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
Which molecule carries energy from glucose breakdown to the electron transport chain?
AH2O
BCO2
CNADH
DATP
Explanation
📌 NADH and FADH2 are electron carriers. They transport high-energy electrons from glycolysis and Krebs cycle to the ETC.
Question 3 of 10
Use the Punnett square to determine the probability of offspring with the homozygous recessive (aa) genotype.
A3/4 (75%)
B1/2 (50%)
C1/4 (25%)
D0
Explanation
Aa × Aa cross: AA, Aa, Aa, aa. Only one box (aa) shows the homozygous recessive: 1/4 = 25%.
Question 4 of 10
In a Punnett square cross Bb × Bb, what fraction of offspring are expected to be homozygous recessive (bb)?
A25%
B50%
C75%
D0%
Explanation
📌 BB:Bb:bb = 1:2:1
bb = 1/4 = 25%
bb = 1/4 = 25%
Question 5 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)
BNitrogen fixation (absorbs CO₂) and decomposition (releases O₂)
CPhotosynthesis (absorbs CO₂) and cellular respiration (releases CO₂)
DTranspiration (releases CO₂) and condensation (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 6 of 10
A student designed an experiment to test how light affects plant growth. Identify the components of this experiment. 
AIndependent: temperature; Dependent: light
BIndependent: water; Dependent: soil
CIndependent: plant height; Dependent: light
DIndependent: light; Dependent: plant height
Explanation
📌 Independent variable = what you change (light)
Dependent variable = what you measure (plant height)
Control group = no light (to compare against)
Constants = same soil, water, temperature, pot size
Dependent variable = what you measure (plant height)
Control group = no light (to compare against)
Constants = same soil, water, temperature, pot size
Question 7 of 10
In a DNA nucleotide, which component carries the genetic code through its specific sequence?
APhosphate group
BNitrogenous base
CHydrogen bond
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 8 of 10
The Hardy-Weinberg principle states that allele frequencies remain constant when:
Amutations are common
Bnatural selection is strong
Cthere is no evolution occurring
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 9 of 10
Alternative splicing allows:
Achromosomes to separate
Bmutations to be prevented
CDNA to be repaired
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 10 of 10
Lipids store roughly twice as much energy per gram as carbohydrates. Which property of lipid molecules best explains this?
ALong hydrocarbon chains contain many C–H bonds that can be oxidized to release energy
BThey contain more nitrogen atoms than carbohydrates
CThey are insoluble in water, so they take up less space when stored
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.