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Week 16 · Final study guide

Final Exam — Study Guide

Introduction to Biology Free sample edition

Coverage — what the final covers

The final is cumulative: its questions reach all eight course objectives, across the fifteen teaching weeks. It is given in Week 16, the finals week, which has no new material. The exam has 40 questions, and every question counts the same. Thirty are multiple choice with one best answer, five ask you to select every choice that fits, and five are true/false statements. There is no time limit, and you get one attempt. It opens in Week 16, in Canvas, when your instructor sets it to open.

The questions were drawn from the course's question bank, and every objective appears at least once. The draw leans hard on the second half of the term. Here is what this form actually contains:

The final's 40 questions by the week whose material each question comes from, with the objectives those questions assess
Week Topic Questions Objectives assessed
7 Photosynthesis 1 Objective 4 (1)
9 The cell cycle and mitosis 6 Objective 5 (5), Objective 3 (1)
10 Meiosis and sexual reproduction 4 Objective 5 (3), Objective 1 (1)
11 Mendelian genetics 5 Objective 6 (4), Objective 5 (1)
12 Patterns of inheritance 6 Objective 6 (5), Objective 5 (1)
13 DNA structure and replication 7 Objective 7 (5), Objective 2 (2)
14 Gene expression 4 Objective 7 (4)
15 Gene regulation, mutation, and biotechnology 7 Objective 8 (6), Objective 7 (1)
The final's eight objectives, the weeks that teach each one, and the number of the exam's 40 questions on each
Objective What you do Weeks Questions on this exam
Objective 1 Describe the practice of science and evolution as biology's unifying framework 1 1
Objective 2 Explain the chemistry of life and relate each macromolecule's structure to its function 2, 3 2
Objective 3 Compare cell types, relate organelles to their jobs, and explain membrane transport and cell size 4 1
Objective 4 Explain energy, enzymes, respiration, and photosynthesis as ordered, located processes 5, 6, 7 1
Objective 5 Describe the cell cycle, mitosis, and meiosis, and how variation arises 9, 10 10
Objective 6 Predict the outcomes of genetic crosses as probabilities 11, 12 9
Objective 7 Explain DNA's structure and replication and trace gene expression 13, 14 10
Objective 8 Describe gene regulation, classify mutations, and explain the biotechnology tools 15 6

That is 39 of 40 questions from Weeks 9–15 and one from Week 7. Cell division (10 questions), inheritance (9), and DNA with gene expression (10) carry 29 of the 40 between them, so put most of your review there. The Week 1–7 ideas still earn their place: five questions assess Objective 1 through Objective 4, four of them inside a later week's material, and structure determines function runs through nearly everything.

Topic-by-topic review

Each unit gives the idea in plain words first, then the course's exact definitions, then the mistakes students make most often and the cure for each. The "deeper review" line tells you where to look in that week's materials. Units 4–10 carry the weight of the exam, so they get the most space.

Unit 1 — The science of biology and the chemistry of life (Weeks 1, 2, and 3)

