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.

Type

Multiple choice Written

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Easy Medium Hard

Question 1

Multiple choiceHard1 mark

In a plant, aqueous phloem sap carries substance P to cells, where a cytoplasmic enzyme uses P as a substrate. Molecule L is found in the hydrophobic interior of the cell-surface membrane. Which explanation links water’s solvent properties to these roles?

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Answer: A. Hydrophilic substances dissolve in water, supporting transport and availability in aqueous environments; hydrophobic substances are insoluble and can associate with a membrane’s hydrophobic interior. P dissolves in aqueous phloem sap and is present in aqueous cytoplasm, where enzymes catalyse reactions. L’s insolubility is consistent with its membrane location.

B: Treats dissolution as preventing enzyme–substrate interaction; enzymes catalyse reactions in aqueous solution. C: Reverses the effect of solubility on transport: dissolution enables P to be carried in water-based phloem sap. D: Reverses the hydrophilic and hydrophobic roles; hydrophobic P would not dissolve in aqueous sap, and hydrophilic L is not suited to the membrane interior.

Remember: water-soluble molecules can be transported in aqueous fluids and participate in metabolism in aqueous solution.

Question 2

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 3

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 4

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]

Question 5

Multiple choiceHard1 mark

In a beetle population, 20% of adults have dark shells before the substrate darkens. After the change, 70% of the same adults have dark shells. Adults of both shades contribute equally to an offspring cohort, of which 20% have dark shells when raised on the original substrate. Which interpretation applies the definition of evolution to shell shade?

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Answer: C. Evolution is a change in the heritable characteristics of a population, not a change acquired by individuals during their lives. The proportion of dark-shelled adults rises from 20% to 70%, but their offspring, raised on the original substrate, have the initial 20% frequency. Thus, no inherited shift in shell shade is demonstrated. A: treats a change in adult appearance as an evolutionary change in heritable population characteristics. B: applies Lamarckian inheritance, but the offspring do not retain the increase in dark shells. D: confuses some offspring having a characteristic with the frequency of that characteristic changing across generations. Remember: evolution requires a change in heritable population characteristics across generations.

Question 6

Paper 2Hard16 marks

Two case studies of ecosystem loss were investigated: mixed dipterocarp forest in Indonesian Borneo, Southeast Asia, and the wetlands of the Florida Everglades, USA. Field teams mapped the areas of these ecosystems in selected landscape regions in 1990 and 2020. The loss categories in Figure 1 are non-overlapping estimates of areas no longer mapped as the named ecosystem by 2020. All areas are rounded to the nearest 100 km².

In Borneo, roads were opened for timber extraction. Market demand for timber and palm oil encouraged extraction and plantation development. Some areas were burned to clear land.

In the Everglades, canals were built to drain land and alter water supply. Farming and urban areas expanded, increasing demand for land and water.

(a)

Calculate the percentage of the 1990 ecosystem area that had been lost by 2020 in each case study.

[2]

(b)

Compare the largest category of ecosystem loss in each case study, using Figure 1.

[2]

(c)

Explain a causal chain linking an indirect human pressure to the loss of mixed dipterocarp forest in Indonesian Borneo. Use information from the stem and Figure 1.

[3]

(d)

Explain how drainage or canalization can cause loss of Everglades wetland even where the land is not mapped as farmland or urban land.

[2]

(e)

An adviser claims that preventing direct conversion of the remaining ecosystems to plantations, farms, or urban and transport land would be sufficient to prevent further ecosystem loss in both regions. Evaluate this claim using Figure 1 and the information in the stem.

[3]

(f)

Suggest one action for each case study and explain how each action could address a cause of ecosystem loss that would not necessarily be stopped by drawing a boundary around the remaining ecosystem.

[4]

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