Starch, glycogen + cellulose (specific polysaccharides)

Question 1

Describe the structure of starch

Answer 1

• made up of chains of alpha-glucose (formed by condensation reactions)
• chains can be branched or unbranched
• unbranched chain: wound into a tight coil which make the molecule very compact

Question 2

Name two types of starch

Answer 2

Amylose

Amylopectin

Question 3

Describe the function of starch

Answer 3

• Forms an important component in food
• The major energy source in most diets
• Energy storage

Question 4

Describe the role of structure in the function of starch (energy storage)

Answer 4

Insoluble so doesn’t affect water potential - means water is not drawn into cells by osmosis
Large + insoluble - doesn’t diffuse out of cells
Compact - lots can be stored in a small space
When hydrolysed forms alpha-glucose - means it’s easily transported + readily used in respiration
Branched form has many ends - so can be acted on by enzymes simultaneously meaning glucose monomers are released very rapidly

Question 5

State where starch is found (type of cells)

Answer 5

only found in plants cells

Question 6

Describe the structure of glycogen

Answer 6

• Very similar to starch but has shorter chains + more highly branched
• In animals stored as small granules mainly in the nucleus + liver

Question 7

Describe the function of glycogen

Answer 7

• Major carbohydrate storage product of animals

- Mass of carbohydrate stored is relatively small as fast is the main storage molecule in animals

Question 8

Describe the role of the structure in the function of glycogen (storage)

Answer 8

Insoluble - so doesn’t tend to draw water into cells by osmosis
Insoluble - doesn’t diffuse out of cells
Compact - lots can be stored in a small space
More highly branched than starch so has more ends that can be acted on simultaneously by enzymes so rapidly broken down to form glucose monomers used in respiration - important to animals with high metabolic + respiratory rate than plants (as they’re more active)

Question 9

Draw a simple diagram of starch/glycogen structure (same but glycogen has shorter chains + more highly branched) and a quick description

Answer 9

a-glucose unbranched helical chain

The OH groups pointing inwards form the hydrogen bonds it holds the helix chain in place

Question 10

Describe the function of cellulose

Answer 10

• Major component of plant cell walls + provide rigidity to plant cell
• Cellulose cell wall prevents cell from bursting as water enters it by osmosis (exerts inward pressure that stops anymore influx of water
• turgid plant cells push against one another + makes the plant semi-rigid - important to maintaining stems +leaves in turgid state to provide max. surface area for photosynthesis

Question 11

Describe the role of structure in the function of cellulose (support + rigidity)

Answer 11

• The molecules are made up of B-glucose so form long, straight + unbranched chains
• Cellulose molecular chains run parallel to each other + are cross-linked by H bonds which add collective strength
• Molecules are grouped to form microfibrils which are grouped to from fibres + provides yet more strength

Question 12

State where glycogen is found (type of cells)

Answer 12

Animal and bacteria cells

Question 13

State where cellulose is found (type of cells)

Answer 13

Plant cells

Question 14

Draw a simple diagram of cellulose with a quick description

Answer 14

Cellulose molecules composed of B-glucose molecules

Microfibrils made up of cellulose molecules