1.4 starch, glycogen and cellulose

Question 1

describe starch

Answer 1

• polysaccharide
• found in seeds and storage organs (eg: potato tubers)
• made up of chains of alpha glucose linked by glycosidic bonds formed in condensation reactions
• chains can be branched or unbranched
• unbranched chains are wound into a tight coil that makes the molecule very compact.
• never found in animal cells

Question 2

what is the role of starch and how is it well adapted for this?

Answer 2

the main role of starch is energy storage, it’s structure is suited to this because;

• it is insoluble and therefore doesn’t effect water potential so water is not drawn into the cell by osmosiss
• it is large and insoluble so doesn’t diffuse out of cells
• it is compact so a lot can be stored in a small area
• it forms alpha glucose when hydrolysed which is easily transported and readily used in respiration
• branched form has many ends, so each can be acted on individually by enzymes simultaneously meaning glucose monomers are released rapidly.

Question 3

describe glycogen.

Answer 3

• found in animals and bacteria but not plants
• similar in strucure to starch but has shorter, more highly branched chains
• major carbohydrate storage product for animals
• stored as granules in muscles and liver

Question 4

how is the structure of glycogen suitable for storage?

Answer 4

• insoluble so doesn’t draw water into cells by osmosis
• insoluble, so doesn’t diffuse out of cells
• compact, lots can be stored in a small area
• highly branched, can be acted on simultaneously by enzymes and broken down into glucose monomers which are used for respiration.
• it is important that it is more highly branched than starch because animals require more glucose than plants since they are more active.

Question 5

describe cellulose

Answer 5

• different in structure and function to glycogen and starch, as it is made up of beta glucose monomers.
• straight, unbranched chains running adjacent to eachother allowing hydrogen bonds to form cross links between chains.
• sheer number of hydrogen bonds strengthen the molecule, helping it oerform its function as a structural material.
• cellulose molecules are grouped to form microfibrils which run in parrallel to form fibres.

Question 6

What is the function of cellulose and how does its structure aid this?

Answer 6

cellulose provides rigidity to plant cells and stops them from bursting when water enters. it does this by exerting inward pressure, making non-woody area rigid and helping to maintain a high surface area.
it’s structure suits this because:
- beta glucose forms long unbranched chains with cross links with hydrogen bonds which have high collective strength
- these are grouped into microfibrils, then fibres providing more strength