0.19 Consider a spherical bacterial cell with diameter 2 um and a eukaryotic cell of spherical
shape with a diameter of 20 um. The surface area to volume (in um!) ratio of the bacterial
cell (round off to I decimal place) is_____ times more than that of the eukaryotic cell.
Answers
Answer:
Bacteria are prokaryotic, unicellular microorganisms, which lack chlorophyll pigments. The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles.
Due to the presence of a rigid cell wall, bacteria maintain a definite shape, though they vary as shape, size and structure.
When viewed under light microscope, most bacteria appear in variations of three major shapes: the rod (bacillus), the sphere (coccus) and the spiral type (vibrio). In fact, structure of bacteria has two aspects, arrangement and shape. So far as the arrangement is concerned, it may Paired (diplo), Grape-like clusters (staphylo) or Chains (strepto). In shape they may principally be Rods (bacilli), Spheres (cocci), and Spirals (spirillum).
Size of Bacterial Cells
The average diameter of spherical bacteria is 0.5-2.0 µm. For rod-shaped or filamentous bacteria, length is 1-10 µm and diameter is 0.25-1 .0 µm.
E. coli , a bacillus of about average size is 1.1 to 1.5 µm wide by 2.0 to 6.0 µm long.
Spirochaetes occasionally reach 500 µm in length and the cyanobacterium
Oscillatoria is about 7 µm in diameter.
The bacterium, Epulosiscium fishelsoni , can be seen with the naked eye (600 µm long by 80 µm in diameter).
One group of bacteria, called the Mycoplasmas, have individuals with size much smaller than these dimensions. They measure about 0.25 µ and are the smallest cells known so far. They were formerly known as pleuropneumonia-like organisms (PPLO).
Mycoplasma gallicepticum, with a size of approximately 200 to 300 nm are thought to be the world smallest bacteria.
Thiomargarita namibiensis is world’s largest bacteria, a gram-negative Proteobacterium found in the ocean sediments off the coast of Namibia. Usually it is 0.1—0.3 mm (100—300 µm) across, but bigger cells have been observed up to 0.75 mm (750 µm).
