Ch. 28 Multicellularity

Question 1

which eukaryotic organisms have complex multicellularity?

Answer 1

land plants
animals
fungi

Question 2

how many major groups are present within the 7 superkingdoms? how many contain single celled organisms? how many are simple multicellular?

Answer 2

119 major groups total
83 contain single celled organisms
remaining 36 groups are simple multicellular

Question 3

characteristics of single celled organisms

Answer 3

• cells eat other microorganisms
• ingest small organic particles
• live suspended in water columns
• are parasites living within other organisms

Question 4

who are simple multicellulars?

Answer 4

• Fungi
• Algae
• Slime molds
• Sporozoans and Cnidosporas
• Dinoflagellates

Question 5

characteristics of simple multicellulars

Answer 5

• Form is filamentous, hollow balls or flat sheets
• Adhesion molecules for sticking together
• Most cells retain a full range of functions
• All cells are still in contact with environment

Question 6

coenocytic organization

Answer 6

• Nuclei divide multiple times but do not partition into
individual cells.
• Results in sometimes very large multinucleated cells

Question 7

why be multicellular? advantages?

Answer 7

• Because there is some selective advantage to
being multicellular…
• So, what are those advantages? Maybe:
– Avoid predators 
– Float better 
– Hold together better than cluster of single cells 
– Withstand disturbance better 
– Withstand desiccation better

Question 8

who are the complex multicellulars?

Answer 8

red algae 
brown algae 
fungi 
animals 
land plants 
*collectively evolved at least 6 different times, fungi evolved 2 times

Question 9

what features do complex multicellulars have in common?

Answer 9

1. Highly developed mechanisms for adhesion between
   cells
2. Specialized structures for cell communication
3. Tissue and organ differentiation
4. A small subset of cells contribute to reproduction
5. Cell or tissue loss can be lethal for the organism
6. Presence of both interior and exterior cells

Question 10

what is one serious problem for multicellulars?

Answer 10

limitations of diffusion

Question 11

define diffusion

Answer 11

Movement of molecules from areas of
high to low concentration acting over small
distances

Question 12

define bulk transport

Answer 12

The means by which molecules move through organisms at rates beyond those possible by diffusion across a concentration gradient (by means of vascular system)

Question 13

what are 3 requirements for complex multicellular life?

Answer 13

1. Adhesion: Stick together
   2.Communicate with one another
   3.Have a genetic program to guide growth
   and development

Question 14

how do animal cells perform cell adhesion?

Answer 14

cadherins, integrins and transmembrane proteins

Question 15

how do plant cells perform cell adhesion?

Answer 15

pectins

Question 16

how do choanoflagellates perform cell adhesion?

Answer 16

cadherins

Question 17

how do animal cells communicate?

Answer 17

gap junctions (intercellular connections made of a ring of protein)

Question 18

how do plant cells communicate?

Answer 18

plasmodesmata (tubules that connect the intermembranes of neighboring plant cells)

Question 19

how do animal cells develop?

Answer 19

gastrulation (the movement of cells during embryogenesis that transforms a blastula to a gastrula)

Question 20

how do plant cells develop?

Answer 20

Meristems - the actively growing cells at the tips of stems and roots

Question 21

define gastrula

Answer 21

an embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells

Question 22

define blastula

Answer 22

an animal embryo at the early stage of development when it is a hollow ball of undifferentiated cells