Evolution Of Multicellularity

Question 1

What’s the difference in lifespan between unicellular and multicellular organisms?

Answer 1

Unicellular have short life spans

Question 2

How many body cells and cell types do humans have?

Answer 2

~37 trillion

200 cell types

Question 3

What does the ectoderm become?

Answer 3

• Skin cells of epidermis
• Neuron of brain
• Pigment cell

Question 4

What does mesoderm become?

Answer 4

• Cardiac muscle
• Skeletal muscle
• Smooth muscle of gut
• Tubule cell of kidney
• Red blood cells

Question 5

What does endoderm become?

Answer 5

• Alveolar cells
• Thyroid cells
• Pancreatic cells

Question 6

How to Euglena, Paramycium and Amobae divide?

Answer 6

Euglena- longitudinal binary fission

Paramecium- Transverse binary fission

Amobae- irregular binary fission

Question 7

What is the symbiotic theory of evolution?

Answer 7

1. Different species derive mutual benefits from association
2. Each evolves to be dependant
3. Fusion of genomes makes new species and single germ line
4. Differential gene expression maintains differential phenotypes

Question 8

What is the coenocytial theory of evolution?

Answer 8

1. Individual cells form a coenocyte through incomplete cell division
2. Membranes form between nuclei creating separate cells
3. Somatic and germ cell lines are formed and cells arrange to form inside out polarity
4. Hollow sphere invaginates to form cell layers and tissue types (like embryonic stages in animals)

Question 9

What is the colonial theory of evolution?

Answer 9

1. Cells derive benefits from aggregation and cooperation
2. Somatic and germ cell lines are formed and cells arrange to form inside out polarity
3. Hollow sphere invaginates to form cell layers and tissue types (like embryonic stages in animals)

Question 10

Describe the structure of Volvox

Answer 10

• Individual cells form colonies (up to 50,000)
• Eyespots allow them to swim near light
• Flagellates allow locomotion

Question 11

What is a gonidium?

Answer 11

Reproductive cell of Volvox

Question 12

Outline the asexual lifecycle of Volvox

Answer 12

1. Juveniles and gonidia mature
2. Embryogenesis- mature to adults and juveniles
3. Death of parental somatic cells and juvenile release

Question 13

Outline the sexual reproduction of Volvox

Answer 13

1. Modified embryonic development of gonidia

2. -> gametes not juveniles

Question 14

What is a choanocyte?

Answer 14

Sponge collar cell

Question 15

What does a choanocyte do?

Answer 15

• Wafts water up vase of sponge with flagellum

* Food particles caught in mucus and taken in by phagocytosis

Question 16

What are choanoflagellates?

Answer 16

Unicellular organism

Similar to choanocytes

Question 17

Outline the lifecycle of dictyostelium

Answer 17

1. Aggregation- competent cells form aggregation stream
2. Mound forms
3. Tipped aggregate forms
4. Slug forms, with prespore cells and prestalk cells
5. Culminant forms fruiting body
6. Spores released -> growth phase and repeat

Question 18

What are the most important genes for multicellularity?

Answer 18

• Hox genes- anterior/posterior patterning
• Cell signalling molecules- FGF, Wnt, Notch, Hedgehog
• Adhesion molecules and extracellular matrix- forming tissues and organs, Cadherins, NCAM, Integrins, Collagen, Laminin