Q1.
Phenylketonuria (PKU) is an inherited condition. PKU makes people ill.
(a)
PKU is caused by a recessive allele.
(i)
What is an allele?
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(1)
(ii)
What is meant by recessive?
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(1)
(b)
The diagram below shows the inheritance of PKU in one family.
(i)
Give one piece of evidence from the diagram that PKU is caused by a recessive
allele.
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...............................................................................................................
(1)
(ii)
Persons 6 and 7 are planning to have another child.
Use a genetic diagram to find the probability that the new child will have PKU.
Use the following symbols in your answer:
N = the dominant allele for not having PKU
n = the recessive allele for PKU.
Probability = ..................................................
(4)
Page 1 of 20
(c)
Persons 6 and 7 wish to avoid having another child with PKU.
A genetic counsellor advises that they could produce several embryos by IVF treatment.
(i)
During IVF treatment, each fertilised egg cell forms an embryo by cell division.
Name this type of cell division.
...............................................................................................................
(1)
(ii)
An embryo screening technique could be used to find the genotype of each embryo.
An unaffected embryo could then be placed in person 7’s uterus.
The screening technique is carried out on a cell from an embryo after just three cell
divisions of the fertilised egg.
How many cells will there be in an embryo after the fertilised egg has
divided three times?
(1)
(iii)
During embryo screening, a technician tests the genetic material of the embryo to
find out which alleles are present.
The genetic material is made up of large molecules of a chemical substance.
Name this chemical substance.
...............................................................................................................
(1)
(d)
Some people have ethical objections to embryo screening.
(i)
Give one ethical objection to embryo screening.
...............................................................................................................
(1)
(ii)
Give one reason in favour of embryo screening.
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(1)
(Total 12 marks)
Page 2 of 20
Q2.
CADASIL is an inherited disorder caused by a dominant allele.
CADASIL leads to weakening of blood vessels in the brain.
The diagram shows the inheritance of CADASIL in one family.
(a)
CADASIL is caused by a dominant allele.
(i)
What is a dominant allele?
...............................................................................................................
...............................................................................................................
(1)
(ii)
What is the evidence in the diagram that CADASIL is caused by a dominant allele?
...............................................................................................................
...............................................................................................................
(1)
(iii)
Person 7 has CADASIL.
Is person 7 homozygous or heterozygous for the CADASIL allele?
Give evidence for your answer from the diagram.
...............................................................................................................
...............................................................................................................
(1)
Page 3 of 20
(b)
Persons 7 and 8 are planning to have another baby.
Use a genetic diagram to find the probability that the new baby will develop into a person
with CADASIL.
Use the following symbols to represent alleles.
D = allele for CADASIL
d = allele for not having CADASIL
Probability = ........................................................................
(4)
(c)
Scientists are trying to develop a treatment for CADASIL using stem cells.
Specially treated stem cells would be injected into the damaged part of the brain.
(i)
Why do the scientists use stem cells?
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...............................................................................................................
...............................................................................................................
(2)
(ii)
Embryonic stem cells can be obtained by removing a few cells from a human
embryo. In 2006, scientists in Japan discovered how to change adult skin cells into
stem cells. Suggest one advantage of using stem cells from adult skin cells.
...............................................................................................................
...............................................................................................................
(1)
(Total 10 marks)
Page 4 of 20
Q3.
Cats normally have four toes on each back paw.
The picture shows the back paw of a cat with an inherited condition called polydactyly.
By Onyxrain (Own work) [Public domain], via Wikimedia Commons
The family tree shows the inheritance of polydactyly in three generations of cats.
(a)
What combination of alleles did the original parents, A and B, have?
Explain how you work out your answer.
You may use a genetic diagram in your answer.
Use the symbol H to represent the dominant allele.
Use the symbol h to represent the recessive allele.
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A = ................................................... B = ......................................................
(4)
Page 5 of 20
(b)
(i)
Give two possible combinations of alleles for cat D.
1 .................................................... 2 ....................................................
(1)
(ii)
You cannot be sure which one of these two is the correct combination of alleles for
cat D.
Why?
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...............................................................................................................
...............................................................................................................
(1)
(Total 6 marks)
Q4.
The black pigment in human skin and eyes is called melanin.
A single gene controls the production of melanin.
A person who is homozygous for the recessive allele of the gene has no melanin and is said to
be albino.
The diagram shows the inheritance of albinism in a family.
Page 6 of 20
(a)
Use a genetic diagram to explain the inheritance of the albino allele by children of parents
P and Q.
(3)
(b)
R and S decide to have a child.
What is the chance that this child will be an albino? ...............................................
Use a genetic diagram to explain your answer.
(3)
(Total 6 marks)
Page 7 of 20
Q5.
Isomerase is an enzyme which can change glucose into fructose.
Fructose is often used instead of glucose in products like slimming foods.
In industry, isomerase is often ‘immobilised’ within beads of gel.
