1. 01

   A heterozygous brown-eyed parent (Bb) crosses with a blue-eyed parent (bb). What percentage of offspring are predicted to have blue eyes?

   A 0% B 25% C 50% D 75%
   Why: Bb × bb gives 50% Bb (brown) and 50% bb (blue). This is the classic test cross.
2. 02

   Which of the following mutations is most likely to have NO effect on the protein produced?

   A Frameshift B Nonsense C Missense D Silent
   Why: Silent mutations change a base but not the amino acid (because the genetic code is degenerate). The protein is identical.
3. 03

   If both parents are heterozygous (Aa) for a recessive disease, what fraction of their children will be affected?

   A 0 B 1/4 C 1/2 D 3/4
   Why: Aa × Aa gives 1 AA : 2 Aa : 1 aa. Only the 1/4 that are aa are affected (carry both recessive alleles).
4. 04

   DNA replication is described as 'semiconservative' because:

   A Half the DNA is destroyed B Each new helix has one old strand and one new strand C Only one strand is copied D Replication only happens in half the cells
   Why: Semi = half. Each daughter molecule conserves one of the original strands and pairs it with a newly synthesized complementary strand.
5. 05

   How many codons code for the 20 amino acids?

   A 20 B 30 C 60 D 64
   Why: There are 4³ = 64 possible codons. 61 code for amino acids (most amino acids have multiple codons) and 3 are stop codons.

1. 01

   In RNA, adenine pairs with which base?

   A Uracil B Thymine C Cytosine D Guanine
   Why: RNA uses uracil (U) instead of thymine (T). A-U in RNA, A-T in DNA.
2. 02

   Two parents are heterozygous (Ff) for cystic fibrosis (recessive). What fraction of children are NOT affected?

   A 1/4 B 3/4 C 1/2 D 1
   Why: Ff × Ff gives 1 FF : 2 Ff : 1 ff. The 3/4 with at least one F allele are unaffected.
3. 03

   Which molecule carries the genetic message from the nucleus to the ribosome?

   A DNA B tRNA C mRNA D rRNA
   Why: Messenger RNA (mRNA) is transcribed from DNA in the nucleus and travels to ribosomes to be translated into protein.
4. 04

   DNA polymerase's main job during replication is to:

   A Unzip the helix B Stabilize single strands C Glue Okazaki fragments D Add complementary nucleotides to the new strand
   Why: Polymerase reads the template strand and adds matching bases (A-T, G-C) to build the new strand.
5. 05

   A mutation that inserts a single extra base into a coding gene is called a:

   A Frameshift mutation B Silent mutation C Nonsense mutation D Missense mutation
   Why: An insertion shifts the reading frame for every codon downstream, usually destroying the protein.

1. 01

   Which is NOT a base found in DNA?

   A Adenine B Uracil C Cytosine D Thymine
   Why: Uracil belongs to RNA. DNA uses adenine, thymine, cytosine, and guanine.
2. 02

   A man with type AB blood and a woman with type O blood have a child. What blood types are possible for the child?

   A A or B only B AB only C O only D A, B, AB, or O
   Why: AB parent contributes A or B. O parent contributes O. Child genotypes: AO (type A) or BO (type B).
3. 03

   A mother is XᴮXᵇ (color-blind carrier) and the father is XᴮY (normal). What percent of their sons will be color-blind?

   A 0% B 25% C 50% D 100%
   Why: Sons inherit Y from dad and X from mom. Half get Xᴮ (normal), half get Xᵇ (color-blind).
4. 04

   Sickle cell anemia is caused by a single base change that swaps one amino acid in hemoglobin. This is a:

   A Frameshift mutation B Silent mutation C Nonsense mutation D Missense mutation
   Why: Missense = a base change that produces a different amino acid. Sickle cell is the classic example.
5. 05

   Which enzyme unwinds the DNA double helix at the start of replication?

   A Helicase B DNA polymerase C Ligase D RNA polymerase
   Why: Helicase breaks the hydrogen bonds between base pairs and separates the two strands.

1. 01

   If the DNA template strand reads 3'-TAC-5', the mRNA codon transcribed from it is:

   A UAC B ATG C AUG D GTA
   Why: Transcription is antiparallel and uses U instead of T. Template TAC → mRNA AUG (the start codon).
2. 02

   What does the codon AUG do in translation?

   A Stop translation B Code for methionine and start translation C Code for phenylalanine D Code for tryptophan
   Why: AUG is the start codon and codes for methionine. Every protein begins with methionine.
3. 03

   If a Punnett cross is TT × tt, what fraction of offspring show the dominant phenotype (T is dominant)?

   A 0% B 25% C 50% D 100%
   Why: All offspring are Tt heterozygotes, which show the dominant phenotype.
4. 04

   On a pedigree, a filled (solid) square represents:

   A An affected male B An unaffected male C An affected female D A carrier
   Why: Square = male, circle = female. Filled = affected, half-filled = carrier, empty = unaffected.
5. 05

   Which of these is a STOP codon?

   A AUG B GCA C UAA D AAA
   Why: UAA, UAG, and UGA are the three stop codons that terminate translation.

1. 01

   How many chromosomes are in a normal human gamete (sperm or egg)?

   A 23 B 46 C 92 D 24
   Why: Gametes are haploid (n = 23). They fuse at fertilization to restore the diploid number 46.
2. 02

   When a heterozygote (Aa) self-fertilizes, what fraction of offspring are homozygous (AA or aa)?

