Chapter 12 Key Concepts

Define haustoria

A specialized hyphae unique to parasitic fungi that protrude into host cells to gain nutrients.

Explain how various types of algae differ from one another and from other members of the eukaryotic microbial world

Algae differ from other eukaryotic photosynthetic organisms because they lack an organized vascular system and have simple reproductive structures. The various types of algae share some fundamental characteristics, but they are not necessarily related. Different types are often characterized by the pigments they contain. All algae contain chlorophyll a, but different types also contain other pigments that absorb different wavelengths of light.

Compare and contrast the two types of slime molds with one another and with water molds.

All are types of protists. Cellular slime molds: Exist in their vegetative form as uninucleate ameboid cells. Live out most of their lives as unicellular protists. Cluster in response to chemical signals forming a mass called a 'slug'. Model eukaryotic organism is Dictyostelium discoideum. Plasmodial slime molds: Enclosed within a single membrane without walls, forming one large cell. Following germination of haploid spores, the cells fuse to form a diploid cell in which the nucleus divides repeatedly to form a multinucleated stage called a plasmodium. Water molds/oomycetes: Form masses of white threads on decaying material. Like fungi, they secrete digestive enzymes onto a substrate and absorb small molecules for nutrients, but have cellulose in cell wall rather than chitin. Can cause serious diseases of food crops, such as late blight of potato and mildew of grapes.

Explain what arthropods are and how they are related to disease in humans.

Animals that include insects and arachnids. Main role in disease is to serve as vectors that can transmit microorganisms and viruses to humans. Two kinds of vectors: mechanical--simply transfers a pathogen from one surface to another, or biological--plays an essential role in the life cycle of the pathogen. Ex: species of Plasmodium that cause malaria multiply within a mosquito during their life cycle, and species of Anopheles that cause African sleeping sickness multiple within tsetse flies. Some arthropods can directly cause disease even when they don't act as a vector. For example, the louse Phthirus pubis is transmitted during sexual intercourse and causes crabs. Dust mites can cause allergies, trigger asthma, and cause severe itching. Scabies is caused by another mite.

Describe 6 groups of protozoa that cause disease, and name an example of each

Apicomplexans are parasites with a structure called an apical complex at one end that help them penetrate the cell membrane of host cells. Ex: plasmodium species, causes malaria. Diplomonads lack mitochondria. They have two nuclei and live within hosts where conditions are anaerobic / low O2. Ex: Giardia lamblia, causes diarrhea. Reproduce asexually. Parabasalids also lack mitochondria. They live within the host organism. Have a structure called the hydrogenosome, which produces some ATP. Most reproduce asexually. Example: Trichomonas vaginalis, may cause disease. Kinetoplastids have at least one flagellum and are characterized by a distinctive mass of DNA in their large single mitochondrion. May be a useful target for medication. Example: Trypanosoma brucei, causes African sleeping sickness. T cruzi, causes Chagas, Leishmania, which causes leishmaniasis. Loboseans have a flexible/amoebic body form. They change shape as they move by extending and retracting pseudopodia and engulfing food via phagocytosis. Ex: Entamoeba histolytica causes diarrhea Heteroloboseans also have a flexible/amoebic body form, but are only distantly related to loboseans. They are ameobi during part of their life cycle, but also form flagellated cells. Ex: Naegleria fowleri eats the brain of its host.

Describe the four major fungal groups

Ascomycetes: 75% of all fungi. Includes baker's yeast, penicillium, truffles. Unicellular and multicellular. Multicellular forms have septate hyphae--means that septa walls separate the cells. Basidiomycetes: Mushrooms are often collected and grown for food. Groups also include some plant parasites--rust and smuts. Zygomycetes: Includes common black bread mold (rhizopus) and other organisms that often spoil fruits and vegetables. Black growth is composed of reproductive structures called sporangia that house sporangiospores. Chytrids: Usually live in water, some live in the guts of mammalian herbivores. Some are parasitic. Only type of fungus with motile forms--reproductive cells have flagella.

