Carbohydrates (3.1.2)

Question 1

What are the monosaccharides (monomers) of carbohydrates?

Answer 1

-alpha glucose
-beta glucose
-fructose
-galactose

Question 2

What is the difference in structure between alpha and beta glucose?

Answer 2

Beta glucose has the same structure as alpha glucose, however beta glucose H and OH on carbon 1 are reversed

Question 3

Define a monosaccharide

Answer 3

The monomers from which larger carbohydrates are made

Question 4

Define a disaccharide

Answer 4

Formed by the condensation of 2 monosaccharides

Question 5

How is the disaccharide maltose formed?

Answer 5

The condensation of 2 glucose molecules

Question 6

How is the disaccharide sucrose formed?

Answer 6

The condensation of a glucose and a fructose molecule

Question 7

How is the disaccharide lactose formed?

Answer 7

The condensation of a glucose and a galactose molecule

Question 8

What bond does a condensation reaction between 2 monosaccharides form?

Answer 8

A glycosidic bond

Question 9

What are the 2 isomers of glucose?

Answer 9

Alpha and Beta glucose

Question 10

How are polysaccharides formed?

Answer 10

By the condensation of many glucose units

Question 11

How are the polysaccharides glycogen and starch formed?

Answer 11

The condensation of alpha glucose

Question 12

How is the polysaccharide cellulose formed?

Answer 12

By the condensation of beta glucose

Question 13

Describe the food test for reducing sugars (all monosaccharides and some disaccharides)

Answer 13

1. Heat Benedict’s reagent with sample in a water bath until it boils
2. If sample turns blue = no reducing sugar present
   2b. If sample turns green-yellow-orange-brick red = reducing sugar present

Question 14

What does the colour of a positive reducing sugars food test indicate?

Answer 14

Concentration of reducing sugars present

Question 15

If you want to food test a solid substance, what should you do?

Answer 15

Prepare the sample (solid) as a solution and proceed with the test

Question 16

If the reducing sugars test is negative, there could be non reducing sugars present, how do we test for this?

Answer 16

1. Test for reducing sugars, if none present
2. Heat a new sample with hydrochloric acid
3. Neutralise the sample with sodium hydrogen carbonate
4. Heat sample with Benedict’s reagent in a water bath until it boils
5. Same colour identification

Question 17

Describe the food test for starch

Answer 17

1) add iodine solution to the sample
2) stays same (orange) = no starch present
3) blue/black = starch present

Question 18

What happens to every second beta glucose molecule in the formation of cellulose?

Answer 18

It is flipped in order for glycosidic bonds to form

Question 19

Describe the structure of cellulose

Answer 19

An unbranched straight chain allowing cellulose molecules to be close together in order for hydrogen bonds to form between the chains, making it very strong for a plants cell wall.

Question 20

How is a plant cell wall formed?

Answer 20

1) microfibril formed by cellulose chains grouped together
2) macrofibrils formed by microfibrils grouping together
3) cellulose fibre formed by macrofibrils grouped together which form the cell wall

Question 21

Why is it important that the cell wall is strong?

Answer 21

Means it can resist outward pressure, preventing it from bursting whilst also allowing it to fill with water (as cell wall is permeable) and become turgid - giving the plant its upright structure

Question 22

What molecules does starch contain?

Answer 22

Amylose and Amylopectin

Question 23

Describe the structure of amylose

Answer 23

-unbranched polymer of alpha glucose
-amylose molecules twist into a compact helix - hydrogen bonds form between glucose molecules

Question 24

Why is starch important in plant cells?

Answer 24

-starch is a store of glucose
-when a cell needs glucose, enzymes are used to hydrolyse the glycosidic bonds

Question 25

Describe the structure of amylopectin

Answer 25

branched polymer of alpha glucose molecules, the branches allowing enzymes to break down starch rapidly

Question 26

What is the importance of amylose forming a tight helix and making starch compact?

Answer 26

So it can store a lot of glucose

Question 27

Starch is insoluble in water, why is this important?

Answer 27

So it does not cause water to enter the cell via osmosis

Question 28

Define what is meant by a ‘branched’ molecule

Answer 28

Attachment of side chains to a polymers backbone chain

Question 29

What is glycogen used for in animal cells?

Answer 29

Store of glucose

Question 30

Where is glycogen stored in the body?

Answer 30

Liver and muscle cells

Question 31

Describe the structure of glycogen

Answer 31

-polymer of alpha glucose
-similar structure to amylopectin as it is a branched molecule, only glycogen has more branches

Question 32

What is the importance of glycogen being a branched molecule?

Answer 32

-so enzymes can convert glycogen back to glucose rapidly and be released
-important as animals have a high rate of respiration and energy needs change frequently

Question 33

Glucose is soluble, is this the same for glycogen?

Answer 33

No, glycogen is insoluble in water so it does not draw water into cells via osmosis