What’s on the Ohio Biology EOC

The exam tests four strands of the Ohio Learning Standards. Roughly equal weight across all four:

• About 70 questions total (mix of multiple choice, drag-and-drop, hot-spot, and short constructed response)
• 2 hours, 1 sitting
• Passing scale score in Ohio: 700+ (proficient), 725+ (accelerated), 740+ (advanced)
• A graphing calculator is allowed but rarely needed
• A periodic table and formula sheet are provided

How to use this guide

There are four strands, then a full reteach of photosynthesis and cellular respiration, then a timed mock EOC. Estimated total study time: 2 hours of focused review (or 4 sessions of 30 min each).

Every section has a quick practice quiz at the end. Use the floating Pomodoro at the bottom-right to time your study sessions. Use the mock EOC test timer at the very end to simulate test conditions.

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Strand 1: Heredity

You have two of each chromosome: one from each parent. Genes on those chromosomes carry instructions for traits. The interactive parts of this strand cover DNA structure, replication, transcription, translation, mutations, and Mendelian genetics.

DNA structure

Below is the actual molecular structure of a short B-form DNA double helix from the Protein Data Bank. Drag to rotate. Notice the double helix, the base pairs holding the two strands together, and the sugar-phosphate backbone running on the outside.

Loading molecule...

Drag to rotate, scroll to zoom

Memorize the base pairing rules

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Base pairing rules

Critical for replication, transcription, and translation

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Per device

📖 Read ✏️ Cloze 🔤 First letter 🎭 Cold recall

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DNA replication walk-through

Replication happens before a cell divides. The double helix unwinds, both strands serve as templates, and DNA polymerase builds a new complementary strand on each. Every daughter cell ends up with one old strand and one new strand. This is called semiconservative replication.

Step 0

The DNA double helix sits coiled.

1

1. Closed double helix

Before replication, DNA is wound into the familiar double helix. Two complementary strands held together by hydrogen bonds between paired bases (A-T, G-C).

2

2. Helicase unwinds

The enzyme helicase (yellow) breaks the hydrogen bonds, separating the strands at the replication fork. Each strand is now a template.

3

3. DNA polymerase adds new bases

DNA polymerase reads each template strand 3' to 5' and adds complementary nucleotides 5' to 3'. A new strand grows on each old strand.

4

4. Two identical daughter helices

You end with two double helices, each containing one parental (old) strand and one new strand. This is called semiconservative replication: half conserved, half new.

↓ scroll through each step. The stage above updates as you go. ↓

Central dogma: DNA → RNA → Protein

flowchart LR
  DNA[DNA<br/>nucleus] -->|Transcription| mRNA[mRNA<br/>nucleus to cytoplasm]
  mRNA -->|Translation| Protein[Protein<br/>ribosome]

• Transcription copies a gene from DNA into mRNA. Happens in the nucleus.
• Translation reads the mRNA in groups of 3 bases (a codon) and assembles amino acids into a protein. Happens at the ribosome.

The genetic code in action

Below is a real human gene fragment. Hover any codon to see which amino acid it codes for.

Start 0-3 Continuing... 42-45

ATGGCGAGCA GAGAGGAACT GGTGAGAATT AGCCAAGAGT TGCAA

Mutations

A mutation is any change in the DNA sequence. Mutations are the raw material for evolution. Four common types:

Mendelian genetics

Gregor Mendel worked out the rules of inheritance with pea plants in the 1860s, decades before anyone knew DNA existed. His three laws still drive every Punnett square you’ll do.

Punnett square: try it yourself

Cross two heterozygous brown-eyed parents. Change either parent’s genotype to see the offspring ratios shift in real time.

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Punnett square: Eye color

Change the parents to see how offspring ratios shift.

Parent 1 Parent 2

Genotype ratio

Phenotype ratio

Pedigrees

A pedigree is a family tree that tracks a trait across generations. The Ohio EOC will give you one and ask whether the trait is dominant, recessive, X-linked, or autosomal.

Heredity practice

Drag to match: genotype → phenotype

M

Drag to match

Self-quiz: heredity

Q

Self-quiz

0 of 5 answered

Reset

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.

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Strand 2: Evolution

Evolution = change in the allele frequencies of a population over time. Natural selection is one of several mechanisms (others: genetic drift, gene flow, mutation, non-random mating). The Ohio EOC focuses on natural selection, evidence for evolution, and reading phylogenetic trees.

