1. STRUCTURE OF DNA & RNA
A1. D A2. D
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2. STRUCTURE OF DNA & RNA
A3.
four nucleotides shown in diagram with one nucleotide clearly labeled;
base, phosphate and deoxyribose (shown as pentagon) connected between the correct carbons and labeled at least once;
backbone labeled as covalent bond between nucleotides correctly shown as 3′ to 5′ bond;
two base pairs linked by hydrogen bonds drawn as dotted lines and labeled;
two H bonds between A and T and three H bonds between C and G;
adenine to thymine and cytosine to guanine; (do not accept initials of bases)
antiparallel orientation shown;
J WERBA – IB BIOLOGY 2

3. DNA REPLICATION, TRANSCRIPTION & TRANSLATION
N15 isotope has a greater mass than the N14 isotope Generation 0 contained DNA with only N15 isotopes (giving it a greater density) With each generation, the proportion of N14 isotopes would increase After four generations, most strands contain only N14 isotopes
J WERBA – IB BIOLOGY 3

4. DNA REPLICATION, TRANSCRIPTION & TRANSLATION
The N15 isotope band = 1.730g cm-3 The N14 isotope band = g cm-3 After one generation, the DNA would be 50/50 N15/N14 Average mass = g cm-3
conservative replication would be falsified
if conservative replication had occurred, all generations after generation 0 should have had the two distinct bands.
J WERBA – IB BIOLOGY 4

5. DNA REPLICATION, TRANSCRIPTION & TRANSLATION
Results = 2 bands One band with a mixture of N15 & N14 – semi-conservative replication means that some DNA strands would still contain the N15 isotopes One band contains only N14 – N14 strand from generation 1 would become parent strand for generation 2, forming DNA with two N14 strands This would falsify the theory of dispersive replication
Results = 3 bands One band contains only N15 – no replication has occurred yet in generation 0 One band with a mixture of N15 & N14 – from generation 2 One band contains only N14 – from generation 2
J WERBA – IB BIOLOGY 5

6. DNA REPLICATION, TRANSCRIPTION & TRANSLATION
DNA replication is semi-conservative;
DNA is split into two single/template strands;
nucleotides are assembled on/attached to each single/template strand;
by complementary base pairing;
adenine with thymine and cytosine with guanine / A with T and C with G;
strand newly formed on each template strand is identical to other template strand;
DNA polymerase used;
Marks may be awarded for any of the above points if clearly presented in a well-annotated diagram.
J WERBA – IB BIOLOGY 6

7. DNA REPLICATION, TRANSCRIPTION & TRANSLATION
A3. D
A4.
A-T and C-G in DNA;
A-U and C-G in RNA;
complementary base pairing in replication ensures identical nucleotide sequence of new complementary strands;
semi-conservative replication;
transcription produces RNA sequence complementary to the DNA sequence (of the gene);
triplets of nucleotides on mRNA are codons;
translation converts mRNA sequence of information into a specific amino acid chain (polypeptide);
(each class of) tRNA carries a specific triplet of (three) bases called an anticodon;
anticodons bind to codons by complementary base pairing;
(each class of) tRNA with specific complementary anticodons carry specific amino acids;
sequence of mRNA codons translates into specific amino acid sequence;
enables conservation of information transfer from DNA to RNA to polypeptide;
J WERBA – IB BIOLOGY 7

8. DNA REPLICATION, TRANSCRIPTION & TRANSLATION
A5. GAU, GAC
A6.
Leu, Thr, Lys, Arg, Ser, Gly.
GAC TGA TCC AGG CCT
A7. ACT AAC
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9. CELL RESPIRATION
A1. C A2. C A3. B
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10. CELL RESPIRATION
A4.
aerobic cell respiration if oxygen available and anaerobic if unavailable;
pyruvate enters mitochondrion for aerobic respiration;
whereas pyruvate stays in the cytoplasm for processing under anaerobic conditions;
pyruvate converted aerobically into carbon dioxide and water;
whereas pyruvate converted anaerobically to lactate;
large ATP yield when oxygen available/from aerobic cell respiration;
no (further) ATP yield without oxygen;
J WERBA – IB BIOLOGY 10

11. PHOTOSYNTHESIS
A1. B
A2. D
A3.
chlorophyll is the (main) photosynthetic pigment;
absorbs (mainly) red and blue light;
green light is reflected;
light energy absorbed is converted into chemical energy;
ATP produced;
water split;
to form oxygen and hydrogen;
ATP and hydrogen used to fix carbon dioxide to make organic molecules;
J WERBA – IB BIOLOGY 11