Carbohydrates

Question 1

What are the 3 key monosaccharides?

Answer 1

Glucose
Galactose
Fructose

Question 2

How do you form a disaccharide from two monosaccharides?

Answer 2

A condensation reaction forms a glycosidic bond between the monosaccharides and releases a water molecule.

Question 3

What are the 3 key disaccharides?

Answer 3

Maltose
Lactose
Sucrose

Question 4

What is maltose formed from?

Answer 4

Alpha Glucose + Alpha Glucose

Question 5

What is lactose formed from?

Answer 5

Alpha Glucose + Galactose

Question 6

What is sucrose formed from?

Answer 6

Alpha Glucose + Fructose

Question 7

What is the difference between alpha glucose and beta glucose?

Answer 7

The hydroxide on the right side of the monomer is switched with the hydrogen (up not down).

Question 8

Give the 3 key polysaccharides.

Answer 8

Starch
Glycogen
Cellulose

Question 9

What is glycogen and starch polymers of?

Answer 9

Alpha Glucose

Question 10

What is cellulose a polymer of?

Answer 10

Beta Glucose

Question 11

What is the structure of cellulose?

Answer 11

Long, unbranched chains of beta glucose. Microfibrils are long cellulose chains running parallel to each other with hydrogen bonds as cross-linkages.

Question 12

What is the function of cellulose structure?

Answer 12

Plant cell rigid because of strong-in-large-numbers hydrogen bonds. Strong microfibrils so doesn’t change shape of cell which will not burst, maintaining pressure. Turgid cell maximises photosynthesis.

Question 13

What is the structure of starch?

Answer 13

Made of amylose and amylopectin. Amylose is an unbranched, coiled chain. Amylopectin is branched with lots of side branches.

Question 14

What is the function of starch’s structure?

Answer 14

Coiled amylose is very compact, storing a lot of energy in small space. Amylopectin’s side branches can be rapidly hydrolysed to release a lot of energy. Insoluble so doesn’t affect water potential of cell.

Question 15

What is the structure of glycogen?

Answer 15

Has 1,4 and 1,6 glycosidic bonds between alpha glucose molecules. Shorter chains, more branches than starch.

Question 16

What is the function of glycogen’s structure?

Answer 16

Side branches can be easily hydrolysed releasing a lot of energy for respiration (higher metabolic rate than plants). Compact so stores a lot of energy in small amount of space. Insoluble so doesn’t affect water potential and will not diffuse out of cells.

Question 17

Where is starch found?

Answer 17

In plants ONLY, as small grains.

Question 18

Where is glycogen found?

Answer 18

In animal cells as small granules.

Question 19

Where is cellulose found?

Answer 19

In plant cells ONLY.

Question 20

How do you test for reducing sugars?

Answer 20

Add Benedict’s reagent to food sample. Heat mixture in a heated water bath for some time, a brick-red precipitate will form which is a positive result.

Question 21

How do you test for non-reducing sugars?

Answer 21

Add Benedict’s reagent to food sample and heat mixture. Solution will remain blue. Boil with hydrochloric acid and then add sodium hydroxide to nuetralise the acid. Add Benedict’s reagent again and a brick-red precipitate should form. This is a positive result.

Question 22

How do you test for starch?

Answer 22

Add potassium iodide or iodine solution to the food sample. Mixture should turn from orange-brown to a blue-black colour for a positive result.