The five lines of evidence

Watch natural selection happen: Galápagos finches

This is the textbook story, brought to life. Each finch has a beak depth (the trait under selection). Two seed types fall on the beach:

• Small green seeds any finch can eat (1 calorie)
• Big brown seeds only finches with beak ≥ 10 mm can crack (3 calories)

Each “year” lasts 7 seconds. At the end of the year, finches with fewer than 2 calories starve. Survivors mate and offspring inherit the parent’s beak depth (with mild mutation).

Press ▶ Run, watch the histogram on the right, then click ☀ Trigger drought. During drought the small seeds vanish, so only big-beaked finches eat. Within 3-4 years the mean beak depth shifts noticeably right. End the drought and watch it drift back. This is exactly what Peter and Rosemary Grant observed on Daphne Major in 1977.

F

Galápagos finch evolution

Year 0 · Finches 32 · Mean beak 10.0 mm · Weather normal

▶ Run ☀ Trigger drought Reset

Beak depth distribution

Mean beak depth (mm)

Population

Small seed (any beak, 1 cal)

Big seed (beak ≥ 10 mm, 3 cal)

Need 2 cal/year to survive.

PhET: bunnies through generations

PhET’s classic Natural Selection simulation lets you breed bunnies with different traits and watch which combinations survive different environments. Try the Equator preset, then add a wolf predator and watch which fur color dominates.

Sim by PhET, University of Colorado Boulder

The Galápagos finches

When the medium ground finch population on Daphne Major faced a 1977 drought, only finches with bigger beaks could crack the few large seeds available. The next generation was measurably bigger-beaked. This is natural selection observed in real time, by Peter and Rosemary Grant.

A 0.5 mm shift in just 2 years. Multiply that across millions of years and you get the 13 distinct Darwin’s finch species we see today, each with a beak adapted to a different food source.

Identify a vertebrate (interactive key)

Biologists use dichotomous keys to identify unknown organisms. Each step is a yes/no question that narrows the possibilities. Try this one for the five vertebrate classes.

K

What kind of vertebrate is it?

Click to answer. Each answer narrows the identification.

Step 1 Start over

Phylogenetic trees

A phylogeny shows evolutionary relationships. Tip = present-day species. Internal node = common ancestor. The closer two tips share a common ancestor, the more closely related they are.

flowchart LR
  Vert[Vertebrate ancestor] --> Lamprey
  Vert --> Jawed[Jawed ancestor]
  Jawed --> Shark
  Jawed --> Bony[Bony fish ancestor]
  Bony --> Salmon
  Bony --> Tetra[Tetrapod ancestor]
  Tetra --> Frog
  Tetra --> Amniote[Amniote ancestor]
  Amniote --> Lizard
  Amniote --> Mammal[Mammal ancestor]
  Mammal --> Mouse
  Mammal --> Human

Geologic timeline

Life has been around for about 3.8 billion years. Mass extinctions reset the playing field five times. The most recent (and most relevant for the EOC) is the K-Pg extinction 66 million years ago that ended the dinosaurs.

Hardy-Weinberg equilibrium

When a population is in Hardy-Weinberg equilibrium, allele frequencies don’t change. The conditions are strict (no mutation, no migration, no selection, infinite population, random mating) so it never quite holds in nature. The math gives you a baseline to compare real populations against.

The equation: $p^2 + 2pq + q^2 = 1$

where $p$ = frequency of the dominant allele, $q$ = frequency of the recessive allele, $p^2$ = fraction of homozygous dominant, $2pq$ = fraction of heterozygous, $q^2$ = fraction of homozygous recessive. By definition $p + q = 1$.

Worked example

If $q^2 = 0.16$ (16% of the population is homozygous recessive), then:

• $q = \sqrt{0.16} = 0.4$ (recessive allele frequency)
• $p = 1 - 0.4 = 0.6$ (dominant allele frequency)
• $p^2 = 0.36$ (36% homozygous dominant)
• $2pq = 2(0.6)(0.4) = 0.48$ (48% heterozygous)
• Check: $0.36 + 0.48 + 0.16 = 1.00$ ✓

Evolution practice

Q

Self-quiz

0 of 5 answered

Reset

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.

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Strand 3: Diversity and Interdependence (Ecology)

Ecology is the study of how living things interact with each other and their environment. The EOC tests levels of organization, food webs, energy flow, biogeochemical cycles, biomes, and human impact.

