Fungi Lab

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Molds are

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multicellular, filamentous fungi.

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The mold colony is called a

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thallus.

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Term) Thalus (sing) Thalli (pl)

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Colony of mold

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Thalli are composed of

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bundles of filaments called mycelia.

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Mycelia

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filaments bundles creating a thalus or mold colony

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Mycelia are composed of

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long filament-like structures called hyphae

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Vegetative hyphae grow

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on the agar surface;

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Rhizoidal hyphae grow

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below the surface;

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Reproductive hyphae grow

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extended into the air.

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Hyphae are divided into individual cells by wall-like structures called

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septa.

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Term) Septa

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wall-like structures which divide hyphae into individual cells

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Molds which have septa are comprised of

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septate hyphae.

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Hyphae which lack septa are called

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coenocytic hyphae.

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Coenocytic hyphae

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hyphae which lack septa to divide them into individual cells

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The reproductive hyphae bear

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sexual or asexual reproductive structures.

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The reproductive structures often appear as

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flower like structures of sacs.

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spores.

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When observing the mold spores under oil immersion, you should be able to see

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new hyphae being formed from the fungal spores.

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Each spore you see has the potential to produce a

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new organism.

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The production of spores by molds is a method of

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reproductions (sexual or asexual)

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Term) Aseptate

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lacking septa

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When observing the yeast cells under 40X or oil immersion, you should be able to see

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the cells' nuclei as well as budding.

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Over time, most of the buds

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detached themselves from the parent.

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Budding is a form of

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asexual reproduction.

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Some yeast cells produce buds which did not detach themselves and give the appearance of producing hyphae. These are called

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psuedohyphae

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Pathogenic yeasts exhibit

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dimorphism.

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Term) Dimorphism

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the ability to have two (di-) different forms apparent

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Wet mounts will be performed using 1 drop each of

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water and Gram's iodine.

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To prepare a wetmount of fungi

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use 1 drop of each water and Gram’s iodine. Fungi will then be added to the mixture and covered by a coverslip.

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When you inoculate the mold spores onto the TSA plate, each spore produces

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a new mold.

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Yeasts reproduce by

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budding

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Bacteria reproduce by

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binary fission

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The word colony is only used to describe microbes growing

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on an agar surface.

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The word colony is not used to describe cells growing

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in liquid culture.

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Growth of yeast colonies on Sabouraud agar, produces colonies that are

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very large.

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Which is larger of eukaryotic and prokaryotic cells

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eukaryotic cells are larger than prokaryotic cells.

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Fermentation by yeasts involves the conversion of

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carbohydrates to some other organic product such as alcohol.

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Yeasts conversion of carbohydrates to some other product is

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Fermentation

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Fermentation tests of yeasts are read as positive if the medium becomes

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turbid and carbon dioxide is produced.

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During fermentation carbon dioxide is formed, and the media becomes

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acidified.

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You can visualize fermentation indirectly by looking for the formation of

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a carbon dioxide bubble inside the Durham tube

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You can detect acidification by noticing the development of

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yellow color in the fermentation tube.

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Occurs if an organic acid byproduct is produced instead of alcohol

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Acidification

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Production of _______ often does not change the color of the medium

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Alcohol

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The medium contains

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phenol red ( a pH indicator) which is red at neutral and alkaline pH and yellow at acidic pH.

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This substance is red at neutral and alkaline pH and yellow at acidid pH

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Phenol red

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In order to judge whether anything has happened in your fermentation tubes, you must first be able to

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observe growth.

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Growth in a liquid culture is noted as

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turbidity (cloudiness).

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Something is wrong if you do not see turbidity, but you see

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a color change

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Alkalinization can occur as alcohol is metabolized and converted back into an alkaline product if you allow your fermentation tube to sit for

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48 hours or longer

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In phenol red medium, fermentation by yeasts will lead to a yellow color. If continued fermentation is allowed, and alkalinization occurs, the substance will be what color

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will return to red

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Candida albicans is

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a yeast found in healthy individuals as normal flora. Under conditions where this organism overgrows or when an individual is immunocompromised, oral and genital candidiasis can result.

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Aspergillus niger is

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black bread mold which is fast growing and produces thousands of spores in sacs called sporangia

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Term) Sporangia

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spore sacs

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Saccharomyces, is

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a yeast which is commonly used in the bread industry and ferments sugars

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Sabouraud agar is

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a low pH, high sugar medium which is selective for fungi.

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Fungal cultures will be cultivated at

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25oC which is the preferred temperature.

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Preferred temperature of fungal cultures

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25c

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When incubating fungal cultures do not

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invert the plates in the incubator.

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When incubating fungal cultures, caps should be

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loose, since fungi are aerobic organisms

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Inoculate A. niger onto a slant by

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spot inoculation.

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To prepare wet mounts of molds and yeasts use

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2 loops of water and 1 loop of Gram’s iodine. Mix a loopful of yeast into water mixture. For molds - Tease mold off of agar using an inoculating needle then add to water mixture.

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Observe yeasts and molds at what magnification

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40X.

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What magnification may be used to observe spores

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100X

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During fermentation, yeasts will convert organic molecules such as sugars to new organic products such as

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alcohols, acids and CO2 with the production of a small amount of energy.

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Alcohol or other alkaline products in phenol red media will produce what color

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fuchsia color.

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Gas production is seen as the trapping of a gas bubble in the

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Durham tube.

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What do yeast colonies look like when they grow

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larger than bacterial colonies, white in color, raised and have odor of fresh bread.

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Yeast cells divide by a process called

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budding

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Rhizoidal hyphae

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are those embedded in the agar like roots.

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Vegetative hyphae

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those spread out across agar involved in gathering nutrients and oxygen.

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Aerial or reproductive hyphae

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those extending into the air which are involved in reproduction (spore formation).

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The tips of the reproductive hyphae may have _________, sacs filled with spores,

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sporangia

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Term) conidia

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chains of spores extending like fingers.

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Do fungi reproduce sexually or asexually

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both sexually and asexually

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Pathogenic yeasts are

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dimorphic, that is they grow as a yeast under certain conditions and as a mold under other environmental conditions.

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Candida albicans is a common pathogenic yeast in humans responsible for

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urogenital infections (Candidiasis) as well as oral infections (Thrush).