1.4- STARCH, GLYCOGEN AND CELLULOSE

Question 1

What is starch?

Answer 1

a polysaccharide found in many parts of a plant in the form of small grains

Question 2

Where do especially large amounts of starch occur?

Answer 2

in seeds and storage organs, such as potato tubers

Question 3

Why is starch an important component of food?

Answer 3

major energy source in most diets

Question 4

What is starch made up of?

Answer 4

chains of α-glucose monosaccharides linked by glycosidic bonds

Question 5

How are glycosidic bonds formed?

Answer 5

by condensation reactions

Question 6

How can the chains of starch be?

Answer 6

branched or unbranched

Question 7

What happens to the unbranched chains of starch?

Answer 7

wound into a tight coil that makes the molecule very compact

Question 8

What is the main role of starch?

Answer 8

energy storage

Question 9

How is starch being insoluble helpful?

Answer 9

doesn’t affect water potential, so water is not drawn into the cells by osmosis

Question 10

How is starch being large and insoluble helpful?

Answer 10

does not diffuse out of cells

Question 11

How is starch being compact helpful?

Answer 11

so a lot of it can be stored in a small space

Question 12

How is when starch is hyrdrolysed it forms α-glucose helpful?

Answer 12

easily transported and readily used in respiration

Question 13

How does the starch with branched forms having many ends helpful?

Answer 13

the ends can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly

Question 14

Where is starch never found?

Answer 14

in animal cells

Question 15

What similar polysaccharide similar to starch serves the same role?

Answer 15

glycogen

Question 16

Where can glycogen be found?

Answer 16

in animals and bacteria but never in plant cells

Question 17

Glycogen is very similar to the structure of what?

Answer 17

the structure of starch but glycogen has shorter chains and is more highly branched

Question 18

Why is glycogen sometimes called “animal starch”?

Answer 18

as it is the major carbohydrate storage product of animals

Question 19

How is glycogen stored in animals?

Answer 19

as small granules mainly in the muscles and the liver

Question 20

Why is the mass of carbohydrates that is stored relatively small?

Answer 20

as fat is the main storage molecule in animals

Question 21

How is glycogen being insoluble helpful?

Answer 21

does not tend to draw water into the cells by osmosis

does not diffuse out of cells

Question 22

How is glycogen being compact helpful?

Answer 22

so a lot of it can be stored in a small space

Question 23

How is glycogen being more highly branched than starch and having more ends make is helpful?

Answer 23

it can be acted on simultaneously by enzymes. Therefore more can be rapidly broken down to form glucose monomers, which are used in respiration

Question 24

Why is glycogen being broken down into glucose important?

Answer 24

it’s important to animals which have a higher metabolic rate and therefore respiratory rate than plants because they are more active

Question 25

In what major aspect does cellulose differ from starch and glycogen?

Answer 25

it is made of monomers of β-glucose rather than α-glucose

Question 26

How does cellulose being made up of β-glucose monomers make it differ from starch and glycogen?

Answer 26

in structure and function of this polysaccharide

Question 27

How are celluloses’ chains?

Answer 27

straight and unbranched rather than forming a coiled chain like starch

Question 28

How are the cellulose chains arranged?

Answer 28

run parallel to one another

Question 29

What does cellulose chains running parallel allow?

Answer 29

allows the hydrogen bonds to form cross-linkages between adjacent chains

Question 30

What is the effect of the cross-linkages between each individual bond in cellulose?

Answer 30

the sheer overall number of them makes a considerable contribution to strengthening cellulose, making it the valuable structural material it is

Question 31

What does cellulose molecules grouped together form?

Answer 31

microfibrils

Question 32

How is microfibrils arranged?

Answer 32

in parallel groups called fibres

Question 33

Why is cellulose a major component of plant cells walls?

Answer 33

provides rigidity to the plant cell

Question 34

What does the cellulose cell wall prevent?

Answer 34

prevent the cell from bursting as water enters it by osmosis

Question 35

How does the cellulose cell wall prevent the cell from bursting?

Answer 35

by excreting an inward pressure that stops any further influx of water

Question 36

What is the result of cellulose cell walls being able to prevent cells from bursting?

Answer 36

living plant cells are turgid and push against one another, making non-woody parts of the plant semi-rigid

Question 37

Why is this especially important for plant cells to be turgid?

Answer 37

in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis

Question 38

How is cellulose being made up of β-glucose helpful?

Answer 38

form long straight, unbranched chains

Question 39

How is cellulose molecular chains running parallel to each other and being cross linked by hydrogen bonds helpful?

Answer 39

add collective strength

Question 40

How is cellulose molecules being grouped to form microfibrils which in turn are grouped to form fibres helpful?

Answer 40

provide yet more strength