1. Being Multicellular Chapter 28

2. SIMPLE MULTICELLULARITY Unicellular eukaryotes evolved first Then simple multicellular eukaryotes evolved In the form of filaments, hollow balls, or sheets of undifferentiated cells Simple multicellularity involves: Adjacent cells stick together, but few specialized cells Most cells have full range of functions Every cell is in direct contact with external environment

3. COENOCYTIC ORGANIZATION Coenocytic organization: where nuclei divided but cytokinesis did not occur Results in very large cells with many nuclei

4. COMPLEX MULTICELLULARITY Red and brown algae Land plants Fungi Animals Properties of complex multicellular organisms: Adhesion molecules Specialized structures for cell communication Tissue and organ differentiation……...including reproduction Only some cells in contact with external environment Helps organisms avoid predators Cell or tissue loss can be fatal for organism 28.1 Complex multicellularity arose several times in evolution.

5. EVOLUTION OF MULTICELLULARITY Complex multicellularity evolved 6 separate times in Eukaryotes: Animals Vascular plants Red algae Brown algae 2 times in fungi

6.  How do simple multicellular cells differ from complex multicellular organisms? QUICK CHECK

7.  Simple multicellular organisms:  All cells are undifferentiated; they each have full range of functions  All cells are in direct contact with external environment  Complex multicellularity:  Have differentiated cells and tissues  Most cells are completely surrounded by other cells ANSWER

8. 28.2 In complex multicellular organisms, bulk transport eliminates the problems of diffusion.  Diffusion: Movement of molecules from areas of high to low concentration acting over small distances  Main limitation of cell size  Effective only over short distances  Main limitation of cell size  Bulk transport: Active process that allows multicellular organisms to nourish cells located far from external environment  Eliminates problems of diffusion DIFFUSION AND BULK TRANSPORT

9. CIRCUMVENTING LIMITS IMPOSED BY DIFFUSION

10. BULK TRANSPORT Don’t have a size limitation as with diffusion

11. 28.3 Complex multicellularity depends on cell adhesion, communication, and a genetic program for development.  Requirements: Cells must….. 1.Stick together 2.Communicate with one another 3.Have a genetic program to guide growth and development COMPLEX MULTICELLULAR LIFE

12. CELL ADHESION Mechanisms of adhesion in animals: Cadherins Integrins Other transmembrane proteins Mechanisms of adhesion in plants: Pectins Closest protistan relative of animals: Choanoflagellates Same proteins for cell adhesion as animals But use it to capture bacteria

13. COMMUNICATION IN ANIMALS– GAP JUNCTIONS Gap Junctions: protein channels in animals that allow ions and signaling molecules To move from one cell to another

14. COMMUNICATION IN PLANTS– PLASMODESMATA Plasmodesmata: intracellular strands of cytoplasm in plants that extend to neighboring Cells to allow communication

15. PLANT MULTICELLULARITY 28.4 Plants and animals developed multicellularity independently of each other and solved similar problems with different sets of genes. Plants and animals evolved multicellularity separately….do not share a common ancestor i.e. plant cell wall allows for support, but no movement i.e.plant growth confined to meristems

16. ANIMAL MULTICELLULARITY Unconstrained by cell walls, animal cells can move relative to one another i.e. during animal development, embryos undergo gastrulation, a process in which cells migrate inward to form a layered structure called a gastrula

17. EVOLUTION OF COMPLEX MULTICELLULARITY 28.5 The evolution of large and complex multicellular organisms, which required abundant oxygen, is recorded in the fossil record. Oxygen may be required for evolution of complex multicellularity Fossil record correlates with increased atmospheric oxygen at 580-560 mya

18. FOSSIL RECORD FOR ANIMALS

19. RELATIONSHIP BETWEEN O 2 AND COMPLEX MULTICELLULARITY More oxygen permitted greater greater size, which led to evolution of bulk transport, which then permitted even larger size

20. RELATIONSHIP BETWEEN O 2 AND COMPLEX MULTICELLULARITY This treelike fossil is actually a 375 mya fungusInterior of fungus It was well after marine animals and algae that complex multicellular land plants evolved

21. ROLE OF REGULATORY GENES Evolutionary-developmental biology (Evo- Devo) A new field of research that looks at both individual development and evolutionary patterns i.e.Regulatory genes (homeotic genes) play an important role in butterfly wing coloration Mutations in these genes can account for differences in wing colorations among species