Lecture 8 - Cell walls & their role in regulating plant cell shape

Question 1

What is the main component of a cell wall?

Answer 1

Cellulose - Organic macromolecule of glucose polymers

Question 2

Cellulose forms…

Answer 2

Microfibrils

Question 3

What are the two phases of cell wall structure?

Answer 3

P1 - Microfibrils (Cellulose)
P2 - Matrix (Pectin and hemicellulose)

Question 4

What is hemicellulose?

Answer 4

A heterogeneous group of
polysaccharides. Long chain
of one type of sugar and
short side chains form a rigid
structure.

Question 5

What is pectin?

Answer 5

Branched, negatively charged
polysaccharides. Bind water and have gel-like properties.

Question 6

The extensibility (expansion) of cells can be controlled by…

Answer 6

Extensin cross-linking

Question 7

What does extensin cross-linking of pectin and cellulose do?

Answer 7

Dehydrates the cell wall, reduces extensibility and increases strength

Question 8

Cellulose is a polymer of ___________________ subunits linked together to
form strong structures called _________________.

Answer 8

Cellulose is a polymer of GLUCOSE subunits linked together to
form strong structures called MICROFIBRILS.

Question 9

Synthesis of cellulose microfibrils occurs at:

Answer 9

Plasma membrane

Question 10

Synthesis of pectin and hemicellulose occurs in:

Answer 10

The Golgi apparatus where they are then delivered to cell wall in vesicles

Question 11

Pectin and hemicellulose are which type of saccharide?

Answer 11

Polysaccharide

Question 12

What are extensins?

Answer 12

Cell wall proteins

Question 13

Synthesis of extensins occurs at:

Answer 13

Rough ER, where they then fuse into plasma membrane

Question 14

What is the structure of the cytoskeleton?

Answer 14

A network of microtubules,
microfilaments (and intermediate filaments) that extend throughout
the cytoplasm

Question 15

What is the main function of the cytoskeleton?

Answer 15

Structural support

Question 16

What produces cellulose microfibrils?

Answer 16

Rosettes in the plasma membrane

Question 17

What are rosettes?

Answer 17

Protein complexes (enzymes) that span the plasma membrane

Question 18

What is the basic structure of a cell wall?

Answer 18

Plasma membrane, primary cell wall, middle lamelae

Question 19

T or F

Cellulose forms microfibrils that are highly ordered and provide strength to the cell wall

Answer 19

True

Question 20

T or F

Extensin cross links polysaccharides this increases the extensibility of the cell wall

Answer 20

False, it decreased the extensibility

Question 21

T or F

Pectin and hemicellulose are transported to the cell surface by exocytosis

Answer 21

True

Question 22

T or F

The plant cell wall allows excessive water uptake

Answer 22

False

The cell wall PREVENTS excessive water uptake

Question 23

T or F

Orientation of the cellulose microfibrils influences cell morphology

Answer 23

True

Question 24

What happens to cell shape if cellulose microfibrils are ordered randomly?

Answer 24

The cell will expand
equally in all
directions.

Question 25

What happens to cell shape if cellulose microfibrils are ordered right angles to the ultimate long axis of the cell?

Answer 25

The cell will expand longitudinally along that axis.

Question 26

What is a protoplast?

Answer 26

Inside of the cell (cell minus call wall)

Question 27

Why does wilting of a plant occur?

Answer 27

The protoplast is not pushing against the cell wall.

Question 28

Protoplast pushing against the cell wall leads the plant to be...

Answer 28

Rigid and maintaining structure

Question 29

What is a vacoule? (3 statements)

Answer 29

- Organelle with single membrane - Highly selective - Water enters and leaves via osmosis

Question 30

What is osmosis?

Answer 30

The diffusion of water across a selectively permeable membrane A high water (low solute) concentration to a low water (high solute) concentration

Question 31

T or F All plant cells have a secondary cell wall

Answer 31

False

Question 32

T or F The secondary cell wall is produced only after cell growth has stopped

Answer 32

True

Question 33

T or F The secondary cell wall provides more structural support than the primary cell wall

Answer 33

True It is thicker and stronger

Question 34

Why is the secondary cell wall thicker and stronger than primary cell walls? (3)

Answer 34

- Made up of multiple layers - Microfibrils in each layer have different orientations - More cellulose

Question 35

Where is ligin found?

Answer 35

In the secondary cell walls

Question 36

What is ligin?

Answer 36

A complex polymer that confers strength and rigidity to the secondary cell wall and acts to exclude water

Question 37

What is plasmodemata?

Answer 37

Cell communication. Plasmodesmata are intercellular connections, that enable cell to cell communication.