Question 1 of 10
In a DNA nucleotide, which component carries the genetic code through its specific sequence?
AHydrogen bond
BDeoxyribose sugar
CPhosphate group
DNitrogenous base
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 2 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 3 of 10
A theory in science is:
Aan untested guess
Ba well-supported explanation based on extensive evidence
Ca proven fact that can never change
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 4 of 10
All three domains of life (Bacteria, Archaea, and Eukarya) share which structural feature?
ARibosomes for protein synthesis
BMulticellular organization
CA membrane-bound nucleus
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).
Question 5 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:
ANatural selection
BSpontaneous generation
CGenetic engineering
DArtificial 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 6 of 10
A student designed an experiment to test how light affects plant growth. Identify the components of this experiment. 
AIndependent: water; Dependent: soil
BIndependent: light; Dependent: plant height
CIndependent: temperature; Dependent: light
DIndependent: plant height; Dependent: light
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
Which graph correctly shows exponential growth?
ANeither
BBoth
CB
DA
Explanation
📌 Exponential growth = J-shaped curve (slow start, rapid increase)
Linear growth = straight line (constant rate)
Graph A shows exponential growth.
Linear growth = straight line (constant rate)
Graph A shows exponential growth.
Question 8 of 10
The Hardy-Weinberg principle states that allele frequencies remain constant when:
Amutations are common
Bnatural selection is strong
Cthe population is very small
Dthere is no evolution occurring
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
During which phase of the cell cycle does DNA replication occur? 
AG2 phase
BS phase
CM phase
DG1 phase
Explanation
📌 DNA replication occurs during S phase (Synthesis) of interphase.
Interphase: G1 → S → G2, then Mitosis.
Interphase: G1 → S → G2, then Mitosis.
Question 10 of 10
Which organelle is labeled X in the cell diagram below? 
ANucleus
BGolgi apparatus
CMitochondria
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