Cellulose and starch

Question 1

What is cellulose

Answer 1

Cellulose is a polymer of beta glucose, every other beta glucose molecule inverts. Because it is unbranched, it allows cellulose molecules to pack together. Hydrogen bonds hold parallel cellulose chains together to form microfibrils. Multiple hydrogen bonds makes cellulose stable. Larger structure is a microfibril

Question 2

What is a reason for cellulose strength

Answer 2

Microfibrils are laid down in a cross cross arrangement which adds to strength. Parallel chains of cellulose are held together by hydrogen bonds, forming microfibrils. Individually, hydrogen bonds are relatively weak compared to glycosidic bonds, but the large number of them produces a strong structure.
Pectin and hemicellulose hold microfibrils together

Question 3

What is structure of starch

Answer 3

Starch is a polysaccharide made from alpha glucose. 2 forms of starch are amylose and amylopectin.

Question 4

What glycosidic bonds to straight chains lead to

Answer 4

Straight chains lead to 1,4 glycosidic bonds

Question 5

What glycosidic bonds do branched chains lead to

Answer 5

Branched chains lead to 1,6 glycosidic bonds.

Question 6

Properties of starch

Answer 6

Properties of starch include: tightly packed, insoluble so doesn’t exert osmotic pressure.

Question 7

What are similarities and differences between cellulose and starch

Answer 7

Similarities are:
Both are polysaccharides
Both contain 1,4 glycosidic bonds
Differences:
Cellulose contains beta glucose whereas starch has alpha glucose
Cellulose doesn’t have 1,6 glycosidic bonds
Starch is an energy storage molecule in plants, cellulose is a structural molecule of plant cell walls.

Question 8

Compare properties of cellulose and starch

Answer 8

Cellulose and starch are insoluble, so n osmotic effect
Cellulose has Hbonds between parallel chains to give strength
Cross cross arrangement of cellulose microfibrils make cell wall very strong.
Starch is compact so lots can fit in small area
Large so can’t diffuse out of cell

Question 9

What is pectin and where is it found

Answer 9

Pectin is a glue which holds the cellulose microfibrils together. It is an important component of middle lamella, it holds cells together.

Question 10

What is hemicellulose

Answer 10

Hemicellulose is a glue which holds together microfibrils of cellulose

Question 11

What happens if cell wall isn’t maintained

Answer 11

If cell wall isn’t maintained plant will become flaccid and wilt.

Question 12

How are cellulose polymers held together and what does this form

Answer 12

Cellulose polymers form H bonds with each other as they are unable to coil and form branches.
This forms microfibrils

Question 13

What are microfibrils held together by

Answer 13

Microfibrils are held together by polysaccharides hemicellulose and pectin.

Question 14

Where is the bond between microfibrils that holds them together

Answer 14

The bond is between the O of OH molecule with a H on the adjacent molecule.

Question 15

Why is glucose soluble

Answer 15

Glucose is soluble because it has a large number of hydroxyl groups (which are polar).

Question 16

What is the problem with glucose being soluble

Answer 16

Problem with glucose being soluble is that if there is a large amount of dissolved glucose in a cell, it can cause water to enter via osmosis.

Question 17

How does strength of cellulose cell wall help carry out its functions

Answer 17

Strength of cellulose allows cell wall to carry out its functions because cellulose cell wall is permeable to molecules e.g water, as water moves in by osmosis, plant cell contents push outwards against cell wall and strength of cell wall means it can resist outward pressure of cell contents, this prevents plant from bursting.