   A 1/2 B 1/4 C 3/4 D 1
   Why: Aa × Aa gives 1 AA : 2 Aa : 1 aa. The homozygotes (AA + aa) total 2/4 = 1/2.
3. 03

   On a pedigree, a trait that skips a generation is most likely:

   A Dominant B Recessive C Codominant D X-linked dominant
   Why: Recessive traits hide in heterozygous carriers and only appear when two carriers have a homozygous-recessive child.
4. 04

   Which best describes incomplete dominance?

   A Both alleles fully expressed B One allele dominates the other C Heterozygotes show a blended phenotype D Neither allele is expressed
   Why: Red flower × white flower → pink flower is the classic example. Neither allele is fully dominant; the heterozygote is intermediate.
5. 05

   If the original DNA is ATCG and a mutation changes it to ATTG, this is a:

   A Frameshift B Substitution (point mutation) C Insertion D Deletion
   Why: Replacing one base with another (C → T here) is a substitution. The reading frame stays intact.

1. 01

   Sex-linked traits in humans are usually carried on which chromosome?

   A Chromosome 1 B Chromosome 21 C X chromosome D Y chromosome
   Why: Most known sex-linked traits (color blindness, hemophilia) are X-linked because the Y chromosome carries very few genes.
2. 02

   A homozygous dominant parent (BB) crosses with a heterozygote (Bb). What percent of offspring show the dominant phenotype?

   A 25% B 50% C 75% D 100%
   Why: BB × Bb gives 1/2 BB and 1/2 Bb. Both genotypes show the dominant phenotype.
3. 03

   What does the term 'phenotype' refer to?

   A The observable physical trait B The genetic makeup C A pair of alleles D The chromosome number
   Why: Phenotype = what you see (eye color, height). Genotype = the alleles you carry (BB, Bb, bb).
4. 04

   RNA polymerase synthesizes which type of nucleic acid during transcription?

   A DNA B mRNA C tRNA D rRNA
   Why: RNA polymerase reads a DNA template and produces mRNA, which is then translated into protein.
5. 05

   If a mother is XᴬXᵃ (carrier) and the father is XᴬY, what percent of daughters will be carriers?

   A 0% B 25% C 50% D 100%
   Why: Daughters get Xᴬ from dad. Half get Xᴬ from mom (homozygous normal); half get Xᵃ from mom (carrier).

1. 01

   Which is the BEST evidence that whales descended from land mammals?

   A Whales swim like fish B Whales have lungs and vestigial pelvic bones C Whales live in the ocean D Whales are large
   Why: Vestigial structures (pelvis bones disconnected from any limb) and lungs reveal a land-dwelling ancestor. Convergent traits like swimming don't show ancestry.
2. 02

   After a drought killed off small-seed-eating finches, the next generation had bigger beaks. This is an example of:

   A Genetic drift B Natural selection C Mutation D Gene flow
   Why: Selective pressure (only big-beaked birds could eat the remaining tough seeds) caused differential reproduction. Classic natural selection.
3. 03

   Two species of birds look almost identical but live on different continents and have different DNA. Their similarity is best explained by:

   A Common ancestry B Convergent evolution C Genetic drift D A shared mutation
   Why: Different DNA + different geography means they evolved similar appearances independently in similar environments. That's convergent evolution (analogous structures).
4. 04

   On a phylogenetic tree, which two species are most closely related?

   A The two whose tips look the most similar B The two whose tips are next to each other C The two that share the most recent common ancestor D The two on the same branch
   Why: Tree relationships are about shared ancestors, not tip position or appearance. Always trace down to find the most recent node both species share.
5. 05

   If a population is in Hardy-Weinberg equilibrium and the frequency of the recessive allele is 0.3, what fraction of the population is homozygous recessive?

   A 0.3 B 0.09 C 0.42 D 0.49
   Why: q² = 0.3² = 0.09 (or 9%). The Hardy-Weinberg equation gives genotype frequencies directly from allele frequencies.

1. 01

   Vestigial structures like the human appendix or whale pelvic bones are evidence of:

   A Mutation rate B Genetic drift C Convergent evolution D Common ancestry
   Why: Vestigial structures are leftovers from an ancestor that used them. They reveal a shared evolutionary past.
2. 02

   Which scientist is credited with proposing natural selection as the mechanism of evolution?

   A Charles Darwin B Gregor Mendel C James Watson D Carl Linnaeus
   Why: Darwin (and independently Wallace) published the theory of natural selection in 1859.
3. 03

   A hurricane wipes out 80% of an island lizard population at random. The surviving allele frequencies are most affected by:

   A Natural selection B Migration C Genetic drift D Mutation
   Why: Random survival, not fitness, drives the change. That's the bottleneck variant of genetic drift.
4. 04

   Two distantly related species' embryos look nearly identical in early development. This is evidence of:

   A Convergent evolution B Common ancestry C Coevolution D Genetic drift
   Why: Shared embryonic stages suggest a shared ancestor that had those features.
5. 05

   Antibiotic resistance evolving in bacterial populations exposed to penicillin is a real-time example of:

   A Goal-directed adaptation B Mutation only C Genetic drift D Natural selection
   Why: Resistant individuals survive and reproduce, non-resistant ones don't. Allele frequencies shift each generation.

1. 01

   On a phylogenetic tree, the points where branches split apart are called:

   A Tips B Nodes C Roots D Clades
   Why: Each node represents a most recent common ancestor of the lineages that branch from it.
2. 02

   If the dominant allele frequency p = 0.6 in a Hardy-Weinberg population, what fraction is homozygous dominant (p²)?

