Download A-level Biology B Question paper Unit 2 - Genes and Genetic

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Centre Number
For Examiner’s Use
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General Certificate of Education
January 2009
Advanced Subsidiary Examination
BIOLOGY (SPECIFICATION B)
Unit 2 Genes and Genetic Engineering
Thursday 8 January 2009
BYB2
9.00 am to 10.00 am
For this paper you must have:
● a ruler with millimetre measurements.
You may use a calculator.
For Examiner’s Use
Question
Mark
Question
Mark
1
Time allowed: 1 hour
2
Instructions
● Use black ink or black ball-point pen.
● Fill in the boxes at the top of this page.
● Answer all questions.
● You must answer the questions in the spaces provided. Answers
written in margins or on blank pages will not be marked.
● If you need extra space use page 16 for your answers.
● Do all rough work in this book. Cross through any work you do not
want to be marked.
Information
● The maximum mark for this paper is 54.
● The marks for questions are shown in brackets. One mark will be
awarded for Quality of Written Communication.
● You are reminded of the need for good English and clear presentation
in your answers.
● Use accurate scientific terminology in your answers.
● Answers for Questions 1 to 6 are expected to be short and precise.
● Answer Question 7 in continuous prose. Quality of Written
Communication will be assessed in the answer.
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Quality of Written
Communication
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Examiner’s Initials
BYB2
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Answer all questions in the spaces provided.
1 The diagram shows a short section of a DNA molecule.
P
Q
R
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(a) Use the letters in the diagram to indicate a part of the molecule which contains
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(a)
(i) phosphate ..................................................................................................................
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(a)
(ii) nitrogen. ....................................................................................................................
(2 marks)
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(b)
(i) How are the two strands of the DNA molecule held together?
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(1 mark)
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(b)
(ii) Give one advantage of DNA molecules having two strands.
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(1 mark)
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(c) A piece of DNA consisted of 54 base pairs. The two strands of the DNA, strands A
and B, were analysed to find how many bases of each type were present. Some of the
results are shown in the table.
Number of bases
C
G
Strand A
19
Strand B
11
A
T
9
Calculate the missing values for the number of bases and complete the table.
(2 marks)
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2 The diagram shows an egg cell.
X
Nucleus
Cytoplasm
100 µm
2
Y
(a) Calculate the length of the egg cell between X and Y in micrometres.
Answer ............................................. µm
(1 mark)
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(b) Explain the advantage of
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(b)
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(i) the egg cell having a large amount of cytoplasm
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(2 marks)
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(b)
(ii) producing many more sperm than egg cells.
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(2 marks)
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(a) The table has statements describing different events during mitosis. Use a tick to
indicate during which stage of mitosis each event takes place.
Stage of mitosis
Statement
Interphase
Prophase Metaphase Anaphase Telophase
Sister chromatids separate
DNA replication occurs
Chromosomes shorten and
thicken
(3 marks)
3
(b) The bar chart shows the average duration of each stage of mitosis in the cells of an
insect embryo.
100
90
80
70
Average
duration
of each
stage / mins
60
50
40
30
20
10
In
ter
p
ha
se
Pr
op
ha
se
M
eta
ph
a
An se
ap
ha
se
Te
lop
ha
se
0
Stage of mitosis
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(b)
(i) Give one piece of evidence from the bar chart which indicates that these cells are
dividing rapidly.
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(1 mark)
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(b)
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(ii) Calculate the time required in minutes for one of these cells to produce
eight cells.
Answer ............................... minutes (1 mark)
3
(c) The diagram represents an insect cell in which the diploid number of chromosomes is
six.
3
(c)
(i) Draw a diagram to show the chromosomes in a gamete produced from this cell
by meiosis.
(2 marks)
3
(c)
(ii) Apart from producing gametes that are genetically different, meiosis is important
in sexual reproduction. Explain why.
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(2 marks)
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4 Cystic fibrosis is caused by a mutation of the gene coding for the protein, CFTR. This
protein consists of 1480 amino acids.
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(a) What is the minimum number of nucleotide bases needed to code for this protein?
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(1 mark)
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(b) Give two factors which might increase the frequency at which a mutation in a gene
occurs.
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2 .........................................................................................................................................
(2 marks)
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(c) One method of treating people with cystic fibrosis involves the transfer of healthy
CFTR genes into epithelial cells in their lungs.
