Chapter 6b Multicellular organization

1
Chapter 6b- Multicellular organization

• Organisms exhibit various levels of organization.
  
• Unicellular organisms may form groups, chains,
  films, colonies, etc. but this does not make them
  multicellular. Each cell is fully independent.
• Volvox is an example of a unicellular colonial
  eukaryotic microorganism (algae) living in
  freshwater ponds. They have anucleus, a vacuole,
  chloroplasts, and flagella.
• Daughter colonies develop inside of the main
  colony, which eventually bursts, releasing them.

2
Biofilms of prokaryotic (unicellular) cells

• Even prokaryotic cells have some means of
  cell-to-cell communication.
• Colonies of cells of the same species may form
  films.
• Also, groups of cells of different species, but
  similar environmental requirements may form
  biofilms.
• Biofilm formation allows stabilizing the
  individual cells onto a surface so they are not
  easily dislodged. Also, substances secreted by
  individual cells are contained in the biofilm (in
  the spaces between cells), and be utilized by
  members of the group.
• Biofilms also protect individual cells from
  environmental changes, including the effects of
  antibiotics and other medicines.

3
Division of labor

• As the complexity of organisms increases, there
  is the need for having more than just one cell.
• Individual cells and groups of cells have
  limitations as to their maximum size, largely due
  to their ability to exchange materials with their
  outside environment. Therefore, individual cells
  cannot grow large enough to carry out the
  specialized functions of multicellular organisms.
  
• Below, a simple multicellular freshwater organism
  (Hydra), shows specialization of individual cells
  for specific functions.
• This level of organization is much higher that in
  prokaryotic biofilms, where each individual cell
  is essentially equivalent to any other, and they
  are truly independent organisms. In multicellular
  organisms each cell is not fully independent.

4
Increased specialization with multicellularity

• Tissue group of similar cells that work
  together.
• Organ Various types of tissues forming an
  structure with a unique function.
• System various organs working together for a
  purpose.
• Reasons systems are needed
• 1- there is division of labor
• 2- cells that work together must be
  regulated/coordinated
• 3- since not all cells are in contact with the
  outside environment, some means of exchange of
  materials is needed.

5
The extracellular matrix

• The extracellular matrix is a solution of
  macromolecules (proteins and carbohydrates) that
  surrounds the cells of most multicellular
  organisms.
• The plasma membrane of neighboring cells often
  have junctions
• - some hold cells together
• - channels of communication.
• - Desmosomes hold cells but allow material
  exchanges.
• - Gap-junctions allow passage of certain small
  substances among cells.
• - Pits (in plants) connect strands of cytoplasm
  thru areas called plasmodesmata.

6
Levels of structural organization

• Quarks
• subatomic particles
• Atoms non-living
• Molecules
• Organelles
• __________________________________________________
  ________________
• Cells, groups or cells, multicellular
  orgs.
• Tissues
• Organs living
• Organ systems
• Organisms
• Populations
• Communities
• __________________________________________________
  ________________
• Habitats living
  non-living
• Ecosystems
• Biosphere