   A 0.6 B 0.84 C 0.16 D 0.36
   Why: p² = 0.6² = 0.36, or 36% of the population.
3. 03

   Bat wings and bird wings have different bone arrangements but serve the same function. They are:

   A Analogous structures B Homologous structures C Vestigial structures D Coevolved structures
   Why: Same function, different evolutionary origin = analogous (convergent evolution).
4. 04

   In evolutionary biology, 'fitness' refers to:

   A Physical strength B Lifespan C Reproductive success D Body size
   Why: Fitness = how many offspring an individual leaves to the next generation, not how athletic it looks.
5. 05

   Hardy-Weinberg equilibrium requires which condition?

   A Active natural selection B No mutations, no migration, no selection, large random-mating population C Small population size D Asexual reproduction only
   Why: All five conditions must hold for allele frequencies to stay constant. If any one breaks, the population is evolving.

1. 01

   When a single ancestral species splits and rapidly diversifies into multiple new species filling different niches, this is called:

   A Convergent evolution B Coevolution C Speciation D Adaptive radiation
   Why: Galápagos finches are the textbook example: one ancestor, many beak shapes, many islands, many species.
2. 02

   Which of these events happened most recently on the geologic timeline?

   A Mass extinction of dinosaurs (Cretaceous-Paleogene) B Cambrian explosion C Origin of photosynthesis D Origin of multicellular life
   Why: Dinosaur extinction happened 66 million years ago. The other events are hundreds of millions to billions of years older.
3. 03

   A new finch species evolving on each Galápagos island is an example of:

   A Genetic drift only B Convergent evolution C Coevolution D Adaptive radiation
   Why: Adaptive radiation: one ancestor, many descendants, each adapted to a different environment.
4. 04

   Two animals both have backbones, four-chambered hearts, and produce milk. They are most likely:

   A Identical species B Closely related (probably both mammals) C Distantly related D Unrelated
   Why: Multiple shared derived traits point to recent common ancestry. These three traits define mammals.
5. 05

   What does 'survival of the fittest' really mean?

   A The strongest survive B The smartest survive C Those best suited to the current environment reproduce most D Only the fastest survive
   Why: Fitness is about leaving offspring, not athletic ability. The 'best fit' depends entirely on the environment.

1. 01

   Humans and chimpanzees share roughly 98% of their DNA. This is strong evidence of:

   A Convergent evolution B Mutation rate C Genetic drift D Common ancestry
   Why: Shared DNA at this level is only explained by descent from a recent common ancestor.
2. 02

   What is a population bottleneck?

   A A species going extinct B A drastic drop in population size that lowers genetic diversity C A population splitting in two D An increase in mutation rate
   Why: A bottleneck removes most alleles from the gene pool by chance, leaving the survivors less diverse than the original population.
3. 03

   Fossils found in deeper layers of undisturbed sedimentary rock are usually:

   A Younger than fossils above them B The same age as fossils above them C Older than fossils above them D From a different planet
   Why: Sediment deposits in layers over time. Deeper rock = older deposits = older fossils.
4. 04

   If any Hardy-Weinberg condition is broken, the population is:

   A Evolving B In stable equilibrium C Going extinct D Speciating
   Why: Evolution = change in allele frequency. Any broken condition (mutation, selection, migration, drift, non-random mating) shifts frequencies.
5. 05

   Which provides the strongest evidence that two organisms share a common ancestor?

   A Similar appearance B Same habitat C Same diet D Similar DNA sequences and shared genes
   Why: Genetic data is the most reliable evidence. Two species can look alike from convergent evolution but their DNA reveals true ancestry.

1. 01

   Why do antibiotic-resistant bacteria become more common in hospitals?

   A Hospitals create new mutations B Bacteria choose to resist antibiotics C Antibiotics kill non-resistant bacteria, leaving resistant ones to reproduce D Patients become immune
   Why: Selection by antibiotics is the textbook example of natural selection in action.
2. 02

   On a phylogenetic tree, two species that share a more recent common ancestor are:

   A More closely related B Less closely related C The same species D Convergently evolved
   Why: Recency of the shared ancestor measures how closely two species are related, not the position on the page.
3. 03

   What major scientific concept was missing from Darwin's original theory of evolution?

   A Observations of variation in populations B The idea of selection C The struggle for survival D A mechanism of inheritance (genetics)
   Why: Darwin didn't know about Mendel's work or DNA. The 'modern synthesis' combined Darwin's natural selection with genetics in the 20th century.
4. 04

   If p = 0.7 in a Hardy-Weinberg population, what is the recessive allele frequency q?

   A 0.7 B 0.3 C 0.49 D 0.09
   Why: p + q = 1. So q = 1 - 0.7 = 0.3.
5. 05

   Coevolution is best illustrated by:

   A Two unrelated species evolving similar wings B A population reduced to a few individuals C Flowering plants and their pollinators evolving together over time D Bacteria evolving antibiotic resistance
   Why: Coevolution = two species evolving in response to each other. Flowers and pollinators are the textbook case.

1. 01

   If a producer level has 100,000 kcal of energy, about how much should reach the secondary consumers?

