ATI Biology Practice Test 2 — Questions and Answers
Question 1: Which organelle is responsible for producing ATP through oxidative phosphorylation?
- Ribosome
- Mitochondria (Correct answer)
- Golgi apparatus
- Endoplasmic reticulum
Correct answer: Mitochondria
Mitochondria are the powerhouse of the cell, producing ATP through oxidative phosphorylation during cellular respiration.
Mitochondria contain the electron transport chain embedded in their inner membrane. During oxidative phosphorylation, electrons pass through protein complexes (I-IV), creating a proton gradient that drives ATP synthase to produce ATP. This process generates approximately 34 ATP molecules per glucose molecule, making it the most efficient stage of cellular respiration.
Question 2: During DNA replication, which enzyme unwinds the double helix at the replication fork?
- DNA polymerase
- Ligase
- Helicase (Correct answer)
- Primase
Correct answer: Helicase
Helicase unwinds the double-stranded DNA by breaking hydrogen bonds between complementary base pairs at the replication fork.
Helicase binds to the origin of replication and uses energy from ATP hydrolysis to break the hydrogen bonds holding the two DNA strands together. This creates a replication fork where single-stranded binding proteins stabilize the separated strands. DNA polymerase then synthesizes new complementary strands, while primase lays down RNA primers and ligase joins Okazaki fragments on the lagging strand.
Question 3: What is the primary function of transfer RNA (tRNA) during translation?
- Carrying the genetic code from the nucleus
- Forming the ribosomal subunits
- Delivering amino acids to the ribosome (Correct answer)
- Splicing introns from mRNA
Correct answer: Delivering amino acids to the ribosome
Transfer RNA carries specific amino acids to the ribosome during translation, matching its anticodon to the mRNA codon.
Each tRNA molecule has an anticodon region that base-pairs with a complementary codon on mRNA, and an acceptor stem that carries the corresponding amino acid. Aminoacyl-tRNA synthetases charge each tRNA with the correct amino acid. During translation, tRNAs enter the ribosomal A site, form peptide bonds in the P site, and exit from the E site, ensuring the polypeptide chain is assembled in the correct sequence.
Question 4: Which type of inheritance pattern is demonstrated when both alleles are fully expressed in the heterozygous phenotype?
- Complete dominance
- Incomplete dominance
- Codominance (Correct answer)
- Epistasis
Correct answer: Codominance
Codominance occurs when both alleles in a heterozygote are fully and simultaneously expressed, such as AB blood type.
In codominance, neither allele is dominant or recessive. Both alleles produce their respective proteins and both phenotypes are visible simultaneously. The classic example is the ABO blood group system: individuals with genotype I^A I^B express both A and B antigens on their red blood cells, resulting in type AB blood. This differs from incomplete dominance, where the heterozygote shows a blended intermediate phenotype.
Question 5: Which process describes the movement of water across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration?
- Active transport
- Osmosis (Correct answer)
- Facilitated diffusion
- Exocytosis
Correct answer: Osmosis
Osmosis is the passive movement of water molecules across a selectively permeable membrane toward the region of higher solute concentration.
Osmosis occurs because water moves down its own concentration gradient — from where water is more concentrated (low solute) to where it is less concentrated (high solute). This is a passive process requiring no ATP. In clinical settings, understanding osmosis is critical: placing red blood cells in a hypotonic solution causes them to swell and lyse, while a hypertonic solution causes crenation. Isotonic solutions like 0.9% normal saline maintain cell integrity.
Question 6: During meiosis, genetic diversity is increased by the exchange of segments between homologous chromosomes. What is this process called?
- Nondisjunction
- Crossing over (Correct answer)
- Cytokinesis
- Independent assortment
Correct answer: Crossing over
Crossing over occurs during prophase I of meiosis when homologous chromosomes exchange genetic material at points called chiasmata.
Crossing over is a key mechanism for generating genetic variation. During prophase I, homologous chromosomes pair up (synapsis) and form tetrads. At chiasmata, non-sister chromatids exchange corresponding segments of DNA. This recombination creates new allele combinations on each chromosome that differ from both parents. Combined with independent assortment of chromosomes during anaphase I, crossing over ensures that each gamete is genetically unique.
ATI Biology Practice Test 2
Which organelle is responsible for producing ATP through oxidative phosphorylation?