1.4 Starch, Glycogen, Cellulose

Question 1

What is starch

Answer 1

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

Question 2

what form is starch found in

Answer 2

Starch is found in parts of a plant in the form of small grains, however large amounts occur in seeds and storage organs eg potato tubers

Question 3

What is the role of starch
How is compactness good

Answer 3

Major energy source, so its main role is for energy storage.

This is because its compact so can store lots of glucose for its volume

Question 4

How is the amylose helix of starch held in place

Answer 4

Hydrogen bonds between the OH (hydroxyl groups) let the amylose molecule twist into a compact helix.

Question 5

Why does glucose have to be stored as starch?

Answer 5

Glucose is very soluble in water and dissolves due to it containing lots of hydroxyl groups which lets it form hydrogen bonds with water molecules.

This lets water move into the cell by osmosis, so that’s why it’s stored as starch

Question 6

Where are the glycosidic bonds in starch:
How do they differentiate between amylose and amylopectin

How do these affect the shape of starch?

Answer 6

. There are 1-4 glycosidic bonds in amylose
There are 1-4 and 1-6 glycosidic bonds in amylopectin

so eg carbon 1 of one glucose bonds to carbon 4 of another glucose

• 1-4 glycosidic bonds make an unbranched straight-line structure
• 1-6 bonds make a branched structure

So this means amylose makes an unbranched helix, and amylopectin makes a branched structure

Question 7

Why is starch being insoluble good for energy storage

Answer 7

. Doesn’t affect water potential so water isn’t drawn into cells by osmosis, keeping cells osmotically stable so they don’t burst

Question 8

Why does starch being large good for its function

Answer 8

Amylose and amylopectin are polymers in starch, and they are too large to diffuse through the cell membrane and leave the cell

Question 9

What happens when starch is hydrolysed

Answer 9

A molecule of water is added to it to break glycosidic bonds to release alpha glucose monomers which can be easily transported and used in respiration

Question 10

Starch has both branched and unbranched chains

Why is the unbranched chain good

Answer 10

The unbranched chain is wound into a tight coil that makes the molecule very compact

Question 11

Starch has both branched and unbranched chains.

Why are the branched ones good

Answer 11

It has many ends, each of which can be acted on by enzymes simultaneously so glucose monomers can be released very quickly.

Question 12

What is glycogen

Where is it found and stored

Answer 12

Its a polysaccharide of alpha glucose monomers, which are linked by glycosidic bonds.

Animals and bacteria, but never in plant cells

Stored as small granules mainly in muscles and liver.

Question 13

How is glycogen different from starch?

What glycosidic bonds are found in glycogen

Answer 13

. It has shorter chains and is more highly branched

. 1-4 and 1-6 bonds so it is branched and unbranched

Question 14

Role of glycogen

Why is there not much stored in animals

Answer 14

Its a major carbohydrate storage product of animals,

The mass of it stored is relatively small as fat is the main storage molecule in animals

Question 15

Why is the structure of glycogen good for storage
4 points

Answer 15

. Insoluble so doesn’t draw in water through osmosis, keeping cell osmotically stable

. It is large and insoluble so can’t diffuse out of cells

. It is compact so lots of glucose can be stored in a small volume

. Highly branched

Question 16

Glycogen has lots of branches, why is this good

Answer 16

. It’s more highly branched than starch so has more ends that can be acted on simultaneously by enzymes.

. This means it’s more rapidly broken down to form glucose monomers, which are used in respiration

. This is important for animals which have a higher metabolic rate and therefore respiratory rate than plants because they’re more active…
Energy needs of animals can change rapidly eg run from predator

Question 17

How is cellulose different from starch and glycogen

What is cellulose

Answer 17

. It’s made of monomers of beta glucose rather than alpha. This produces fundamental differences in the function and structure of this polysaccharide.

A polysaccharide of beta glucose monomers joined together by glycosidic bonds formed in condensation reaction

Question 18

What is the structure of cellulose

Answer 18

. It has straight, unbranched chains running parallel to each other
.This lets hydrogen bonds form crosslinks between the chains
. These hydrogen bonds make a big contribution to the strength of cellulose as there is a large number of them

c-c-c-c-c-c-c-c-c-c-c-c-c-c-c-c
| | | |
c-c-c-c-c-c-c-c-c-c-c-c-c-c-c-c
| | | |
c-c-c-c-c-c-c-c-c-c-c-c-c-c-c-c

Question 19

How do beta glucose monosaccharides bond to make cellulose

What type of glycosidic bonds found on cellulose?

Answer 19

. Every second one has to rotate 180 degrees which allows glycosidic bonds to form between them

.1-4 glycosidic bonds

Question 20

what are cellulose molecules grouped together called

Answer 20

Microfibrils which are then grouped to form fibres which all provide more strength

Question 21

What is the role of cellulose and how does it prevent plant cells from bursting

Answer 21

. Major component of plant cell walls and provides righty to plant cell

. It prevents the cell wall from bursting as water enters it by osmosis:
It does this by exerting an inward pressure that stops any further influx water

As a result, the plant cells are turgid so push against each other making parts of plant semi rigid.

It leaves stems and leaves in a turgid state so they can provide max surface area for photosynthesis