   A 10,000 kcal B 1,000 kcal C 100 kcal D 100,000 kcal
   Why: 10% rule: 100,000 → 10,000 (1° consumer) → 1,000 (2° consumer). 90% lost at each step as heat.
2. 02

   Two species of warblers in the same tree have evolved to feed at different heights to avoid each other. This is most likely a result of:

   A Mutualism B Predation C Competition D Commensalism
   Why: Resource partitioning is a classic outcome of competition. Both species suffered when they overlapped, so natural selection favored individuals that used different parts of the tree.
3. 03

   The temperate deciduous forest biome is characterized by:

   A No rainfall and very high temperatures B Four distinct seasons and trees that lose leaves in winter C Permafrost and no trees D Year-round rainfall and the highest biodiversity on Earth
   Why: Ohio is in this biome! Four seasons, deciduous trees (maples, oaks), moderate rainfall.
4. 04

   A population growing exponentially eventually slows as it approaches:

   A Mutation rate B Natural selection C Carrying capacity D Trophic cascade
   Why: Carrying capacity (K) is the maximum population the environment can sustain. Resources run low, growth slows to zero.
5. 05

   Without nitrogen-fixing bacteria, plants would not be able to:

   A Photosynthesize B Make proteins and DNA C Absorb water D Reproduce
   Why: Plants need nitrogen to make proteins and nucleic acids. They can't fix N2 themselves; they depend entirely on bacteria to convert atmospheric nitrogen into a usable form.

1. 01

   Which is the correct order of ecological organization, from smallest to largest?

   A Population, community, ecosystem, biome, biosphere B Community, population, ecosystem, biome, biosphere C Population, community, biome, ecosystem, biosphere D Biome, ecosystem, community, population, biosphere
   Why: Population (one species) → community (multiple species) → ecosystem (community + abiotic) → biome (regional climate type) → biosphere (all life on Earth).
2. 02

   In the food chain grass → grasshopper → frog → snake → hawk, the hawk is the:

   A Producer B Primary consumer C Secondary consumer D Quaternary consumer
   Why: Count from the producer up: grass (producer), grasshopper (1°), frog (2°), snake (3°), hawk (4° / quaternary).
3. 03

   Which best describes mutualism?

   A One species benefits, the other is harmed B Both species benefit C One species benefits, the other is unaffected D Both species are harmed
   Why: +/+ interaction. Bees get nectar, flowers get pollinated. Both win.
4. 04

   What process converts atmospheric N₂ into a form plants can absorb from the soil?

   A Photosynthesis B Decomposition C Nitrogen fixation D Cellular respiration
   Why: Nitrogen-fixing bacteria (like Rhizobium in legume roots) turn N₂ into ammonia / nitrate, which plants can take up.
5. 05

   Which biome has the highest biodiversity on Earth?

   A Tropical rainforest B Tundra C Desert D Temperate grassland
   Why: Year-round warmth, abundant rainfall, and stable conditions support enormous species diversity in tropical rainforests.

1. 01

   When the snowshoe hare population grows, the lynx population grows shortly after, then the hare population crashes. This is an example of:

   A Mutualism B Parasitism C Predator-prey dynamics D Commensalism
   Why: Classic oscillating cycle: more prey → more predators → predators overhunt → prey crash → predators starve → cycle restarts.
2. 02

   Decomposers play which essential role in ecosystems?

   A Producing energy from sunlight B Returning nutrients to the soil for producers to reuse C Hunting top predators D Pollinating plants
   Why: Without decomposers (bacteria, fungi), nutrients stay locked in dead matter and the cycle stalls.
3. 03

   Burning fossil fuels releases carbon into the atmosphere mainly as:

   A Methane B Oxygen C Nitrogen oxides D Carbon dioxide
   Why: Combustion of hydrocarbons produces CO₂ and water vapor. Rising atmospheric CO₂ drives climate change.
4. 04

   A population sitting at carrying capacity has a long-term growth rate of approximately:

   A Zero B Negative C Maximum D Doubling per generation
   Why: Births and deaths balance. Logistic growth flattens at K (carrying capacity).
5. 05

   Which interaction is parasitism (+/-)?

   A A bee pollinating a flower B A remora hitching a ride on a shark without harming it C A tapeworm living in a dog's intestine D Two oak trees competing for sunlight
   Why: Tapeworm benefits, dog is harmed. Pollination is +/+, remora is +/0, competition is -/-.

1. 01

   A producer level captures 10,000 kcal of light energy. About how much reaches the tertiary (3°) consumer?

   A 100 kcal B 10 kcal C 1,000 kcal D 1 kcal
   Why: 10% rule applied three times: 10,000 → 1,000 → 100 → 10. Most energy is lost as heat at each step.
2. 02

   The water cycle is driven primarily by:

   A Decomposition B Photosynthesis C Volcanic activity D Solar energy and gravity
   Why: Sun heats water → evaporation. Gravity returns it as precipitation. Plants and animals contribute small amounts via transpiration and respiration.
3. 03

   Permafrost, lichens, and very low precipitation describe which biome?

   A Tundra B Taiga C Tropical rainforest D Savanna
   Why: The Arctic tundra is too cold for trees; ground stays frozen year-round below the surface.
4. 04

   Which is a density-DEPENDENT factor that limits populations?

   A Drought B Forest fire C Disease spread D Volcanic eruption
   Why: Disease spreads more easily in dense populations, so its impact depends on density. Weather and disasters affect populations regardless of density.
5. 05

   Removing a keystone species from an ecosystem typically causes:

   A No noticeable change B Major changes throughout the food web C Only the keystone's prey to thrive briefly D An immediate increase in producer biomass
   Why: Keystones have an outsized effect: removing wolves from Yellowstone changed everything from elk numbers to river paths.