  • Key idea. Biologists decide what is true by testing, and life runs on a few kinds of molecules whose shapes decide their jobs.
  • What counts as alive. The characteristics of life are the seven properties biologists use together: order, energy processing, growth and development, reproduction, response to the environment, regulation and homeostasis, and evolutionary adaptation. Something counts as alive only when it shows the whole set.
  • Levels of organization, smallest to largest: atom, molecule, organelle, cell, tissue, organ, organ system, organism, population, community, ecosystem, and biosphere. An emergent property appears at one level but not in its separate parts.
  • The controlled experiment. The independent variable is the factor the experimenter deliberately changes; the dependent variable is the result the experimenter measures. The control group is the no-treatment baseline. A confound is a second, unplanned difference between the groups. Evidence supports or fails to support a hypothesis; it never proves it.
  • Hypothesis and theory. A hypothesis is a proposed explanation that can be tested and must be falsifiable. A theory is a broad explanation backed by a large body of repeated tests and observations, the opposite of a hunch. Evolution is change in the heritable traits of a population over generations, the unifying framework of biology.
  • Bonds. A covalent bond shares a pair of electrons. An ionic bond forms when one atom transfers an electron and the charged ions attract. A hydrogen bond is a weak attraction between a slightly positive hydrogen and a slightly negative atom on another molecule. One is weak, but many together are powerful, which is what holds DNA's two strands together.
  • pH. pH measures hydrogen-ion concentration on an inverse logarithmic scale from 0 to 14, where 7 is neutral, a lower number means more hydrogen ions, and each whole unit is a tenfold change. Count the steps, then raise ten to that power. A buffer resists a change in pH; it never prevents one.
  • The four macromolecules. Carbohydrates are built from monosaccharides, such as glucose. Lipids are not polymers; a triglyceride is one glycerol and three fatty acids. Proteins are built from amino acids, 20 common kinds. Nucleic acids are built from nucleotides, each a sugar, a phosphate, and a base. Dehydration synthesis builds by removing a water molecule; hydrolysis breaks by adding one. DNA carries deoxyribose and thymine; RNA carries ribose and uses uracil where DNA uses thymine.
  • Predictable mistakes → cures. Calling a theory a guess: it is the best-supported idea in science. Swapping the independent and dependent variables: you change the independent; the result depends on it. Reading pH as a ruler: pH 4 against pH 7 is three steps, 10³ = 1,000 times more hydrogen ions. Putting thymine in RNA: RNA uses uracil.
  • Deeper review: the Week 1, Week 2, and Week 3 chapters and slides, and the Week 8 review module.

Unit 2 — The cell (Week 4)

  • Key idea. The cell is the unit of life; it controls what crosses its border, and it has to stay small.
  • Two kinds of cell. A prokaryotic cell has no nucleus and no membrane-bound organelles, and its DNA sits in the nucleoid; it is typically about 0.1 to 5.0 μm across. A eukaryotic cell has a true nucleus and membrane-bound organelles and is typically about 10 to 100 μm across. Every cell has a plasma membrane, cytoplasm, DNA, and ribosomes.
  • Organelles as structure to function. The nucleus holds the DNA and directs the making of proteins. The ribosome builds proteins. The rough endoplasmic reticulum makes and folds proteins for export; the Golgi apparatus modifies, sorts, and ships them. The mitochondrion makes ATP, and its folded cristae add surface. The chloroplast carries out photosynthesis. Plant cells have both mitochondria and chloroplasts. The cell wall supports plants, fungi, and bacteria; animal cells have none.
  • Crossing the membrane. Passive transport moves a substance down its gradient with no energy spent. Osmosis is the diffusion of water toward the side with more dissolved solute; it moves water, not the solute. Read tonicity from the cell's point of view: in a hypotonic solution water moves in, in a hypertonic solution water moves out, and in an isotonic solution there is no net change. Active transport moves a substance against its gradient with a pump paid for with ATP.
  • Why cells stay small. The surface-area-to-volume ratio falls as a cell grows, because surface area grows as the square and volume as the cube. For a cube of side s, surface area = 6s², volume = s³, and the ratio = 6 ÷ s.
  • Predictable mistakes → cures. Giving animal cells a wall: only plants, fungi, and bacteria have one. Saying osmosis moves the salt: it moves water. Flipping hypertonic and hypotonic: the reference is the inside of the cell. Writing 54:27 or dividing backwards: simplify to 2:1.
  • Deeper review: the Week 4 chapter and the cube-cell table; Week 9 brings the nucleus and the cell wall back.

Unit 3 — Energy, respiration, and photosynthesis (Weeks 5, 6, and 7, with Week 8's habit)

