Bio1151 Chapter 6 A Tour of the Cell
  1. All organisms are made of        , which are either              or             .

      A cell and its skeleton viewed by fluorescence microscopy.
     
     
     
     
  2. Cells are generally microscopic, which enables them to have a high          area to         ratio, to facilitate the exchange of materials into and out of the cell.

      Most cells are too small to see with the naked eye.


      The surface area to volume ratio of an object decreases when its size increases.
     
     
     
     
  3. All cells are bounded by a         membrane, and contain              ,            , and a semifluid substance called the          .

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  4.             cells have membrane-bound             and can be grouped into 2 main types: animal cells and plant cells.



     
     
     
     
  5. The          contains most of the          material in the cell, and is bounded by a nuclear           with many nuclear        .

      The nucleus and its envelope. In the nucleus are chromatin (DNA and proteins), and one or more nucleoli (singular, nucleolus), which synthesize ribosomes. The double membrane of the nuclear envelope is perforated with nuclear pores and lined by the nuclear lamina made of protein filaments.
     
     
     
     
  6.            carry out          synthesis.

      Ribosomes. This electron micrograph of part of a pancreas cell shows many ribosomes, both free (in the cytosol) and bound (to the ER). Ribosomes are composed of two subunits each made of ribosomal RNA (rRNA) and protein.
     
     
     
     
  7. The endoplasmic            (ER) is continuous with the nuclear           .

      Endoplasmic reticulum (ER). A membranous system called cisternae, enclosing a compartment called the lumen, the ER is continuous with the nuclear envelope. Rough ER, which is studded on its outer surface with ribosomes, can be distinguished from smooth ER. Transport vesicles bud off and travel to the Golgi apparatus and other destinations.
     
     
     
     
    •        ER, which contains            , produces           and            .
       
       
       
       
    •         ER lacks ribosomes and are involved in        synthesis.
     
     
     
     
  8. The        apparatus is the cell's "Shipping and Receiving Center".

      The Golgi apparatus consists of stacks of flattened sacs, or cisternae. They receive and process the transport vesicles produced in the ER to be delivered to other parts of the cell.
     
     
     
     
  9. The           contains enzymes to carry out intracellular digestion by               (cell eating ), and breaks down damaged organelles by            (self eating ).

      Phagocytosis. Lysosomes digest (hydrolyze) materials taken into the cell and recycle intracellular materials. Top: a macrophage can ingest bacteria and viruses and destroy them using lysosomes. Bottom: a lysosome can fuse with a food vacuole during phagocytosis.


      Autophagy. Top: a lysosome engulfs 2 disabled organelles, a mitochondrion and a peroxisome. Bottom: a lysosome fuses with a vesicle containing a damaged mitochondrion.
     
     
     
     
  10. The membrane-bound organelles involved in cellular transport form the               system.

      The Endomembrane System.
     
     
     
     
  11. Plant cells contain a large central          , which stores organic compounds and water.

      The central vacuole, surrounded by a membrane called the tonoplast, holds organic compounds and water in plant cells. It is usually the largest organelle seen under the light microscope.
     
     
     
     
  12.               are the cell's "power plant" and perform cellular              .

      The mitochondrion, site of cellular (aerobic) respiration. A mitochondrion has a double membrane: an outer membrane and an inner membrane folded into cristae enclosing a lumen called the matrix which contains circular DNA and ribosomes.


      At the cell level, energy from sunlight is stored in organic compounds by photosynthesis in chloroplasts. A byproduct of this process is oxygen. The organic compounds and oxygen are used by mitochondria to produce ATP for work in a process called cellular respiration. Byproducts of respiration are water and carbon dioxide, which are used as raw material for photosynthesis. Heat is released into the environment in this cycle.
     
     
     
     
  13.               perform                 in leaves and other green organs of         and in        .

      A chloroplast has a double membrane: the inner membrane encloses a compartment containing the fluid stroma as well as ribosomes and DNA. A third membrane called thylakoids contains the photosynthetic pigment chlorophyll and is stacked to form structures called grana (singular, granum).
     
     
     
     
  14. The               is a network of fibers which provides          for the cell, and enables           .

      The cytoskeleton. This TEM shows the thicker, hollow microtubules and the thinner, solid microfilaments.
     
     
     
     
    •               help maintain cell        , and guide the movement of cell components.

        Microtubules from fibroblast cells. Microtubules are made of tubulin subunits and help maintain cell shape and guide the movement of cell components. The centrosome in amimal cells is a "microtubule-organizing center" and contains a pair of centrioles.
       
       
       
       


        Cilia have a back-and-forth motion that moves the cell in a direction perpendicular to the axis of the cilium. A dense nap of cilia, beating at a rate of about 40 to 60 strokes a second, covers this Colpidium, a freshwater protozoan. Videos: protists humans


        A flagellum usually undulates, its snakelike motion driving a cell in the same direction as the axis of the flagellum. Propulsion of a human sperm cell is an example of flagellate locomotion. Videos: protists sperm


        Ultrastructure of a eukaryotic flagellum or cilium. Both cilia and flagella have a "9 + 2" arrangement of microtubules arising from a basal body of 9 triplets. The 9 doublets have attached motor proteins, the dynein arms.
       
       
       
       
    •                 called        and         are protein filaments that function in cellular motility, such as the contraction in         fibers.

        Microfilaments from fibroblast cells. Microfilaments are made of actin and myosin subunits that slide past each other to cause contraction.
       
       
       
       
      • Contraction of actin and myosin            , together with sol-gel reversals, also result in           crawling of a cell through the movements of              .

          Amoeboid movement. The cytoplasm can fluctuate between a fluid state called sol, or endoplasm, and a stiffer state called gel, or ectoplasm. Interaction of actin filaments with myosin near the cell's trailing end (right) squeezes the fluid forward (left) into the psudopodium.
         
         
         
         
      • Cytoplasmic            in        cells also involve microfilaments to circulate nutrients among organelles.


      Cytoplasmic streaming in plant cells. A layer of cytoplasm cycles around the cell, moving over a carpet of parallel actin filaments. Myosin motors attached to organelles in the fluid cytosol drive the streaming by interacting with the actin.
     
     
     
     
    Review: Animal Cell Structure and Function.   Cell types.
     
     
     
     
    Review: Plant Cell Structure and Function.   Differences.