IB Biology 3 — Questions and Answers
Question 1: What distinguishes a competitive inhibitor from a non-competitive inhibitor of an enzyme?
- Competitive inhibitors bind the active site; non-competitive inhibitors bind an allosteric site (Correct answer)
- Competitive inhibitors permanently deactivate the enzyme; non-competitive inhibitors do not
- Competitive inhibitors lower Vmax; non-competitive inhibitors raise Km
- Competitive inhibitors only act at high pH; non-competitive inhibitors act at low pH
Correct answer: Competitive inhibitors bind the active site; non-competitive inhibitors bind an allosteric site
A competitive inhibitor mimics the substrate and binds the active site, while a non-competitive inhibitor binds a separate allosteric site and changes the enzyme's shape.
Question 2: Which process in cellular respiration directly produces the most ATP per glucose molecule?
- Glycolysis
- Pyruvate oxidation
- The Krebs cycle
- Oxidative phosphorylation (electron transport chain) (Correct answer)
Correct answer: Oxidative phosphorylation (electron transport chain)
Oxidative phosphorylation uses the proton gradient generated by the electron transport chain to synthesize approximately 32–34 ATP per glucose, far exceeding glycolysis and the Krebs cycle.
Question 3: What is crossing over and when does it occur?
- Exchange of segments between non-homologous chromosomes during mitosis
- Exchange of segments between homologous chromosomes during prophase I of meiosis (Correct answer)
- Separation of sister chromatids during anaphase II
- Fusion of gametes during fertilization
Correct answer: Exchange of segments between homologous chromosomes during prophase I of meiosis
Crossing over (recombination) occurs at chiasmata during prophase I of meiosis, when homologous chromosomes exchange corresponding segments, generating genetic variation.
Question 4: A population of rabbits is in Hardy-Weinberg equilibrium. If the frequency of the recessive allele (q) is 0.3, what is the expected frequency of heterozygotes?
- 0.09
- 0.49
- 0.42 (Correct answer)
- 0.21
Correct answer: 0.42
Heterozygote frequency = 2pq = 2(0.7)(0.3) = 0.42, where p = 1 − q = 0.7.
Question 5: Which structure in the kidney is responsible for selective reabsorption of glucose and amino acids?
- Glomerulus
- Bowman's capsule
- Proximal convoluted tubule (Correct answer)
- Loop of Henle
Correct answer: Proximal convoluted tubule
The proximal convoluted tubule reabsorbs virtually all filtered glucose and amino acids via active transport into the surrounding capillaries.
Question 6: Which hormone triggers ovulation in the human menstrual cycle?
- Estrogen
- Progesterone
- FSH
- LH (Correct answer)
Correct answer: LH
A surge in luteinizing hormone (LH) around day 14 triggers the release of a mature egg from the dominant follicle.
Question 7: What is the function of myelin sheaths around axons?
- To produce neurotransmitters for synaptic transmission
- To insulate the axon and increase the speed of nerve impulse conduction (Correct answer)
- To anchor the neuron to surrounding tissue
- To supply glucose directly to the axon terminal
Correct answer: To insulate the axon and increase the speed of nerve impulse conduction
Myelin sheaths electrically insulate the axon and force action potentials to jump between Nodes of Ranvier (saltatory conduction), greatly increasing transmission speed.
IB Biology 3
What distinguishes a competitive inhibitor from a non-competitive inhibitor of an enzyme?