Year 10 Science
Biology Unit Test
May 2014
ANSWERS
PART A: MULTIPLE CHOICE QUESTIONS
1.
2.
3.
4.
D
D
D
A
5.
6.
7.
8.
B
D
B
A
9. C
10. B
PART B: SHORT ANSWER SECTION
1.
(a) James Watson, Francis Crick (and Rosalind Franklin)
[1]
(b) DNA molecule has the shape of a double helix
2 strands
composed of subunits called nucleotides
nucleotides contain phosphate, sugar and nitrogen base
covalent bonds hold the nucleotides together, forming the sugar-phosphate backbone
Hydrogen bonds hold the bases together across the centre
complementary base pairing exits between the nitrogen bases (A=T, C=G)
Explain DNA structure, including its subunits and the way in which they are bonded
[4]
(Total 5 marks)
2.
(a) locus
[1]
(b) sex-linked
[1]
(c) males only need one copy of the recessive allele to be colour blind (because they only have
one X chromosome);
females need two copies of the recessive allele to be colour-blind;
[2]
(d)
i.
[3]
x
E
e
e
Ee
ee
e
Ee
ee
Parents: Ee (mum) x ee (dad)
Phenotype ratio: 50% round shaped blood
: 50% elliptical shaped blood
Page 1 of 10
Year 10 Science
Biology Unit Test
ii.
iii.
I
II
May 2014
Work out the possible phenotype for this child with regards to colour-blindness.
Remember to use correct symbols and show all necessary working.
[3]
XC
Xc
Parents: XCXc (mum) x XCY (dad)
x
Phenotype ratio: 50% normal females
: 25% normal males
: 25% colour blind males
XC
X CX C X CX c
Y
XC Y
Xc Y
Key (1 mark), correct structure (1 mark), genotypes (1 mark)
XcY
?
?
[3]
?
XCY
XC Xc
?
III
(Total 13 marks)
3.
(a) A heterozygote for a disorder – can pass it on without any symptoms themselves
[1]
(b) 2
[1]
(c)
[3]
Key: H = normal, h = haem
x
Parents: XHXh (mum) x XHY (dad)
Phenotype ratio: 50% normal female : 25% normal male
: 25% haemophiliac male
XH
Xh
XH
XHXH XHXh
Y
XHY
XhY
(Total 5 marks)
Page 2 of 10
Year 10 Science
Biology Unit Test
May 2014
4.
(a) meiosis
[1]
(b) Phases: 2 (meiosis) and 1 (mitosis)
Parent cell: reproductive cell (meiosis) and body cell (mitosis)
Daughter cells: 4 (meiosis) and 2 (mitosis)
Daughter cells: gametes (meiosis) and body cells (mitosis)
Daughter cells: haploid (meiosis) and diploid (mitosis)
Chromosomes in daughter cells: 23 (meiosis) and 46 (mitosis)
[3]
(c) Change in DNA sequence caused spontaneously or by environmental factors
(d) Increased mutation  increased variation
[3]
More variation allows for more competition and natural selection
 better suited organisms survive struggle
Species begins to change over time as adaptations accumulate and increase in frequency
(Total 6 marks)
5.
(a) Divergent evolution
[1]
(b) DNA analysis
Comparative embryology or anatomy
Check if they can still mate to produce viable offspring
Any other acceptable answer
[2]
(c) Variation existed
geographical isolation occurred due to continental drift
restricted gene flow between two groups of snakes
different selection pressures acted on each group
natural selection occurs
different adaptations result in each group until they can no longer interbreed to produce
viable offspring
[4]
(Total 7 marks)
6.
(a) chimpanzee
[1]
(b) red kangaroo
[1]
(c) number of differences = estimation of time since the two species shared a common
ancestor
chimpanzee and human share a more recent common ancestor than the red kangaroo and
human
[2]
(Total 4 marks)
Page 3 of 10