Carbohydrates and Lipids A1

Question 1

Define the term monomer with examples.

Answer 1

1. small identical or similar molecules
2. can be joined together to make larger molecules called polymers
3. eg. monosaccharides (alpha and beta glucose), amino acids, nucleotides

Question 2

Define the word polymer.

Answer 2

Large molecules made from joining many similar or identical monomers together.

Question 3

Describe hydrolysis and condensation reactions.

Answer 3

1. hydrolysis reactions involve adding one molecule of water to break the bond between two monomers
2. condensation reactions join two monomer units together with the removal of one water molecule

Question 4

Give the elements found in carbohydrates.

Answer 4

Carbon (C)
Hydrogen (H)
Oxygen (O)

Question 5

Give the molecular formula for glucose.

Answer 5

C6-H12-O6

Question 6

Be able to draw the structure of alpha and beta glucose.

Question 7

Glucose + glucose =

Answer 7

maltose

Question 8

Glucose + galactose =

Answer 8

lactose

Question 9

Glucose + fructose =

Answer 9

sucrose

Question 10

What bond is formed in the reaction of two monosaccharides?

Answer 10

glycosidic bond

Question 11

What is the molecular formula of disaccharides?

Answer 11

C12 H22 O11 (due to the loss of 1 water molecule)

Question 12

What is a polysaccharide?

Answer 12

1. a type of polymer formed by joining many monosaccharides together
2. storage - starch (plants) + glycogen (human)
3. structural - cellulose

Question 13

Describe the structure of amylose (starch)
(5)

Answer 13

1. long and straight chains of alpha glucose which coil into a helix
2. carbon 1:4 glycosidic bonds
3. compact structure for storage
4. insoluble so does not affect water potential
5. does not diffuse out of cells

Question 14

Describe the structure of amylopectin (starch)
(5)

Answer 14

1. branched chain of alpha glucose molecules
2. carbon 1:4 and 1:6 glycosidic bonds
3. provides large SA for rapid hydrolysis by enzymes
4. insoluble so does not affect water potential
5. does not diffuse out of cells

Question 15

How does glycogen differ to starch and why?

Answer 15

similar however:
1. shorter chains - more readily hydrolysed into glucose (quicker)
2. more branched
3. large SA
4. stored in muscles and liver
5. like starch glycogen is insoluble so does not affect water potential or diffuse out of cells.

Question 16

A starch molecule has a spiral shape.
Explain why this shape is important to its functions in cells.

Answer 16

compact/occupies small space/tightly packed

Question 17

Explain one way in which starch molecules are adapted for their functions in plant cells.

Answer 17

1. insoluble
2. don’t affect water potential
   or
3. helical
4. compact
   or
5. large molecule
6. cannot leave cell

Question 18

Give the structure of alpha glucose and two examples.

Answer 18

1. alpha helix
2. starch and glycogen

Question 19

Give the structure of beta glucose and an example.

Answer 19

1. beta pleated sheets
2. cellulose

Question 20

Give the structure of cellulose.

Answer 20

1. beta glucose joined together through condensation reactions to form long straight chains
2. every other glucose molecule rotates 180 degrees to allow OH groups on carbon 1 and 4 to be adjacent to each other to form a glycosidic bond.

Question 21

The structure of cellulose is related to its role in plant cell walls.
Explain how.

Answer 21

1. long/straight/unbranched chains of glucose
2. joined by hydrogen bonds
3. form micro/macrofibrils
4. provides rigidity/strength/support

Question 22

Hydrogen bonds are important in cellulose molecules. Explain why.

Answer 22

1. holds chains/cellulose molecules together/forms crosslinks between chains/cellulose molecules/forms microfibrils
2. providing strength/rigidity to cellulose/cell wall
3. hydrogen bounds strong in large numbers

Question 23

What are the three tests for carbohydrates?
Give the names of the carbohydrates being tested.