  • Key idea. A cell never makes energy; it captures and transfers it, in an ordered chain of stages, each in its own place.
  • Energy and enzymes. The first law of thermodynamics: energy is never created or destroyed, so a cell captures and transfers it. ATP is the cell's energy currency, adenosine with three phosphates; ADP is the spent form with two. An enzyme is a protein that lowers the activation energy, comes out unchanged, and is reused. Heat far past the optimum can denature an enzyme for good, as boiling does to the catalase in the Week 5 lab; cold only slows it.
  • Cellular respiration, in order and in place. Glycolysis (cytoplasm) → pyruvate oxidation (mitochondrion) → citric acid cycle (mitochondrial matrix) → electron transport chain (inner mitochondrial membrane). Glycolysis nets 2 ATP and 2 NADH per glucose and uses no oxygen. The electron transport chain makes the most ATP, and oxygen is the final electron acceptor, joining hydrogen to form water. Fermentation is a low-energy backup that keeps glycolysis and its 2 ATP running.
  • Photosynthesis, in order and in place. The light-dependent reactions run in the thylakoid membrane: chlorophyll absorbs light, water is split to release oxygen, and ATP and NADPH are made. The Calvin cycle runs in the stroma and spends that ATP and NADPH to build the three-carbon sugar G3P. The oxygen a plant releases comes from water; the carbon in its sugar comes from carbon dioxide.
  • The order-and-location habit (Week 8). For any process, name the stages in the order they happen and the compartment where each one runs, before adding any other detail. The second half of the course leans on this habit for mitosis, meiosis, replication, and gene expression.
  • Predictable mistakes → cures. "Cellular respiration is breathing": it is chemistry inside cells. "Plants photosynthesize instead of respiring": they do both. Placing the citric acid cycle in the cytoplasm: it runs in the matrix. Swapping thylakoid and stroma: the light reactions are in the thylakoid membrane, the Calvin cycle in the stroma.
  • Deeper review: the Week 5, 6, and 7 chapters and the Week 8 order-and-location slides.

Unit 4 — The cell cycle and mitosis (Week 9)

  • Key idea. One cell becomes two identical cells, in a fixed order, and cancer is division without the brakes.
  • The loop. The cell cycle is interphase (G1, S, and G2) followed by the M phase, which is mitosis plus cytokinesis. In the S phase the cell copies its DNA, so afterward each chromosome is two identical sister chromatids joined at the centromere. The order is a fact: G1 → S → G2 → M. Most of a cell's life is spent in interphase.
  • Chromosome or chromatid. A chromosome is one long DNA molecule with its packing proteins; after the S phase it is made of two sister chromatids, and it still counts as one chromosome. After anaphase each separated chromatid counts as a chromosome in its own right.
  • Mitosis in order. Prophase: the chromosomes condense, the nuclear envelope breaks down, and the spindle forms; this course counts prometaphase as its end. Metaphase: the chromosomes line up single file across the middle. Anaphase: the sister chromatids separate and move to opposite poles. Telophase: two new nuclear envelopes form. Then cytokinesis: an animal cell pinches in two at a cleavage furrow, and a plant cell, which has a cell wall, builds a cell plate.
  • What mitosis is for. Growth, repair, replacement, and asexual reproduction. Every time, it makes two identical diploid daughter cells.
  • The brakes. A checkpoint is a point where the cell checks that conditions are right before moving on. A proto-oncogene pushes the cycle forward; mutated, it becomes an oncogene, an accelerator stuck down. A tumor-suppressor gene is a brake. The tumor suppressor p53 detects damaged DNA and either pauses the cycle for repair or triggers apoptosis, programmed cell death.
  • The mitotic index is the percent of counted cells that are in mitosis: (cells in mitosis ÷ total cells counted) × 100. The course's illustrative onion root tip count gives 20 of 100 cells, a 20% index, about one cell in five.
  • Predictable mistakes → cures. "DNA is copied in mitosis": it is copied in the S phase, before mitosis. Calling the X shape two chromosomes: it is one chromosome made of two chromatids. Dividing by the interphase count: the denominator is always the total counted. Reporting the interphase share as the index: the index counts only the cells in mitosis.
  • Deeper review: the Week 9 chapter, the phase slides, and the onion-root-tip lab.

Unit 5 — Meiosis and sexual reproduction (Week 10)

