IB Biology HL – 2.1 ORIGINS OF CELLS

1. What were oxygen levels like during the prebiotic period?

Very low.

2. What gases were abundant in the prebiotic atmosphere?

Methane (CH₄) and carbon dioxide (CO₂).

3. Why was there no ozone layer?

Ozone (O₃) forms from oxygen, which was absent.

4. What was the consequence of lacking an ozone layer?

High UV radiation reached Earth’s surface.

This caused increased mutation rates and hindered the development of complex life.

5. What environmental conditions were common?

High temperatures and frequent lightning.

6. What drove formation of organic compounds?

UV radiation + lightning (theoretical).

7. How did early life change the atmosphere?

Increased oxygen; decreased methane and CO₂.

8. Why is a cell the smallest unit of life?

It can self‑sustain, use energy, maintain order, and reproduce.

9. Why aren’t organelles considered living?

They cannot live independently or self‑sustain.

10. What is catalysis?

Controlled chemical reactions to avoid chaos.

11. What is self‑assembly?

Spontaneous formation of macromolecules (e.g., DNA).

12. What is compartmentalization?

Formation of membranes separating internal/external environments.

13. What is self‑replication?

Ability to replicate genetic material.

14. What gases were used in the experiment?

CH₄, NH₃, H₂, H₂O vapor.

15. What simulated lightning?

Electrical discharges.

16. What did the experiment produce?

Over 20 amino acids.

17. What did the experiment demonstrate?

Organic compounds can form spontaneously under early Earth conditions.

18. Why are membranes essential?

They allow compartmentalization.

19. What property of phospholipids enables membrane formation?

Amphipathic nature (hydrophilic head + hydrophobic tail).

20. What structures do phospholipids form spontaneously?

Bilayers, vesicles, protocells.

21. Why is RNA considered the original genetic material?

It can self‑replicate without enzymes.

22. Why is DNA unlikely to have been first?

DNA replication requires enzymes, which require DNA instructions.

23. Why did life transition to DNA?

DNA is more stable → better for large genomes.

24. What is LUCA?

The most recent common ancestor of all living organisms.

25. Is LUCA the first life form?

No — earlier forms likely existed.

26. What evidence supports LUCA?

Universal genetic code; shared essential genes.

27. What does paleontology tell us about LUCA?

LUCA existed at least 3.42 billion years ago.

28. What does genetic analysis reveal?

LUCA had genes for anaerobic metabolism using CO₂ and nitrogen.

LUCA also possessed genes for the basic cellular machinery and replication processes.

29. Where did LUCA likely live?

Hydrothermal vents (low oxygen, rich in minerals).

30. What is the prebiotic period?

Time before life existed; low O₂, high CH₄ and CO₂.

31. What is catalysis?

Controlled chemical reactions.

32. What is self‑assembly?

Spontaneous formation of macromolecules.

33. What is compartmentalization?

Membrane formation creating internal environments.

34. What is self‑replication?

Ability to copy genetic material.

35. What is an amphipathic molecule?

Has hydrophilic and hydrophobic regions.

36. What is a hydrothermal vent?

Mineral‑rich, heated water environment from Earth’s crust.