Download SNAB Topic 6 Test Answers File

E6.00L
Teacher/Lecturer .
Mark scheme for Topic 6 Exam-style topic test
General information
The following symbols are used in the mark schemes for all questions.
; semicolon – indicates the end of a marking point.
eq – indicates that credit should be given for other correct alternatives to a word or
statement.
/ oblique – words or phrases separated by an oblique are alternatives to each other.
{ } – indicate the beginning and end of a list of alternatives (separated by obliques)
where necessary to avoid confusion.
( ) – words in round brackets are not required to award the point.
Crossed out work should be marked UNLESS the candidate has replaced it with an
alternative response.
In general, an error made in an early part of a question is penalised when it occurs but
not subsequently. The candidate is penalised once only and can gain credit in later
parts of the question for correct reasoning from the earlier incorrect answer.
The spelling of technical words must be sufficiently correct to be unambiguous, e.g. for
mitosis, mytosis would be acceptable whereas meitosis would not.
The meaning of an answer must be clear to gain the marks.
A correct statement that is contradicted by an incorrect statement in the same part of an
answer gains no mark.
Question 1
(a)
Maximum mark
Each species of insect changes conditions on the body;
Changes to body due to bacterial decomposition / abiotic factors;
Makes the body suitable for different insects;
Correct reference to succession;
Some insects feed on other insects;
(b)(i) 4–8 months;
2 marks
1 mark
(ii) Insect development affected by temperature;
Corpse may not have been exposed to insects immediately after death;
Body could be indoors / eq;
1 mark
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2009. © University of York Science Education Group.
This sheet may have been altered from the original.
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E6.00L
Topic 6 Exam-style topic test
(c)
Teacher/Lecturer
Look for stage of development of insects;
Ref. to eggs / larvae / pupae;
Take account of ambient temperature / ref. to graphed data;
(d)
2 marks
Core temperature of corpse;
Rigor of muscles / degree of muscle contraction;
Decomposition / odour / colour of skin;
2 marks
Total 8 marks
Question 2
(a)
Cells killed before virus replication cycle complete;
Reduced production of viruses;
Fewer viruses to infect new cells;
(b)
2 marks
Loss of cells could damage functioning of tissues / organs;
Costs of producing the T cells;
(c)
1 mark
Mutation / change of {gene / DNA} leads to change in virus protein;
Ref. to transcription / translation;
Peptide shape changed;
T killer cell receptors do not fit changed peptide;
So T killer cells do not destroy infected cells;
Ref. to possibility of changed peptide resembling self peptide;
4 marks
(d)
Mutation could make virus unable to infect new cells / control host cell’s protein
synthesis / replicate DNA / eq;
1 mark
(e)
Ref. to clone of T helper cells with correct receptors for antigen;
More rapid response if same antigen re-infects;
More rapid activation of T killer cells / B cells / antibody production;
2 marks
Total 10 marks
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2009. © University of York Science Education Group.
This sheet may have been altered from the original.
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E6.00L
Teacher/Lecturer
Topic 6 Exam-style topic test
Question 3
(a)
Cell wall
ribosomes
plasmid
chromosome
mitochondria
A
B
C
D
4 marks
(b)
(c)
Size: bacteria much larger / viruses about 1/10 -1/20 diameter of
bacteria;
1 mark
Genetic material: Bacteria have loop of DNA;
Bacteria sometimes have plasmid;
Bacteria always have DNA, some viruses have DNA and some RNA; 2 marks
(d)
Response to antibiotics: Bacteria can be killed by (bacteriocidal) antibiotics /
prevented from reproducing by (bacteriostatic) antibiotics / viruses unaffected;
Antibiotics work by inhibiting bacterial cell wall synthesis / disrupt bacterial
membrane / correct ref. to other factor, e.g. enzymes, specific to bacteria;
2 marks
(e)
1. mRNA lines up at the ribosome / eq ;
2. tRNA picks up specific amino acids ;
3. Codon-anticodon bonding (at the ribosome) / tRNA-mRNA complementary
base pairing ;
4. Formation of peptide bonds (between adjacent amino acids) ;
5. Ribosome moves along the mRNA strand ;
6. Use of {start / stop} codons ;
7. Polypeptide released and folds into tertiary structure ;
4 marks
Total 13 marks
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2009. © University of York Science Education Group.
This sheet may have been altered from the original.
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Topic 6 Exam-style topic test
Teacher/Lecturer
Question 4
(a)
Lysozyme in tears, etc;
Skin as a physical barrier;
Skin flora inhibit / compete with harmful bacteria;
Stomach acid;
3 marks
(b) (i) Phagocytosis;
Ref. to non-self / foreign cells / material;
Vacuole formation;
Role of lysosomes;
Digestion of antigens by enzymes;
3 marks
(ii) Present antigen on surface;
Initiate action of T cells;
Ref. to complementary receptors;
Details of T cell action;
3 marks
Total 9 marks
Salters-Nuffield Advanced Biology, Pearson Education Ltd 2009. © University of York Science Education Group.
This sheet may have been altered from the original.
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