Microbe Diversity

Question 1

Viruses – a borrowed life

Answer 1

Viruses are not cells
Viruses are very small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope
Viruses called bacteriophages can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli
Viruses lead “a kind of borrowed life” between life-forms and chemicals

Question 2

Viruses reproduce only in host cells

Answer 2

Viruses are obligate intracellular parasites, i.e. they can reproduce only within a host cell
Each virus has a host range, a limited number of host cells that it can infect

Question 3

Virus reproduction

Answer 3

Once a viral genome has entered a cell, the cell begins to manufacture viral proteins*
The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules
*Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses

Question 4

Viruses as pathogens

Answer 4

Diseases caused by viral infections affect humans, agricultural crops, and livestock worldwide
Viruses may damage or kill cells by causing the release of hydrolytic enzymes from lysosomes
Some viruses cause infected cells to produce toxins that lead to disease symptomsOthers have envelope proteins that are toxic

Question 5

Vaccines

Answer 5

Vaccines are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen

Question 6

Viroids

Answer 6

circular RNA molecules that infect plants and disrupt their growth

Question 7

Prions

Answer 7

slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals
Prions propagate by converting normal proteins into the prion version

Question 8

Prokaryote structure

Answer 8

Most prokaryotes are unicellular, although some species form coloniesMost prokaryotic cells are 0.5–5 μm, much smaller than the 10–100 μm of many eukaryotic cells [1 mm = 1000 μm]
*Prokaryotic cells have a variety of shapes
*The three most common shapes are spheres (cocci), rods (bacilli), and spirals
*Prokaryotes = bacteria and archaea
*Archaea share certain traits with bacteria and other traits with eukaryotes

Question 9

Prokaryotic cell wall

Answer 9

maintains cell shape, provides physical protection, and prevents the cell from bursting

Question 10

Eukaryote cell wall

Answer 10

made of cellulose or chitin

Question 11

Bacterial cell wall

Answer 11

contain peptidoglycan, a network of sugar polymers cross-linked by polypeptide

Question 12

Archaea contain

Answer 12

polysaccharides and proteins but lack peptidoglycan*Using

Question 13

Using the Gram stain

Answer 13

bacterial species classified into Gram-positiveand Gram-negative groups based on cell wall composition

Question 14

Gram-negative bacteria

Answer 14

have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant

Question 15

Fungi

Answer 15

*Fungi are diverse and widespread
*Fungi are heterotrophs but do not ingest their food
*They secrete exoenzymes that break down complex molecules, and then they absorb the smaller compounds
*Can be decomposers, parasites, mutualistic symbiont

Question 16

Fungi origin

Answer 16

*Fungi and Animalia as sister kingdoms
*Molecular evidence that fungi and animals diverged from a common unicellular, flagellated ancestor
*Fungi probably evolved before the colonization of land by multicellular organisms
Undisputed fossils of fungi dated 460 million years oldFungi were among the earliest colonizers of land, probably as symbionts with early land plants

Question 17

Fungi structure

Answer 17

*The morphology of multicellular fungi enhances their ability to absorb nutrients
*Fungi consist of mycelia, networks of branched hyphae, adapted for absorption
Most fungi have cell walls made of chitinSeptate fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement
*Coenocytic fungi lack septaSeptate hyphaCoenocytic hypha

Question 18

Fungi life cycle

Answer 18

Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually
*In sexual reproduction, two parent mycelia unite (plasmogamy); the haploid nuclei from each parent do not fuse right away, they coexist in the mycelium (heterokaryon); after hours, days, or even centuries the haploid nuclear fuse (karyogamy) producing diploid cells; the diploid phase is short-lived and undergoes meiosis, producing haploid spores

Question 19

Asexual fungi

Answer 19

*Asexual reproduction occurs where spores are produced by haploid mycelia
*Instead of producing spores, yeasts reproduce asexually by simple cell division

Question 20

Chytrids

Answer 20

saprobic or parasitic
*diverged earliest in fungal evolution
*unique among fungi in having flagellated spores, called zoosporesChytrids

Question 21

Zygomycetes

Answer 21

Heterokaryotic phase a zygosporangium*E.g. bread moldZygomycetes

Question 22

Ascomycetes

Answer 22

*defined by the production of sexual spores in saclike asci, usually contained in fruiting bodies called ascocarps
*includes yeast, Penicillium

Question 23

Basidiomycetes

Answer 23

*Mushrooms, shelf fungi
*Club-like structure (basidium), a transient diploid stage in the life cycle
The numerous basidia in a basidiocarp are sources of sexual spores called basidiosporesAsexual reproduction is much less common

Question 24

Fungi in ecosystems and human welfare

Answer 24

Fungi are efficient decomposers; recycling of chemical elements between the living and nonliving worldFungi form symbiotic relationships with plants, algae, and animals
*Mycorrhizae are enormously important in natural ecosystems and agriculture
*About 30% of known fungal species are parasites, mostly on or in plants; animals are much less susceptible to parasitic fungi than are plants
*Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread; antibiotics produced by fungi treat bacterial infections

Question 25

Fungi as symbionts

Answer 25

*Lichens are a symbiotic association of millions of photosynthetic microbes (algae or bacteria) held in a mass of fungal hyphae

Question 26

Fungi – animal symbiosis

Answer 26

*Some fungi share their digestive services with animals
*Help break down plant material in the guts of cows and other grazing mammals
*Many species of ants and termites use the digestive power of fungi by raising them in “farms