The beads are placed in a glass column.
The isomerase stays attached to the beads and a solution of glucose is allowed to flow between
the beads in the column.
The diagram shows how immobilised isomerase is used.
(a)
An alternative method of changing glucose into fructose would be to mix a solution of the
isomerase with the glucose solution in a large container.
Suggest two advantages of using isomerase immobilised in a column of beads.
1......................................................................................................................
........................................................................................................................
2......................................................................................................................
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(2)
Page 8 of 20
(b)
A manufacturer investigated the effect of using different flow rates of glucose solution on
the rate of fructose production.
The table shows the results.
Flow rate in
dm3 per minute
Rate of fructose
production in
mg per minute
1
150
2
325
3
480
4
608
5
650
6
650
7
650
The manufacturer decides to use a flow rate of 5 dm3 per minute.
Suggest why the manufacturer chose this flow rate.
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........................................................................................................................
........................................................................................................................
(2)
(c)
Fructose is a much sweeter sugar than glucose.
Explain why manufacturers of slimming foods may wish to use fructose as a sweetener
instead of glucose.
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........................................................................................................................
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(2)
(Total 6 marks)
Page 9 of 20
Q6.
The diagram shows the apparatus used to investigate the digestion of milk fat by an
enzyme. The reaction mixture contained milk, sodium carbonate solution (an alkali) and the
enzyme. In Experiment 1, bile was also added. In Experiment 2, an equal volume of water
replaced the bile. In each experiment, the pH was recorded at 2-minute intervals.
Either: Experiment 1
or:
milk (contains fat)
sodium carbonate solution
bile
enzyme
Experiment 2
milk (contains fat)
sodium carbonate solution
water
enzyme
The results of the two experiments are given in the table.
(a)
Milk fat is a type of lipid. Give the name of an enzyme which catalyses the breakdown of
lipids.
...................................................................................................................................
(1)
Page 10 of 20
(b)
What was produced in each experiment to cause the fall in pH?
...................................................................................................................................
(1)
(c)
(i)
For Experiment 1, calculate the average rate of fall in pH per minute, between
4 minutes and 8 minutes. Show clearly how you work out your final answer.
...........................................................................................................................
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...........................................................................................................................
............................................. pH units per minute
(2)
(ii)
Why was the fall in pH faster when bile was present?
...........................................................................................................................
...........................................................................................................................
(1)
(Total 5 marks)
Q7.
There are enzymes in biological washing powders. Biological washing powder has to be
used at temperatures below 45 °C.
(a)
The enzymes in biological washing powders do not work on the stains on clothes at
temperatures above 45 °C.
Explain why.
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(2)
Page 11 of 20
(b)
Some bacteria, called thermophilic bacteria live in hot springs at temperatures of 80 °C.
Scientists have extracted enzymes from these thermophilic bacteria. These enzymes are
being trialled in industrial laundries.
The laundries expect to increase the amount of clothes they can clean by using enzymes
from thermophilic bacteria instead of using the biological washing powders the laundries
use now.
(i)
The laundries expect to be able to increase the amount of clothes that they can clean
each day.
Suggest why.
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(2)
(ii)
Using washing powders with enzymes from thermophilic bacteria may be more
harmful to the environment than using the biological washing powders that laundries
use now.
Suggest why.
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(2)
(Total 6 marks)
Page 12 of 20
M1.
(a)
(i)
one form of a / one gene
do not allow ‘a type of gene’
allow a mutation of a gene
1
(ii)
not expressed if dominant / other allele is present / if heterozygous
or
only expressed if dominant allele not present / or no other allele present
allow need two copies to be expressed / not expressed if only one
copy / only expressed if homozygous
1
(b)
(i)
two parents without PKU produce a child with PKU / 6 and 7 → 10
allow ‘it skips a generation’
1
(ii)
genetic diagram including:
accept alternative symbols if defined
Parental gametes:
6: N and n
and 7: N and n
1
derivation of offspring genotypes:
NN
Nn
Nn
nn
allow genotypes correctly derived from student’s parental gametes
1
identification: NN and Nn as non-PKU
OR nn as PKU
allow correct identification of student’s offspring genotypes
1
correct probability only: 0.25 / ¼ / 1 in 4 / 25% / 1 : 3
do not allow 3 : 1 / 1 : 4
do not allow if extra incorrect probabilities given
1
(c)
(i)
mitosis
correct spelling only
1
(ii)
8
1
Page 13 of 20
(iii)
DNA
allow deoxyribonucleic acid
do not allow RNA / ribonucleic acid
1
(d)
(i)
may lead to damage to embryo / may destroy embryos / embryo cannot give
consent
allow avoid abortion
allow emotive terms – eg murder religious argument must be
qualified
allow ref to miscarriage
allow idea of avoiding prejudice against disabled people
allow idea of not producing designer babies
1
(ii)
any one from:
•
•
prevent having child with the disorder / prevent future suffering / reduce
incidence of the disease
ignore ref to having a healthy child
ignore ref to selection of gender
embryo cells could be used in stem cell treatment
allow ref to long term cost of treating a child (with a disorder)
allow ref to time for parents to become prepared
1
[12]
M2.
