Bio Tutorial 30 Q/a

Front 1

Review the Protist “Kingdom.” Why is it this “kingdom” difficult to classify?

Back 1

The protist kingdom is difficult to classify because the organisms classified as protists have extraordinarily diverse nutritional modes and probably have arisen from many different ancestral organisms.

Front 2

What types of organisms are Stramenopilans? Describe these organisms. What characteristic do they share that puts them into this taxon?

Back 2

Stramenopilans are organisms within a diverse, yet monophyletic group, that includes planktonic diatoms, whose microscopic glassy shells comprise diatomaceous earth; large multicellular marine seaweeds (brown algae or phaeophytes); and water molds, which include the pathogen responsible for the potato blight that drove millions of people hungry from Ireland in the nineteenth century. Although this group is diverse, they all share a common ancestral trait. Namely, the presence of hair-like projections on their flagella; "stramen" means flagellum in Latin, and "pilos" means hair; hence, stramenopilans.

Front 3

Into what phylum are diatoms classified? How do they acquire energy? What unique structures and characteristics do they have?

Back 3

Diatoms are members of the phylum Bacillariophyta. Diatoms are mostly photosynthetic, but there are also heterotrophic species. Diatoms are encased in a glass-like silica shell, lined with perforations to allow gas exchange at the cell surface. These shells, invisible to the naked eye, are exceptionally beautiful structures. Each one consists of two components that fit together, like the bottom and lid of a pillbox.

Front 4

What is diatomaceous earth? Where is it found and what do humans use it for? What property of diatomaceous earth makes it especially effective?

Back 4

After the death of individual diatoms, their microscopic shells sink and gradually form thick layers of sediment, called diatomaceous earth. Diatomaceous earth, which essentially consists of microscopic fragments of glass, has numerous applications. For example, it is commonly used as a diatomaceous earth pesticide; the sharp edges of diatom shells scrape arthropod exoskeletons and gut linings, causing water loss and eventually death by desiccation. It also damages the tissues of worms and other small creatures, and often is incorporated into animal feed to reduce the occurrence of intestinal parasites. It has myriad other uses (e.g., giving scouring power to cleaning products, and allowing ultra fine filtration for scientific applications and water-purification systems).

Front 5

Why would someone who studies ancient earth’s climate be interested in a soil core of diatomaceous earth?

Back 5

A climatologist (someone who studies climate) can look at the assemblages of diatom species in soil cores taken from diatomaceous earth, where the deepest layers of the sample are the oldest and represent the most distant past. They can date the samples and examine changes in the number of warm-climate diatom species and cool-climate species over time, gaining clues about ancient climatic patterns.

Front 6

Into what phylum are golden algae classified? What unique structures and characteristics do they have, and what pigments are responsible for the name “golden” algae?

Back 6

Golden algae belong to the phylum Chrysophyta. Chrysophytes are planktonic organisms that possess a rich golden color due to the presence of carotenoids and xanthophylls. Most chrysophytes are unicellular, but some species are colonial and quite elaborate in structure.

Front 7

What advantage does the pigmentation of golden algae confer?

Back 7

The accessory pigments of golden algae allow them to expand the range of light wavelengths they can use during photosynthesis.

Front 8

Do all Chrysophytes acquire energy by photosynthesis alone? Are there any other methods by which these organisms acquire energy?

Back 8

Do all Chrysophytes acquire energy by photosynthesis alone? Are there any other methods by which these organisms acquire energy?

Front 9

How do some Chrysophytes enter a state of dormancy?

Back 9

Some Chrysophytes possess silica scales, similar in composition to the shells of diatoms; silica also coats the quiescent cysts that form under unfavorable conditions, allowing chrysophytes to remain dormant for decades.

Front 10

Describe the types of organisms that are included in the Phylum Oomycota. What unique structures and characteristics do they have? Where does the phylum name come from?

Back 10

Phylum Oomycota include the water molds and downy mildews. Some are unicellular, and many others are colonial. Most are heterotrophic decomposers that feed on dead and decaying organic matter in aquatic and terrestrial environments, but a number attack living plants and animals. The name "oomycete" means "egg fungi," which is a reference to the reproductive structures of sexually reproducing oomycetes.

Front 11

Why are oomycetes not classified in the Kingdom Fungi? What similarities do they share that would lead one to consider classifying these organisms as fungus? What separates these organisms from fungus?

