments and use alternative pathways, such as glycolysis, to generate energy. Each diplomonad cell has two identical nuclei and uses several flagella for locomotion.

Cell Structure

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. Protist cells may be enveloped by animal-like cell membranes or plant-like cell walls. Others are encased in pellicles

Life Cycle

Most undergo some form of asexual reproduction, such as binary fission, to produce two daughter cells. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary

Habitats

Nearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow. Several protist species are parasites that infect animals or plants. A few protist species live on dead organisms or their wastes, and contribute to their decay.

How does killing Anopheles mosquitoes affect the Plasmodium protists?

Plasmodium parasites infect humans and cause malaria. However, they must complete part of their life cycle within Anopheles mosquitoes, and they can only infect humans via the bite wound of a mosquito. If the mosquito population is decreased, then fewer Plasmodium would be able to develop and infect humans, thereby reducing the incidence of human infections with this parasite.

Plant Parasites

Protist parasites of terrestrial plants include agents that destroy food crops.

Primary Producers/Food Sources

Protists are essential sources of nutrition for many other organisms. As primary producers, protists feed a large proportion of the world's aquatic species. Approximately one-quarter of the world's photosynthesis is conducted by protists, particularly dinoflagellates, diatoms, and multicellular algae. Certain anaerobic parabasalid species exist in the digestive tracts of termites and wood-eating cockroaches, where they contribute an essential step in the digestion of cellulose ingested by these insects as they bore through wood.

Explain in your own words why sexual reproduction can be useful if a protist's environment changes.

The ability to perform sexual reproduction allows protists to recombine their genes and produce new variations of progeny that may be better suited to the new environment. In contrast, asexual reproduction generates progeny that are clones of the parent.

Alveolates

The alveolates are named for the presence of an alveolus, or membrane-enclosed sac, beneath the cell membrane. he alveolates are further categorized into some of the better-known protists: the dinoflagellates, the apicomplexans, and the ciliates.

Agents of Decomposition

The fungus-like protist saprobes are specialized to absorb nutrients from nonliving organic matter, such as dead organisms or their wastes. Many types of oomycetes grow on dead animals or algae. Saprobic protists have the essential function of returning inorganic nutrients to the soil and water. This process allows for new plant growth, which in turn generates sustenance for other organisms along the food chain.

Without treatment, why does African sleeping sickness invariably lead to death?

The trypanosomes that cause this disease are capable of expressing a glycoprotein coat with a different molecular structure with each generation. Because the immune system must respond to specific antigens to raise a meaningful defense, the changing nature of trypanosome antigens prevents the immune system from ever clearing this infection. Massive trypanosome infection eventually leads to host organ failure and death.

The chlorophyte (green algae) genera Ulva and Caulerpa both have macroscopic leaf-like and stem-like structures, but only Ulva species are considered truly multicellular. Explain why.

Unlike Ulva, protists in the genus Caulerpa actually are large, multinucleate, single cells. Because these organisms undergo mitosis without cytokinesis and lack cytoplasmic divisions, they cannot be considered truly multicellular.

Ciliates

a group of protists 10 to 3,000 micrometers in length that are covered in rows, tufts, or spirals of tiny cilia. Vacuole based digestion.

What is the function of the raphe in diatoms? a. locomotion b. defense c. capturing food d. photosynthesis

a. locomotion

Forams

are unicellular heterotrophic protists, ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails. Have tests... house photosynthetic algae.

Which of these locomotor organs would likely be the shortest? a. a flagellum b. a cilium c. an extended pseudopod d. a pellicle

b. a cilium

Conjugation between two Paramecia produces ________ total daughter cells. a. 2 b. 4 c. 8 d. 16

c. 8

Alternation of generations describes which of the following? a. The haploid form can be multicellular; the diploid form is unicellular. b. The haploid form is unicellular; the diploid form can be multicellular. c. Both the haploid and diploid forms can be multicellular. d. Neither the haploid nor the diploid forms can be multicellular.

c. Both the haploid and diploid forms can be multicellular.

