Cell Walls and their role in regulating plant cell shape

Question 1

what are the components in a Plant Cell

Answer 1

• nucleus
• golgi apparatus
• central vacuole
• mitochondria
• chloroplast
• cell wall
• plasmodesmata

Question 2

What is the primary cell wall structure made of

Answer 2

• cellulose - a major structure

Question 3

describe what cellulose is

Answer 3

• the most abundant organic macromolecule on earth
• glucose polymer
• highly ordered
• long, ribbon-like structures

Question 4

what does cellulose form, also describe it

Answer 4

microfibers

• highly organized structures
• are strong and form major component of both primary and secondary cell walls

Question 5

what is the 1st phase of the cell structure called

Answer 5

• crystalline Microfibrillar phase

- cellulose

Question 6

what is the second phase called

Answer 6

• Noncrystalline Matrix
• makes pectin polysaccharides + hemicellulose polysaccharides
• also a network of Extensin

Question 7

describe what hemicellulose is

Answer 7

is a heterogeneous group of polysaccharide.

- long chain of one type of sugar and short side chains form a rigid structure

Question 8

describe what Pectin is

Answer 8

• is branched, negatively charged polysaccharides.

- they bind water and have gel-like properties

Question 9

describe what extensin does

Answer 9

• the expansion of cells can be controlled by extension cross linking
• extensin cross-linking of pectin and cellulous dehydrates the cell wall, reduces extensibility and increases strength

Question 10

what are the processes that happens during the synthesis of the primary cell wall

Answer 10

• coordinated synthesis and delivery

- exocytosis

Question 11

what is the coordinated synthesis and delivery stage known for

Answer 11

1) cellulose microfibers at cell wall/plasma membrane
2) polysaccharides (pectin + hemicellulose) in the golgi apparatus are transported to the wall in vesicles
3) cell wall proteins (extensins) from the rough ER, the vesicles fuse to the membrane

Question 12

what is exocytosis

Answer 12

• transports material out of the cell or delivers it to the cell surface
• CONSITUTIVE EXOCYTOSIS releases extracellular matrix proteins

Question 13

what direction does the cellulose-producing rosettes move towards

Answer 13

• they move parallel to the cortical microtubules

Question 14

what 3 functions does the cell wall do to regulate the cell shape

Answer 14

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

Question 15

describe how cell morphology helps regulate the cell structure

Answer 15

• the orientation of the cellulose microfibrils influence cell morphology.
• randomly oriented : the cell will expand equally in all directions
• right angles to the ultimate long axis of cell: the cell will expand longitudinally along that axis

Question 16

describe how it provides structural support

Answer 16

• the protoplast pushes against the cell wall. the cells become turgid and this maintains the plant structure
• wilting occurs when the protoplast is not pushing against the cell wall
• water loss from cells reduce the protoplast volume and the protoplast does not press in the wall, it will become flaccid

Question 17

describe how it prevent excessive water uptake

Answer 17

• this is through osmosis
• as water enters the cell, the protoplast expands and pushes against the cell wall
• pressure from the cell wall limits the volume that can be taken up
• the amount of water in the cell determines the pressure in the cell

Question 18

describe the structure of the vacuoles

Answer 18

• a vacuole of an organelle surrounded by a single membrane
  
  • is highly selective, controlling much of what enters and leaves the vacuole
  • water moves in the vacuole by osmosis
• typical nature plant cell has a single large vacuole

Question 19

what functions does the vacuoles have to help regulate the cell shape

Answer 19

• there is a high concentration of solutes in the vacuole, resulting in water uptake into the vacuole by osmosis. the plant cell wall limits water uptake and prevents the cell bursting.
• the plant cells build up a larger internal pressure that contributes to plant structural support

Question 20

what is osmosis

Answer 20

• the diffusion of water across a selectively permeable membrane

Question 21

describe the secondary cell wall

Answer 21

• not all plant cells have this
• produced only after cell growth has stopped
• thicker and stronger than primary walls
• provides more structural support than primary cell wall

Question 22

what are the chemical characteristics of the secondary cell wall

Answer 22

• more cellulose
• less pectin
• lost of lignin

Question 23

describe what lignin is

Answer 23

• is the second most abundant organic macromolecule
• is a complex polymer
• confers strength, rigidity to the secondary cell wall and acts to exclude water

Question 24

what does the secondary cell wall provide structural support for

Answer 24

• specific cell types, such as water transporting cells and for the whole plant

Question 25

what is Plasmodesmata

Answer 25

• are intercellular connections, that enable cell to cell communication

Question 26

describe plasmodesmata

Answer 26

• the plasma membrane is continuous
• small enough to prevent organelle movements - although endoplasmic reticulum is connected through plasmodesmata
• allows the free exchange of small molecules