Question 1 of 10
Which pair of processes drives the most direct exchange of CO₂ between living organisms and the atmosphere?
APhotosynthesis (releases CO₂) and cellular respiration (absorbs CO₂)
BTranspiration (releases CO₂) and condensation (absorbs CO₂)
CPhotosynthesis (absorbs CO₂) and cellular respiration (releases CO₂)
DNitrogen fixation (absorbs CO₂) and decomposition (releases O₂)
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 2 of 10
Why does the left ventricle have a thicker muscular wall than the right ventricle?
AIt contains valves that the right ventricle lacks
BIt is in direct contact with the lungs
CIt must pump blood at higher pressure to reach the entire body
DIt receives more deoxygenated blood from the 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 3 of 10
Lipids store roughly twice as much energy per gram as carbohydrates. Which property of lipid molecules best explains this?
AThey contain more nitrogen atoms than carbohydrates
BThey are insoluble in water, so they take up less space when stored
CLong hydrocarbon chains contain many C–H bonds that can be oxidized to release energy
DThey form longer polymer chains than carbohydrates
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
Alternative splicing allows:
ADNA to be repaired
Bchromosomes to separate
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 5 of 10
In the food web below, what would happen if all the frogs were removed? 
AAll organisms die
BInsect population increases and snake population decreases
CSnake population increases
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 6 of 10
In a Punnett square cross Bb × Bb, what fraction of offspring are expected to be homozygous recessive (bb)?
A75%
B50%
C25%
D0%
Explanation
📌 BB:Bb:bb = 1:2:1
bb = 1/4 = 25%
bb = 1/4 = 25%
Question 7 of 10
A theory in science is:
Aa proven fact that can never change
Ban untested guess
Ca well-supported explanation based on extensive evidence
Dthe same as a hypothesis
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 8 of 10
Which class of biomolecule is built from nucleotide monomers?
ACarbohydrates
BProteins
CLipids
DNucleic acids (DNA and RNA)
Explanation
Nucleic acids (DNA, RNA) are polymers of nucleotide monomers — each nucleotide is a phosphate + sugar + nitrogenous base. Distractors: Proteins are polymers of *amino acids*. Carbohydrates are polymers of *monosaccharides* (e.g., glucose). Lipids are not true polymers — they assemble from fatty acids and glycerol but don't repeat a single monomer.
Question 9 of 10
In a DNA nucleotide, which component carries the genetic code through its specific sequence?
ANitrogenous base
BDeoxyribose sugar
CHydrogen bond
DPhosphate group
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
All three domains of life (Bacteria, Archaea, and Eukarya) share which structural feature?
AA membrane-bound nucleus
BMulticellular organization
CRibosomes for protein synthesis
DChloroplasts for photosynthesis
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).