IB Biology 5 — Questions and Answers
Question 1: Which gas exchange organ allows insects to obtain oxygen without a circulatory system carrying it to cells?
- Gills
- Lungs
- Tracheae (Correct answer)
- Book lungs
Correct answer: Tracheae
Insects have a tracheal system — a network of air tubes (tracheae) that deliver oxygen directly to tissues, bypassing the need for blood to transport it.
Question 2: What is the significance of the semi-conservative replication model demonstrated by Meselson and Stahl?
- Each new DNA molecule retains one original strand and one newly synthesized strand (Correct answer)
- Both strands of the original DNA are fully replaced during replication
- One daughter molecule is entirely new and the other retains both original strands
- DNA is replicated only at specific chromosome ends called telomeres
Correct answer: Each new DNA molecule retains one original strand and one newly synthesized strand
The Meselson-Stahl experiment showed that after one round of replication each daughter double helix contains one parental strand and one newly made strand.
Question 3: Which type of immunity involves memory B and T cells that respond rapidly upon re-exposure to an antigen?
- Innate immunity
- Active acquired immunity (Correct answer)
- Passive immunity
- Non-specific immunity
Correct answer: Active acquired immunity
Active acquired immunity results from exposure to an antigen (through infection or vaccination) and creates immunological memory for faster secondary responses.
Question 4: What is a keystone species?
- A species with the largest population in an ecosystem
- A species that occupies the highest trophic level in a food web
- A species that has a disproportionately large effect on community structure relative to its abundance (Correct answer)
- A species introduced from another region that outcompetes native species
Correct answer: A species that has a disproportionately large effect on community structure relative to its abundance
A keystone species exerts an outsized influence on its ecosystem, often through predation or habitat modification, and its removal causes dramatic community changes.
Question 5: What is the product of translation?
- A molecule of mRNA complementary to a DNA template
- A polypeptide chain assembled from amino acids (Correct answer)
- A double-stranded DNA molecule identical to the original
- An ATP molecule generated by ribosomal activity
Correct answer: A polypeptide chain assembled from amino acids
Translation is the process by which ribosomes read mRNA codons and assemble a corresponding sequence of amino acids into a polypeptide.
Question 6: Which type of cell division produces genetically identical daughter cells?
- Meiosis I
- Meiosis II
- Mitosis (Correct answer)
- Binary fission in eukaryotes
Correct answer: Mitosis
Mitosis produces two genetically identical diploid daughter cells used for growth, repair, and asexual reproduction in eukaryotes.
Question 7: What is the difference between a habitat and a niche?
- A habitat describes an organism's functional role; a niche is the physical location it occupies
- A habitat is the physical environment where an organism lives; a niche is its functional role and interactions within that environment (Correct answer)
- Habitat and niche are synonyms referring to the same ecological concept
- A niche applies only to plants; a habitat applies only to animals
Correct answer: A habitat is the physical environment where an organism lives; a niche is its functional role and interactions within that environment
A habitat is the physical place an organism lives, while an ecological niche encompasses all aspects of its role — what it eats, how it behaves, and how it interacts with other species.
IB Biology 5
Which gas exchange organ allows insects to obtain oxygen without a circulatory system carrying it to cells?