Biological molecules: Starch, Glycogen And Cellulose

Question 1

What is starch made of?

Answer 1

Chains of alpha glucose monosaccharides linked by glycosidic bonds that are formed by condensation reactions.

Question 2

How is the helix of a starch molecule held in place?

Answer 2

There are hydrogen bonds between the OH groups as they are pointing inwards

Question 3

What are the two types of starch?

Answer 3

Amylose and amylopectin

Question 4

For amylopectin,
What monomer is it made from?
What are the bonds between the monomers?
What is it’s shape?

Answer 4

• alpha glucose
• 1,4 glycosidic bond
• helix shape

Question 5

For amylopectin,
What monomer is it made from?
What are the bonds between the monomers?
What is it’s shape?

Answer 5

• alpha glucose
• 1,4 and 1,6 glycosidic bonds
• helix shape with branches

Question 6

What are the 5 ways the structure of starch allows its main role to be energy storage

Answer 6

• its insoluble so doesn’t affect water potential so water’s not drawn into cells by osmosis
• its largeness and insolubility stops it diffusing out of cells
• its compact so a lot can be stored in a small space
• when hydrolysed it forms alpha glucose which is both easily transported and readily used in respiration
• amylopectin ( the branched form) has many ends which can be acted upon by enzymes simultaneously meaning glucose monomers are released very rapidly

Question 7

What cells is starch never found in?

Answer 7

Animal cells

Question 8

Where is glycogen found?

Answer 8

Animal and bacterial cells ( never plant cells)

Question 9

How is the structure of glycogen different to starch?

Answer 9

Its more highly branched but has shorter chains than starch

Question 10

How and where is glycogen stored in animals?

Answer 10

As small granules in the muscles and liver

Question 11

Why is the mass of carbohydrate stored in animals relatively small?

Answer 11

Because fat is the main storage molecule in animals

Question 12

Why is the structure of glycogen suited for its storage?

Answer 12

• its insoluble so doesn’t draw water into cells by osmosis and doesn’t diffuse out of cells
• its compact so a lot of it can be stored in a small space
• its more highly branched than starch and so has more ends that can be acted on simultaneously by enzymes and so is more rapidly broke down into glucose monomers which are used in respiration. Important to animals that have a higher metabolic rate and so higher respiratory rate than animals as they are more active

Question 13

What monomers make up cellulose?

Answer 13

Beta glucose monomers

Question 14

What cells is cellulose found in?

Answer 14

Plant cells

Question 15

What is the name of the bonds between the monomers of cellulose

Answer 15

Beta 1,4 bonds

Question 16

What is the structure of cellulose like?

Answer 16

• it has a straight chain
• its unbranched
• every other beta glucose molecule flips by 180 degrees

Question 17

How is cellulose a good structural material in a plant cell wall?

Answer 17

Because between each beta glucose chain, there are weak hydrogen bonds caused by the polarity of the hydrogen bonding with oxygen. As there are many of them, the overall number makes a large contribution to strengthening cellulose

Question 18

What are microfibrils?

Answer 18

The cellulose molecules once they have been grouped together

Question 19

What are fibres?

Answer 19

When the microfibrils have been arranged into parallel groups

Question 20

How is cellulose useful in plant cells?

Answer 20

• provides rigidity in plant cells
• prevents plant cells bursting when water enters by osmosis
• maintains turgidity and rigidity in the cells so the stems and leaves can have maximised surface area for photosynthesis

Question 21

How does cellulose keep the cell wall from bursting?

Answer 21

it exerts an inward pressure that stops any further influx of water and so making non woody parts of the plant semi rigid

Question 22

Why is it important that cellulose maintains stems and leaves in a turgid state?

Answer 22

So that they can provide the maximum surface area for photosynthesis

Question 23

How is the structure of cellulose suited to its function of providing support and rigidity?

Answer 23

1. cellulose molecules are made of beta glucose and so form straight unbranched chains
2. These molecular chains run parallel to each other and are cross linked by hydrogen bonds that add collective strength
3. These molecules are grouped to form microfibrils which in turn are grouped to form fibres all of which provides yet more strength