Units 1-2
Explain how hydrogen bonding between water molecules leads to both of these properties.
Water has a high specific heat and high heat of vaporization.
A toxin blocks the electron transport chain (ETC) in mitochondria. Predict the immediate effect on ATP production.
ATP production will drastically decrease because the ETC produces the majority of ATP through oxidative phosphorylation.
In a certain species, red flowers (R) and white flowers (W) show incomplete dominance. What phenotype results from RW?
RW produces pink flowers.
A population of insects becomes resistant to a pesticide over several generations. Clarify whether the pesticide caused the mutations.
The pesticide did not cause the mutations; it selected for individuals that already had them.
A scientist observes that adding a substance decreases the rate of an enzyme reaction. Increasing substrate concentration restores the reaction rate.
What type of inhibition is occurring?Explain why increasing substrate concentration reverses the effect.
Competitive inhibition. The inhibitor competes with the substrate for the active site. When substrate concentration increases, it outcompetes the inhibitor, restoring enzyme activity.
Water molecules form hydrogen bonds with each other. Explain how hydrogen bonding contributes to water’s high specific heat.
Hydrogen bonds require energy to break. Because many hydrogen bonds exist between water molecules, a large amount of heat energy is needed to increase water’s temperature, giving it a high specific heat
A plant is exposed to light but has no available CO₂. Predict what happens to the light-dependent reactions.
Light-dependent reactions will continue temporarily because they rely on light and water, producing ATP and NADPH.
Explain how meiosis contributes to genetic variation. Include at least two mechanisms.
Crossing over during prophase I exchanges DNA between homologous chromosomes and Independent assortment randomly distributes maternal and paternal chromosomes into gametes.
A population is not in Hardy-Weinberg equilibrium. List two assumptions that must be violated
Possible violated assumptions: natural selection, genetic drift, gene flow, mutation, non-random mating.
A cell is deprived of oxygen. Which process stops first? How does this affect ATP production overall?
The electron transport chain stops first because oxygen is the final electron acceptor. ATP production drops significantly because oxidative phosphorylation stops, leaving only glycolysis (which produces much less ATP)
A mutation replaces a nonpolar amino acid with a charged amino acid in the interior of a protein. Predict the effect on protein folding.
The interior of proteins is typically hydrophobic. Replacing a nonpolar amino acid with a charged one disrupts hydrophobic interactions, causing improper folding.
A signaling molecule binds to a receptor on the cell membrane. Explain why the signal does not need to enter the cell.
The signal does not need to enter because the receptor changes shape when the ligand binds, triggering a response inside the cell.
A mutation changes a DNA base but does not change the amino acid produced. What type of mutation is this?
This is a silent mutation
Compare genetic drift and gene flow.
Genetic drift: random changes in allele frequencies, especially in small populations (e.g., bottleneck effect)
Gene flow: movement of alleles between populations due to migration Drift reduces genetic variation, while gene flow increases it
A mutation occurs in the promoter region of a gene. Predict how this affects transcription. Explain the downstream effect on the organism.
Transcription may decrease or stop because RNA polymerase cannot bind effectively. This leads to reduced or absent protein production, which can affect traits and cellular function.
Explain how the structure of phospholipids contributes to the selective permeability of the cell membrane.
Phospholipids have hydrophilic heads and hydrophobic tails. The hydrophobic interior of the bilayer prevents polar or charged molecules from passing freely, while small nonpolar molecules can diffuse through. This structure allows the membrane to selectively control what enters and exits the cell.
A mutation disables a checkpoint protein that normally stops the cell cycle when DNA is damaged. Predict the effect on the cell cycle.
The cell cycle will continue even when DNA is damaged.
In prokaryotes, the lac operon is only active when lactose is present and glucose is absent. Explain why glucose presence inhibits the operon.
Glucose inhibits the operon because the cell prefers glucose; low cAMP levels prevent activation.
Explain why energy decreases at each trophic level in an ecosystem.
Energy is lost as heat due to metabolic processes at each level. Only about 10% of energy is transferred to the next trophic level, limiting the number of levels in a food chain
A population shows a shift toward one extreme phenotype over time. Identify the type of selection. Explain what environmental condition might cause this.
Directional selection. A consistent environmental pressure (like climate change or a new predator) favors one extreme phenotype, increasing its frequency.
A plant cell is placed in a hypotonic solution. Predict what will happen to the cell
Water will enter the cell by osmosis, causing it to swell.
Explain how one signaling molecule can produce a large cellular response.
Signal amplification occurs because one activated receptor can activate multiple downstream molecules (like enzymes or second messengers), each of which activates even more molecules. This cascade greatly increases the strength of the signal.
Two heterozygous individuals for a trait (Aa × Aa) have a child. Explain why genotype and phenotype ratios differ.
Genotype ratio is 1 AA : 2 Aa : 1 aa, but both AA and Aa show the dominant phenotype, so phenotype ratio becomes 3:1
A population grows rapidly and then levels off. Identify the type of growth and Explain what causes the leveling off.
This is logistic growth. The population levels off at carrying capacity due to limited resources like food, space, and competition
A mutation causes a receptor protein to remain permanently active, even without a signaling molecule.
Predict the effect on the cell. Explain how this relates to diseases like cancer.
The cell will continuously respond as if it is receiving a signal, leading to constant activation of pathways (like cell division). This can lead to uncontrolled cell growth, a hallmark of cancer.