1. 01

   Which gas makes up about 78% of Earth's atmosphere but cannot be used directly by plants?

   A Carbon dioxide B Oxygen C Methane D Nitrogen
   Why: Atmospheric N₂ has a triple bond plants can't break. They need bacteria to fix it into ammonia or nitrate first.
2. 02

   What is a 'niche' in ecology?

   A The role and resource use of a species in its environment B The physical place where a species lives C A taxonomic group D Another word for habitat
   Why: Habitat = address (where it lives). Niche = job (what it does, what it eats, when it's active, how it interacts).
3. 03

   If a wolf population in a forest decreases sharply, the deer population they prey on will most likely:

   A Decrease B Stay the same C Increase, then crash from overgrazing D Become extinct
   Why: Without predators, deer multiply, then run out of food and crash. Classic boom-bust cycle.
4. 04

   Which of these is a primary producer?

   A Mushroom B Algae C Earthworm D Hawk
   Why: Algae photosynthesize. Mushrooms are decomposers, earthworms are detritivores, hawks are top consumers.
5. 05

   Habitat fragmentation harms wildlife mainly because it:

   A Increases mutation rates B Improves pollination C Eliminates all predators D Reduces gene flow and isolates small populations
   Why: Roads and farms cut habitats into small islands. Small isolated populations lose genetic diversity and risk drift / inbreeding.

1. 01

   Which process is NOT part of the carbon cycle?

   A Photosynthesis B Cellular respiration C Nitrogen fixation D Combustion
   Why: Nitrogen fixation is the nitrogen cycle. Photosynthesis pulls CO₂ out of the air; respiration and combustion put it back.
2. 02

   An invasive species typically thrives in a new environment because:

   A It has no natural predators in the new environment B It is more intelligent than native species C It mutates faster than native species D It can reproduce without genetic material
   Why: Invasives left their predators, parasites, and competitors behind. They explode in numbers and outcompete natives.
3. 03

   Which ecosystem service is provided primarily by bees?

   A Decomposition B Soil aeration C Predator control D Pollination
   Why: Bees pollinate roughly a third of human food crops. Without them, fruit, nut, and vegetable yields collapse.
4. 04

   Two species of squirrels compete for the same nuts in the same forest. Their interaction is best described as:

   A Mutualism B Competition C Predation D Commensalism
   Why: Both species suffer when they share a limiting resource. -/- interaction.
5. 05

   Acid rain is caused primarily by:

   A Excess CO₂ emissions B Methane emissions from livestock C Sulfur and nitrogen oxide emissions from burning fossil fuels D Plastic pollution in oceans
   Why: SO₂ and NOₓ from coal plants and vehicles react with water vapor in clouds to form sulfuric and nitric acid.

Drag the phases into the correct order

• Cytokinesis: cytoplasm divides, two cells form
• Anaphase: sister chromatids pulled to opposite poles
• Telophase: nuclear envelopes reform, chromosomes uncondense
• Metaphase: chromosomes line up at the middle
• Prophase: chromosomes condense, nuclear envelope dissolves

1. 01

   Which organelle is found ONLY in plant cells?

   A Mitochondrion B Nucleus C Chloroplast D Ribosome
   Why: Chloroplasts are exclusive to plants and algae. Plant cells also have mitochondria; both organelles work together (photosynthesis stores energy, respiration releases it).
2. 02

   During mitosis, what happens during anaphase?

   A Chromosomes line up at the middle B Sister chromatids are pulled to opposite poles C Chromosomes condense D The cytoplasm divides
   Why: Anaphase = chromatids APART. Sister chromatids separate and move to opposite poles via spindle fibers.
3. 03

   How many UNIQUE daughter cells does meiosis produce from one starting cell?

   A 1 B 2 C 4 D 8
   Why: Meiosis I makes 2 haploid cells, then meiosis II splits each, giving 4 total. All 4 are genetically unique due to crossing over and independent assortment.
4. 04

   The light-dependent reactions of photosynthesis happen in the:

   A Stroma B Thylakoid membrane C Outer chloroplast membrane D Cytoplasm
   Why: Photosystems and the electron transport chain are embedded in the thylakoid membrane. The stroma hosts the Calvin cycle (stage 2).
5. 05

   Which stage of cellular respiration produces the MOST ATP?

   A Glycolysis B Krebs cycle C Electron transport chain D Fermentation
   Why: ETC + oxidative phosphorylation produces ~28-32 ATP. Glycolysis and Krebs each produce only 2 ATP directly. Fermentation produces 2 total.
6. 06

   A red blood cell placed in pure water would:

   A Shrivel B Stay the same C Burst D Die immediately
   Why: Pure water = hypotonic. Water rushes IN to the cell via osmosis. Animal cells without cell walls burst (lyse). Plant cells in this situation don't burst because the cell wall holds them rigid (turgor pressure).
7. 07

   Why is fermentation less efficient than aerobic respiration?

   A It produces too much waste B It only completes glycolysis, skipping the Krebs cycle and ETC C It happens in the wrong organelle D It uses oxygen
   Why: Fermentation produces only 2 ATP from glucose because it stops after glycolysis. Without oxygen, there's no final electron acceptor for the ETC, so cells can't run stages 2-3.

1. 01

   Which organelle makes ATP in animal cells?

   A Chloroplast B Mitochondrion C Ribosome D Lysosome
   Why: Mitochondria run cellular respiration, producing ~30-32 ATP per glucose.
2. 02

   What does the cell membrane primarily regulate?

