Chapter Capsule

A. Major organelles and other structural features include: Appendages (cilia, flagella), glycocalyx, cell wall, cytoplasmic (or cell) membrane, ribosomes, organelles (nucleus, nucleolus, endoplasmic reticulum, Golgi complex, mitochondria, chloroplasts, cytoskeleton, microfilaments, microtubules). A review comparing the major differences between eucaryotic and procaryotic cells is provided in table 2.6, page 52.

A. Overall Morphology: At the cellular (microscopic) level, typical eucaryotic cell, with thick cell walls. Yeasts are single cells that form buds and pseudohyphae. Hyphae are long, tubular filaments that can be septate or nonseptate and grow in a network called a mycelium; hyphae are characteristic of the filamentous fungi called molds. Some fungi (mushrooms) produce multicellular structures such as fleshy fruiting bodies. Fungal cells are largely nonmotile, except for some motile gametes.

B. Nutritional Mode/Distribution: All are heterotrophic. The majority are harmless saprobes living off organic substrates such as dead animal and plant tissues. A few are parasites, living on the tissues of other organisms, but none are obligate. Preferred temperature of growth is 20°–40°C. Distribution is extremely widespread in many habitats.

C. Reproduction: Primarily through spores formed on special reproductive hyphae. In asexual reproduction, spores are formed through budding, partitioning of a hypha, or in special sporogenous structures; examples are conidia and sporangiospores. In sexual reproduction, spores are formed following fusion of male and female strains and the formation of a sexual structure; sexual spores are one basis for classification.

D. Major Groups: The four main divisions among the terrestrial fungi, given with sexual spore type, are Zygomycota (zygospores), Ascomycota (ascospores), Basidiomycota (basidiospores), and Deuteromycota (no sexual spores).

E. Importance: Essential decomposers of plant and animal detritis in the environment with return of valuable nutrients to the ecosystem. Economically beneficial as sources of antibiotics; used in making foods and in genetic studies. Adverse impact: decomposition of fruits and vegetables; several fungi cause infections, or mycoses; some produce substances that are toxic if eaten.

A. The Algae

Include plantlike protists, kelps, and seaweeds. Specific groups are the euglenids, green algae, diatoms, dinoflagellates, brown algae, and red seaweeds.

1. Overall Morphology: Contain chloroplasts with chlorophyll and other pigments; cell wall; may or may not have flagella. Microscopic forms are unicellular, colonial, filamentous; macroscopic forms are colonial and multicellular.

2. Nutritional Mode/Distribution: Photosynthetic; most are free-living in the aquatic environment, both fresh water and marine (common component of plankton).

3. Major Groups: Classification according to types of pigments and cell walls. Microscopic algae: Euglenophyta, Chlorophyta, Chrysophyta, Pyrrophyta: Macroscopic algae: Phaephyta (kelps) and Rhodophyta (seaweeds) are multicellular algae.

4. Importance: Algae provide the basis of the food web in most aquatic habitats, and they produce a large proportion of atmospheric O₂ through photosynthesis. Some are harvested as a source of cosmetics, food, and medical products. Dinoflagellates cause red tides and give off toxins that are harmful to humans and animals.

B. The Protozoa

Include animal-like protists; unicellular animals such as amebas, flagellates, ciliates, sporozoa.

1. Overall Morphology: Most are unicellular, colonies rare, no multicellular forms; most have locomotor structures, such as flagella, cilia, pseudopods; special feeding structures can be present; lack a cell wall; extreme variations in shape. Can exist in trophozoite, a motile, feeding stage, or cyst, a dormant resistant stage.

2. Nutritional Mode/Distribution: All are heterotrophic. Most are free-living in a moist habitat (water, soil); feed by engulfing other microorganisms and organic matter. A number of animal parasites; can be spread from host to host by insect vectors.

3. Reproduction: Asexual by binary fission and mitosis, budding; sexual by fusion of free-swimming gametes, conjugation.

4. Major Groups: Protozoa are subdivided into four groups based upon mode of locomotion and type of reproduction: Mastigophora, the flagellates, motile by flagella; Sarcodina, the amebas, motile by pseudopods; Ciliophora, the ciliates, motile by cilia; Apicomplexa, all parasites; motility not well developed; produce unique reproductive structures.

5. Importance: Ecologically important in food webs and decomposing organic matter. Medical significance: hundreds of millions of people are afflicted with one of the many protozoan infections (malaria, trypanosomiasis, amebiasis).

A. Overall Morphology: Animal cells; multicellular; individual organs specialized for reproduction, digestion, movement, protection, though some of these are reduced.

B. Nutritional/Reproductive Mode: Parasitize host tissues; have mouthparts for attachment to or digestion of host tissues. Most have well-developed sex organs that produce eggs and sperm. Fertilized eggs go through larval period in or out of host body.

C. Major Groups:

1. Flatworms have highly flattened body; no definite body cavity; digestive tract a blind pouch; simple excretory and nervous systems. Cestodes (tapeworms) are long chains of segments; attach to host’s intestine by hooked mouthpart. Trematodes, or flukes, are flattened, nonsegmented worms with sucking mouthparts.

2. Roundworms (nematodes) have round bodies, a complete digestive tract, a protective surface cuticle, spines and hooks on mouth; excretory and nervous systems poorly developed.

D. How Transmitted and Acquired: Through ingestion of larvae or eggs in food; from soil or water; some are carried by insect vectors.

E. Importance: Afflict billions of humans. Because these worms are so common, they have medical and economic impact of staggering proportions.