Back 11

Although oomycetes are not closely related to fungi, the two groups have some similarities. In particular, both groups are heterotrophs that break down food externally and then absorb nutrients from their surroundings. Additionally, many of the multicellular oomycetes form hyphae, which are very similar to fungal hyphae, although the structures are not identical. There are actually more differences than similarities. The cell walls of oomycetes are composed of cellulose, not chitin, the compound found in the cell walls of fungi. Unlike true fungi, which are haploid in the feeding stage, the hyphae of most oomycetes are composed of diploid cells. Further, the presence of the storage compound mycolaminarin, along with molecular evidence and the presence of flagellated cells similar to those of other stramenopiles, indicate that oomycetes belong within Kingdom Stramenopila.

Front 12

What is convergent evolution? Explain it in terms of fungi and phylum oomycetes and find another example of convergent evolution in other organisms.

Back 12

Convergent evolution is the process by which unrelated organisms that occupy similar environments evolve similar functional traits. Both oomycetes and fungi are decomposers and therefore stand to gain an advantage from maximizing their surface area for the absorption of food; thus, the filamentous growth form might have been favored by independent evolution in both lineages.

Many other examples, for instance:

Placental mammals and marsupial mammals

Cacti in the New World (Americas), and cacti-look alikes in the Old World (i.e. Africa, etc.)

Birds’ wings and flies’ wings.

Front 13

What organisms in the phylum have had devastating impacts on humans? Describe these disasters.

Back 13

Oomycetes have been responsible for a number of catastrophic historical events, including the outbreak of downy mildew that nearly wiped out the French wine industry in the late nineteenth century. Plasmopara, a native of the New World, was inadvertently brought to France from the United States in 1870 in a shipment of American grape root stock. It quickly became a devastating problem.

The oomycete, Phytophthora infestans or potato blight, was responsible for another cataclysmic event, the Great Potato Famine, which killed nearly one million people in Ireland in the late 1800s, and drove one-and-a-half-million more out of the country. Phytophthora secretes enzymes that break down leaf and stem tissue, killing plants very rapidly. Tubers can become infested, turning soft and black, seemingly overnight. Potato fields in Ireland became infested with Phytophthora, which thrived in the cool damp climate of Ireland and wiped out nearly the entire country's crop in one week. In nineteenth-century Ireland, potatoes were the primary food source of the poorest classes, who often grew nothing other than potatoes. The loss of this staple crop led to mass starvation.

Front 14

nto which phylum are brown algae classified? Name some examples of well-known brown algae which are popular or used by humans.

Back 14

Brown algae are members of the Phylum Phaeophyta. Phaeophytes include the largest of the protists, with some growing over 100 feet in length. The giant multicellular species that comprise "kelp forests" in temperate marine waters belong to this group. The edible alga "kombu," which is harvested by the Japanese, is also a phaeophyte. It is particularly rich in minerals, as are other marine algae. Like the chrysophytes, phaeophytes contain specific accessory pigments that give them their characteristic colors.

Front 15

What is meant by “seaweed”? How do the protists discussed thus far fit into this category? What other organisms outside of this “brown algae” phylum are considered to be seaweeds?

Back 15

Although it is not a taxonomic term, the word "seaweed" is a useful way of distinguishing large intertidal algae from other species (e.g., planktonic algae). Organisms within the Phylum Phaeophyta are “seaweeds.” Many types of seaweed, including those within the Phylum Phaeophyta, have complex structures that are reminiscent of plants. Two other kingdoms (Rhodophyta and Chlorophyta) contain organisms which are considered “seaweeds.”

Front 16

hat is kelp? How do they compare to seaweeds? What type of protist are kelp?

Back 16

Kelp” refers to giant seaweeds that grow in the deeper waters outside of the intertidal zone. All kelps, which form vast "forests" that support thriving marine ecosystems, are phaeophytes.

Front 17

Draw an example of a seaweed. Use proper terminology to label the different structures of the seaweed.

Back 17

The thallus refers to the entire body of any seaweed that is plant-like in appearance. The thallus consists of three main parts: a stipe, which is analogous to the stem of plants; a holdfast, which secures the seaweed to a substrate; and leaf-like blades, which provide extensive surface area for photosynthesis, much as leaves do for plants.

Front 18

What is alternation of generations? Using correct terminology, describe a life cycle that undergoes alternation of generations. What types of organisms usually undergo alternation of generations?

