cell walls & their role in regulating plant cell shape (lecture 8)

Question 1

describe the structure and function of the primary plant cell wall

Answer 1

cell wall structure is a two phase process:
phase one: microfibrils (crystalline phase)
- cellulose forms microfibrils (highly organised structures)
phase two: matrix (non-crystalline matrix)
- pectin polysaccharides
- hemicellulose polysaccharides

Question 2

outline the structure of the vacuole and how it maintains plant cell shape

Answer 2

• key balance in turgor pressure within the cell for structural plant support
• high concentrations of solutes in the vacuole
• osmosis allows water to pass in out of vacuole
• limits water uptake to prevent hypertonic cells

Question 3

explain the process of synthesising the plant cell wall

Answer 3

• cellulose microfibrils are synthesised at the plasma membrane
• pectin & hemicellulose are synthesised at the Golgi, then vesicles transport to the plasma membrane
• extensin is synthesised in the rER and vesicle transported to plasma membrane via the Golgi
• with all vesicles fusing to the plasma membrane

Question 4

outline the structure and function of the secondary plant cell wall

Answer 4

• not present in all plant cells
• only produced once cell growth has stopped
• thicker and stronger than primary due to multi layer structure and differentiation in microfibril orientation
• less pectin, more cellulose, and lignin present

Question 5

outline the structure and function of plasmodesmata

Answer 5

• these connections enable intercellular communication
• allows passive exchange of small molecules
• ER prevents walls forming through them

Question 6

describe hemicellulose & pectin

Answer 6

hemicellulose - a heterogeneous group of polysaccharides. singular long chain of one sugar with additional short side chains forming rigid structure

pectin - brached, negatively charged polysaccharides, they bind water due ti they gel like properties

Question 7

describe the extensibility of the plant cell wall, how does this happen

Answer 7

the protein extensin binds the componenets of the cell wall allows for the extensibility/expansion of cells to be controlled, where cross linking of pectin and cellulose reduces the cell walls ability to expand and therefore is stronger, but also dehydrated

Question 8

describe lignin and its benefits for the secondary cell wall structure

Answer 8

• second most abundant organic molecule
• complex polymer
• ensures strength and rigidity while excluding water