Answer 23

1. Benedict’s test for reducing sugars (alpha glucose, galactose, lactose, maltose, fructose)
2. Benedict’s test for non-reducing sugar (sucrose)
3. iodine test (starch)

Question 24

Describe how a student would show that reducing sugars were present in a solution.
(3)

Answer 24

1. add equal volumes of Benedict’s solution
2. heat to 95 degrees celsius
3. red/orange/yellow/green precipitate (shows reducing sugar is present)

Question 25

Describe how a student would show that a non-reducing sugar is present in a solution.

Answer 25

1. add dilute hydrochloric acid (HCI) to sugar solution (to hydrolyse into monomer units) 2. boil sugar solution 3. add sodium hydrogen carbonate (NaHCO3) to neutralise 4. add equal volume of Benedict's solution to the sugar solution 5. heat to 95 degrees celsius 6. red/orange/yellow/green precipitate (shows reducing sugar present)

Question 26

Describe how you would test a sample of food for the presence of starch.

Answer 26

1. add iodine solution to the food sample 2. blue/black/purple indicates starch is present

Question 27

Benedict's test is only a semi-qualitative test for sugars. How would you test for an unknown concentration of reducing sugars?

Answer 27

use a calibration curve

Question 28

Describe how you would produce a calibration curve and use it to obtain results.

Answer 28

1. make up several known concentrations of maltose/glucose/lactose/galactose/fructose. 2. carry out the Benedict's test on each sample 3. use a colorimeter to measure the colour of each solution and plot a calibration curve 4. find the concentration of the unknown sample reading off the calibration curve

Question 29

Name the two types of lipid structures.

Answer 29

1. triglycerides (commonly found in food) 2. phospholipids (helps form cell membrane of a cell)

Question 30

How are triglycerides formed?

Answer 30

1. made from one glycerol head (molecule) 2. linked to three fatty acid tails 3. joined together by a condensation reaction 4. to form ester bonds

Question 31

How many water molecules does the condensation reaction of a triglyceride form and where do the ester bonds form?

Answer 31

1. 3 condensation reactions so 3 water molecules 2. ester bonds form at the carboxylic acid group

Question 32

Name and explain two different types of fatty acids.

Answer 32

1. saturated fatty acid: single covalent bonds between carbons in the hydrocarbon chain 2. unsaturated fatty acids: double bonds between carbons in hydrocarbon chain

Question 33

Describe how to carry out the emulsion test for lipids.

Answer 33

1. place small amount of sample in test tube with 2cm³ of ethanol 2. the mixture is shaken so that the fat dissolves 3. water is then added drop by drop and shaken again 4. a white and cloudy emulsion layer of fat droplets should be visible if fat is present

Question 34

The concentration of glucose in blood rises slower if the carbohydrate is starch rather than sucrose. Explain why.

Answer 34

1. starch gets digested to maltose first and then into glucose as its a polysaccharide 2. sucrose can be digested into glucose straight away as its a disaccharide

Question 35

What are phospholipids made up of and what are their charges?

Answer 35

1. a glycerol head 2. two fatty acid tails (no charge - non-polar) 3. phosphate group (negative charge - polar)

Question 36

How do phospholipids form a bilayer in the cell membrane?

Answer 36

1. the phospho-glycerol head is hydrophilic (attracts water-soluble) 2. the fatty acid tails are hydrophobic (repel water - not soluble) 3. the hydrophobic fatty acid tails are arranged in the middle away from the water 4. the hydrophilic heads are arranged on the outside in contact with the water 5. this allows the phospholipids to form a bilayer in water

Question 37

What is the structural formula of a glycerol?

Answer 37

C3-O8-H3

Question 38

What's the general formula of a fatty acid?

Answer 38

CH3-nCOOH

Question 39

Describe how the structure of a phospholipid is different to a triglyceride.

Answer 39

1. fatty acid removed 2. replaced with a phosphate group