IB Biology SL Theme A: Unity and diversity questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

A student is examining a reaction mixture used to build an RNA strand. Which description identifies the monomers and reaction involved?

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Answer: B. RNA is a polymer formed when nucleotide monomers are joined by condensation.

A: substitutes hydrolysis, which breaks polymers rather than joining monomers.
C: substitutes amino acids, which are monomers used to form polypeptides.
D: substitutes DNA for the RNA polymer specified.

Remember: condensation builds polymers from monomers; hydrolysis breaks them down.

Question 2

Multiple choiceEasy1 mark

During a practical, students compare a skeletal muscle fibre with a mature phloem sieve tube element. Which nuclear arrangement should they record?

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Answer: D. Skeletal muscle fibres have many nuclei, whereas mature phloem sieve tube elements lack a nucleus.

A: assumes both cell types have the usual single nucleus.
B: assumes a mature sieve tube element retains one nucleus.
C: treats the skeletal muscle fibre as having only one nucleus.
Remember: skeletal muscle fibres are multinucleate, while mature sieve tube elements are anucleate.

Question 3

Paper 2Easy5 marks

Researchers compare a short region of the same gene in three island lizard species. Figure 1 shows the aligned DNA base sequences.

(a)

Determine the number of base differences between species P and species R in Figure 1.

[1]

(b)

Identify the pair of species with the most similar DNA sequences and state the number of base differences between them.

[2]

(c)

Explain why the similar DNA sequences of this pair provide evidence of common ancestry.

[2]

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