Levels of organization

flowchart LR
  Org[Organism] --> Pop[Population]
  Pop --> Comm[Community]
  Comm --> Eco[Ecosystem]
  Eco --> Bio[Biome]
  Bio --> Bios[Biosphere]

• Organism = one individual
• Population = same species in same area
• Community = all species in same area
• Ecosystem = community + abiotic factors (water, soil, temperature)
• Biome = group of similar ecosystems (e.g., all deserts)
• Biosphere = all life on Earth

Forest food web

Click any species below to see how it’s connected. Producers are at the bottom. Apex predators at the top. Energy flows up the chain.

Energy pyramid (the 10% rule)

Only about 10% of the energy at one trophic level is passed up to the next. The rest is lost as heat (cellular respiration), waste, or never eaten. This is why apex predators are rare.

The biogeochemical cycles

Carbon cycle

Carbon moves through the atmosphere, oceans, organisms, and rocks. Photosynthesis pulls CO₂ out of the air; respiration and combustion put it back.

Nitrogen cycle

Nitrogen is 78% of the atmosphere as N₂, but plants can’t use it directly. Nitrogen-fixing bacteria in soil and root nodules convert N₂ into ammonia (NH₃), which becomes nitrate (NO₃⁻) that plants absorb.

flowchart LR
  N2[N2 atmosphere] -->|Nitrogen-fixing bacteria| NH3[Ammonia NH3]
  NH3 -->|Nitrification| NO3[Nitrate NO3-]
  NO3 -->|Plant uptake| Plants
  Plants -->|Eaten by| Animals
  Animals -->|Death + waste| Decomp[Decomposers]
  Decomp -->|Ammonification| NH3
  NO3 -->|Denitrifying bacteria| N2

Water and phosphorus cycles

• Water cycle: evaporation → condensation → precipitation → runoff/groundwater → back to evaporation. Driven by the sun.
• Phosphorus cycle: unique in that there’s no atmospheric form. Phosphorus moves through rocks → soil → plants → animals → decomposers → soil → eventually back to rocks via geological uplift. Slow.

World biomes

A biome is a major ecosystem type defined by its climate (temperature + rainfall) and characteristic plants. The Ohio EOC focuses on these eight.

Population dynamics

Two growth models you must know:

• Exponential growth (J-curve): unlimited resources, no predators. Bacteria in fresh agar. Real for very short bursts.
• Logistic growth (S-curve): limited resources cause growth to slow as population approaches carrying capacity (K). The realistic model.

Predator-prey: lynx and snowshoe hare

Hudson Bay fur trapping records (1845-1935) showed beautiful predator-prey oscillations. When hares are abundant, lynxes thrive. Lots of lynxes → hares decline. Few hares → lynxes starve. Few lynxes → hares rebound. Cycle.

Symbiosis

Type	Effect on A	Effect on B	Example
Mutualism	+	+	Bee + flower (pollination + nectar)
Commensalism	+	0	Barnacle + whale (ride + nothing)
Parasitism	+	–	Tapeworm + human
Competition	–	–	Two species fighting for same niche

Human impact

Atmospheric CO₂ has gone from ~280 ppm (pre-industrial) to over 420 ppm today, a level not seen in 3 million years.

Ecology practice

Q

Self-quiz

0 of 5 answered

Reset

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.

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Strand 4: Cells

The smallest unit of life. The Ohio EOC tests cell structure, membrane transport, mitosis, meiosis, and a deep understanding of photosynthesis and cellular respiration (the energy pathways).

Cell structure

The 12 organelles you must know

Organelle	Job	Found in
Nucleus	Stores DNA, controls cell	All eukaryotes
Mitochondrion	Makes ATP via cellular respiration	All eukaryotes
Chloroplast	Photosynthesis	Plants, algae only
Ribosome	Makes proteins	All cells
Endoplasmic Reticulum (ER)	Synthesizes proteins (rough) and lipids (smooth)	All eukaryotes
Golgi apparatus	Modifies, packages, ships proteins	All eukaryotes
Lysosome	Digestive enzymes, cleanup	Animals mostly
Vacuole	Storage (HUGE in plants for water)	All eukaryotes
Cell wall	Structural support	Plants, fungi, bacteria
Cell membrane	Selective barrier	All cells
Cytoplasm	Fluid where reactions happen	All cells
Cytoskeleton	Cell shape, organelle transport	All cells

Membrane transport

The cell membrane is selectively permeable. Three kinds of transport:

Mitosis

Mitosis is how somatic (body) cells divide. One cell → two genetically identical daughter cells. Used for growth, repair, and asexual reproduction.

