lipids and carbs

Question 1

what reaction forms lipids,

what bonds forms between them

and between what?

Answer 1

condensation reaction, ester bonds, three fatty acids and glycerol

Question 2

What are the monomers for carbohydrates

Answer 2

Monosaccharides

Question 3

what is the test for starch

Answer 3

add iodine solution, turns from orange to blue/ black if positive

Question 4

what is the test for non- reducing sugars

Answer 4

Test for reducing sugars test is -ve
heat in HCL
cool then neutralise with sodium hydrogen carbonate
add Benedict and heat in a water bath
turns from blue to green, yellow, orange, red and brick red

Question 5

what is the structural difference between alpha and beta glucose

Answer 5

the OH group on carbon 1 is on the bottom for Alpha but on the top for beta glucose

Question 6

what type of bonds are found in cellulose and what are the monomers for this polymer

Answer 6

1,4 glycosidic bonds
beta glucose

Question 7

what are these disaccharides made of: maltose? Sucrose? Lactose?

Answer 7

Maltose - two alpha glucose
sucrose - glucose and fructose
lactose - glucose and galactose

Question 8

Compare and contrast the structure of phospholipid and triglycerides

Answer 8

triglycerides have a glycerol molecule attached to three fatty acid chains whereas a phosopholipid also has a glycerol molecule and two fatty acid chains with a phophate head attached

Question 9

Structure to function of triglycerides

Answer 9

lots of C-H bonds, stores a lot of energy, good energy store,

non polar- good insulator,

hydrophobic- waterproofing

Question 10

test for lipids?

Answer 10

add ethanol, shake, add water, shake, white emulsion forming is positive

Question 11

Structure to function of phospholipids?

Answer 11

hydrophobic tail which prevents water from simple diffusing through membranes and a

hydrophilic head to attract water, forming a bilyer in membranes

Question 12

How is the structure of starch and glycogen related to its function?

Answer 12

polymer of glucose so can provide the respiratory substrate (glucose),

helical/ spherical so compact and can store more energy in a small space,

branched so large surface area and

multiple enzymes can act on them at one time,

insoluble so doesn’t affect water potential of the cell,

large so cannot diffuse out of the cell

Question 13

What type of bonds are found in glycogen and starch? and what are the monomers for these two polymers?

Answer 13

1,4 and 1,6 glycosidic bonds
alpha glucose

Question 14

what is the test for reducing sugars?

Answer 14

add Benedicts solution
heat in water bath
turns from blue to green/ yellow/ orange/ red/ brick red

Question 15

what is the difference between a saturated and unsaturated fatty acid?

Answer 15

saturated - no C=c double bonds, unsaturated - one or more C=C double bonds

Question 16

what type of bonds forms between beta glucose chains and why is this good?

Answer 16

hydrogen bonds, lots of these form high strength, adding high strength for its job in cell walls

Question 17

what type of reaction occurs to join two monosaccharide together and what bond is formed?

Answer 17

condensation reaction and glycosidic bond

Question 18

Unsaturated

Answer 18

double bond

Question 19

starch

Answer 19

1,6 glycosidic bonds

Question 20

Compare and contrast the structure of starch and the structure of cellulose 6 marks

Answer 20

1. Both polysaccharides;
   OR
   Both are glucose polymers
   OR
   Both are made of glucose monomers;
   2. Both contain glycosidic bonds (between monomers);
   3. Both contain carbon, hydrogen and oxygen/C, H and O;
   4. Starch made of α-glucose and cellulose made of β-glucose;
   5. Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
   6. Starch (molecule) is branched and cellulose is not/unbranched;
2. Cellulose has (micro/macro) fibrils and starch does not;

Question 21

Describe how the structure of glycogen is related to its function. 4 marks

Answer 21

1. Helix/coiled/branched so compact;
   Accept description of ‘compact’, eg many glucoses packed closely/densely/tightly
   2. Polymer of glucose so easily hydrolysed;
   3. Branched so more ends for faster hydrolysis;
   4. Glucose (polymer) so provides respiratory substrate for energy (release);
   5. Insoluble so not (easily) lost (from cell)
   OR
   Insoluble so does not affect water potential/osmosis;

