starch

Question 1

what type of carbohydrate is starch?

Answer 1

a storage carbohydrate

Question 2

where is starch stored?

Answer 2

in starch grains (amyloplasts) in the cytoplasm of plants

Question 3

what is the formation of starch?

Answer 3

long, branched chains of α glucose molecules

Question 4

what two types of polymer make up starch?

Answer 4

amylose and amylopectin

Question 5

amylose is the result of …
amylopectin is the result of …

Answer 5

• 1,4 glycosidic bonds
• 1,4 and 1,6 glycosidic bonds

Question 6

what is the structure of amylose?

Answer 6

straight, unbranched chains

Question 7

what is the structure of amylopectin?

Answer 7

branched chains due to the 1,6 glycosidic bonds

Question 8

what is the benefit of the branched ends?

Answer 8

each branch has an end which enzymes can act on so the more branched ends, the easier it is to hyrolyse

Question 9

explain the structure of starch

Answer 9

• long branched chains of α glucose molecules
• formed of the polymers amylose and amylopectin
• amylose is the result of 1,4 glycosidic bonds and amylopectin is the result of 1,4 glycosidic bonds and 1,6 glycosidic bonds
• amylose forms straight, unbranched chains and amylopectin forms branched chains due to the 1,6 glycosidic bonds

Question 10

how is starch ideally suited to it’s function as a storage compound?

Answer 10

• large and insoluble therefore osmotically inactive ie doesn’t draw water into a cell by osmosis which could lead to cell damage
• hydrolysed easily due to many branched ends
• molecule has a helical shape as amylose can coil forming a compact store

Question 11

how is starch hydrolysed?

Answer 11

by the enzyme amylase to produce the disaccharide maltose
starch + water –amylase–> maltose

Question 12

how to test for starch?

Answer 12

• iodine test
• add 2-3 drops of iodine solution
• if starch is present a blue/black colour is produced
• if no starch is present the iodine solution remains orange/yellow