Question 27

Protists

Answer 27

*Protists are more diverse than all other eukaryotes and are no longer classified in a single kingdom (polyphyletic)
*Most protists are unicellular, but there are some colonial and multicellular species
*Protists are also diverse in habitat, including freshwater and marine species

Question 28

Protists, the most nutritionally diverse of all eukaryotes, include

Answer 28

Photoautotrophs, which contain chloroplasts
Heterotrophs, which absorb organic molecules or ingest larger food particles
Mixotrophs, which combine photosynthesis and heterotrophic nutrition

Question 29

Algae

Answer 29

*Aquatic origin, appeared between 2-1 billion years before present; diverse lineages (aquatic)
*Evolved from endosymbiotic engulfing of cyanobacterium by eukaryotic cell
*Single origin of red algae, green algae & land plants
*Multiple secondary endosymbiosis lead to diverse brown algae lineages

Question 30

Alveolata

Answer 30

*have small membrane–bound cavities (alveoli) under cell surface; Each has a characteristic shape that in many species is reinforced by internal plates of cellulose
*2 flagella make them spin as they move through the water
*c. 3000 species in fresh & salt water; aquatic photoautotrophs and heterotrophs; may be symbiotic with other organisms e.g. in corals
*periodic death causes algal blooms (carotenoids give reddish colour)

Question 31

Apicomplexans (alveolata)

Answer 31

are parasites of animals, and some cause serious human diseases (e.g. Plasmodium - malaria)
They have a nonphotosynthetic plastid, the apicoplast
*Most have sexual and asexual stages that require two or more different host species for completionCiliatesa large varied group of protistsare named for their use of cilia to move and feed

Question 32

Stramenopila

Answer 32

The clade includes several groups of heterotrophs (e.g. water molds) as well as certain groups of algae (e.g. diatoms, brown algae)
*Most have a “hairy” flagellum paired with a “smooth” flagellumPhytophthora infestans (water mold)

Question 33

Stramenopila (diatoms)

Answer 33

*100,000 species in fresh & marine waters; major component of phytoplankton
*Unicellular; cell walls made of 2 elaborately sculptured silicon; lack flagella (except reproductive cells of centric diatoms)
*Fossilized diatoms mined

Question 34

Stramenopila: brown algae (phaeophytes

Answer 34

*Multicellular; marine, common in cool temperate waters (sea weeds, e.g. kelp)
*have the most complex anatomy, including specialized tissue similar to plants (holdfast, stipe, blades)
*Cell wall contains gel-forming polysaccharide to cushion from waves & reduce drying
Reproductive cells have 2 flagella; alternation of generations, sporophyte & gametophytes alike or notchlorophyl a, c & carotenoid; food storage reserved as a glucose polymer
*Many seaweeds are important commodities; are harvested for food

Question 35

Rhodophyta: red algae

Answer 35

*6000 species, abundant in warm tropical waters
*Have chlorophyll a plus accessory (phycobilins, giving colour); some lack pigment and are parasitic
*Mostly multicellular; filamentous, branched or interwoven
Diverse life cycles, no flagellated stagesEg. Gigartina

Question 36

Chlorophyta (green algae

Answer 36

*Origin 1000 million year before present (MYBP)
*Closest to land plants (included in viridophytes): evidence from DNA sequence data, structural features (e.g. transfer of genes from chloroplast to nucleus, cellulose in cell wall)
*Have chlorophyll a, b; lost phycobilins (found in red algae, cyanobacteria)

Question 37

Chlorophyta (green algae) cont

Answer 37

*Store of carbohydrates in form of starch granules
*Unicellular (free or symbiotic in lichens), aggregate colonies (Volvox), filamentous (Spirogyra) or multicelluar (Ulva)
*Alternation of generations (isomorphic generations in Ulva)

Question 38

Transition to land - challenges

Answer 38

*Desiccation
*UV light damage radiation
*Gaseous exchange
*CO2 fixation
*Support

Question 39

Nurturing of an embryo – a key innovation

Answer 39

*in embryophytes, some Charophytes
*Delayed meiosis and interpolation of a multicellular diploid phase via mitotic divisions of the zygote
*In embryophytes, the fertilized egg (embryo) is protected in a multicellular structure (archegonium)Nurturing of the embryo – a key innovation

Question 40

Four key traits appear in nearly all land plants but are absent in the charophytes:

Answer 40

–Alternation of generations (with multicellular, dependent embryos)
–Walled spores produced in sporangia
–Multicellular gametangia
–Apical meristems

Question 41

Alternation of Generations and Multicellular, Dependent Embryos

Answer 41

*Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations
*The gametophyte is haploid and produces haploid gametes by mitosis
*Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis
*The diploid embryo is retained within the tissue of the female gametophyte
*Nutrients are transferred from parent to embryo through placental transfer cells
*Land plants are called embryophytes because of the dependency of the embryo on the parent
Fig

Question 42

Walled Spores Produced in Sporangia

Answer 42

*The sporophyte produces spores in organs called sporangia
*Diploid cells called sporocytes undergo meiosis to generate haploid spores
*Spore walls contain sporopollenin, which makes them resistant to harsh environments

Question 43

Multicellular Gametangia

Answer 43

*Gametes are produced within organs called gametangia
*Female gametangia, called archegonia,produce eggs and are the site of fertilization
*Male gametangia, called antheridia, are the site of sperm production and release

Question 44

Apical Meristems

Answer 44

*Plants sustain continual growth in their apical meristems
*Cells from the apical meristems differentiate into various tissues