Biological molecules Questions with Correct Answers

Biological molecules Questions with
Correct Answers
Describe the difference between the structure of a triglyceride molecule and the
structure of a phospholipid molecule.
(1 MARK) - ANSWERSIn phospholipid, one fatty acid replaced by a phosphate;

Describe how you would test for the presence of a lipid in a sample of food
(2 MARKS) - ANSWERSDissolve in ethanol, then add water;
White (emulsion shows lipid);

Describe how a saturated fatty acid is different from an unsaturated fatty acid
(1 MARK) - ANSWERSSaturated single/no double bonds (between carbons)

This fat substitute cannot be digested in the gut by lipase. Suggest why.
(2 MARKS) - ANSWERS(Fat substitute) is a different/wrong shape/not complementary
Unable to fit/bind to (active site of) lipase/no ES complex formed

This fat substitute is a lipid. Despite being a lipid, it cannot cross the cell-surface
membranes of cells lining the gut. Suggest why it cannot cross cell-surface membranes.
(1 MARK) - ANSWERSIt is hydrophilic/is polar/is too large/is too big

Describe how ATP is resynthesised in cells.
(2 MARKS) - ANSWERSFrom ADP and phosphate
By ATP synthase
During respiration/photosynthesis;

Give two ways in which the hydrolysis of ATP is used in cells.
(2 MARKS) - ANSWERSTo provide energy for other reactions/named process
To add phosphate to other substances and make them more reactive/change their
shape;

When HIV infects a human cell, the following events occur. • A single-stranded length of
HIV DNA is made. • The human cell then makes a complementary strand to the HIV
DNA. The complementary strand is made in the same way as a new complementary
strand is made during semi-conservative replication of human DNA.

,Describe how the complementary strand of HIV DNA is made
(3 MARKS) - ANSWERS(Complementary) nucleotides/bases pair
OR A to T and C to G
DNA polymerase
Nucleotides join together (to form new strand)/phosphodiester bonds form

Contrast the structures of DNA and mRNA molecules to give three differences
(3 MARKS) - ANSWERSDNA double stranded/double helix and mRNA single-stranded
DNA (very) long and RNA short
Thymine/T in DNA and uracil/U in RNA
Deoxyribose in DNA and ribose in RNA
DNA has base pairing and mRNA doesn't/ DNA has hydrogen bonding and mRNA
doesn't
DNA has introns/non-coding sequences and mRNA doesn't;

Describe the induced-fit model of enzyme action.
(2 MARKS) - ANSWERS(before reaction) active site not complementary to/does not fit
substrate
Shape of active site changes as substrate binds/as enzymesubstrate complex forms
Stressing/distorting/bending bonds (in substrate leading to reaction

AS Biology Question paper Paper 1 June 2016 Q[0.6.3]
Explain the results shown in Figure 4.
(2 MARKS) - ANSWERS(Rate of) increase in concentration of maltose slows as
substrate/starch is used up OR High initial rate as plenty of starch/substrate/more E-S
complexes
No increase after 25 minutes/at end/levels off because no substrate/starch left;

A quantitative Benedict's test produces a colour whose intensity depends on the
concentration of reducing sugar in a solution. A colorimeter can be used to measure the
intensity of this colour. The scientist used quantitative Benedict's tests to produce a
calibration curve of colorimeter reading against concentration of maltose.
Describe how the scientist would have produced the calibration curve and used it to
obtain the results in Figure 4. Do not include details of how to perform a Benedict's test
in your answer
(3 MARKS) - ANSWERSMake/use maltose solutions of known/different concentrations
(and carry out quantitative Benedict's test on each)
(Use colorimeter to) measure colour/colorimeter value of each solution and plot
calibration curve/graph described
Find concentration of sample from calibration curve;

Describe the function of each of these enzymes.
DNA helicase
DNA polymerase
(2 MARKS) - ANSWERSDNA helicase - (unwinding DNA and) breaking hydrogen
bonds / bonds between chains / bases / strands

, DNA polymerase - joins (adjacent) nucleotides OR forms phosphodiester bond /
sugarphosphate backbone;

Adenosine triphosphate (ATP) is a nucleotide derivative. Contrast the structures of ATP
and a nucleotide found in DNA to give two differences.
(2 MARKS) - ANSWERS1. ATP has ribose and DNA nucleotide has deoxyribose;
2. ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate (group);
3. ATP- base always adenine and in DNA nucleotide base can be different / varies;

Which test could the scientists have used to identify that there are amino acids in white
wine?
(1 MARK) - ANSWERSBiuret

Name the chemical element found in all amino acids that is not found in triglycerides.
(1 MARK) - ANSWERSNitrogen;

The scientists used a statistical test to determine whether there was a significant
difference in the amino acid concentration in the two types of white wine. They obtained
a value for P of 0.04.
Name the statistical test the scientists used and give a reason for your answer. Was the
difference significant? Give a reason for your answer.
(3 MARKS) - ANSWERSChoice: (Student's) t-test;
Reason for choice: Looking for differences between two means;
Explanation: Difference is significant / not due to chance because the P value is 0.04 / is
less than 0.05;

What is a monomer?
(1 MARK) - ANSWERS(a monomer is a smaller / repeating) unit / molecule from which
larger molecules / polymers are made;

Lactulose is a disaccharide formed from one molecule of galactose and one molecule of
fructose. Other than both being disaccharides, give one similarity and one difference
between the structures of lactulose and lactose.
(2 MARKS) - ANSWERSSimilarity 1. Both contain galactose / a glycosidic bond;
Difference 2. Lactulose contains fructose, whereas lactose contains glucose;

Following digestion and absorption of food, the undigested remains are processed to
form faeces in the parts of the intestine below the ileum. The faeces of people with
constipation are dry and hard. Constipation can be treated by drinking lactulose.
Lactulose is soluble, but is not digested or absorbed in the human intestine.
Use your knowledge of water potential to suggest why lactulose can be used to help
people suffering from constipation.
(2 MARKS) - ANSWERS1. (Lactulose) lowers the water potential of faeces / intestine /
contents of the intestine;
2. Water retained / enters (due to osmosis) and softens the faeces;