(a)
(i)
allele expressed even when other allele present or expressed if just one copy of
allele is present or expressed if heterozygous
if present other allele not expressed
1
(ii)
2 affected parents have unaffected child or 1 and 2 → 5 / 6
or if recessive all of 1 and 2’s children would have CADASIL
1
(iii)
heterozygous – has unaffected children or because if homozygous all children
would have CADASIL
1
(b)
genetic diagram including:
accept alternative symbols, if defined
1
correct gametes:
D and d
and d (and d)
ignore 7 / 8 or male / female
1
Page 14 of 20
derivation of offspring genotypes:
Dd Dd dd dd
allow just Dd dd if ½-diagram
allow ecf if correct for student’s gametes
1
identification of Dd as CADASIL
or dd as unaffected
allow ecf if correct for student’s gametes
1
correct probability: 0.5 / ½ / 1 in 2 / 50% / 1 : 1
1
(c)
(i)
stem cells can differentiate or are undifferentiated / unspecialised
1
can form blood vessel cells / brain cells
or
stem cells can divide
1
(ii)
ethical argument - eg no risk of damage to embryo or adult can give consent
for removal of cells or adult can re-grow skin
more ethical qualified
ignore religion unqualified
or
if from a relative then less chance of rejection or if from self then no chance of
rejection
or
skin cells more accessible
1
[10]
M3.
(a)
A = Hh
B = Hh
may not be in answer space
accept heterozygous or description
1
(allele for) polydactyly is dominant or polydactyly is H,
for marking points 1, 2 and 3 accept evidence in clearly labelled /
annotated genetic diagram
1
cats with polydactyly have H
accept if polydactyly was recessive all offspring would have
polydactyly
1
E or (some) offspring of A and B, does not have polydactyly,
so A and B must both have h
1
Page 15 of 20
(b)
(i)
HH and Hh or
homozygous dominant and heterozygous
both required, in either order
allow description
1
(ii)
any one from:
accept annotated genetic diagram to explain answer
•
polydactyly is dominant
•
parents are both Hh
•
if D is Hh all offspring could inherit H
1
[6]
M4.
(a)
gametes A or a A or a
1
F1 genotypes correctly derived
1
albino identified
OR
gametes – 1
F1 genotypes corresponding to ‘lines’ – 1
lines must be correct
Albino (aa) identified – 1 (lower case)
1
OR
A
A
a
AA
a
Aa
Aa
aa
gametes –1
boxes all correct –1
albino (aa) identified –1
Page 16 of 20
(b)
do not credit 1 to 2 or 50/50
1
gametes A or a a or a or one
parent heterozygous, one parent
homozygous recessive
1
F1 genotypes correctly derived
OR
(R)
(S)
gametes correctly identified – 1
F1 genotypes correctly derived – 1
OR
gametes correctly derived – 1
F1 genotypes correctly derived – 1
1
[6]
M5.
(a)
any two from:
•
product not contaminated with enzyme or is pure
•
enzyme can be reused
allow enzyme not wasted / less
enzyme is needed
•
continuous flow process possible
•
enzyme more stable / can be used at higher temperature
allow enzyme lasts longer
ignore refs. to cost / cheaper
2
Page 17 of 20
(b)
maximum fructose production / maximum enzyme activity
accept optimum / best
or
increase in flow rate does not increase production
1
higher rate leaves some glucose unchanged
allow glucose not wasted / extra glucose wastes money
1
(c)
less (fructose) needed (for same sweetness)
ignore fructose is sweeter unqualified
1
(less fructose ) → less fattening / fewer ‘calories’
ignore refs. to cost / cheaper
1
[6]
M6.
(a)
lipase
1
(b)
fatty acid
ignore glycerol
1
(c)
(i)
0.25 or
if correct answer ignore working or lack of working
for 1 mark
2
(ii)
fats emulsified or described re. Small droplets or large S.A.
(for enzyme action) or fats ‘mix’ better with water
do not allow breakdown / breakup unqualified
1
[5]
M7.
(a)
shape changed / destroyed (above 45 °C)
accept denatured
accept active site changed
do not accept enzyme killed
1
(shape) doesn’t fit (other molecules / stain)
1
Page 18 of 20
(b)
(i)
any two from:
•
can wash the clothes at higher temperature
•
so wash / enzyme action will be quicker
do not accept idea of bacteria working faster
•
enzyme not destroyed at high temperature / 80 °C
accept denaturation or description
2
(ii)
high(er) temperature / 80 °C uses more energy / fuel
1
more pollution / named (eg carbon dioxide / global warming) (from electricity
production)
or
increased release of hot water (into the environment)
1
[6]
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Page 20 of 20