Microbiology

Microbiology Study Guide

Types of Eukaryotes Fungi A fungus is a member of a large group of eukaryotic organisms that includes microorganisms, such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria. One major difference is that fungal cells have cell walls that contain chitin, unlike the cell walls of plants, which contain cellulose. The growth of fungi as hyphae on or in solid substrates or as single cells in water environments is adapted for the efficient extraction of nutrients because these growth forms have high surface area to volume ratios. Hyphae (fungi “feet”) are specifically adapted for growth on solid surfaces and to invade substrates and tissues. Most fungi grow as hyphae, which are cylindrical, thread-like structures 2–10 µm in diameter and up to several centimeters in length. Hyphae grow at their tips (apices); new hyphae are typically formed by emergence of new tips along existing hyphae by a process called branching, or occasionally growing hyphal tips bifurcate (fork) giving rise to two parallel-growing hyphae. The combination of apical growth and branching/forking leads to the development of a mycelium, an interconnected network of hyphae. Fungal reproduction is complex, reflecting the differences in lifestyles and genetic makeup within this kingdom of organisms. It is estimated that one-third of all fungi reproduce by different modes of propagation; for example, reproduction may occur in two well-differentiated stages within the life cycle of a species, the teleomorph and the anamorph. Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore- containing propagules. Asexual reproduction via vegetative spores (conidia) or through mycelial fragmentation is common. Sexual reproduction with meiosis exists in all fungi. Algae Algae are a large and diverse group of simple, typically autotrophic (make their own food) organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and “simple” because their tissues are not organized into the many distinct organs found in land plants. The largest and most complex marine forms are called seaweeds. Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism, providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples are lichens, coral reefs, and sea sponges. Almost all forms of algae have chloroplasts. These contain chlorophylls a and b, giving them a bright green color (as well as the accessory pigments beta carotene and xanthophylls), and have stacked thylakoids. All green algae have mitochondria with flat cristae. When present, flagella are typically anchored by a cross-shaped system of microtubules and fibrous strands, but these are absent among the higher plants and charophytes, which instead have a raft of microtubules, known as the spline. Flagella are

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