Question 22

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample. 5 marks

Answer 22

4 max if marks gained from only 2 substance tests.
Lipid
1.   Add ethanol/alcohol then add water and shake/mix
OR
Add ethanol/alcohol and shake/mix then pour into/add water;
Reject heating emulsion test.
Accept ‘Add Sudan III and mix’.
2.   White/milky emulsion
OR
emulsion test turns white/milky;
Ignore cloudy.
Reject precipitate.
Accept (for Sudan III) top (layer) red.
Non-reducing sugar
3.   Do Benedict’s test and stays blue/negative;
Ignore details of method for Benedict’s test for this mp.
4.   Boil with acid then neutralise with alkali;
Accept named examples of acids/alkalis.
5.   Heat with Benedict’s and becomes red/orange (precipitate);
Do not credit mp5 if no attempt at mp4.
For ‘heat’ ignore ‘warm’/’heat gently’/’put in a water bath’ but accept stated temperatures ≥ 60°C.
Heat must be stated again, do not accept using residual heat from mp4.
Accept ‘do the Benedict’s test’ if full correct method given elsewhere.
Accept ‘sodium carbonate, sodium citrate and copper sulfate solution’ for Benedict’s but must have all three if term ‘Benedict’s’ not used.
Amylase
6.   Add biuret (reagent) and becomes purple/violet/mauve/lilac;
Accept ‘sodium or potassium hydroxide and copper sulfate solution’ for ‘biuret’.
Reject heating biuret test.
7.   Add starch, (leave for a time), test for reducing sugar/absence of starch;

Question 23

(c) Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached.
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein. 4 marks

Answer 23

1. Glucose and galactose;
   Ignore α or β for glucose
   2. Joined by condensation (reaction);
   3. Joined by glycosidic bond;
2. Added to polypeptide in Golgi (apparatus);;

Question 24

Describe how the structures of starch and cellulose molecules are related to their functions. 5 marks

Answer 24

Starch (max 3)
1. Helical/ spiral shape so compact;
2. Large (molecule)/insoluble so osmotically inactive;
Accept: does not affect water potential/ψ.
3. Branched so glucose is (easily) released for respiration;
Ignore: unbranched.
4. Large (molecule) so cannot leave cell/cross cell-surface membrane;
Cellulose (max 3)
5. Long, straight/unbranched chains of β glucose;
6. Joined by hydrogen bonding;
Note: references to ‘strong hydrogen bonds’ disqualifies this mark point.
7. To form (micro/macro)fibrils;
8. Provides rigidity/strength;

Question 25

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.

Answer 25

Lipid
1.   Add ethanol/alcohol then add water and shake/mix
OR
Add ethanol/alcohol and shake/mix then pour into/add water;
Reject heating emulsion test.
Accept ‘Add Sudan III and mix’.
2.   White/milky emulsion
OR
emulsion test turns white/milky;
Ignore cloudy.
Reject precipitate.
Accept (for Sudan III) top (layer) red.
Non-reducing sugar
3.   Do Benedict’s test and stays blue/negative;
Ignore details of method for Benedict’s test for this mp.
4.   Boil with acid then neutralise with alkali;
Accept named examples of acids/alkalis.
5.   Heat with Benedict’s and becomes red/orange (precipitate);
Do not credit mp5 if no attempt at mp4.
For ‘heat’ ignore ‘warm’/’heat gently’/’put in a water bath’ but accept stated temperatures ≥ 60°C.
Heat must be stated again, do not accept using residual heat from mp4.
Accept ‘do the Benedict’s test’ if full correct method given elsewhere.
Accept ‘sodium carbonate, sodium citrate and copper sulfate solution’ for Benedict’s but must have all three if term ‘Benedict’s’ not used.
Amylase
6.   Add biuret (reagent) and becomes purple/violet/mauve/lilac;
Accept ‘sodium or potassium hydroxide and copper sulfate solution’ for ‘biuret’.
Reject heating biuret test.
7.   Add starch, (leave for a time), test for reducing sugar/absence of starch;

Question 26

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids.
Compare and contrast the structure and properties of triglycerides and phospholipids.

Answer 26

1. Both contain ester bonds (between glycerol and fatty acid);
   All statements must be clearly comparative or linked by the candidate, not inferred from separate statements.
   Accept mark points shown on adjacent annotated diagrams.
   2. Both contain glycerol;
   3. Fatty acids on both may be saturated or unsaturated;
   4. Both are insoluble in water;
   5. Both contain C, H and O but phospholipids also contain P;
   Must relate to element.
   6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
   7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
   Accept ‘non-polar’ for hydrophobic and ‘polar’ for hydrophilic.
   8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;