CARB AND LIPIDS

Question 1

What is a monomer? —-

Answer 1

a small identical/ repeating unit / molecule from which larger molecules / polymers are made;

Question 2

What term is used to
describe the different
structures of α-glucose and
β-glucose?

Answer 2

Isomer(ism)

Question 3

ThE structure of cellulose is
related to its role in plant cell
walls. Explain how. (3)

Answer 3

· Long, straight, unbranched chains of Beta glucose; · (Joined by) many WEAK hydrogen bonds; · Form microfibrils / macrofibrils; · Provide rigidity/strength/support;

Question 4

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

Answer 4

Compact/occupies small space/tightly packed;

Question 5

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

Answer 5

. 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 has α-glucose and cellulose has βglucose; 5. Starch (molecule) is helical/coiled and cellulose (molecule) is straight; 6. Starch (molecule) is branched and cellulose is not/unbranched; 7.Cellulose has (micro/macro) fibrils and starch does not; 8. Starch has 1–6 glycosidic bonds and cellulose does not OR Starch contains two types of molecule and cellulose contains one type of molecule OR Starch is amylose and amylopectin and cellulose is one type of molecule;

Question 6

Give one feature of starch
and explain how this feature
enables it to act as a
storage substance.

Answer 6

Helical / spiral So compact / tightly packed / can fit (lots) into a small space; · Insoluble So no osmotic effect / does not leave cell / does not affect water potential; · Large molecule / long chain (So) does not leave cell / contains large number of glucose units; · Branched chains (So) rapid hydrolysis to remove glucose for respiration;

Question 7

Hydrogen bonds are
important in cellulose
molecules. Explain why.

Answer 7

· Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils; · Providing strength/rigidity (to cellulose/cell wall); · Weak Hydrogen bonds provide strength in large numbers;

Question 8

A student carried out the
Benedict’s test. Suggest a
method, other than using a
colorimeter, that this student could use to measure the quantity of reducing sugar in a solution

Answer 8

1. Filter and dry (the precipitate); 2. Find mass/weight

Question 9

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

Answer 9

Non-reducing sugar 3. Do Benedict’s test and stays blue/negative; 4. Boil with acid then neutralise with alkali; 5. Heat with Benedict’s and becomes red/orange (precipitate); Amylase 6. Add biuret (reagent) and becomes purple/violet/mauve/lilac; 7. Add starch, (leave for a time), test for reducing sugar/absence of starch;

Question 10

Compare and contrast the
structure and properties of
triglycerides and phospholipids

Answer 10

· Both contain ester bonds · Both contain glycerol · Fatty acids on both may be saturated or unsaturated · Both are insoluble in water · Both contain C, H and O but phospholipids are also contain P · Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group · Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region · Phospholipids form monolayer/micelle/bilayer but triglycerides don’t

Question 11

What are the differences
between a triglyceride and a
phospholipid?

Answer 11

1. Fatty acid removed; 2. Replaced with a phosphate group;

Question 12

Some seeds contain lipids.
Describe how you could use
the emulsion test to show
that a seed contains lipids.
(3)

Answer 12

1. Crush/grind; 2. With ethanol/ alcohol, to dissolve the lipid; 3. Then add water then shake; 4. Forms a white emulsion / goes white;

Question 13

Describe how an ester bond
is formed in a phospholipid

Answer 13

1. Condensation (reaction) OR Loss of water; 2. Between of glycerol and fatty acid;

Question 14

Omega-3 fatty acids are
unsaturated. What is an
unsaturated fatty acid?

Answer 14

Double bond(s); (Bonds) between carbon atoms within the hydrocarbon chain;

Question 15

Describe how the student
would show that reducing
sugars were present in a
solution.

Answer 15

1. Add Benedict’s; 2. Heat to 95°C; 3. Red/orange/yellow/green precipitate (shows reducing sugar present

Question 16

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

Answer 16

· Glucose and galactose · Joined by condensation · Joined by glycosidic bond · Added to polypeptide in Golgi

Question 17

Describe the chemical reactions involved in the conversion of polymers to
monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to
illustrate your answer. 5

Answer 17

Ignore reference to dimers.
A condensation reaction joins monomers together and forms a
(chemical) bond and releases water;

A hydrolysis reaction breaks a (chemical) bond between
monomers and uses water;
A suitable example of polymers and the monomers from which
they are made;
3. and 4. Polymers must contain many monomers.
3. and 4: suitable examples include
* amino acid and polypeptide, protein, enzyme,
antibody or specific
example
* nucleotide and polynucleotide, DNA or RNA
* Alpha glucose and starch/glycogen
* Beta glucose and cellulose.
If neither specific carbohydrate example is given, allow
monosaccharide/glucose and polysaccharide.
3. and 4. Reject (once) reference to triglycerides.
A second suitable example of polymers and the monomers
from which they are made;
Reference to a correct bond within a named polymer;
Reject reference to ester bond.