Order these

Shuffle Check

Drag the phases into the correct order

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

Meiosis

Meiosis makes gametes (sperm and eggs). One cell → four genetically UNIQUE haploid cells (half the chromosome number). Two divisions: meiosis I and meiosis II.

flowchart LR
  Cell["1 diploid cell (2n=46)"] -->|Meiosis I| Two["2 haploid cells (n=23) but each chromosome has 2 chromatids"]
  Two -->|Meiosis II| Four["4 unique haploid gametes (n=23)"]

Two key events make every gamete unique:

1. Crossing over (prophase I): homologous chromosomes swap chunks
2. Independent assortment (metaphase I): each chromosome pair lines up randomly

Cell cycle and cancer

The cell cycle has checkpoints that ensure DNA is replicated correctly before division. Cancer is what happens when a cell loses control of those checkpoints and divides uncontrollably.

flowchart LR
  G1[G1: cell grows] --> S[S: DNA replicates]
  S --> G2[G2: cell prepares to divide]
  G2 --> M[M: mitosis]
  M --> G1

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Photosynthesis: full reteach

The Ohio EOC always has at least 3 questions on photosynthesis. Lock this down.

The big equation

$$6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{light}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$$

In words: carbon dioxide + water + light energy → glucose + oxygen.

Where it happens

Inside the chloroplast (only in plants and algae):

• Thylakoid membrane: stage 1, the light-dependent reactions. Captures light energy.
• Stroma: stage 2, the Calvin cycle (light-independent reactions). Builds glucose.

Stage 1: Light reactions

1. Photon hits chlorophyll in Photosystem II, exciting an electron.
2. Electron passes down the electron transport chain, pumping H⁺ into the thylakoid lumen.
3. PSII replaces its lost electron by splitting water (releasing O₂ as waste).
4. Electron arrives at Photosystem I, gets re-energized by another photon.
5. Final destination: NADP⁺ + H⁺ → NADPH (loaded with energy).
6. The H⁺ gradient powers ATP synthase to make ATP via chemiosmosis.

Outputs of light reactions: ATP, NADPH, O₂.

Stage 2: Calvin cycle

Uses the ATP and NADPH from Stage 1 to fix CO₂ into glucose. Three phases:

1. Carbon fixation: RuBisCO attaches CO₂ to RuBP.
2. Reduction: ATP and NADPH convert it into G3P. Some G3P leaves to make glucose.
3. Regeneration: remaining G3P recycled into RuBP.

Stoichiometry: 6 turns of the cycle, 18 ATP, 12 NADPH → 1 glucose.

Photosynthesis energy flow

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Cellular respiration: full reteach

The reverse of photosynthesis. Take glucose, extract its energy as ATP. Happens in mitochondria (and the cytoplasm for stage 1) in all eukaryotes (and the cytoplasm of bacteria/archaea).

The big equation

$$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$$

In words: glucose + oxygen → carbon dioxide + water + energy (ATP).

Notice: this is photosynthesis run backwards. Plants store energy in glucose; respiration releases it.

The three stages

Stage 1: Glycolysis (in cytoplasm)

Glucose (6C) → 2 pyruvate (3C each).

• Inputs: 1 glucose, 2 ATP, 2 NAD⁺
• Outputs: 2 pyruvate, 4 ATP (net 2), 2 NADH
• Doesn’t need oxygen. This is the only stage that anaerobic organisms have.

Stage 2: Krebs cycle / Citric Acid Cycle (in mitochondrial matrix)

Each pyruvate gets converted to acetyl-CoA, then enters the cycle.

• Per glucose (2 pyruvates): 2 ATP, 6 NADH, 2 FADH₂, 4 CO₂
• The CO₂ you exhale comes from here.

Stage 3: Electron Transport Chain (on inner mitochondrial membrane)

NADH and FADH₂ from Stages 1 and 2 dump their electrons into the ETC. Electrons cascade down protein complexes, pumping H⁺ across the inner membrane. The H⁺ flows back through ATP synthase, making ATP. Final electron acceptor: O₂ (forms water).

