Bio

• Bacteria


  A type of microorganism that lacks a true nucleus and is typically found in soil, water, and the gastrointestinal tracts of animals
• The first organisms that appeared on Earth are undoubtedly single-celled, like the prokaryotes
• Protists


  Exhibits remarkable variety in terms of structure, mode of nutrition, and habitat
• Some protists are so simple that they are mistaken as prokaryotes
• Others are very huge that they are mistaken as plants
• Kingdom Protista is an artificial grouping of organisms coming from different evolutionary lineages
• Biologists generally agree that fungi, plants, and animals arose from protist ancestors
• Protists


  • All protists are eukaryotes
  • They have a well-defined nucleus, and may carry only one nucleus or several nuclei
  • The protist cell also contains several other membrane-bound organelles, including the endoplasmic reticulum, Golgi complex, lysosomes, mitochondria, and, in some, chloroplasts
  • They also hold ribosomes and a cytoskeleton made up of microtubules
  • Unlike plants and animals, the cells of protists are not organized into specialized tissues
• Size range of protists

  Fractions of a millimeter for a green alga, to about 2 mm diameter for a dinoflagellate, with the notable exception of the giant kelp whose length can reach 65 m
• Habitats of protists


  • Oceans (as part of plankton)
  • Hydrothermal vents
  • Rocky intertidal pools
  • Freshwater ponds
  • Arable soil
  • Desert sand
  • Land covered with ice and snow
  • Forest litter
  • Barks of trees
• Lifestyles of protists


  • Heterotrophs
  • Autotrophs
  • Symbiosis with other organisms
  • Parasites
• Informal categories of protists

  • Animal-like protists (protozoans)
  • Fungus-like protists
  • Plant-like protists
• Animal-like protists (protozoans)


  • Like animals, protozoans are heterotrophs
  • They ingest food obtained from the environment which includes bacteria, other protists, and nonliving organic compounds
  • Unlike animals which are multicellular, protozoans are unicellular organisms
  • They lack the protection of a cell wall typical of prokaryotes
• Habitats of protozoans


  • Freshwater
  • Marine waters
  • Damp soil
  • Droplets of water on plants (free-living)
  • Body fluids of living hosts (parasitic)
• Parasitic protozoans cause many significant diseases such as malaria and African sleeping sickness
• Structures used by protozoans for movement


  • Flagella
  • Pseudopodia
  • Cilia
• Some parasitic protozoans lack structures for motility as food is abundant in the surrounding body fluids of the host
• Protozoans with flagella (zooflagellates)

  • Fast swimmers with one or more flagella
  • The flagella beat rhythmically to push or pull the whole cell through the fluid environment
  • They generally reproduce by binary fission, producing genetically identical individuals
• Protozoans with pseudopodia (amoeba)


  • Appear as a shapeless mass of cytoplasm bounded by a thin outer cell membrane
  • The cytoplasmic content streams constantly, presses against the membrane, and creates fingerlike projections called pseudopodia
  • Pseudopodia aid in the characteristic creeping movement and engulfing of food
• Amoeba


  • The thin outer membrane assists in the exchange of substances between the amoeba and its environment
  • An organelle called contractile vacuole pumps out excess water and bulky waste materials
• Entamoeba histolytica


  A parasitic species that causes amoebiasis or amoebic dysentery
• Amoebiasis


  • May be mild or severe
  • Mild infection includes nausea, loose stool, abdominal tenderness, and occasional fever
  • Severe infection occurs when the parasite attacks the large intestine and moves beyond, to the liver for example, causing liver abscess
• There is a high incidence of amoebiasis in the tropics and subtropics where animal excrement is used as fertilizer for agricultural land
• Other protozoans with pseudopodia

  • Heliozoans
  • Radiolarians
  • Foraminiferans
• Protozoans with cilia (Paramecium)


  • The oral groove is lined with cilia that sweep water with suspended food into the mouth pore
  • Food vacuoles contain the ingested food particles and fuse with lysosomes for digestion
  • Has a contractile vacuole that prevents the accumulation of excess water inside the cell
  • Has a large macronucleus that controls many metabolic activities and a micronucleus involved in sexual reproduction
• Stentor


  A trumpet-shaped freshwater ciliate with cilia arranged in rows lining the entire body and others arranged spirally around its mouth pore, creating feeding currents
• Colonial ciliates (Epistylis)


  • Grows on the outside surface of crustaceans and fishes
  • Stalked ciliate that can measure from 200 to 250 μm in length, with branched colonies up to 2 mm
  • Does not harm fishes and crustaceans unless the colonies amass and impede with water flow and draw out dissolved oxygen
• Parasitic ciliates (Balantidium coli)


  • The only ciliate known to parasitize humans
  • Attacks tissues of the large intestine and causes diarrhea when cysts are ingested from contaminated food and water
• Immobile protozoans (apicomplexans)


  • Lack structures for motility
  • Have an "apical complex" that enables them to enter a host cell
  • Are parasites that cause serious human diseases like malaria
• Plasmodium


  • A well-known apicomplexan that causes malaria
  • Its life cycle involves two different host species - the Anopheles mosquito and humans
• Antimalarial drugs are now available but certain Plasmodium strains have become resistant to some of them
• Fungus-like protists


  • Like fungi, they are heterotrophs that decompose dead organic matter
  • They do not photosynthesize and produce their own food
  • Their bodies consist of threadlike filaments and they reproduce through spores
  • Unlike fungi, they produce flagellated cells at some stage in their life cycle
  • Their cell walls are made up of a different polysaccharide and they contain centrioles
• Groups of fungus-like protists

  • Plasmodial slime molds
  • Cellular slime molds
  • Water molds
  • Downy mildews
• Plasmodial slime molds


  • Colorful fungus-like protists found creeping on decaying logs, moist forest soil and dead leaves
  • Move by forming pseudopodia and feed on microbes and organic matter
  • The large, branching, motile structure is known as the plasmodium
  • When nutrients are depleted, the plasmodium produces stalked fruiting bodies called sporangia with reproductive cells
• Cellular slime molds (Dictyostelium discoideum)

  • Provides a simple model for determining how eukaryotic genes influence many cellular processes
  • Its complete life cycle, including both unicellular and multicellular stages, can be simulated in the laboratory
• Water molds and downy mildews (oomycetes)

  • Have long, hollow, filamentous bodies containing several nuclei
  • Their cell wall is composed of cellulose, not chitin as found in true fungi
  • Produce sporangia that release flagellated reproductive cells called zoospores
• Water molds


  Aquatic saprophytes that obtain nutrition from decomposing plants and animals in freshwater habitats
• Water molds can be seen on dead insects, on salmon after it has completed its spawning run, and on immobile eggs
• Dictyostelium discoideum


  • It is easily grown and its complete life cycle, including both unicellular and multicellular stages, can be simulated in the laboratory
• Oomycetes


  Literally means "egg fungus"