   A DNA replication B Protein folding C Energy storage D What enters and exits the cell
   Why: Selective permeability is the membrane's main job. Phospholipid bilayer + transport proteins control flow.
3. 03

   During interphase, what is the cell doing?

   A Growing, copying DNA, and preparing for division B Splitting into two cells C Lining chromosomes up at the equator D Pulling sister chromatids apart
   Why: Interphase is the long G1 → S → G2 stretch before mitosis even starts. DNA replication happens in S phase.
4. 04

   Crossing over occurs during which stage of meiosis?

   A Anaphase II B Metaphase II C Prophase I D Telophase II
   Why: Homologous chromosomes pair up and exchange segments during prophase I, creating new genetic combinations.
5. 05

   What is the main waste product of the light reactions of photosynthesis?

   A Glucose B Oxygen C ATP D Carbon dioxide
   Why: Splitting water molecules releases O₂ as a byproduct. Earth's atmospheric oxygen comes from photosynthesis.
6. 06

   Roughly how many ATP does aerobic respiration produce per glucose molecule?

   A 2 ATP B 4 ATP C 16 ATP D About 30 to 32 ATP
   Why: Glycolysis (2) + Krebs (2) + ETC and oxidative phosphorylation (~26-28) ≈ 30-32 total.
7. 07

   When cells divide uncontrollably and lose normal regulation, this can lead to:

   A Cancer B Apoptosis C Differentiation D Mitosis being skipped
   Why: Cancer = unchecked cell division. Mutations in tumor suppressor or proto-oncogenes break the cell-cycle brakes.

1. 01

   Which transport process across a membrane requires ATP?

   A Osmosis B Facilitated diffusion C Active transport D Simple diffusion
   Why: Active transport moves molecules against their concentration gradient, which costs energy.
2. 02

   Where does glycolysis take place in the cell?

   A Cytoplasm B Mitochondrial matrix C Inner mitochondrial membrane D Nucleus
   Why: Glycolysis happens in the cytoplasm. Pyruvate then enters the mitochondrion for stages 2 and 3.
3. 03

   Which organelle is sometimes called the 'suicide sac' because it digests damaged cell parts?

   A Ribosome B Chloroplast C Endoplasmic reticulum D Lysosome
   Why: Lysosomes contain digestive enzymes. They break down worn organelles, foreign invaders, and even the cell itself during apoptosis.
4. 04

   How does meiosis differ from mitosis?

   A It produces 2 cells instead of 4 B It produces 4 genetically unique haploid cells C It does not involve DNA replication D It happens only in prokaryotes
   Why: Mitosis: 1 → 2 identical diploid cells. Meiosis: 1 → 4 unique haploid cells (gametes).
5. 05

   The Calvin cycle uses which inputs to make sugar?

   A Oxygen and ATP B Glucose and water C CO₂, ATP, and NADPH D Light and chlorophyll directly
   Why: Calvin cycle is light-independent. It pulls in CO₂ and uses the ATP and NADPH made by the light reactions to build sugar.
6. 06

   Why do plants do photosynthesis?

   A To store energy from sunlight in glucose B To release ATP from glucose C To make oxygen from carbon dioxide and proteins D To produce nitrogen for the soil
   Why: Photosynthesis converts light energy into chemical energy stored in glucose. Plants then run respiration to release that energy as ATP.
7. 07

   Cancer is fundamentally a disease of:

   A Old age only B Bacteria C The immune system only D Uncontrolled cell division
   Why: Mutations break the cell cycle's checkpoints. Cells divide when they shouldn't, forming a tumor.

1. 01

   Which two organelles are responsible for converting energy in cells?

   A Nucleus and ribosome B Chloroplast and mitochondrion C Lysosome and Golgi apparatus D Endoplasmic reticulum and vacuole
   Why: Chloroplasts capture light and store energy in glucose. Mitochondria release that energy as ATP.
2. 02

   What does ATP stand for?

   A Adenine triphosphate B Adenosine diphosphate C Acetyl thiamine phosphate D Adenosine triphosphate
   Why: Adenosine = adenine + ribose. Three phosphate groups make ATP a high-energy molecule (the cell's energy currency).
3. 03

   If an animal cell is placed in a hypertonic solution (more solute outside), water will:

   A Move out of the cell, shriveling it B Move into the cell, swelling it C Stay still D Reverse direction repeatedly
   Why: Water moves toward higher solute concentration. Outside hypertonic = water leaves the cell.
4. 04

   During which phase of mitosis do chromosomes line up at the metaphase plate?

   A Prophase B Anaphase C Metaphase D Telophase
   Why: Metaphase plate = the imaginary line at the cell's center where chromosomes line up. The name gives it away.
5. 05

   What is the role of NADPH in photosynthesis?

   A Captures light energy directly B Carries high-energy electrons from the light reactions to the Calvin cycle C Splits water molecules D Transports glucose to the cytoplasm
   Why: NADPH is a reduced electron carrier. Light reactions make it; Calvin cycle uses it to reduce CO₂ into sugar.
6. 06

   In the electron transport chain, oxygen acts as the:

   A Energy source B Initial electron donor C Carbon source D Final electron acceptor
   Why: Electrons flow down the ETC and combine with O₂ and protons at the end to form H₂O. Without O₂, the chain stalls.
7. 07

   Apoptosis is best described as:

   A Uncontrolled cell growth B DNA replication C Programmed cell death that removes damaged or unneeded cells D Movement of organelles
   Why: Apoptosis is a controlled, scheduled self-destruction. It shapes development (e.g., separating fingers in embryos) and removes precancerous cells.

