[1.4] starch, glycogen and cellulose

Question 1

how is starch produced and where is it found?

Answer 1

• produced as a result of photosynthesis
  > made from the formation of glycosidic bonds between alpha glucose molecules in condensation reactions after photosynthesis
• found in all plant cells and are storage organs

Question 2

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

Answer 2

insoluble so does not affect water potential of the plant cell and cause water movement through osmosis

Question 3

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

Answer 3

• compact so can be stored in a small space
• there are unbranched chains of 1,4 glycosidic bonds and branched chains of 1,6 glycosidic bonds
• unbranched chains form tight coils, helices, that make it compact

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

what are the 2 subunits in starch?

Answer 7

amylose

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

amylopectin

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

Question 8

what is glycogen made up of?

Answer 8

alpha glucose molecules that are bonded together via glycosidic bonds

Question 9

how is glycogen structurally different from starch?

Answer 9

• more highly branched than starch
• therefore, there is a higher surface area for enzymes to act on and release glucose molecules for respiration

Question 10

why is glycogen different from starch?

Answer 10

• glycogen is more branched than starch
• greater end chains so a readier source of energy, which can be rapidly broken down, is provided
• animals have a much higher metabolic rate than plants as they are more active

Question 11

what are 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 and what is it made up of?

Answer 12

• cellulose is a structural polysaccharide
• it is composed of monomers of beta glucose

Question 13

what is the structure of cellulose?

Answer 13

• cellulose chains are long and straight and are parallel to each other
  > this is due to the rotation of every other beta glucose molecule
• there are cross linkages via hydrogen bonds 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 are grouped together to form microfibrils, then macrofibrils, which are then arranged into parallel groups called fibres
• these groupings provide both strength and rigidity to the plant cell wall

Question 17

what is the purpose of the cellulose cell wall?

Answer 17

• it prevents plants from bursting when water enters by osmosis
• it exerts an inward pressure that stops any further influx of water