Question 1 of 10
Use the Punnett square to determine the probability of offspring with the homozygous recessive (aa) genotype.
A1/4 (25%)
B0
C3/4 (75%)
D1/2 (50%)
Explanation
Aa × Aa cross: AA, Aa, Aa, aa. Only one box (aa) shows the homozygous recessive: 1/4 = 25%.
Question 2 of 10
The Hardy-Weinberg principle states that allele frequencies remain constant when:
Athere is no evolution occurring
Bnatural selection is strong
Cmutations are common
Dthe population is very small
Explanation
📌 Conditions: no mutation, no migration, random mating, large population, no natural selection.
Any violation → evolution occurs.
Any violation → evolution occurs.
Question 3 of 10
Lipids store roughly twice as much energy per gram as carbohydrates. Which property of lipid molecules best explains this?
AThey form longer polymer chains than carbohydrates
BLong hydrocarbon chains contain many C–H bonds that can be oxidized to release energy
CThey contain more nitrogen atoms than carbohydrates
DThey are insoluble in water, so they take up less space when stored
Explanation
Lipid fatty-acid tails are long chains of carbon–hydrogen bonds. Oxidizing each C–H bond releases energy, so the more C–H bonds per gram, the more energy is stored. Carbohydrates have fewer C–H bonds per carbon because oxygen atoms are already attached. Distractors: water insolubility relates to *where* lipids are stored, not how much energy they hold. Lipids aren't true polymers. Lipids contain almost no nitrogen — that's a feature of proteins and nucleic acids.
Question 4 of 10
During which phase of the cell cycle does DNA replication occur? 
AG2 phase
BS phase
CG1 phase
DM phase
Explanation
📌 DNA replication occurs during S phase (Synthesis) of interphase.
Interphase: G1 → S → G2, then Mitosis.
Interphase: G1 → S → G2, then Mitosis.
Question 5 of 10
Epigenetics studies how:
Agene expression changes without altering DNA sequence
Borganisms evolve
Ccells divide
DDNA sequence changes
Explanation
📌 Epigenetics = changes in gene expression WITHOUT changing DNA sequence.
Mechanisms: DNA methylation, histone modification.
Affected by environment, diet, stress.
Mechanisms: DNA methylation, histone modification.
Affected by environment, diet, stress.
Question 6 of 10
The graph shows the change in a moth population over time. Dark moths increased after industrial pollution darkened tree bark. This is an example of:
AGenetic engineering
BSpontaneous generation
CArtificial selection
DNatural selection
Explanation
📌 This is the classic peppered moth example of natural selection.
Before pollution: light bark → light moths camouflaged → survived
After pollution: dark bark → dark moths camouflaged → survived
The environment selected for the trait that provided camouflage.
Before pollution: light bark → light moths camouflaged → survived
After pollution: dark bark → dark moths camouflaged → survived
The environment selected for the trait that provided camouflage.
Question 7 of 10
Which molecule carries energy from glucose breakdown to the electron transport chain?
ACO2
BH2O
CNADH
DATP
Explanation
📌 NADH and FADH2 are electron carriers. They transport high-energy electrons from glycolysis and Krebs cycle to the ETC.
Question 8 of 10
Why does the left ventricle have a thicker muscular wall than the right ventricle?
AIt receives more deoxygenated blood from the body
BIt contains valves that the right ventricle lacks
CIt is in direct contact with the lungs
DIt must pump blood at higher pressure to reach the entire body
Explanation
The left ventricle pumps oxygenated blood through the *systemic circuit* — every tissue in the body — which requires high pressure. The right ventricle only needs to push blood a short distance to the lungs (pulmonary circuit), so its wall is thinner. Distractors: the left ventricle pumps *oxygenated* blood, not deoxygenated. Both ventricles have valves (AV and semilunar). The right ventricle, not the left, is closer to the lungs.
Question 9 of 10
In a DNA nucleotide, which component carries the genetic code through its specific sequence?
AHydrogen bond
BNitrogenous base
CPhosphate group
DDeoxyribose sugar
Explanation
The nitrogenous base (adenine, thymine, guanine, or cytosine) is the part of a DNA nucleotide that varies — its sequence along the strand IS the genetic code. The phosphate and deoxyribose sugar are identical in every nucleotide and form the structural 'backbone' of the DNA strand; they don't store information. Hydrogen bonds hold the two strands together at the bases but are not part of a single nucleotide.
Question 10 of 10
Alternative splicing allows:
Aone gene to code for multiple proteins
Bchromosomes to separate
Cmutations to be prevented
DDNA to be repaired
Explanation
📌 One gene → multiple proteins by including/excluding different exons. Increases protein diversity without needing more genes.