Zadanie 7, Paper 2, listopad 2025, TZ1, Biologia IB HL
Wzorowane na: Biology HL Paper 2, November 2025, TZ1, pytanie 7. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Polecenie
A museum exhibit explores biological diversity from genetic sequences to infectious particles.
(a) Explain how nucleic acids can encode a wide variety of base sequences.
(b) Describe structural diversity among viruses, using named examples.
(c) Suggest evolutionary mechanisms that can produce different chromosome numbers in plant and animal lineages.
One additional mark is available for clear, concise construction of the complete response.
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Odpowiedź z klucza
(a) Maximum 4:
DNA or RNA uses four bases OR the four DNA bases are adenine, cytosine, guanine and thymine OR the four RNA bases are adenine, cytosine, guanine and uracil. ✔
Bases fall into purines and pyrimidines OR RNA uses uracil in place of thymine. ✔
Nucleotides can occur in many different orders. ✔
Many base combinations are possible OR a sequence of n positions has4ⁿ possibilities OR there are64 possible base triplets. ✔
Nucleic-acid chains can vary greatly in length. ✔
Mutation introduces sequence changes. ✔
Encoding many different proteins requires many distinct coding sequences. ✔
Each amino acid is specified by a triplet OR genetic-code degeneracy permits multiple codons for an amino acid. ✔
(b) Maximum 7:
Viruses differ in size and shape, such as helical and roughly spherical forms. ✔
T4 phage has a head-and-tail architecture, whereas influenza virions are often roughly spherical or filamentous. ✔
Viral genomes may consist of DNA or RNA. ✔
Retroviruses contain reverse transcriptase, unlike many other viruses. ✔
T4 contains DNA, whereas influenza contains RNA. ✔
Genomes may be single- or double-stranded. ✔
T4 has double-stranded DNA, whereas influenza has single-stranded RNA. ✔
Genomes may be circular or linear; T4 has linear DNA. ✔
The number of genome molecules varies OR influenza has eight RNA segments. ✔
Some viruses have a host-derived lipid envelope. ✔
T4 lacks an envelope, whereas influenza has one. ✔
Rapid mutation, short replication cycles or strong selection can generate viral diversity. ✔
Influenza surface proteins can change during evolution. ✔
(c) Maximum 4:
Chromosome fusion can reduce chromosome number. ✔
Humans have fewer chromosomes than chimpanzees OR humans have46 versus48 in chimpanzees OR human chromosome2 corresponds to two ancestral chromosomes still separate in chimpanzees. ✔
Chromosome fission can increase the number. ✔
Genome doubling can produce fertile even-numbered polyploids. ✔
Failure of segregation across the whole set OR genome replication without cell division can produce extra chromosome sets. ✔
Polyploid wheat is a suitable plant example. ✔
A chromosome-number change can create reproductive isolation and speciation OR follow divergence into species. ✔
Construction:1 mark for clear, concise, well-organized communication across the response, without substantial repetition or irrelevant material.
Schemat punktowania
Parts(a),(b),(c):any4,7,4 distinct points respectively, max15 content marks. Add1 independent construction mark; total16. All printed Section B alternatives are retained as separate tasks. Accept other correct named viral examples and labelled diagrams. For7(a), four bases alone suffices; if listing names use full names, and listing all DNA and RNA bases can support both first two points. Sequence-combination diversity and the need to encode diverse proteins are separate points.