Which characteristic is shared by prokaryotes and eukaryotes? a. cytoskeleton b. nuclear envelope c. DNA-based genome d. mitochondria

c. DNA-based genome

Mitochondria most likely evolved by _____________. a. a photosynthetic cyanobacterium b. cytoskeletal elements c. endosymbiosis d. membrane proliferation

c. Endosymbiosis

Which protist group exhibits mitochondrial remnants with reduced functionality? a. slime molds b. diatoms c. parabasalids d. dinoflagellates

c. parabasalids

Protists that have a pellicle are surrounded by ______________. a. silica dioxide b. calcium carbonate c. carbohydrates d. proteins

d. proteins

Phagolysosome

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

What genus of protists appears to contradict the statement that unicellularity restricts cell size? a. Dictyostelium b. Ulva c. Plasmodium d. Caulerpa

d. Caulerpa

Which of these protists is believed to have evolved following a secondary endosymbiosis? a. green algae b. cyanobacteria c. red algae d. chlorarachniophytes

d. chlorarachniophytes

What event is thought to have contributed to the evolution of eukaryotes? a. global warming b. glaciation c. volcanic activity d. oxygenation of the atmosphere

d. oxygenation of the atmosphere

Chromalveolata

derived from a common ancestor that engulfed a photosynthetic red algal cell, which itself had already evolved chloroplasts from an endosymbiotic relationship with a photosynthetic prokaryote ( a hypothesis-based working group that is subject to change). The chromalveolates can be subdivided into alveolates and stramenopiles.

Plankton

diverse group of mostly microscopic organisms that drift in marine and freshwater systems and serve as a food source for larger aquatic organisms

Endosymbiosis

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

Dinoflagellates

exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic.These protists exist in freshwater and marine habitats, and are a component of plankton. Some dinoflagellates are bioluminescent.

Radiolarians

exhibit intricate exteriors of glassy silica with radial or bilateral symmetry (Figure). Needle-like pseudopods supported by microtubules radiate outward from the cell bodies of these protists and function to catch food particles.

Parabasalids

exhibits semi-functional mitochondria, these structures function anaerobically and are called hydrogenosomes.

Rhizaria

includes many of the amoebas, most of which have threadlike or needle-like pseudopodia

Euglenozoans

includes parasites, heterotrophs, autotrophs, and mixotrophs, ranging in size from 10 to 500 µm. Move through their aquatic habitats using two long flagella that guide them toward light sources sensed by a primitive ocular organ called an eyespot.

Stramenopiles

includes photosynthetic marine algae and heterotrophic protists. The unifying feature of this group is the presence of a textured, or "hairy," flagellum. Diatoms, Brown Algae, Golden Algae and Oomycetes

Cytoplasmic streaming

movement of cytoplasm into an extended pseudopod such that the entire cell is transported to the site of the pseudopod hydrogenosome. Means of locomotion for many Rhizaria.

Characteristics of Eukaryotes

oCells with nuclei surrounded by a nuclear envelope with nuclear pores. This is the single characteristic that is both necessary and sufficient to define an organism as a eukaryote. All extant eukaryotes have cells with nuclei. o Mitochondria o Cytoskeleton oFlagella and cilia oChromosomes oMitosis oSexual reproduction o cell walls

Plastid

one of a group of related organelles in plant cells that are involved in the storage of starches, fats, proteins, and pigments. Have endosymbiotic origins... maybe.

Hydrogenosomes

organelle carried by parabasalids (Excavata) that functions anaerobically and outputs hydrogen gas as a byproduct; likely evolved from mitochondria

Mixotrophs

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

Pellicles

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.

An example of carbon fixation is _____________. a. photosynthesis b. decomposition c. phagocytosis d. parasitism

photosynthesis

Tests

porous shell of a foram that is built from various organic materials and typically hardened with calcium carbonate

Biological carbon pump

process by which inorganic carbon is fixed by photosynthetic species that then die and fall to the sea floor where they cannot be reached by saprobes and their carbon dioxide consumption cannot be returned to the atmosphere as carbon dioxide

Raphe

slit in the silica shell of diatoms through which the protist secretes a stream of mucopolysaccharides for locomotion and attachment to substrates

Excavata

symmetrical, single-celled organisms with a feeding groove "excavated" from one side. This supergroup includes heterotrophic predators, photosynthetic species, and parasites. Its subgroups are the diplomonads, parabasalids, and euglenozoans.

Trypanosome

the parasite that is responsible for African sleeping sickness, confounds the human immune system by changing its thick layer of surface glycoproteins with each infectious cycle

Apicomplexans

their microtubules, fibrin, and vacuoles are asymmetrically distributed at one end of the cell in a structure called an apical complex.The apical complex is specialized for entry and infection of host cells. Indeed, all apicomplexans are parasitic.

Endosymbiotic theory

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

Contractile vacuoles

vesicle that fills with water (as it enters the cell by osmosis) and then contracts to squeeze water from the cell; an osmoregulatory vesicle