W4L3: Multicellularity

Question 1

Origin of Multicellularity (1)

Answer 1

Earliest fossil evidence of life 3.5 billion years ago (Stromatolites)

Question 2

Defining “Multicellularity” (5)

Answer 2

1. Multiple cells which physically attach to each other
2. Cell differentiation with different functions/Division of Labour
3. Ability for cell-cell communication
4. Never permanently multicellular
5. Individual cells can be sacrificed for good of the organism

Question 3

Examples of Multicellular Organisms (3)

Answer 3

Cyanobacteria

Dictyostelium

Sponges

Question 4

How are Cyanobacteria multicellular? Multiple cells which physically attach to each other? (1)

Answer 4

Hetereocysts and other cells are attached to one another and benefit from sharing resources

Question 5

Cell differentiation with different functions? (1)

Answer 5

Heterocyst

Question 6

How are Cyanobacteria multicellular? Heterocyst Function

Answer 6

Fix/make nitrogen using nitrogenase (Requires low oxygen)

Question 7

How are Cyanobacteria multicellular? Heterocyst Structure (2)

Answer 7

• Kept separate from oxygen-generating photosystem
• Thick glycolipid layer to reduce gas exchange. Can’t photosynthesise

Question 8

How are Cyanobacteria multicellular? Heterocyst Formation (2)

Answer 8

• Only formed with nitrogen is scarce, at regularly spaced intervals
• If chains are broken, new heterocysts are formed

Question 9

How are Cyanobacteria multicellular? Heterocyst Regulation (1)

Answer 9

Small signalling molecule (PatS) is made by heterocyst and block other cells becoming heterocyst

Question 10

How are Cyanobacteria multicellular? The ability for cell-cell communication? (1)

Answer 10

Fixed nitrogen is exchange for products of photosynthesis with neighbouring cells (2 types of cells within an organisation)

Question 11

How are Cyanobacteria multicellular? Never permanently multicellular? (1)

Answer 11

All cells have the ability to become heterocyst

Question 12

How are Cyanobacteria multicellular? Individual cells can be sacrificed for good of the organism? (1)

Answer 12

Heterocyst do not divide (i.e., give up reproduction) to make nitrogen. Genes go on.

Question 13

Multicellularity in lab? (1)

Answer 13

Predator + Prey (Unicellular) > Multicellular prey after 10-20 generations.

Question 14

Example of multicellular evolution (2)

Answer 14

Amorphous (No shape) multicellular mass evolves over generations into an 8-cell colony

Too large to eat, but not too large to absorb essential nutrients