  • Key idea. A body makes egg and sperm cells with half the chromosomes, and no two of them are quite the same.
  • Sets of chromosomes. A diploid cell carries two full sets, written 2n; a human body cell has 46. A haploid cell carries one complete set, written n; a human gamete has 23. Homologous chromosomes are a matched pair, one from each parent, carrying the same genes in the same order, possibly as different versions. Sister chromatids are two identical copies of one chromosome.
  • Halve, then restore. Meiosis turns one diploid cell into four genetically different haploid cells after a single round of DNA copying. Fertilization restores the diploid number: 23 + 23 = 46.
  • Two divisions, in order. Meiosis I is the reductional division: homologous chromosomes pair up (synapsis) and then separate, leaving two haploid cells whose chromosomes are still doubled. Meiosis II is the equational division: sister chromatids separate, leaving four haploid cells.
  • Two sources of variation. Crossing over swaps matching segments between nonsister chromatids in prophase I, making new combinations within a chromosome. Independent assortment is the random, independent way each pair lines up in metaphase I, making new combinations between chromosomes. Random fertilization multiplies both.
  • The 2ⁿ count. From independent assortment alone, a cell with n chromosome pairs makes 2ⁿ genetically different gametes. For a human, 2²³ = 8,388,608, a floor that crossing over raises without limit.
  • Mitosis against meiosis. One division against two; two cells against four; diploid against haploid; identical against unique; homologs never pair against homologs pair; growth and repair against gametes. Variation is the raw material natural selection acts on.
  • Models are models. A paper chromosome is a classroom model, simple enough to hold in one hand; it teaches the principle and does not describe every real case.
  • Predictable mistakes → cures. "Meiosis I separates sister chromatids": I separates homologs; II separates sisters. "DNA is copied between meiosis I and II": it is copied once, before meiosis I. Giving the gamete count as 23 or 46: each pair doubles the count, so it is 2²³. "Haploid means half a chromosome": it means one complete set.
  • Deeper review: the Week 10 chapter, the mitosis-against-meiosis table, and the paper-model lab.

Unit 6 — Mendelian genetics (Week 11)

  • Key idea. Given the parents, you can predict the odds of each kind of offspring before any are born.
  • The vocabulary. A gene is a stretch of DNA that carries the instructions for a trait; an allele is one version of it. A dominant allele shows whenever it is present (capital letter); a recessive allele shows only when it is the only version present (lowercase). The genotype is the pair of alleles; the phenotype is the trait shown. Homozygous means two matching alleles; heterozygous means two different ones. Dominant does not mean more common.
  • Mendel, placed factually. Gregor Mendel (1822–1884) crossed garden peas and published Experiments in Plant Hybridization in 1866. His F2 seeds came out about 3 to 1; the 3:1 ratio is the fact to keep.
  • Two laws. The law of segregation: each parent passes exactly one allele of each gene to each offspring. The law of independent assortment: alleles of different genes go into gametes independently, because each chromosome pair lines up at random in meiosis I.
  • Two probability rules. The product rule: for two independent events both happening, multiply. The sum rule: for either of two outcomes that cannot happen together, add.
  • The canonical crosses. Tt × Tt gives genotypes 1:2:1 and phenotypes 3:1. A test cross with tt tells TT (all offspring dominant) from Tt (offspring 1:1). TtYy × TtYy fills 16 boxes and gives 9:3:3:1: both dominant 9⁄16, each mixed class 3⁄16, both recessive 1⁄16.
  • Odds, not promises. A Punnett square gives odds over many offspring, never a promise in one family. Each child is a separate event.
  • Predictable mistakes → cures. Giving 1:2:1 as the phenotype ratio: that is the genotype ratio. Saying each parent passes both alleles: one each, by segregation. Expecting exactly 3:1 in four children: a probability shows only over many offspring. Mislabeling the dihybrid classes: 9 is both dominant, 1 is both recessive, and the 3s are mixed.
  • Deeper review: the Week 11 chapter and the coin-toss lab.

Unit 7 — Patterns of inheritance (Week 12)

