lecture three

Question 1

what does cell growth require?

Answer 1

• increase in cell volume
• increase in protein synthesis and respiration
• cell wall must be able to accommodate the growth

Question 2

how are cellulose microfibrils made?

Answer 2

by cellulose synthase enzymes in the plasma membrane

Question 3

primary cell walls vs secondary cell walls

Answer 3

primary walls:
- deposited during cell expansion
- thin and flexible
- one layer with middle lamella
- usually no lignin
- hydrophilic
secondary walls:
- deposited after cell expansion is completed
- thick and rigid
- can be multiple layers
- lignin is present
- more hydrophobic
- dead after maturity

Question 4

how do secondary cell walls confer mechanical strength?

Answer 4

alternating microfibril orientation: provides structural fortification; resists physical stresses from multiple directions
lignin: provides mechanical strength and hydrophobicity; fortifies walls by filling space between cellulose microfibril bundles and hemicellulose

Question 5

what is a primary pit field?

Answer 5

an area of reduced primary cell wall thickness, often penetrated by numerous plasmodesmata

Question 6

what is the purpose of a meristem?

Answer 6

create new cells to supply the plant while also maintaining itself

Question 7

what are the characteristics of meristematic cells?

Answer 7

• rapid division
• small and cytoplasmically dense
• undifferentiated
• pluripotent (give rise to several different cell types)