Describe the major diseases of humans that are caused by protozoa and name the causative agents and group name.

Disease: Genus (rRNA classification/group) Malaria: Plasmodium (Apicomplexan) Toxoplasmosis: Toxoplasma (Apicomplexan) Cryptosporidiosis: Cryptosporidium (Apicomplexan) Cyclosporiasis: Cylcospora (Apicomplexan) Giardiasis: Giardia (Diplomonad) Trichomoniasis: Trichomonas (Parabasalid) Amebiasis: Entamoeba (Lobosean) Primary amebic meningoencephalitis: Naegleria (Heterolobosean) African sleeping sickness: Trypanosoma (Kinetoplastid)

Name and describe the roles of economically and medically important fungi.

Economic importance: S. cerevisiae is used in the production of wine, beer, and bread. Fungi also cost money--Ophiostoma ulmi caused dutch elm disease that killed all elm streets in many US cities, requiring the trees to be removed. Medical importance: Fungi can both cause, and be used to treat, health issues. Some synthesize important antimicrobial medicines (Penicillium synthesizes penicillin). Can also be genetically modified to produce insulin and vaccines. Causes allergies, infection, and intoxication/poison. Aspergillus species produces aflatoxins, which are carcinogenic. Claviceps purpurea produces toxins that cause hallucinations.

Give an example of a disease related to flies, mosquitoes, fleas, lice, ticks, and mites.

Fly: Onchocerciasis (river blindness), African sleeping sickness Mosquito: malaria Fleas: plague Lice: Typhus Ticks: rocky mountain spotted fever, lyme disease Mites: crabs, scabies

Describe helminths and name their classifications/groupings

Helminths are worms, a type of animal. Some are parasitic. The microscopic eggs of helminth species are distinctive and can be identified by appearance. Helminths are divided into 2 groups: roundworms (nematodes) and flatworms. Flatworms are further divided into tapeworms (cestodes) and flukes (trematodes).

Explain how disease-causing helminths can be transmitted to humans. Provide example helminth for each method of transmission.

Helminths enter the body in a number of ways. They can burrow through human skin (ex: hookworms, a type of roundworm/nematode), be accidentally eaten (ex: Trichinella and Pinworm, types of roundworms/nematodes), or be transmitted through insect bites (ex: Filaria, a type of roundworm/nematode)

Describe the structure of protozoa.

Lack the rigid cell wall found in algae or the chitinous cell wall found in fungi. The exception is members of the group foraminifera secrete a hard shell of calcium carbonate. Most have a specific shape determined by the material beneath the cytoplasmic membrane. Many have cilia, flagella, or pseudopodia.

Explain the important symbiotic relationships of fungi, including lichens, mycorrhizas, and relationships with insects

Lichens: symbiotic life forms that result from the association of a fungus with a photosynthetic organism, such as algae. Found in terrestrial habitats all over the world. Fungal part absorbs water and minerals and provides protection. Photosynthetic part supplies fungus with organic nutrients. Mycorrhizas: mutually beneficial association between a fungus and a plant root. High surface area of fungi increases a plant's ability to absorb water and minerals. Fungus also supplies plant with nitrogen and phosphorus from the soil. The plant supplies fungus with organic compounds. Some insects: leaf cutter ants farm their own fungal gardens. Ants cannot eat tropical vegetation, so they chop plant leaves into bits and then add mycelium (visible mass of hyphae/mold). The fungi grow, secreting enzymes that digest the plant material.

Describe the habitats of protozoa.

Majority are free-living aquatic organisms. Some are parasitic, living in or on host organisms. In marine environments, they make up part of zooplankton. On land, they are abundant in soil and on plants/animals. They also live in the guts of termites, roaches, and cattle. Protozoans help maintain ecological balance by breaking down large numbers of bacteria and algae.

