The Origins Of Multicellularity

Question 1

True multicellularity means

Answer 1

• Having different types of cells
• usually some specialised germline cells for reproduction
• somatic cells for other functions

Question 2

Unicellular

Answer 2

Only one cell

Question 3

Lots of one type of cell

Answer 3

Colonial

Question 4

Lots of different types of cell

Answer 4

Multicellular

Question 5

For most of time, all life was

Answer 5

Single celled

Question 6

How do we answer whether multicellularity evolved one, or multiple times?

Answer 6

By building an evolutionary tree

Question 7

Did multicellularity evolve once, or multiple times?

Answer 7

Multiple times!

Question 8

When did multicellularity evolve?

Answer 8

• in Plantae: green algae + land plants
• in Amoebozoa: mycetozoan slime moulds
• in Opisthokonta: animals and fungi (inc. microsporidia)
• in Chromalveolata: Stramenopiles

Question 9

Why might it be better to be big?

Answer 9

• swim further
• harder to be eaten
• catch more food

Question 10

Choanoflagellates

Answer 10

• Collared flagellates
• the closest thing to an animal without being an animal

Question 11

How do choanoflagellates catch bacteria?

Answer 11

Setting up water currents

Question 12

Why are choanoflagellates indicative of the advantages of multicellularity

Answer 12

More cells = more current = more bacteria

Question 13

Why might it be better to be multicellular?

Answer 13

• big
• split functions
• flagellar retraction
• self-cannibalism

Question 14

What are the advantages of split functions

Answer 14

splitting somatic from germline might help protect germline

Question 15

Describe the self-cannibalism theory of multicellularity (Kerszberg and Wolpert 1998)

Answer 15

• With scarce food, a multicellular organism can autocannibalise
• when Environment recovers and more food is available, the cells can grow back
• seen in the flatworm, hibernating mammals

Question 16

Describe choanoflagellates

Answer 16

• long flagellum surrounded by a collar
• protists
• microscopic
• closely related to animals
• marine and freshwater
• feed on bacteria
• quite diverse

Question 17

What is the collar in choanoflagellates?

Answer 17

Actin-supported tentacles

Question 18

Describe loricate choanoflagellates

Answer 18

Cell secreted a glass basket

Question 19

What is the opposite of a loricate choanoflagellate

Answer 19

Naked choanoflagellates

Question 20

Describe the evolution of animal gametes

Answer 20

• haploid sex cells of very different sizes
• different sizes = different investment of resources
• had a massive effect on subsequent evolution of animal behaviour

Question 21

Describe epithelial cell sheets

Answer 21

• evolutionary innovation in animals
• watertight
• allow maintenance of ion concentrations
• tough
• fold to make complex shapes

Question 22

The cell theory was a

Answer 22

Watershed moment

Question 23

Why is it important to protect the germline?

Answer 23

mutations, predation and damage undesirable

Question 24

How might the germline be protected?

Answer 24

• physical protection: hide em
• cellular mechanisms: molecular repair mechanisms

Question 25

What do the choanoflagellates use to set up their currents?

Answer 25

Flagellum

Question 26

What is the flagellum made of?

Answer 26

Tubulin