chapter 26

Question 1

what do single-celled organisms do?

Answer 1

• eat other microorganisms
• live suspended in water columns

Question 2

simple multicellular organisms are bigger than prokaryotes, why is that, what does their size help them do?

Answer 2

their size helps avoid being eaten and can stabilize location in a water column

Question 3

in organisms with coenocytic organization there are many (blank) but only one (blank)

Answer 3

nuclei, cell

Question 4

coenocytic organization
- the cell nuclei divide multiple times but are not partitioned into individual cells
- multiple divisions of nuclei, along with no partitioning of nuclei, result in very large cells with many nuclei

Answer 4

!

Question 5

what are some features of simple multicellular organisms?

Answer 5

• adhesion molecules present
• complex multicellular are bigger

Question 6

what’s the cost of being a large multicellular organism?

Answer 6

as multicellular organisms get larger, only certain cells are responsible for the organism’s reproduction

Question 7

what are some of the rules for complex multicellularity?

Answer 7

• cell adhesion
• cell communication (gap junctions, plasmodesmata)
• signaling/ sensory systems
• different functions of an organism’s body

Question 8

what do complex multicellular organisms consist of?

Answer 8

• animals
• green algae
• red algae
• brown algae
• fungi

Question 9

how many times have complex multicellularity evolved?

Answer 9

six times

Question 10

what are the best known examples of complex multicellular organisms?

Answer 10

plants and animals

Question 11

define diffusion

Answer 11

the random motion of molecules, with net movement from areas of higher to lower concentration

Question 12

define bulk flow

Answer 12

moving everything all at once

Question 13

why are diffusion and bulk flow highly important mechanisms for multicellular organisms?

Answer 13

they are important for multicellular organisms to transport necessary molecules

Question 14

what is one disadvantage of bulk flow?

Answer 14

it needs ATP to run it

Question 15

how can multicellular organism communicate?

Answer 15

• hormones and receptors
• nervous system
• direct cell contact

Question 16

what are blastula?

Answer 16

when fertilized eggs undergo several rounds of mitosis, they form a ball of undifferentiated cells called a blastula

Question 17

cells differentiate depending on which genes are switched off or on.

Answer 17

!

Question 18

what are gastrula?

Answer 18

it’s a hollow ball that brings new population of cells in direct contact with one another.

Question 19

cells have different fates depending on which genes are turned off or on.

Answer 19

!

Question 20

complex multicellularity requires complex genetic programming of cells

Answer 20

!

Question 21

genes are turned off or on depending on the molecular signals the cell receives

Answer 21

!

Question 22

what is pattern formation?

Answer 22

different gene families playing a role in development in multicellular organisms

Question 23

complex development arises from gradients of signals along the developing body

Answer 23

!

Question 24

what are the three conditions required for development of complex organsims?

Answer 24

1. cell adhesion
2. cell communication
3. growth and development for complex multicellularity

Question 25

complex multicellular land plants orginated a while ago, why was the transition so hard?

Answer 25

photosynthesis had to be carried out in tissues that were surrounded by air instead of water

Question 26

how can two cells of a complex multicellular organism have the same genome but markedly different structures and functions?
A. during differentiation, as cells become specialized, they lose portions of their genome that are no longer needed.
B. different genes are expressed in different cells.
C. part of the process of differentiation of cells is to create mutations in the genome.
D. once differentiation begins, the genome no longer controls cellular functions.

Answer 26

the answer is B

Question 27

the acquisition of traits necessary for complex multicellularity occurred independently in plants and animals but took place in a specific order. In what order did these traits evolve?
A. cell adhesion molecules, a mechanism of communication, bulk flow
B. bulk flow, a mechanism of communication, cell adhesion molecules
C. a mechanism of communication, bulk flow, cell adhesion molecules
D. a mechanism of communication, cell adhesion molecules, bulk flow

Answer 27

the answer is A.

Question 28

which of the following options is believed to be the major event that led to the appearance of large complex animals on earth?
A. the increase in atmospheric oxygen
B. the diversification of seaweeds in the ocean
C. the appearance of plants on land
D. the appearance of bulk flow systems

Answer 28

the answer is A.

Question 29

which of the following characteristics likely contributed to plant colonization of continental regions farther from standing water?

A. absorption of water through diffusion on photosynthetic tissue
B. ability to perform photosynthesis
C. development of vascular tissue for bulk flow
D. cell-cell adhesion, which provides structural support for multicellularity

Answer 29

the answer is C. moving into the interior of terrestrial environments likely limited access to water. developing root systems wherein water is pulled up from the ground, and then transported through the vascular tissue of the plant, relieves the necessity of living near water sources.