Chapter 26 - Multicellularity

types of single celled organisms

1. cells eat other microorganism

2. ingest small organic particles

3. live suspended in water columns

4. are parasites living within other organisms

traits of simple multicellularity

- Form is filamentous, hollow balls or flat sheets

- Adhesion molecules for sticking together

- Most cells of the organism retain full range of functions

- All cells are still in contact with environment

Four key points of evolution of complex multicellularity

1. Complex multicellular organisms can be just a few or as many as a trillion or more cells that work in close coordination.

2. The biological gulf between microbes and complex multicellular organisms is enormous, but complex multicellularity has evolved at least half dozen times.

3. Most prokaryotic organisms are composed of a single cell, although some will form simple filaments (plaque) or live in colonies...this is NOT multicellularity.

4. No bacteria develop macroscopic bodies with functionally differentiated tissues

surface area to volume of cells issues

- More surface contacting the environment increases loss of water and dissolved substances.

- High SA:V also present problems of temperature control in unfavorable environments.

Selective advantages of multicellularity

- Avoid predators

- Float better

- Hold together better than cluster of single cells

- Withstand disturbance better

- Withstand desiccation better

fundamental features of complex multicellulars

1. Highly developed mechanisms for adhesion between cells

2. Specialized structures for cell communication

3. Tissue and organ differentiation

4. A small subset of cells contribute to reproduction

5. Cell or tissue loss can be lethal for the organism

6. Presence of both interior and exterior cells

7. Genome reorganization and increased complexity!

bulk transport

The means by which molecules move through organisms at rates beyond those possible by diffusion. Generally due to a pressure gradient

osmosis

diffusion of water across a selectively permeable membrane

Three scales of transport in vascular plants

- Transport of water and solutes by individual cells, such as root hairs

- Short-distance transport of substances from cell to cell at the levels of tissues and organs

- Long-distance transport within xylem and phloem at the level of the whole plant

three requirements for successful multicellular life

1. adhesion: stick together

2. communicate with one another

3. have genetic program to guide growth and development

what are the molecular mechanisms for animal cell adhesion

cadherins, integrins and transmembrane proteins

what are the molecular mechanisms for plant cell adhesion

pectins

gap junctions

ANIMAL CELLS: protein channels that allow ions and signaling molecules to move from one cell into another

Plasmodesmata

PLANT CELLS: intracellular strands of cytoplasm that extend to neighboring cells allowing the same type of cell communication.

cell fates

determined by which genes are switched off or on

How have plants adapted to being big and anchored

- evolved mechanisms to transport water and nutrients from soil to leaves without use of moving parts or ATP

- adjust to environmental signals by adjusting meristem activity

- evolved mechanical structures and poisons to keep from being eaten