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IB Biology HL A2.1 Origins of Cells Questions

Practise IB Biology HL A2.1 with evidence-led questions on abiogenesis, protocells, endosymbiotic theory and cellular evidence.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • explain abiogenesis using early Earth conditions and synthesis of organic molecules
  • evaluate protocell formation and endosymbiotic evidence using membranes, DNA and prokaryote traits
  • compare mitochondria and chloroplast origins using double membranes and circular DNA

Covered syllabus points

A2.1.1—Conditions on early EarthA2.1.2—Cells as smallest units of lifeA2.1.3—Spontaneous origin of cellsA2.1.4—Evidence for origin of carbon compoundsA2.1.5—Spontaneous formation of vesiclesA2.1.6—RNA as presumed first genetic materialA2.1.7—Evidence for last universal common ancestor (LUCA)A2.1.8—Dating first cells and LUCAA2.1.9—Evolution near hydrothermal vents

Question 1

[Maximum number: 5]

The synthesis of complex organic molecules in sea water is believed to be an important step in the evolution of life on Earth. Researchers investigated whether the evaporation of sea water containing amino acids could catalyse the formation of dipeptides such as divaline (valine-valine) under prebiotic Earth conditions. They placed different amino acid combinations in a chamber to simulate the evaporation cycles between high tides in shallow seas. In one investigation the amino acid valine was used as the substrate and the percentage yield of divaline was measured after different numbers of evaporation cycles. The experiment was repeated without a catalyst and with either glycine or histidine as catalysts.

Figure for Question 1 — IB Biology HL

Question (a)

(a)

This investigation was performed in a chamber at 85∘C85^{\circ} \mathrm{C} leading to total evaporation of the salt water within one day. The atmosphere inside the chamber consisted of nitrogen, carbon dioxide and water vapour. Evaluate the experiment on the basis of similarity with conditions that existed on the prebiotic Earth.

[ 3 ]

Question (b)

(b)

Outline other possible locations where conditions could have allowed the synthesis of organic molecules under prebiotic conditions.

[ 2 ]

Question 2

[Maximum number: 1]

The Miller-Urey experiment carried out in 1952 tested the hypothesis of the chemical origin of life. What were the key findings?

A

Living cells could be produced from a mixture of chemicals.

B

Complex organic molecules could form under simulated primordial conditions.

C

Life could spontaneously emerge without external influence.

D

DNA and RNA could self-replicate in a prebiotic environment.

Question 3

[Maximum number: 1]

State the name for primitive, phospholipid-enclosed structures that may have preceded cells.

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