1. 01

   Which of these is NOT found in animal cells?

   A Mitochondrion B Nucleus C Golgi apparatus D Cell wall
   Why: Cell walls are in plants, fungi, and bacteria. Animal cells have only a flexible plasma membrane.
2. 02

   What does mitosis produce from one parent cell?

   A Two genetically identical diploid daughter cells B Four genetically unique haploid cells C One large cell D Sex cells (gametes) only
   Why: Mitosis maintains chromosome count. Both daughters are clones of the parent. Used for growth and tissue repair.
3. 03

   When a cell breaks down glucose, the first stage is:

   A Krebs cycle B Glycolysis C Electron transport chain D Fermentation
   Why: Glycolysis splits glucose (6C) into two pyruvates (3C each) in the cytoplasm. It happens whether or not oxygen is present.
4. 04

   Which pigment captures light energy in chloroplasts?

   A Hemoglobin B Carotene only C Chlorophyll D Melanin
   Why: Chlorophyll absorbs red and blue light, reflects green (which is why leaves look green).
5. 05

   What's the role of a carrier protein in facilitated diffusion?

   A It uses ATP to actively pump molecules B It consumes the molecules C It blocks transport D It helps molecules cross the membrane down their gradient without using ATP
   Why: Facilitated diffusion is passive. Carrier proteins just provide a pathway through the lipid bilayer for polar / large molecules.
6. 06

   Which respiration stage produces lots of NADH and FADH₂ but only 2 ATP directly?

   A Glycolysis B Krebs cycle C Electron transport chain D Fermentation
   Why: Krebs makes 2 ATP, 6 NADH, and 2 FADH₂ per glucose. The electron carriers go on to make most of the cell's ATP at the ETC.
7. 07

   Mitosis ensures that:

   A Each daughter cell has the same chromosome number as the parent B Each daughter cell has half the chromosomes of the parent C New genetic combinations are generated D Only sex cells are made
   Why: Mitosis is an exact copying process. Diploid parent → two diploid daughters with identical DNA.

1. 01

   Which structure houses ribosomes that synthesize proteins destined for export from the cell?

   A Smooth ER B Golgi apparatus C Rough ER D Lysosome
   Why: Rough ER is studded with ribosomes. Proteins made there are folded, packaged, and shipped via vesicles to the Golgi.
2. 02

   Which equation summarizes cellular respiration?

   A CO₂ + H₂O → C₆H₁₂O₆ + O₂ B C₆H₁₂O₆ + O₂ → CO₂ + H₂O + sunlight C C₆H₁₂O₆ → 2 CO₂ + 2 ATP only D C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ATP
   Why: Glucose + oxygen → carbon dioxide + water + energy (ATP). Photosynthesis is the reverse reaction.
3. 03

   Osmosis specifically refers to:

   A The diffusion of water across a semi-permeable membrane B The active transport of ions C The breakdown of glucose D The replication of DNA
   Why: Osmosis is a special case of diffusion: water moving toward higher solute concentration through a membrane.
4. 04

   Telomeres are located:

   A In the middle of chromosomes B At the ends of chromosomes C In the cytoplasm D In the mitochondria
   Why: Telomeres cap chromosome ends and protect them from degrading. They shorten with each division, contributing to aging.
5. 05

   Which process produces 4 genetically unique cells with HALF the chromosomes of the parent?

   A Mitosis B Binary fission C Meiosis D Apoptosis
   Why: Meiosis is how gametes are made: one diploid parent produces four haploid sex cells, each genetically unique.
6. 06

   In the light reactions, water is split to provide:

   A Electrons for the photosystem and oxygen as a byproduct B Sugar molecules C Carbon for the Calvin cycle D ATP only
   Why: Photolysis: 2 H₂O → 4 H⁺ + 4 e⁻ + O₂. The electrons replace ones lost from chlorophyll; the O₂ leaves as waste.
7. 07

   Why do muscle cells produce lactic acid during intense exercise?

   A Because they want to slow down B Because oxygen is limited, so they switch to fermentation to recycle NAD⁺ C Because lactic acid stores energy for later D Because the muscle cells are dying
   Why: Without enough O₂, the ETC stalls. Cells convert pyruvate to lactate to regenerate NAD⁺ so glycolysis can keep making 2 ATP per glucose.

1. 01

   Which is the correct order of biological organization, from smallest to largest?

   A Cell, tissue, organ, organism, population, ecosystem B Tissue, cell, organism, population, ecosystem, biosphere C Organism, population, community, ecosystem, biome, biosphere D Atom, molecule, organelle, organism, ecosystem
   Why: Cells make tissues, tissues make organs, organs make organisms, organisms in groups make populations, etc.
2. 02

   Two parents are both heterozygous (Tt) for tongue rolling. What is the probability that their child will be a non-roller (tt)?

