Cytology - Part IV


The Eukaryotic Cell

 

Visit the University of Virginia to examine a typical animal cell or interact with a typical plant cell prepared by Ross Koning.

The Eukaryotes comprise the kingdoms animalia, plantae, fungi, and protista

The following table indicates whether each structure is found in plants only, animals only, neither plants or animals, or can be found in both. (click on the terms to find out more about each one.)

a)

microtubules

both

b)

plastids

plants

c)

lysosome

animals

d)

pili

neither

e)

centrioles

animals

f)

nucleolus

both

g)

chloroplast

plants

h)

plasmid

neither

i)

*vacuoles

both

j)

peroxisome

both

k)

plasmodesmata

plants

*plants have a large central vacuole, animals have much smaller vacuoles generally called vesicles


Cell Structures and Organelles in Eukaryotes

Cell walls

Plant cells are surrounded by fairly rigid, nonliving walls composed of cellulose (a polymer of the sugar glucose) and other polysaccharides.

The strength of the cell wall is based on the fact that the microfibril chains are arranged in crisscrossed layers. The result is a very strong but porous covering which can expand in young cells thanks to a certain elasticity and enzymatic rearrangement of microfibril components.

As the cell wall ages hardening compounds such as lignin, (hemicellulose) and pectin impregnate the cellulose fibrils, preventing further growth.

As plant cells divide a new cell wall is formed between them. The two new cell walls are cemented together with pectin to form a layer known as the middle lamella.

The cartoon above labels the parts of a plant cell visible under the light microscope.


A number of substances are deposited in or outside plant cell walls. For example:

  • lignin; technically an alcohol, thickens, hardens and prevents decay
  • suberin and cutin; are waxy materials which acts as a water proof coating (to prevent excessive water loss.)


Modified July 8, 2005