1. AP Biology 2013-14 The Cell Wall

2. AP Biology Cell Walls of Plants  An extracellular structure that distinguishes plant cells from animal cells  Prokaryotes, fungi, and some protists also have cell walls  Function  Protection  Maintains cell shape  Prevents excessive uptake of water © 2011 Pearson Education, Inc.

3. AP Biology  Structure  Made of cellulose fibers embedded in other polysaccharides and protein  Plant cell walls may have multiple layers  Primary cell wall: relatively thin and flexible. Actively growing layer.  Middle lamella: Glues adjacent cells together (Pectin)  Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall.Increases strength (wood)

4. AP Biology Cell Junctions  Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact  Intercellular junctions facilitate this contact  Several types of intercellular junctions (4)  Plasmodesmata  Tight junctions  Desmosomes  Gap junctions © 2011 Pearson Education, Inc.

5. AP Biology Plasmodesmata in Plant Cells  Plasmodesmata are channels that perforate plant cell walls  Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell © 2011 Pearson Education, Inc.

6. AP Biology Figure 6.31 Interior of cell 0.5  m Plasmodesmata Plasma membranes Cell walls

7. AP Biology Figure 6.32 Tight junctions prevent fluid from moving across a layer of cells Tight junction TEM 0.5  m TEM 1  m TEM 0.1  m Extracellular matrix Plasma membranes of adjacent cells Space between cells Ions or small molecules Desmosome Intermediate filaments Gap junction

8. AP Biology Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells  Tight Junctions: membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid  Desmosomes (anchoring junctions): fasten cells together into strong sheets  Gap junctions (communicating junctions): provide cytoplasmic channels between adjacent cells © 2011 Pearson Education, Inc.

9. AP Biology © 2011 Pearson Education, Inc. Animation: Tight Junctions Right-click slide / select “Play”

10. AP Biology © 2011 Pearson Education, Inc. Animation: Desmosomes Right-click slide / select “Play”

11. AP Biology © 2011 Pearson Education, Inc. Animation: Gap Junctions Right-click slide / select “Play”