Chapter 5

• Algae are photosynthetic, eukaryotic organisms
• Algal cells


  • Consist of cytoplasm, a cell wall (usually), a cell membrane, a nucleus, plastids, ribosomes, mitochondria, and Golgi bodies
  • Some have a pellicle, a stigma, and/or flagella
• Algae range in size

  • Unicellular microorganisms (e.g., diatoms)
  • Large, multicellular organisms (e.g., seaweeds or kelp)
• Algae


  • Produce energy by photosynthesis
  • Some may use organic nutrients
• Characteristics and classification of algae

  • Arranged in colonies or strands
  • Found in fresh and salt water, in wet soil, and on wet rocks
  • Most algal cell walls contain cellulose
  • Classified as green, golden, brown, or red algae
  • Include diatoms, dinoflagellates, desmids, Spirogyra, Chlamydomonas, Volvox, and Euglena
• Algae are an important source of food, iodine, fertilizers, emulsifiers, and stabilizers and gelling agents for jams and culture media
• Common pond water algae

  • Euglena sp.
  • Volvox sp.
• Prototheca is a very rare cause of human infections (i.e., protothecosis)
• Algae in several other genera secrete toxic substances called phycotoxins
• Phycotoxins are poisonous to humans, fish, and other animals
• If ingested by humans, the phycotoxins produced by the dinoflagellates that cause "red tides" can lead to a disease called paralytic shellfish poisoning
• Protozoa


  • Nonphotosynthetic, eukaryotic organisms
  • Most are unicellular, free-living, and found in soil and water
  • Protozoal cells are more animal-like than plant-like
  • All possess a variety of eukaryotic structures/organelles
  • Cannot make their own food by photosynthesis; some ingest whole algae, yeasts, bacteria, and smaller protozoa as their source of nutrients
• Protozoa


  Do not have cell walls, but some possess a thickened cell membrane called a "pellicle," which serves the same purpose—protection
• Typical protozoan life cycle

  • Trophozoite (motile, feeding, dividing stage)
  • Cyst (nonmotile, dormant, survival stage)
• Some protozoa are parasites
• Protozoa divided into groups based on method of locomotion

  • Amebae (move by means of pseudopodia)
  • Ciliates (move by means of hairlike cilia)
  • Flagellates (move by means of whiplike flagella)
  • Sporozoa (have no visible means of locomotion)
• Parasitic protozoa cause many human diseases, such as malaria, giardiasis, and trypanosomiasis
• Mycology


  The study of fungi
• Fungi are found virtually everywhere
• Fungi include


  • Yeasts
  • Moulds
  • Microsporidia
  • Fleshy fungi (e.g., mushrooms)
• Fungi


  • Are the "garbage disposers" of nature
  • Are not plants; they are not photosynthetic
• Fungal cell walls


  • Contain a polysaccharide called chitin
• Fungal growth forms


  • Unicellular
  • Filaments called hyphae
  • Hyphae intertwine to form a mass called a mycelium
• Fungal hyphae


  • Septate (divided into cells by cross walls or septa)
  • Aseptate (do not contain septa)
• Fungal reproduction


  • Budding
  • Hyphal extension
  • Formation of spores
• Fungal spores


  • Sexual spores
  • Asexual spores (also called conidia)
• Some fungi produce both asexual and sexual spores
• Fungal spores are very resistant structures
• Fungal phyla


  • Zygomycotina
  • Chytridiomycotina
  • Ascomycotina
  • Basidiomycotina
  • Microsporidia
  • Deuteromycotina (Deuteromycetes)
• Deuteromycotina (Deuteromycetes) include the medically important moulds such as some Aspergillus species and Candida albicans
• Yeasts


  • Eukaryotic, unicellular organisms that lack mycelia
  • Individual yeast cells, also referred to as blastospores or blastoconidia, can be observed only using a microscope
  • Usually reproduce by budding, but occasionally by a type of spore formation
  • A string of elongated buds is known as a pseudohypha (not really a hypha)
  • Some yeasts produce thick-walled, spore-like structures called chlamydospores (or chlamydoconidia)
• Uses of yeasts


  • Found in soil and water and on the skins of many fruits and vegetables
  • Used for centuries to make wine and beer
  • Saccharomyces cerevisiae is a yeast used in baking
  • Candida albicans is the yeast most frequently isolated from human clinical specimens
• Differentiating yeast colonies from bacterial colonies

  • Yeasts are larger than bacteria and are usually oval-shaped
  • Yeasts are often observed in the process of budding
  • Bacteria do not bud
• Moulds


  • Often spelled "molds"
  • Produce cytoplasmic filaments called hyphae
  • Aerial hyphae extend above the surface of whatever the mould is growing on
  • Vegetative hyphae grow beneath the surface
  • Reproduction is by spore formation, either sexually or asexually, on the aerial hyphae (also known as reproductive hyphae)
• Moulds have great commercial importance
• Examples of commercially important moulds

  • Penicillium
  • Acremonium
• The flavor of cheeses like bleu cheese, Roquefort, Camembert, and Limburger are due to moulds that grow in them
• Microsporidia


  • A new addition to the Kingdom Eumycota
  • Originally thought of as protozoa, recent molecular studies show they share more characteristics with the Eumycota
  • About the size of bacteria (1-4 µm) and have a unique organelle called a polar filament
• Fleshy fungi


  • Include mushrooms, toadstools, puffballs, and bracket fungi
  • Consist of a network of filaments or strands (the mycelium) that grows in soil or on rotting logs
  • The fruiting body that grows above the ground forms and releases spores
  • Some are edible; some are extremely toxic
• Fungal infections of humans

  • Superficial mycoses (fungal infections of the outermost areas of the human body—hair, nails, and epidermis)
  • Cutaneous mycoses (fungal infections of the living layer of the skin, the dermis)
  • Subcutaneous mycoses (fungal infections of the dermis and underlying tissues)
  • Systemic mycoses (fungal infections of the internal organs of the body)