Multicellularity

Question 1

What is the Cambrian explosion?

Answer 1

The Cambrian explosion occurred 650 million years ago - it is characterised by the appearance of many multicellular organisms

however fossils of multicellular organisms do date back further than that

2.1 billion years ago - there were worm like structures similar to the mycelia structure

Question 2

Volvox

Answer 2

alga -
all cells in a volvox are the same type and function and they bunch together.

genera of volvox where some species of volvox are multicellular and some are unicellular

Larger spheres encase smaller spheres which are released and can then form smaller spheres within them.

Question 3

Salpingoeca rosetta

Answer 3

Choanoflagellate
- possible sister group to all animals
-similar to sponges
-can grow as a unicellular organism or band together in rosettes (less than 100 cells)
-they form when the cells are hungry (eat bacteria)
-coordinate flagella to move further and find food
facultatively multicellular

Question 4

Dictyostelium discoideum

Answer 4

Protist - slime mould

• usually unicellular
• when hungry it releases signals (cAMP) to which others respond to
• they com together in a pulsing wave
• they coagulate becoming slug like and move together to where better food can be found
• they then grow into a flower (fruiting body of fungus) (swan like) and release spores from the top
• these disperse in the wind and are likely to grow in a location with a better food source
• the cells that make up the stalk dont get to release spores - instead they die in a sacrifice

Question 5

Pseudomonas fluorescens

Answer 5

Bacteria
-can grow a skin/ biofilm
made by bacteria working together 
-stick together and allows bacteria to obtain food from beneath and oxygen from above 
-cooperation

Question 6

Describe an example of experimental evolution

Answer 6

Ratcliff et al

• looks at yeast (unicellular)
• it was grown and centrifuged occasionally

-clumps that precipitated in the centrifuge were chosen
(the larger clumps)
-wanted to see if choosing the larger clumps would cause evolution

• took a few months
• cells evolved into snowflake structures via budding but stayed in contact after cell division

-cell at centre would undergo apoptosis and separate the snowflake

Question 7

Placozoan - trichoplax

Answer 7

Made of a few cells (less than 100)
has no organs
3-4 cell types
has the advantage of being larger.

Question 8

What are some of the advantages of being larger?

Answer 8

1) protection
- Safe from smaller
predators
- If larger can attack
larger prey
2) Movement - faster
3) Attachment
4) Buffering
5) Strength in numbers (motility, filter feeding)

Question 9

Caulerpa taxifolia

Answer 9

Invasive alga used in aquariums
30 cm
multinucleate

Question 10

Syringammina fragilissima

Answer 10

20cm multinucleate cell