Being Multicellular Lecture
Chapter 28
Textbook Reference: Chapter 28 in Biology How Life Works (2nd ed.)
Sections 28-1 to 28-5; pp. 578-592)
Simple Multicellularity
Most organisms represented in the 119 branches of the seven superkingdoms
are unicellular
Only 36 branches show some level of multicellularity such as:
1. Filaments
2. Hollow balls
3. Colonies
• Properties of multicellular organisms include:
1. Adhesion molecules
- cause adjacent cells to stick together
- little communication or transfer between cells
- little differentiation of specialized cell types
2. most of the cells retain a full range of functions including reproduction
3. every cell is in contact with external environment
What is coenocytic organization?
Two algal groups, three protozoan groups and one fungal group
1
, Why Did Simple Multicellularity Evolve?
Possible Selective Advantages:
o Predator avoidance: Helps organisms avoid protozoan predators
Example: Green algae/predatory protist -
o Maintain position: ability to maintain position on a surface or in water
better than single celled relatives
o Co-ordination of movements: co-ordination of movements for different
functions
Example: ciliary movements – for more efficient feeding
Complex Multicellularity
Complex multicellularity evolved at least six
separate times in different eukaryotic
groups:
- Animals
- Vascular plants
- Red algae
- Brown algae
- Twice in fungi
2
Chapter 28
Textbook Reference: Chapter 28 in Biology How Life Works (2nd ed.)
Sections 28-1 to 28-5; pp. 578-592)
Simple Multicellularity
Most organisms represented in the 119 branches of the seven superkingdoms
are unicellular
Only 36 branches show some level of multicellularity such as:
1. Filaments
2. Hollow balls
3. Colonies
• Properties of multicellular organisms include:
1. Adhesion molecules
- cause adjacent cells to stick together
- little communication or transfer between cells
- little differentiation of specialized cell types
2. most of the cells retain a full range of functions including reproduction
3. every cell is in contact with external environment
What is coenocytic organization?
Two algal groups, three protozoan groups and one fungal group
1
, Why Did Simple Multicellularity Evolve?
Possible Selective Advantages:
o Predator avoidance: Helps organisms avoid protozoan predators
Example: Green algae/predatory protist -
o Maintain position: ability to maintain position on a surface or in water
better than single celled relatives
o Co-ordination of movements: co-ordination of movements for different
functions
Example: ciliary movements – for more efficient feeding
Complex Multicellularity
Complex multicellularity evolved at least six
separate times in different eukaryotic
groups:
- Animals
- Vascular plants
- Red algae
- Brown algae
- Twice in fungi
2