• Per glucose: ~28-32 ATP from oxidative phosphorylation
• Total ATP per glucose: ~30-32 (varies slightly by cell type)

Cellular respiration energy flow

Mirror of the photosynthesis Sankey. Glucose comes in; ATP and waste come out.

Aerobic vs anaerobic

When oxygen is available, you do all 3 stages → ~32 ATP per glucose.

When oxygen runs out (sprinting, suffocating bacteria), cells skip stages 2-3 and do fermentation instead:

• Lactic acid fermentation (your muscles, some bacteria): glucose → 2 lactic acid + 2 ATP. The “burn” of intense exercise.
• Alcoholic fermentation (yeast): glucose → 2 ethanol + 2 CO₂ + 2 ATP. How beer and bread happen.

Fermentation gives only 2 ATP per glucose vs 32 for full aerobic respiration. Massively less efficient.

Photosynthesis vs respiration: side by side

	Photosynthesis	Cellular respiration
Reactants	CO₂ + H₂O + light	Glucose + O₂
Products	Glucose + O₂	CO₂ + H₂O + ATP
Site	Chloroplast	Mitochondrion
Cells	Plants, algae, some bacteria	All eukaryotes
Energy	Stores energy in glucose	Releases energy from glucose
Electron carrier	NADPH	NADH

They are the same chemistry, run in reverse. Plants do photosynthesis to STORE energy as glucose. All cells (plants and animals) do respiration to RELEASE that energy as ATP.

Cells practice

Q

Self-quiz

0 of 7 answered

Reset

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.

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Mock EOC: timed practice test

This 20-question mock test draws from all four strands. Set the timer for 60 minutes below and treat it like the real exam: no notes, no breaks. After you finish, check your score and revisit any sections where you missed.

⏱

Mock EOC time limit

60-minute time limit. Click Start when you begin.

60:00

Start Reset

Q

Self-quiz

0 of 20 answered

Reset

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.

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Cheat sheets

Heredity at a glance

Concept	Key fact
DNA pairing	A-T, G-C
RNA pairing	A-U, T-A, G-C, C-G
Codon	3 mRNA bases = 1 amino acid
Start codon	AUG
Stop codons	UAA, UAG, UGA
Total codons	64 (61 amino acid + 3 stop)
Punnett Bb × Bb	1 BB : 2 Bb : 1 bb (3:1 phenotype)
Punnett Bb × bb	1 Bb : 1 bb (1:1)
Mutation types	Silent, missense, nonsense, frameshift

Evolution at a glance

Concept	Key fact
Darwin’s 4 conditions	Variation, heritability, differential survival, differential reproduction
5 lines of evidence	Fossils, anatomy, embryology, biogeography, molecular
Homologous	Same origin, different function (e.g., human arm, whale flipper)
Analogous	Different origin, same function (insect wing, bird wing)
Hardy-Weinberg	p² + 2pq + q² = 1
Speciation	Allopatric (geographic), sympatric (same area)
K-Pg extinction	66 million years ago, ended dinosaurs

Ecology at a glance

Concept	Key fact
10% rule	90% of energy lost between trophic levels
Carrying capacity	Max population sustainable by environment
Mutualism	+ +
Commensalism	+ 0
Parasitism	+ -
Competition	- -
Nitrogen fixation	Bacteria convert N2 → NH3
Ohio’s biome	Temperate deciduous forest

Cells at a glance

Concept	Key fact
Plant-only organelle	Chloroplast, large vacuole, cell wall
ATP factory	Mitochondrion
Photosynthesis equation	6 CO2 + 6 H2O → C6H12O6 + 6 O2
Respiration equation	C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP
ATP per glucose (aerobic)	~32
ATP per glucose (fermentation)	2
Mitosis order	PMATC (Please Make All Teachers Come)
Meiosis output	4 unique haploid cells

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Last-minute review (the night before)

• Get 8 hours of sleep (your brain consolidates memories during sleep)
• Eat breakfast (your brain runs on glucose; cellular respiration is real)
• Bring 2 sharpened pencils, your calculator (if you have one), and a water bottle
• Read every question carefully before answering. The EOC loves “EXCEPT” and “NOT” trick questions.
• For diagram questions, read the LABELS before reading the question
• Don’t change answers unless you’re certain you misread something. First instincts are usually right.
• If you have time at the end, review your “marked” questions, but don’t second-guess everything

You’ve got this. Go get that 740+.

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