Compare mitosis and meiosis

Mitosis: each daughter cell receives the same number of chromosomes as the parent cell. Cells are reproduced with the same genetic material. ASEXUAL. Meiosis: diploid cells (have two copies of genetic information) give rise to haploid cells, which can develop into haploid organisms or into sex cells called gametes. Fusion of two gametes forms a diploid cell, which can recombine different genetic material. SEXUAL.

Describe a disease caused by a roundworm, a tapeworm, and a fluke.

Roundworm/nematode: Ascariasis--abdominal pain, vomiting, intestinal blockage. Tapeworm/cestode: Pork tapeworm--variable symptoms depending on the location and number of eggs that form larval cysts in the body. Can cause neurological damage. Fluke/trematode: Schistosomiasis--liver damage, malnutrition, weakness, and accumulation of fluid in the abdominal cavity.

Describe characteristics of roundworms, tapeworms, and flukes.

Roundworms: cylindrical, tapered body with a digestive tract from mouth to anus. Tapeworms: flat, ribbon-shaped bodies with no digestive system--do not feed directly on the tissues of their host. Scolex/head has suckers/hooks for attachment. Also have segments called proglottids, which contain male and female reproductive structures and fertilized eggs. They absorb predigested nutrients through the host's body. Can reach over 15 meters in length. Flukes: flat, leaf-shaped worms with two suckers that are used to attach and move along surface of host. Have a mouth, but no anus--so nutrients enter and exit from the same opening. Have a complex life cycle that involves at least two hosts, a snail (for asexual reproduction) and a mammalian (for sexual reproduction). Tissue flukes have both sex organs, while blood flukes have separate sexes.

Describe the structure, habitat, and reproductive strategies of a yeast and a mold.

Structure:Yeast and molds are both fungi. Yeast is single-celled and molds are filamentous. Most fungi are molds: multicellular organisms composed of thread like filaments called hyphae. A visible mass of hyphae is called mycelium. Habitat: Fungi are found in almost every habitat on earth. Most prefer an environment from 20-35 celsius, but can easily survive at temperatures below. Grow better on acidic fruits and vegetables than bacteria do, but prefer a pH of 5. Some are resistant to pasteurization. Most are aerobic, but some are facultative anaerobes, producing ethanol by fermentation. Some of these facultative anaerobes live in the stomach of cows. Dimorphic fungi can grow as either a yeast or a mold depending on environmental conditions. Reproduction: Molds reproduce through small spores, which can be either sexual or asexual. Asexual: reproductive cells of molds are called conidia or sporangeospores--carried through wind and germinate, growing in direction of food source. Can also reproduce asexually through fragmentation. Sexual reproduction occurs when hyphae from two different mating types grow toward one another and their nuclei fuse and then undergo meiosis. Most yeast reproduce asexually through mitosis ('budding')-- nucleus divides by mitosis and one nucleus migrates into a smaller daughter cell/'bud'. The daughter cell pinches off from the larger parent cell, which eventually dies.

Define slime molds

Terrestrial organisms composed of amoeboid cells that live on soil, leaf litter, and the surfaces of decaying vegetation, where they ingest organic matter by phagocytosis. Important links in the food chain. Look like act like fungi, but are completely unrelated.

Explain how fungi and water molds provide an example of convergent evolution.

Their shared characteristics show how organisms can develop similar characteristics independently as they adapt to similar environments.

Define protozoa

Unicellular heterotrophic organisms that are not fungi, slime molds, or water molds.

Describe life cycle and methods of reproduction in protozoa.

Vegetative/feeding form = trophozoite. Resting form = cyst. Environmental conditions can trigger the development of a protective cyst. Examples of protozoa that develop a protective cell wall during their cyst stage: Cryptosporidium and Entamoeba. Many protozoa are transmitted to new hosts during their cyst stage. Both asexual and sexual reproduction are common in protozoa and may alternate during the life cycle of some organisms. Binary fission also takes place in many groups of protozoa. Some divide by multiple fissions--called schizogony--results in the release of large numbers of parasites into the host's circulation at regular intervals, producing cyclic symptoms (ex: malaria).