Lecture 7: Cell walls & their role in regulating plant cell shape

Question 1

protoplast means…

Answer 1

everything inside a cell

Question 2

Plant cell =

Answer 2

cell wall + protoplasts

Question 3

Cell wall composition:

Answer 3

cellulose a glucose polymer

most abundant organic macromolecule

Question 4

cellulose forms

Answer 4

microfibrils

Question 5

Phase 1/2 of cell wall structure:

Answer 5

• crystalline microfibrilliar phase

- noncrystalline matrix (non organised)

Question 6

Crystalline microfibrillar phase:

Answer 6

cellulose

Question 7

Noncrystalline matrix phase:

Answer 7

• pectin polysaccharides
• hemicellulose polysaccharides
• network of extensin

Question 8

Hemicellulose:

Answer 8

• heterogeneous group of polysaccharides
• long chain of single sugar
• short side chains form rigid structure

Question 9

Pectin:

Answer 9

negatively charged polysaccharides, that bind water

Question 10

Extensin cross linking:

Answer 10

• occurs with pectin and cellulose
• dehydrates cell wall
• reduces extensibility/increases strength

Question 11

rosettes:

Answer 11

cellulose synthase

that move parallel to cortisol microtubules

Question 12

Synthesis of primary cell wall:

1.

Answer 12

cellulose microfibils are made by rosettes at plasma membrane

Question 13

Synthesis of primary cell wall:

2.

Answer 13

polysaccharides made in the Golgi apparatus are transported to cell wall by vesicles

Question 14

Synthesis of primary cell wall:

3.

Answer 14

extensins made and transported from rER

Question 15

Cell wall functions:

Answer 15

• influence cell morphology
• provides structural support
• prevents excessive water uptake

Question 16

Corticol microfibrils

Answer 16

control microfibril production

Question 17

Cell morphology:

randomly orientated microfibrils

Answer 17

expand equally in all directions

Question 18

Cell morphology:

right angle to long axis of cell microfibrils

Answer 18

expand longitudinally

Question 19

Cell wall structural support:

Answer 19

protoplasts push against cell wall - rigidity

Question 20

Cell wall limits water uptake:

Answer 20

water in the cells pushes protoplasts against cell wall limiting water uptake

Question 21

Vacuoles:

Answer 21

• surrounded by single membrane

- highly selective

Question 22

Vacuoles, function in cell shape regulation:

Answer 22

• high concentration of solutes inside
• causes osmosis
  produces large internal pressure

Question 23

Secondary cell wall:

Answer 23

• not present in all plant cells
• thicker and stronger than primary cell walls
• provides structural support

Question 24

Secondary cell wall structure:

Answer 24

• multiple layers
• microfibrils have different orientations
• strengthens secondary wall

Question 25

Chemical characteristics of secondary cell wall:

Answer 25

• more cellulose
• less pectin
• lignin

Question 26

Lignin:

Answer 26

• second most abundant macromolecule
• complex polymer
• acts to exclude water
• confers rigidity/strength

Question 27

Plasmodesmata:

Answer 27

intercellular connections, that allow intercellular communication

Question 28

Cellular communication:

Answer 28

• continuous plasma membrane
• restricts organelle movement
• ER is connected through plasmodesmata
• allows free exchange of molecules