IB Biology 4 — Questions and Answers
Question 1: Which type of RNA carries amino acids to the ribosome during translation?
- mRNA
- rRNA
- tRNA (Correct answer)
- snRNA
Correct answer: tRNA
Transfer RNA (tRNA) carries specific amino acids and uses its anticodon to match complementary codons on the mRNA during translation.
Question 2: What observation led Charles Darwin to propose that species change over time?
- Identical species on every continent
- Similarity between Galapagos finch beaks and their food sources on different islands (Correct answer)
- Fossilized microbes in ancient rock
- Genetic mutations in laboratory fruit flies
Correct answer: Similarity between Galapagos finch beaks and their food sources on different islands
Darwin noticed that finches on different Galapagos islands had beaks adapted to the specific food sources available, suggesting descent with modification from a common ancestor.
Question 3: What happens to membrane fluidity when cholesterol is added to a phospholipid bilayer at body temperature?
- Fluidity increases because cholesterol repels phospholipids
- Fluidity decreases because cholesterol stabilizes phospholipid packing (Correct answer)
- There is no effect because cholesterol is only found in plant membranes
- Fluidity increases because cholesterol disrupts fatty acid chain packing
Correct answer: Fluidity decreases because cholesterol stabilizes phospholipid packing
At physiological temperature, cholesterol intercalates between phospholipid tails, restraining their movement and reducing membrane fluidity.
Question 4: Which molecule acts as the final electron acceptor in aerobic cellular respiration?
- NAD⁺
- FAD
- Oxygen (Correct answer)
- Carbon dioxide
Correct answer: Oxygen
Oxygen accepts electrons at the end of the electron transport chain and combines with hydrogen ions to form water.
Question 5: In a food web, what percentage of energy is typically transferred from one trophic level to the next?
- 1%
- 10% (Correct answer)
- 50%
- 90%
Correct answer: 10%
The ten percent rule states that only about 10% of energy stored in one trophic level is available to the next, with the rest lost as heat through metabolism.
Question 6: What is the term for a symbiotic relationship in which one species benefits and the other is neither harmed nor helped?
- Mutualism
- Parasitism
- Commensalism (Correct answer)
- Competition
Correct answer: Commensalism
Commensalism describes an interaction where one organism benefits (e.g., barnacles on a whale) while the host is unaffected.
Question 7: Which discovery by Watson, Crick, and Franklin/Wilkins revealed the double-helix structure of DNA?
- Gel electrophoresis patterns of DNA fragments
- X-ray diffraction images showing a helical pattern (Correct answer)
- Autoradiographs of replicating bacterial chromosomes
- Density-gradient centrifugation results after one generation
Correct answer: X-ray diffraction images showing a helical pattern
Rosalind Franklin's X-ray diffraction photograph (Photo 51) showed a characteristic cross pattern indicating a helical structure, key evidence for the double-helix model.
IB Biology 4
Which type of RNA carries amino acids to the ribosome during translation?