Multicellularity Lecture
Multicellularity: Close association of many cells carrying out a specialized
vegetative and reproductive function
- Has occurred in multiple lineages.
- Closest relatives show evolution for cells sticking together as colonies
- Colonial phase is reversible
Vegetative: Not reproductive function
Stromatolites
- Stromatolites are colonies of cyanobacteria.
- The top most layer is the most active layer
- Discovered in Australia in a protected bay.
The fossil record and geological periods:
Eons Eras Periods One key fact
Hadean /////////////// ////////////////// First oceans
Archean /////////////// ////////////////// Origin of life
Proterozoic /////////////// ////////////////// 1st photosynthetic
organisms,
eukaryotes,
multicellular
organisms
Cambrian Explosion of diverse
life forms
Ordovician Radiation of marine
phyla
Silurian Ordovician/silurian
extinction
Paleozoic Devonian 1st vascular plants,
1st jawed fish,
terrestrial plants.
, Fungi, and
arthropods
Phanerozoic Carboniferous Large swamps
Permian Giant insects,
amphibians, diverse
ray finned fish
Triassic Confires became
dominant plants on
land. Frogs and
reptiles begin to
diversify
Mesozoic Jurassic Dinosaurs,
Pnerosaours, ray
finned fish diversify.
1st flowering plants
Cretaceous Flowering plants
diversity, animal
diversity on land and
sea
Cenozoic Tertiary Radiation of
mammals, climates
cool and grasslands
increase
Quaternary Evolution of homo,
four major ice ages
5 requirements for multicellularity:
1. Extracellular environment
a. Someway for the cells to stick together
b. The extracellular matrix holds the cells together
2. Division of labor
a. Cells have different tasks
3. Resource allocation
a. Resources are fairly allocated so that the cells on the inside have the
same amount of access to resources as cells on the outside
4. Proliferation inhibition
, a. Control of cell replication
5. Programmed cell death
a. If some cells go bad or are infected, they should be able to die on
their own
Note: If any of these requirements goes wrong, the result will be cancer
There are many unique origins of multicellular organisms
- You can start from a single celled organism that will eventually become
multicellular
- It happens over and over across the tree
- There may be as many as 20 different origins of multicellularity
This suggests that it's a very easy process. Organisms do it when
it benefits them
Convergent designs of multicellular eukaryotes related to nutrition:
1. Photosynthetic organisms
a. Light is used to produce energy
2. Absorptive organisms
a. Secrete enzymes to absorb nutrients
3. Ingestive organisms
a. Ingesting food and then digesting it
Multicellular photosynthetic organisms:
- Examples:
- Brown alga: postelsia
- Red alga: plocacium
- Green alga: Ulva
- Flowering plant: Tomato
- Convergent design:
- Flat leaves:
- Provide large surface area to capture as much sunlight to
produce energy from photosynthesis
- Tubular stems:
- Hold them up, get them tall and above other organisms
- Attaching roots/holdfasts
- Ground themselves in the right place
Multicellular absorptive organisms
- Unicellular or filamentous vegetative stages
Multicellularity: Close association of many cells carrying out a specialized
vegetative and reproductive function
- Has occurred in multiple lineages.
- Closest relatives show evolution for cells sticking together as colonies
- Colonial phase is reversible
Vegetative: Not reproductive function
Stromatolites
- Stromatolites are colonies of cyanobacteria.
- The top most layer is the most active layer
- Discovered in Australia in a protected bay.
The fossil record and geological periods:
Eons Eras Periods One key fact
Hadean /////////////// ////////////////// First oceans
Archean /////////////// ////////////////// Origin of life
Proterozoic /////////////// ////////////////// 1st photosynthetic
organisms,
eukaryotes,
multicellular
organisms
Cambrian Explosion of diverse
life forms
Ordovician Radiation of marine
phyla
Silurian Ordovician/silurian
extinction
Paleozoic Devonian 1st vascular plants,
1st jawed fish,
terrestrial plants.
, Fungi, and
arthropods
Phanerozoic Carboniferous Large swamps
Permian Giant insects,
amphibians, diverse
ray finned fish
Triassic Confires became
dominant plants on
land. Frogs and
reptiles begin to
diversify
Mesozoic Jurassic Dinosaurs,
Pnerosaours, ray
finned fish diversify.
1st flowering plants
Cretaceous Flowering plants
diversity, animal
diversity on land and
sea
Cenozoic Tertiary Radiation of
mammals, climates
cool and grasslands
increase
Quaternary Evolution of homo,
four major ice ages
5 requirements for multicellularity:
1. Extracellular environment
a. Someway for the cells to stick together
b. The extracellular matrix holds the cells together
2. Division of labor
a. Cells have different tasks
3. Resource allocation
a. Resources are fairly allocated so that the cells on the inside have the
same amount of access to resources as cells on the outside
4. Proliferation inhibition
, a. Control of cell replication
5. Programmed cell death
a. If some cells go bad or are infected, they should be able to die on
their own
Note: If any of these requirements goes wrong, the result will be cancer
There are many unique origins of multicellular organisms
- You can start from a single celled organism that will eventually become
multicellular
- It happens over and over across the tree
- There may be as many as 20 different origins of multicellularity
This suggests that it's a very easy process. Organisms do it when
it benefits them
Convergent designs of multicellular eukaryotes related to nutrition:
1. Photosynthetic organisms
a. Light is used to produce energy
2. Absorptive organisms
a. Secrete enzymes to absorb nutrients
3. Ingestive organisms
a. Ingesting food and then digesting it
Multicellular photosynthetic organisms:
- Examples:
- Brown alga: postelsia
- Red alga: plocacium
- Green alga: Ulva
- Flowering plant: Tomato
- Convergent design:
- Flat leaves:
- Provide large surface area to capture as much sunlight to
produce energy from photosynthesis
- Tubular stems:
- Hold them up, get them tall and above other organisms
- Attaching roots/holdfasts
- Ground themselves in the right place
Multicellular absorptive organisms
- Unicellular or filamentous vegetative stages
