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 choiceWritten
Difficulty
EasyMediumHard

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?

Show answer and explanation

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?

Show answer and explanation

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?

Show answer and explanation

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

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?

Show answer and explanation

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 5

Multiple choiceMedium1 mark

In one case study, mixed dipterocarp forest in Southeast Asia is cleared for oil-palm plantations. In another, a local wetland is drained for housing as population growth increases demand for land. Which option identifies a direct cause in the forest case and an indirect human driver in the wetland case?

Show answer and explanation

Answer: D. A direct cause is the immediate land-use change; an indirect driver is an underlying human pressure that leads to that change. Clearing the mixed dipterocarp forest for plantations is direct. Population growth raises demand for land, indirectly driving wetland loss through drainage for housing. A: identifies the indirect demand for palm oil rather than the direct forest clearance. B: gives the immediate drainage action for the wetland, not its indirect driver. C: gives an indirect forest pressure and the direct wetland action, reversing both requested categories. Remember: distinguish the land conversion itself from the human pressure that motivates it.

The best questions are still waiting

Unlock every question in this topic, then type, photograph or draw your answer and have it marked against the markscheme. Find out where you are dropping marks.

Unlock all questionsCompare Student and Student Plus