Question 1 of 10
A theory in science is:
Athe same as a hypothesis
Ban untested guess
Ca well-supported explanation based on extensive evidence
Da proven fact that can never change
Explanation
📌 A scientific theory is well-tested, widely accepted, and explains a broad range of observations.
It is NOT just a guess — that's a hypothesis.
It is NOT just a guess — that's a hypothesis.
Question 2 of 10
In a DNA nucleotide, which component carries the genetic code through its specific sequence?
APhosphate group
BHydrogen bond
CNitrogenous base
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 3 of 10
In the food web below, what would happen if all the frogs were removed? 
ASnake population increases
BAll organisms die
CInsect population increases and snake population decreases
DNothing changes
Explanation
📌 If frogs are removed:
• Insects (grasshoppers) they ate would INCREASE (no predator)
• Snakes that ate frogs would DECREASE (less food)
• This demonstrates how removing one species affects the entire food web.
• Insects (grasshoppers) they ate would INCREASE (no predator)
• Snakes that ate frogs would DECREASE (less food)
• This demonstrates how removing one species affects the entire food web.
Question 4 of 10
Which pair of processes drives the most direct exchange of CO₂ between living organisms and the atmosphere?
ANitrogen fixation (absorbs CO₂) and decomposition (releases O₂)
BPhotosynthesis (absorbs CO₂) and cellular respiration (releases CO₂)
CTranspiration (releases CO₂) and condensation (absorbs CO₂)
DPhotosynthesis (releases CO₂) and cellular respiration (absorbs CO₂)
Explanation
Photosynthesis consumes atmospheric CO₂ to build glucose (CO₂ → sugar), while cellular respiration breaks glucose back down to CO₂ and water. Together they form the short-term carbon cycle between the biosphere and atmosphere. Distractor B reverses the direction. Transpiration moves water vapor, not CO₂. Nitrogen fixation moves nitrogen, not carbon.
Question 5 of 10
Alternative splicing allows:
Achromosomes to separate
BDNA to be repaired
Cmutations to be prevented
Done gene to code for multiple proteins
Explanation
📌 One gene → multiple proteins by including/excluding different exons. Increases protein diversity without needing more genes.
Question 6 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 is in direct contact with the lungs
CIt contains valves that the right ventricle lacks
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 7 of 10
Which molecule carries energy from glucose breakdown to the electron transport chain?
ANADH
BCO2
CH2O
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
During which phase of the cell cycle does DNA replication occur? 
AM phase
BG1 phase
CG2 phase
DS phase
Explanation
📌 DNA replication occurs during S phase (Synthesis) of interphase.
Interphase: G1 → S → G2, then Mitosis.
Interphase: G1 → S → G2, then Mitosis.
Question 9 of 10
Which organelle is labeled X in the cell diagram below? 
AGolgi apparatus
BMitochondria
CNucleus
DEndoplasmic reticulum
Explanation
📌 Organelle X has the bean-shaped structure with inner folds (cristae) → Mitochondria
Mitochondria = powerhouse of the cell = produces ATP through cellular respiration
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
Mitochondria = powerhouse of the cell = produces ATP through cellular respiration
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
Question 10 of 10
All three domains of life (Bacteria, Archaea, and Eukarya) share which structural feature?
ARibosomes for protein synthesis
BA membrane-bound nucleus
CChloroplasts for photosynthesis
DMulticellular organization
Explanation
All cellular life — Bacteria, Archaea, and Eukarya — uses ribosomes to build proteins. Distractors: a membrane-bound nucleus is found only in Eukarya (Bacteria and Archaea are prokaryotic). Multicellularity appears only in some Eukarya — most life is unicellular. Chloroplasts are organelles found only in plants and algae (a subset of Eukarya).