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A cell is placed in a hypertonic solution. Its volume decreases, but internal ion concentrations stay constant. What process maintains ion balance?
Active transport (ion pumps such as Na⁺/K⁺ pump) maintains internal ion levels while water leaves via osmosis.
A mutation prevents homologous chromosomes from pairing in prophase I. What is the effect on gametes?
No crossing over and incorrect separation in meiosis I → gametes with random aneuploidies (extra chromosomes) and little genetic variation.
A cell has normal transcription but produces nonfunctional proteins. Name two possible defective processes.
Translation error (ribosome/tRNA malfunction)
Protein folding/processing error (chaperones or Golgi malfunction)
A plant is given only green light. Predict the effect on photosynthesis.
Photosynthesis decreases drastically because green light is reflected, not absorbed.
Two genes are found to be inherited together 80% of the time. What does this mean about their location?
They are linked — close together on the same chromosome.
A toxin blocks ATP synthase. Predict what happens to the proton gradient.
The proton gradient increases because H⁺ continues to be pumped into the intermembrane space but cannot flow back through ATP synthase.
A student observes a 1:2:1 phenotypic ratio. What are the possible inheritance patterns this could be and why?
Codominant or Incomplete dominance; heterozygous has a different phenotype than dominant.
What happens to the rate of enzyme action if substrate concentration is extremely high?
Reaction rate plateaus at Vmax because all enzyme active sites are saturated.
A cell shows 92 chromatids during division. How many chromosomes were in the original diploid cell?
46 chromosomes — 92 chromatids represent duplicated sister chromatids.
The non-template strand of a piece of DNA reads 5' TCG 3'
What is the corresponding codon?
UCG
In photosynthesis, if the Calvin cycle stops but light reactions continue, what happens to NADPH and ATP levels?
NADPH and ATP accumulate because they are being produced but cannot be used to fix carbon.
What is the central dogma?
DNA to RNA to Protein
How would removing cholesterol from the membrane affect a cell at high temperature?
Membrane becomes too fluid and loses structural integrity.
A chloroplast has damaged thylakoid membranes. What process is most affected?
Light reactions (since ETC and ATP synthase are embedded in thylakoid membranes).
A researcher inhibits RNA polymerase. Which processes immediately stop?
Transcription — no mRNA, tRNA, or rRNA made → eventually translation stops due to lack of RNA.
A cell has twice the normal amount of DNA, an intact nuclear envelope, and no chromosomes visible. What stage is it in?
G₂ phase — DNA has replicated (2×) but chromatin has not yet condensed.
Helicase is functioning normally, but DNA polymerase is inactive. What would the replication fork look like?
DNA unwinds continuously, creating long single-stranded regions but no new daughter strands.
A cell cannot form spindle fibers. At what specific stage of mitosis it go wrong?
Metaphase — chromosomes cannot align at the metaphase plate.
Why does glycolysis still run during anaerobic fermentation?
Fermentation regenerates NAD⁺, allowing glycolysis to continue producing ATP.
A cell shows uncontrolled progression from G₁ to S phase. Which regulatory proteins are likely mutated?
Cyclins or CDKs (specifically G₁/S checkpoint proteins).
Why does blocking oxygen immediately stop ATP production in the ETC?
Without O₂, electrons cannot be accepted at the end of the chain → electron flow stops → proton gradient collapses → ATP synthase stops.
A mutation occurs in the promoter region of a gene. What happens to transcription?
Decreases or stops entirely because RNA polymerase cannot bind effectively.
A mutation causes a receptor protein to stay permanently active without ligand binding. What is the consequence?
Continuous signaling → uncontrolled cell division or inappropriate gene expression.
A mutation eliminates all aquaporins in a cell. What happens to water movement?
Water still moves but at a much slower rate — osmosis becomes minimal.
Why does independent assortment occur only in meiosis I, not meiosis II?
Because homologous chromosome pairs line up and separate in metaphase I; in meiosis II, sister chromatids separate and do not assort independently.