   A 0% B 25% C 50% D 75%
   Why: Tt × Tt gives 1 TT : 2 Tt : 1 tt. Only 1/4 (25%) are tt.
3. 03

   DNA is to RNA as deoxyribose is to:

   A Adenine B Phosphate C Ribose D Thymine
   Why: RNA's sugar is ribose. DNA's sugar is deoxyribose. The 'D' in DNA = deoxyribose.
4. 04

   If a cell is placed in a hypertonic solution, it will:

   A Burst from water entering B Shrink from water leaving C Stay the same size D Begin photosynthesis
   Why: Hypertonic = more solute outside the cell. Water flows OUT to balance the gradient. Cell shrinks (crenates if animal, plasmolyzes if plant).
5. 05

   The Galápagos finches show that:

   A Different species can never share an ancestor B Beak shape is determined by diet through learning C A single ancestral population can diversify into many species through natural selection D Birds can teach their offspring new beak shapes
   Why: Adaptive radiation: one ancestral finch species spread to different islands and evolved different beak shapes adapted to different food sources, becoming 13 distinct species.
6. 06

   Which level of the energy pyramid contains the LEAST total energy?

   A Producers B Primary consumers C Secondary consumers D Apex predators
   Why: Energy is lost as heat at each trophic level (90% per level). Apex predators get the least because they're highest up the chain.
7. 07

   A frameshift mutation usually has a more severe effect on a protein than a missense mutation because:

   A It only affects one amino acid B It shifts the entire reading frame downstream of the insertion or deletion C It always creates a stop codon D It affects DNA but not RNA
   Why: Frameshift = insertion or deletion that's not a multiple of 3. Every codon downstream is now read in a different frame, producing a completely different (usually nonfunctional) protein.
8. 08

   Which of the following is NOT a product of cellular respiration?

   A ATP B CO2 C H2O D Glucose
   Why: Glucose is a REACTANT (input). Cellular respiration breaks glucose down to release the energy stored in its bonds.
9. 09

   On a phylogenetic tree, dolphins, bats, and whales each have very different forms but share a common mammalian ancestor. The forelimbs of all three are examples of:

   A Convergent evolution B Vestigial structures C Homologous structures D Analogous structures
   Why: Same origin (the mammalian ancestor's forelimb), different functions (swimming, flying, swimming). That's homologous. Analogous structures share function but not origin (insect wings vs bird wings).
10. 10

    Asexual reproduction produces offspring that are genetically:

    A Identical to the parent B Half from each parent C Mutations of the parent D Random
    Why: Asexual reproduction = mitosis = clones. No mixing of two parents' genes.
11. 11

    Carbon enters the food chain primarily through:

    A Animal respiration B Plant photosynthesis C Decomposition D Combustion of fossil fuels
    Why: Plants take inorganic CO2 from the atmosphere and fix it into organic glucose via photosynthesis. That carbon then moves up the food chain when herbivores eat plants.
12. 12

    Which scenario would most likely INCREASE genetic variation in a population?

    A Inbreeding B A bottleneck event killing 90% of the population C Mutation, sexual reproduction, and gene flow from another population D Asexual reproduction
    Why: Mutation introduces NEW alleles. Sexual reproduction recombines them. Gene flow brings alleles from other populations. All three increase variation.
13. 13

    If the producers in an ecosystem all died, what would happen first?

    A Apex predators would starve immediately B Decomposers would dominate C Primary consumers (herbivores) would starve, then everything above them D Nothing - ecosystems can survive without producers
    Why: Producers are the base of the food web. Without them, primary consumers (herbivores) starve first, then the predators that eat them, etc. The ecosystem collapses from the bottom up.
14. 14

    Mitosis differs from meiosis in that mitosis:

    A Produces 4 daughter cells; meiosis produces 2 B Produces gametes; meiosis produces somatic cells C Produces genetically identical daughter cells; meiosis produces genetically unique ones D Happens only in plants; meiosis happens in animals
    Why: Mitosis = clones (somatic cells). Meiosis = unique gametes for sexual reproduction.
15. 15

    A cell uses ATP to move sodium ions OUT of itself, against a concentration gradient. This is an example of:

    A Diffusion B Osmosis C Facilitated diffusion D Active transport
    Why: Against the gradient + uses ATP = active transport. The sodium-potassium pump is the textbook example.
16. 16

    Which of these is direct evidence that all life shares a common ancestor?

    A All organisms reproduce B All organisms use the same DNA-based genetic code C All organisms move D All organisms breathe oxygen
    Why: Every organism on Earth uses the same 4 nucleotides and the same 64-codon genetic code. The probability of independently evolving the same code is essentially zero. So we share an ancestor.
17. 17

    When two species both benefit from their interaction, the relationship is:

    A Predation B Competition C Mutualism D Parasitism
    Why: Both benefit = mutualism. (Bees + flowers: bees get nectar, flowers get pollinated.)
18. 18

    A scientist sees that a population's allele frequencies are NOT changing over time. Which condition could explain this?

    A Strong natural selection B Frequent mutations C Hardy-Weinberg equilibrium D Major migration into the population
    Why: Hardy-Weinberg equilibrium: a population not evolving. The 5 conditions (no selection, no mutation, no migration, infinite size, random mating) are met. Allele frequencies stay constant.
19. 19

    Which adaptation would help a desert plant survive?

    A Large, thin leaves to maximize photosynthesis B Shallow root systems to catch rain quickly C Both: water-storing tissues AND a waxy cuticle D Tall trunks for visibility
    Why: Both succulent water storage (cacti, aloe) AND waxy coverings to reduce evaporation are adaptations to arid environments.
20. 20

    Why does sickle cell disease persist in human populations even though it can be lethal?

    A Mutations cannot be removed by selection B Heterozygous carriers are protected from malaria C It only affects men D It does not affect reproduction
    Why: Heterozygous advantage. People with one sickle cell allele are partially protected from malaria. In malarial regions, that benefit outweighs the cost of homozygous-recessive offspring with the disease, so the recessive allele stays at high frequency.