Back 18

Alternation of generations refers specifically to the alternation between multicellular haploid life stages and multicellular diploid life stages. The key feature is that both the diploid and haploid stages are multicellular. Diploid forms (i.e., sporophytes) produce haploid spores, which divide and develop directly into multicellular haploid structures (i.e., gametophytes). Gametophytes then produce haploid gametes, which join with other gametes to form diploid sporophytes once again. In other words, the diploid and haploid generations alternate, over and over. In some organisms, the diploid stage is the dominant form that is responsible for the majority of growth and resource acquisition, whereas in others (e.g., fungi) the haploid stage is dominant. Many complex organisms, including some algae, and most fungi, plants and animals, undergo alternation of generations.

Front 19

What is meant by “heteromorphic” alternation of generations?

Back 19

Heteromorphic alternation of generations is a type of alternation of generations in which the haploid and diploid stages exhibit different forms.

Front 20

What are red algae, and to what kingdom do they belong? What major differences separate red algae from other algae? How are red algae phylogenetically related to other algae?

Back 20

Red algae are a type of photosynthetic algae which are members of the Kingdom Rhodophyta. Members of Kingdom Rhodophyta differ from other eukaryotic algae because they do not have flagellated cells at any point in their life cycle. DNA sequence data (and other sources) indicate that this lineage arose independently, sometime before Kingdom Stramenopila.

Front 21

Describe the unique structures and characteristics red algae possess. In what type of environment can red algae live in which few other organisms can survive?

Back 21

Like many of the photosynthetic eukaryotes, rhodophytes are characterized by accessory pigments in their chloroplasts, which endow them with unique colors. In the case of rhodophytes, also called red algae, pigments called phycobilins produce rich shades of pink, scarlet, and red that are so deep that they approach black. These red pigments, in particular the phycobilin phycoerythrin, allow rhodophytes to photosynthesize at depths where only high-energy blue and green light can penetrate. In fact, the color of rhodophyte species tends to be correlated with the depth where they commonly occur; deep-water species are often nearly black, concentrated with phycoerythrin, whereas shallow water species can contain so few accessory pigments that they appear almost green, having few pigments to compete with the green color of chlorophyll.

Front 22

Describe the Kingdom Chlorophyta. What major differences separate the members of this kingdom from other algae? What unique structures and characteristics do they have?

Back 22

Chlorophytes, or green algae, resemble plants more closely than do any of the other photosynthetic protists. Chlorophytes occupy a remarkable array of habitats, including marine, freshwater, and terrestrial environments. A number are seaweeds, most are freshwater algae, and some terrestrial chlorophytes (i.e., lichens) live in a symbiotic association with fungi. The 7,000 species that comprise this kingdom range from unicellular to colonial to truly multicellular. Separate evolutionary events might have led to the evolution from single-celled green algae, to colonial organisms (e.g., the beautiful Volvox), to multinucleate single-celled seaweeds and multicellular seaweeds (e.g., Ulva).

Front 23

Why do some systematists classify green algae with the plants instead of the protists? What is the current accepted view of the phylogenetics of chlorophytes?

Back 23

Some classification systems group members of Kingdom Chlorophyta with plants on the premise that green algae actually resemble plants more closely than they resemble other protists. The chlorophyll of green algae (chlorophyll a and chlorophyll b) is strikingly similar to that of plants. Green algae also resemble plants because they store fixed carbon as starch, and they possess cell walls composed of cellulose. Although the issue is contentious, most systematists continue to classify green algae separately.

Front 24

Describe the diversity in the forms of reproduction used by members of the Kingdom Chlorophyta.

Back 24

Most species within the Kingdom Chlorophyta reproduce both asexually and sexually. Bridges can form between different individuals, allowing the exchange of gametes. Like the brown and red algae, many green algae also display alternation of generations during their sexual cycles, switching between haploid and diploid forms.

Front 25

raw an example of alternation of generations. Be sure to show the ploidy of the different forms. Use any of the species mentioned so far.

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Back 25

raw an example of alternation of generations. Be sure to show the ploidy of the different forms. Use any of the species mentioned so far.

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Front 26

What is meant by “isomorphic” alternation of generations? How is it different from the other forms of alternation of generations discussed earlier?

Back 26

Isomorphic alternation of generations refers to the life cycle of an organism which alternates between haploid and diploid forms that are structurally similar. This is different from heteromorphic alternation of generations, in which the haploid and diploid stages exhibit different forms.