Carbohydrates

Question 1

What is a monosaccharide?

Answer 1

A single molecular sugar unit

Question 2

What are three examples of monosaccharides?

Answer 2

• Glucose
• Fructose
• Galactose

Question 3

Draw the structures of alpha and beta glucose and highlight how they differ

Answer 3

The OH and H groups are swapped

Question 4

Describe the test for a reducing sugar

Answer 4

Benedict’s test
- add sample
- add benedict’s reagent and warm in a water bath
- colour change from blue to red/orange/yellow/green (depending on concentration)

Question 5

What type of test is the Benedict’s Test?

Answer 5

Semi-quantitative

Question 6

How could you get a less subjective result, when doing the Benedict’s test?

Answer 6

Filter the ppt, dry and then find the mass
OR use a colorimeter and calibration curve

Question 7

What is the bond between two monosaccharides called and how is it formed?

Answer 7

Glycosidic bond, formed by a condensation reaction

Question 8

What are disaccharides?

Answer 8

Two monosaccharides joined together

Question 9

What are 3 examples of disaccharides?

Answer 9

maltose (2 x alpha glucose)
sucrose (alpha glucose and fructose)
lactose (alpha glucose and galactose)

Question 10

How would you test for a non-reducing sugar?

Answer 10

• add HCl and boil (this will hydrolyse any disaccharides present into monosaccharides)
• add NaHCO3 to neutralise
• add Benedict’s reagent and heat gently in a water bath
• colour change from blue to red/orange/yellow/green (depending on concentration)

Question 11

How do you test for starch?

Answer 11

• add iodine solution and shake
• starch-> blue-black colour

Question 12

How is starch suited for it’s function?

Answer 12

• INSOLUBLE- so doesn’t impact water potential/osmosis
• LARGE- so does not diffuse out of cells
• COILED/COMPACT- lots can be stored in small amounts of space
• MADE FROM ALPHA GLUCOSE- when hydrolysed, alpha glucose is readily used in respiration
• HIGHLY BRANCHED- large SA for the rapid hydrolysis of starch into alpha glucose

Question 13

How does glycogen differ from starch?

Answer 13

It has shorter chains and is more highly branched

Question 14

How is the structure of cellulose suited to its function?

Answer 14

BETA GLUCOSE- so form straight, unbranched chains
CHAINS RUN PARALLEL- cross-linked by H bonds which add collective strength
MICROFIBRILS- add more strength

Question 15

What 2 types of polysaccharides can make up starch?

Answer 15

amylose and amylopecitin

Question 16

Describe the structure of amylose

Answer 16

an unbranched chain of glucose molecules joined by 1, 4- glycosidic bonds, and as a it is coiled and compact

Question 17

Describe the structure of amylopectin

Answer 17

a branched chain made up of glucose molecules joined by 1, 4 and 1, 6
glycosidic bonds. There are side branches, on which enzymes can act

Question 18

How does glycogen act as an energy source?

Answer 18

• Glycogen can be hydrolysed to glucose.
• The glucose could then be used to release energy through the process of respiration