Question 18

how can chromatography be used to identify and separate amino acids from a mixture using known standard solution 5

Answer 18

Paper chromatography can be used to separate a mixture of amino acids
A spot of the unknown amino acid sample mixture is placed on a line at the bottom of the chromatography paper
Spots of known standard solutions of different amino acids are then placed on the line beside the unknown sample spot
The chromatography paper is then suspended in a solvent
Each amino acid will be more or less soluble in the mobile phase than others and will therefore separate out of the mixture travelling with the solvent at different times/distances from the line, depending on their:
Charge
Size
The unknown amino acid(s) can then be identified by comparing and matching them with the chromatograms of the known standard solutions of different amino acids
If a spot from the amino acid sample mixture is at the same distance from the line as a spot from one the known standard solutions, then the mixture must contain this amino acid

Question 18

A precipitate is produced in a positive result for reducing sugar in a
Benedict’s test.
A precipitate is solid matter suspended in solution.
A student carried out the Benedict’s test. Suggest a method, other than
using a colorimeter, that this student could use to measure the quantity of
reducing sugar in a solution. 2

Answer 18

Filter and dry (the precipitate);
find mass/weight;

Question 18

Use of a colorimeter in this investigation would improve the repeatability of
the student’s results.
Give one reason why.

Answer 18

quantitative
OR
(Colour change is) subjective;
Accept: accurate/precise
Standardises (the) method

Question 19

Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage
molecule

Answer 19

insoluble (in water), so doesn’t affect water potential;
Branched / coiled / (α-)helix, so makes molecule compact;
OR
Branched / coiled / (α-)helix so can fit many (molecules) in
small area;
Polymer of (α-)glucose so provides glucose for respiration;
Branched / more ends for fast breakdown / enzyme action;
Large (molecule), so can’t cross the cell membrane
Require feature and explanation for 1 mark

Accept Insoluble so doesn’t affect osmosis
Do not allow ref to ‘doesn’t affect water
leaving cells
Ignore ‘surface area’
Accept ‘branched so glucose readily released’

Question 19

In Test 1, the student used a measuring cylinder to measure 15 cm3 of solution
from a beaker. The measuring cylinder gives a volume with an uncertainty of ±1
cm3. She used a graduated syringe to measure 5.0 cm3 of Benedict’s solution.
The graduated syringe gives a volume with an uncertainty of ± 0.5 cm3. She
mixed these volumes of liquid to do the biochemical test.
(e)
Calculate the percentage error for the measurements used to obtain a 20
cm3 mixture of the solution from the beaker and Benedict’s solution. Show
your working.

Answer 19

16.67 − 17 = 2 marks;
(cumulative percentage error of both measuring vessels)
If incorrect final answer, accept for 1 mark:
0.167 − 0.17 (not a percentage)
OR
evidence of
(correct understanding, but not calculated)
Ignore: ± (plus or minus) in answer
1/15+0.5/5

Question 20

in mammals, in the early stages of pregnancy, a developing embryo exchanges
substances with its mother via cells in the lining of the uterus. At this stage, there
is a high concentration of glycogen in cells lining the uterus.
(a)
(b)
Describe the structure of glycogen.

During early pregnancy, the glycogen in the cells lining the uterus is an
important energy source for the embryo.
Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer.

Answer 20

a)polysaccharide of α-glucose;
OR
polymer of α-glucose;
(Joined by) glycosidic bonds
OR
Branched structure;

b)hydrolysed (to glucose);
Glucose used in respiration;

Ignore ‘Broken down’

Question 21

what are serial dilutions
b)where can be used in biology
c)Serial dilutions are completed to create a standand what can we compare unknown concentrations against
d)if want to obtain most quantitative data to see how much conc of glucose is present in each sample

Answer 21

serial dilutions are created by taking a series of dilutions of a stock solution. The concentration decreases by the same quantity between each test tube
b)counting bacteria or yeast populations
Determining unknown glucose, starch, protein concentrations

c)The comparison can be:
Visual
Measured through a calibration/standard curve +Measured using a colourimeter
d)A colourimeter is used to obtain
quantitative data that can be plotted to create a calibration curve to be used to find unknown concentrations instead of visaully analysing.

Question 22

Describe how a triglyceride molecule is formed 3

Answer 22

one glycerol and three fatty acids;
Condensation (reactions) and removal of three molecules of water;
Ester bond(s) (formed);
Accept all marks in suitably labelled diagram OR in
a balanced equation

Question 22

how can we use chromatography to with known standard solution to separate mixture of monosaccharides and identify their components 5

Answer 22

(Paper chromatography can be used to separate a mixture of monosaccharides
Mixtures containing coloured molecules, such as ink or chlorophyll, do not have to be stained as they are already coloured
Mixtures of colourless molecules, such as a)
mixture of monosaccharides, have to be stained first
A spot of the stained monosaccharide sample mixture is placed on a line at the bottom of the chromatography paper
Spots of known standard solutions of different monosaccharides are then placed on the line beside the sample spot
The chromatography paper is then suspended in a solvent
As the solvent travels up through the chromatography paper, the different monosaccharides within the mixture separate out at different distances from the line
The unknown monosaccharides can then be identified by comparing and matching them with the chromatograms of the known standard solutions of different monosaccharides
If a spot from the monosaccharide sample mixture is at the same distance from the line as a spot from one of the known standard solutions, then the mixture must contain this monosaccharide