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(c)
(i) Individuals who have been treated by this method do not pass on the healthy
CFTR gene to their children. Explain why.
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(1 mark)
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(c)
(ii) Viruses have been used to transfer the healthy CFTR genes into epithelial cells.
Give one reason for using a virus to transfer genes into cells.
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(1 mark)
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(d) A mutation involving a deletion of a base may have a greater effect than one involving
substitution of one base for another. Explain why.
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5 A scientist determined the sequences of nucleotides in small samples of DNA obtained from
the dried muscle of an extinct mammal. The scientist then compared these DNA sequences
with the corresponding DNA sequences in samples obtained from other extinct mammals.
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(a) The scientist compared the DNA samples obtained from the muscle of one mammal
with DNA samples obtained from the bone of another mammal. Explain why this is a
valid comparison.
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(1 mark)
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(b) The scientist required a large quantity of each DNA to make comparisons. Name the
reaction used to amplify a small amount of DNA into a larger quantity.
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(1 mark)
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(c) Explain why the following would be required in the process of producing a large
quantity of DNA.
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(c)
(i) Primers
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(1 mark)
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(c)
(ii) DNA polymerase
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(1 mark)
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(d) As part of the process of sequencing, each DNA sample was broken into fragments.
These fragments were separated using gel electrophoresis. The diagram shows the
banding pattern produced with one DNA sample consisting of eight nucleotides.
T
C
G
– ve
A
Band a
Band b
Band c
Band d
Direction of
movement
of fragments
Band e
Band f
Band g
+ ve
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(d)
Band h
(i) Explain why the DNA fragments move different distances in the gel.
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(1 mark)
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(d)
(ii) The DNA fragments were radioactively labelled. Describe one method used to
make radioactively labelled fragments visible following electrophoresis.
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(2 marks)
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(d) (iii) Which of the bands, a to h contains seven nucleotides?
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(1 mark)
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6 Stem cells are found in human bone marrow and in embryos. These cells can divide to form
a clone. Stem cells are able to develop into different types of cell.
6
(a) What is a clone?
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(1 mark)
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(b) Use your knowledge of genes to explain how stem cells are able to develop into
different types of cell.
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(2 marks)
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(c) Bone marrow transplants used in treating diseases such as leukaemia involve the
transfer of stem cells from a genetically matched donor.
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(c)
(i) Suggest why the stem cells are obtained from a genetically matched donor.
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(1 mark)
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(c)
(ii) The injection of stem cells into specific organs of the body has been used to treat
other diseases. These stem cells develop into similar tissues as their
surroundings. Suggest one way in which the development of these cells is
influenced by their surroundings.
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(1 mark)
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Answer Question 7 in continuous prose, where appropriate.
Quality of Written Communication will be assessed in these answers.
7 A bioluminescent jellyfish has a gene which codes for the production of a green fluorescent
protein (GFP). Scientists have removed the GFP gene from the DNA of a jellyfish and
inserted it into bacteria.
7
(a) Describe how the GFP gene could be removed from the DNA of a jellyfish and
inserted into bacteria.
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Question 7 continues on the next page
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(b) The GFP gene can be used as a marker to identify bacteria which have been
genetically engineered. Bacteria containing the GFP gene glow green under UV light.
Suggest two advantages of using the GFP gene as a genetic marker rather than genes
that confer antibiotic resistance.
1 .........................................................................................................................................
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2 .........................................................................................................................................
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(2 marks)
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(c) The genetically engineered plasmid, pGLO contains three genes involved in controlling
the production of green fluorescent protein in bacteria. The diagram shows the roles of
these genes in controlling the production of green fluorescent protein.
GFP gene
Promoter gene
Regulator gene
Stimulates
Inhibits
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(c)
Production
of mRNA
Production
of mRNA
Green flourescent protein
araC protein
(i) Name the process stimulated by the promoter gene.
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(1 mark)
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(c)
(ii) The regulator gene can inhibit production of green fluorescent protein. Explain
how.
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(1 mark)
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(c) (iii) Arabinose is a sugar which binds to the araC protein. The intensity of the green
light produced by a bacterium can be changed by varying the amount of
arabinose provided to bacteria containing this plasmid. Suggest how arabinose
has this effect.
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(2 marks)
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END OF QUESTIONS
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