Carbohydrates and Lipids

Question 1

What is a monomer?

Answer 1

Smaller units from which larger molecules are made.

Question 2

What is a polymer?

Answer 2

Molecules made from a large number of monomers joined together.

Question 3

Name some monomers?

Answer 3

Monosaccharides, amino acids, nucleotides.

Question 4

What is a condensation reaction?

Answer 4

A reaction that joins two molecules together with the formation of a chemical bond, involving the elimination of a molecule of water.

Question 5

What is a hydrolysis reaction?

Answer 5

A reaction that breaks a chemical bond between two molecules, involving the use of a molecule of water.

Question 6

What is a monosaccharide?

Answer 6

The monomer from which larger carbohydrates are made.

Question 7

Name some monosaccharides?

Answer 7

Glucose, fructose, galactose.

Question 8

How are disaccharides formed?

Answer 8

They are formed in a condensation reaction between two monosaccharides, forming a glycosidic bond and releasing a molecule of water.

Question 9

Name some examples of disaccharides?

Answer 9

glucose + glucose = maltose
glucose + fructose = sucrose
glucose + galactose = lactose

Question 10

What is an isomer?

Answer 10

Molecules with the same molecular formula but the atoms are arranged in a different way.

Question 11

What are the two isomers of glucose?

Answer 11

Alpha glucose - hydroxyls on same side
Beta glucose - hydroxyls on opposite sides

Question 12

What is the test for reducing sugars?

Answer 12

Benedict’s reagent test

1. Add Benedict’s reagent to sample and heat in a water bath at 60°C
2. If a reducing sugar is present there will be a colour change from blue to brick red (as ppt forms)

Question 13

Explain the results of the Benedict’s reagents test?

Answer 13

Benedict’s reagent is made out of CuSO4 so contains Cu2+ ions. Reducing sugars can donate an electron to Cu2+, which turns into Cu+. Cu+ is a brick red precipitate.

Question 14

Name some examples of reducing sugars?

Answer 14

All monosaccharides and some disaccharides e.g. maltose.

Question 15

What is the test for non-reducing sugars?

Answer 15

1. Add dilute hydrochloric acid to the sample and heat in a water bath at 60°C
2. Add sodium hydrogen carbonate to neutralise sample
3. Add Benedict’s reagent to sample and heat in a water bath at 60°C
4. If a reducing sugar is present there will be a colour change from blue to brick red (as ppt forms)

Question 16

What is a polysaccharide?

Answer 16

Molecules in a condensation reaction of many glucose units.

Question 17

Name some examples of polysaccharides?

Answer 17

Glycogen, starch and cellulose

Question 18

Describe the structure of glycogen?

Answer 18

It is made up of alpha-glucose monomers. It is a very branched structure as 1,4 and 1,6 glycosidic bonds are present. It also has many side branches.

Question 19

Where is glycogen found?

Answer 19

In animal and fungal cells. There are high concentrations in liver and muscles cells due to their high metabolic demands.

Question 20

What is the function of glycogen?

Answer 20

It is the main storage of excess glucose in animal and fungal cells. It is needed as glucose is soluble, so if this was stored in cells instead of glycogen, it would cause water to move into cells by osmosis, causing them to burst.

Question 21

How does the structure of glycogen aid its function?

Answer 21

Glycogen being very branched allows for rapid hydrolysis to provide cells with glucose for respiration faster. Having a branched structure also means glycogen is compact. Glycogen is insoluble in water to prevent any osmotic water uptake that would cause the cell to burst/ it is very large so does not leave cells by diffusion.

Question 22

Describe the structure of starch?

Answer 22

Starch is made out of two polysaccharides - amylose and amylopectin.

Question 23

Describe the structure of amylopectin?

Answer 23

It is made up of alpha-glucose monomers. It is a branched structure as 1,4 and 1,6 glycosidic bonds are present. It is less branched than glycogen, however.

Question 24

Describe the structure of amylose?

Answer 24

It is made out of alpha-glucose monomers. It is an unbranched helical structure as only 1,4 glycosidic bonds are present.

Question 25

Where is starch found?

Answer 25

It is found in tubers and bulbs as small granules in plastids in plant cells.

Question 26

What is the function of starch?

Answer 26

It is the main storage of excess glucose in plant cells.

Question 27

How does the structure of amylose aid its function?

Answer 27

Amylose is helical, which makes starch compact.

Question 28

Why is amylopectin less branched than glycogen?

Answer 28

Animals are more active than plants. Therefore animals need faster release of energy for processes such as movement. This means glycogen is more branched to provide faster hydrolysis to release glucose more rapidly.

Question 29

Describe the structure of cellulose?

Answer 29

It is a polysaccharide made out of beta glucose monomers. It contains 1,4 glycosidic bonds. As it is made out of beta glucose, adjacent monomers must be inverted so that hydroxyl groups are close enough for form glycosidic bonds. This means cellulose is made out of long, straight chains.

Question 30

What is the function of cellulose?

Answer 30

Cellulose is found in plant cell walls, and provides the cell with turgidity to allow it to withstand turgor pressure and pressure from when water enters the cell through osmosis.

Question 31

Describe the test for starch?

Answer 31

Iodine solution test
1. Crush sample using a pestle and motar and place into a test tube.
2. Add iodine solution
3. If starch is present there will be a colour change from browny-orange to blue-black.

Question 32

How does the structure of cellulose aid it’s function?

Answer 32

Between adjacent long straight chains, hydrogen bonds form. Alone, these hydrogen bonds are weak but as there are so many of them, they cause microfibrils to form, which makes cellulose strong and turgid,