[1.4] starch, glycogen and cellulose

Question 1

how is starch produced?

Answer 1

when glycosidic bonds form between α glucose molecules in condensation reactions after photosynthesis

Question 2

where is starch found?

Answer 2

all plant cells as storage organs

Question 3

how is starch an important storage molecule: [1] insoluble

Answer 3

doesn’t affect water potential of the plant cell and cause water movement through osmosis

Question 4

how is starch an important storage molecule: [2] compact

Answer 4

• can be stored in a small space
• unbranched chains of 1,4 glycosidic bonds form tight coils, helices, that make it compact

Question 5

how is starch an important storage molecule: [3] large and insoluble

Answer 5

because it is large and insoluble, starch does not diffuse out of cells

Question 6

how is starch an important storage molecule: [4] hydrolysis

Answer 6

can be hydrolysed to form alpha glucose molecules, which can then be used in respiration

Question 7

how is starch an important storage molecule: [5] large surface area

Answer 7

branched form has many ends, so provides a large surface area for the action of enzymes to release glucose monomers

Question 8

what are the 2 subunits in starch?

Answer 8

amylose

• unbranched (coiled)
• 1,4 glycosidic bond
• 20-30%

amylopectin

• branched
• 1,6 glycosidic bond
• 70-80%

Question 9

what is glycogen made up of?

Answer 9

alpha glucose molecules that are bonded together via glycosidic bonds

Question 10

how and why is glycogen different from starch?

Answer 10

• glycogen is more branched than starch
• greater end chains so greater SA for enzymes to act on and release glucose for respiration, which releases energy
• animals have a much higher metabolic rate than plants as they are more active

Question 11

explain 2 important properties of glycogen

Answer 11

1. insoluble
   - does not affect water potential of the cell and so does not affect osmosis
   - does not diffuse out of cell
2. highly compact for efficient storage

Question 12

what is cellulose?

Answer 12

structural polysaccharide composed of monomers of beta glucose

Question 13

describe the structure of cellulose

Answer 13

• cellulose chains are long, straight and parallel to each other due to rotation of every other β glucose molecule
• hydrogen bond cross linkages between adjacent chains

Question 14

what property makes cellulose such an important structural material?

Answer 14

the many hydrogen bond cross linkages between the adjacent chains of the cellulose molecules

Question 15

how is a glycosidic bond formed in cellulose?

Answer 15

in order to form a glycosidic bond between the two beta glucose molecules, each adjacent beta molecule needs to be rotated 180°

Question 16

how are cellulose molecules grouped together?

Answer 16

• cellulose molecules ➞ microfibrils ➞ macrofibrils ➞ parallel groups called fibres
• groupings provide strength and rigidity to plant cell wall

Question 17

what is the purpose of the cellulose cell wall?

Answer 17

• prevents plants bursting when water enters by osmosis
• exerts an inward pressure to stop further influx of water