USABO Practice · Biology Olympiad Style v29
20 题生物奥赛风格选择题 · 点击选项答题 · 自动记录错题本
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Questions
【B-EL-01】 Q1 · Cell Biology · Easy
Which organelle is known as the "powerhouse of the cell"?
- A) Nucleus
- B) Ribosome
- C) Mitochondrion
- D) Golgi apparatus
- E) Lysosome
Answer: C) Mitochondrion. Mitochondria generate ATP through cellular respiration.
【B-GN-01】 Q2 · Genetics · Easy
In Mendelian genetics, if both parents are heterozygous (Aa), what is the probability that their child is homozygous recessive (aa)?
- A) 0%
- B) 25%
- C) 50%
- D) 75%
- E) 100%
Answer: B) 25%. Punnett square: Aa × Aa → AA, Aa, Aa, aa. Probability of aa = 1/4 = 25%.
【B-MB-01】 Q3 · Molecular Biology · Easy
What is the basic unit of DNA structure?
- A) Amino acid
- B) Nucleotide
- C) Monosaccharide
- D) Fatty acid
- E) Peptide
Answer: B) Nucleotide. DNA consists of nucleotides (phosphate + sugar + base).
【B-BC-01】 Q4 · Biochemistry · Easy
Which of the following is NOT a macromolecule?
- A) Protein
- B) Carbohydrate
- C) Lipid
- D) Nucleic acid
- E) Amino acid
Answer: E) Amino acid. Amino acids are monomers, not macromolecules.
【B-EC-01】 Q5 · Ecology · Easy
What is the primary source of energy for most ecosystems?
- A) Water
- B) Sunlight
- C) Carbon dioxide
- D) Oxygen
- E) Minerals
Answer: B) Sunlight. Photosynthetic organisms convert sunlight to chemical energy.
【B-PH-01】 Q6 · Physiology · Easy
Which part of the neuron receives signals from other neurons?
- A) Axon
- B) Dendrite
- C) Cell body
- D) Myelin sheath
- E) Synapse
Answer: B) Dendrite. Dendrites receive incoming signals; axons send outgoing signals.
【B-EL-02】 Q7 · Cell Biology · Medium
During which phase of mitosis do the chromosomes align at the cell's equator?
- A) Prophase
- B) Metaphase
- C) Anaphase
- D) Telophase
- E) Interphase
Answer: B) Metaphase. Chromosomes line up at the metaphase plate during metaphase.
【B-GN-02】 Q8 · Genetics · Medium
A woman with type A blood has a child with type O blood. What is the woman's genotype?
- A) IAIA
- B) IAi
- C) ii
- D) IAIB
- E) Cannot determine
Answer: B) IAi. Type A blood can be IAIA or IAi. To have a type O child (ii), she must be IAi, passing i allele.
【B-MB-02】 Q9 · Molecular Biology · Medium
Which process synthesizes mRNA from a DNA template?
- A) Translation
- B) Transcription
- C) Replication
- D) Mutation
- E) Repair
Answer: B) Transcription. RNA polymerase synthesizes mRNA from DNA during transcription.
【B-BC-02】 Q10 · Biochemistry · Medium
What is the net ATP yield from glycolysis alone?
- A) 0
- B) 2
- C) 4
- D) 36
- E) 38
Answer: B) 2. Glycolysis produces 4 ATP but invests 2 ATP, net yield = 2 ATP.
【B-EC-02】 Q11 · Ecology · Medium
The maximum number of individuals an environment can support is called the:
- A) Birth rate
- B) Carrying capacity
- C) Growth rate
- D) Limiting factor
- E) Survivorship
Answer: B) Carrying capacity (K). It represents the maximum sustainable population size.
【B-PH-02】 Q12 · Physiology · Medium
Which hormone is released in response to low blood calcium levels?
- A) Insulin
- B) Parathyroid hormone
- C) Thyroxine
- D) Cortisol
- E) Estrogen
Answer: B) Parathyroid hormone (PTH). PTH raises blood calcium by stimulating bone resorption.
【B-EL-03】 Q13 · Cell Biology · Hard
A cell is placed in a hypertonic solution. What will happen to the cell?
- A) It swells
- B) It shrinks
- C) It stays the same
- D) It bursts
- E) It becomes turgid
Answer: B) It shrinks. In a hypertonic solution, water moves out of the cell, causing it to shrink (crenation).
【B-GN-03】 Q14 · Genetics · Hard
What is the mode of inheritance for mitochondrial DNA (mtDNA)?
- A) Autosomal dominant
- B) Autosomal recessive
- C) X-linked
- D) Maternal
- E) Paternal
Answer: D) Maternal. mtDNA is inherited exclusively from the mother's egg cell.
【B-MB-03】 Q15 · Molecular Biology · Hard
Which of the following is the correct sequence of events during PCR?
- A) Extension → Annealing → Denaturation
- B) Denaturation → Annealing → Extension
- C) Annealing → Denaturation → Extension
- D) Denaturation → Extension → Annealing
- E) Extension → Denaturation → Annealing
Answer: B) Denaturation → Annealing → Extension. This is the standard PCR cycle: heat to separate strands, cool for primers to anneal, extend with polymerase.
【B-BC-03】 Q16 · Biochemistry · Hard
The enzyme responsible for converting pyruvate to acetyl-CoA is located in the:
- A) Cytoplasm
- B) Mitochondrial matrix
- C) Inner mitochondrial membrane
- D) Outer mitochondrial membrane
- E) Nucleus
Answer: B) Mitochondrial matrix. Pyruvate dehydrogenase complex is in the mitochondrial matrix.
【B-EC-03】 Q17 · Ecology · Hard
Which type of ecological interaction benefits one species while the other is harmed?
- A) Mutualism
- B) Commensalism
- C) Parasitism
- D) Competition
- E) Amensalism
Answer: C) Parasitism. One species (parasite) benefits at the expense of the other (host).
【B-PH-03】 Q18 · Physiology · Hard
The resting membrane potential of a neuron is primarily maintained by:
- A) Na⁺/K⁺ pump
- B) Ca²⁺ channels
- C) Cl⁻ channels
- D) H⁺ pump
- E) Glucose transporters
Answer: A) Na⁺/K⁺ pump. The sodium-potassium pump maintains the resting potential by pumping 3 Na⁺ out and 2 K⁺ in.
【B-EV-01】 Q19 · Evolution · Hard
Which of the following is an example of convergent evolution?
- A) Forelimbs of humans, bats, and whales
- B) Wings of birds and insects
- C) DNA sequences of related species
- D) Embryonic development
- E) Fossil record
Answer: B) Wings of birds and insects. These analogous structures evolved independently for flight, not from a common ancestor.
【B-EL-04】 Q20 · Cell Biology · Hard
Which of the following is NOT part of the endomembrane system?
- A) Rough ER
- B) Smooth ER
- C) Golgi apparatus
- D) Mitochondria
- E) Lysosomes
Answer: D) Mitochondria. Mitochondria have their own membranes and are not part of the endomembrane system (which includes ER, Golgi, vesicles, lysosomes, and nuclear envelope).