  • Key idea. The cross mechanics stay the same; only the rule for what a heterozygote shows changes.
  • Incomplete dominance against codominance. In incomplete dominance the heterozygote is a blend, as red × white snapdragons give pink. The alleles are written R and W so neither looks dominant, and RW × RW gives 1 red : 2 pink : 1 white. In codominance both alleles are fully expressed at once, side by side, as in the AB blood type. The tell: a blend, or both at once?
  • Multiple alleles. The ABO blood group has three alleles, Iᴬ, Iᴮ, and i. Iᴬ and Iᴮ are codominant with each other, and i is recessive to both. Three alleles make six genotypes and four blood types. Type O is ii, common because the i allele is common, not because it is dominant.
  • X-linked recessive inheritance. A male carries one X and one Y, so he is hemizygous for every X-linked gene: one recessive allele on his X shows. A female needs two. A carrier carries one recessive allele and does not show the trait; for an X-linked trait, only a female can be a carrier. A son's X comes from his mother. In the course's carrier cross, XᴬXᵃ × XᴬY, half of the sons are affected, no daughters are affected, and 1⁄4 of all the children are affected, every one a son.
  • Linked genes. Genes close together on one chromosome tend to be passed on together, so they bend the 9:3:3:1. Crossing over can separate them, more often the farther apart they sit.
  • Pedigrees and the two decisions. Squares are males, circles are females, shaded symbols show the trait, and Roman numerals number the generations. Decision one: two unaffected parents with an affected child means recessive. Decision two: a trait far more common in males, passed from carrier mothers to sons, points to X-linked.
  • Predictable mistakes → cures. Blurring incomplete dominance and codominance: pink is a blend; A and B side by side is both. "A man can be a carrier": with one X he is affected or not. "The affected son got it from his father": a son's X comes from his mother. Reading a pedigree by shading alone: run the two decisions in order.
  • Deeper review: the Week 12 chapter and the Blood-Type & Pedigree Detective lab.

Unit 8 — DNA structure and replication (Week 13)

  • Key idea. DNA is a twisted ladder whose pairing rule lets one strand rebuild the other almost perfectly.
  • The double helix. The rails are the sugar-phosphate backbone; the rungs are base pairs joined by hydrogen bonds. Adenine pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. Every rung joins a purine (adenine or guanine, double ring) to a pyrimidine (cytosine or thymine, single ring), which keeps the width even.
  • Direction and partners. The strands are antiparallel: one runs 5′ to 3′ and its partner 3′ to 5′. They are complementary strands, matching partners, not identical copies, so knowing one strand tells you the other.
  • Chargaff's rules. In DNA the percent of adenine equals the percent of thymine, and the percent of guanine equals the percent of cytosine. Find the partner first, subtract the pair from 100, then split the rest evenly.
  • The history, in order. Griffith (1928) discovered transformation. Avery, MacLeod, and McCarty (1944) showed the transforming substance is DNA. Chargaff (1950) reported his base ratios. Hershey and Chase (1952) used labeled bacteriophages to confirm that the genetic material is DNA, not protein. Watson and Crick (1953) built the double helix on Franklin's and Wilkins's X-ray diffraction work.
  • Semiconservative replication. The helix unzips, each original strand serves as the pattern for a new partner, and every copy ends up half old and half new. Meselson and Stahl (1958) ruled out the conservative and dispersive models with heavy and light nitrogen.
  • The three machines, in order. Helicase unzips the helix by breaking the hydrogen bonds; DNA polymerase adds complementary nucleotides and proofreads; DNA ligase seals the backbone.
  • Predictable mistakes → cures. "A pairs with G": A pairs with T, and G with C. Setting %C equal to %A: cytosine matches guanine. "Polymerase unzips the helix": helicase unzips. Calling the two strands identical: they are complementary.
  • Deeper review: the Week 13 chapter and the strawberry DNA lab.

Unit 9 — Gene expression (Week 14)

  • Key idea. A cell copies one gene at a time into a message and reads the message into a protein.
  • The central dogma, in order and in place. DNA → (transcription, in the nucleus) → mRNA → (translation, in the cytoplasm at a ribosome) → protein. Replication copies the whole archive once per division; transcription copies one gene whenever the cell needs it.
  • Transcription. RNA polymerase reads the template strand from its 3′ end to its 5′ end and builds a complementary mRNA from 5′ to 3′: DNA A → mRNA U, T → A, G → C, C → G. The mRNA matches the coding strand except that it carries U where the coding strand carries T. An mRNA never carries a T.
  • The genetic code. Each codon is three bases on the mRNA. There are 64 codons: 61 code for amino acids and 3 are stop codons, UAA, UAG, and UGA. AUG is the start codon; it codes for methionine and sets the reading frame. Most amino acids have more than one codon, the redundancy of the genetic code. You read codons from a supplied table.
  • Translation. The ribosome reads the mRNA one codon at a time from AUG. A tRNA carries one amino acid and an anticodon that pairs with the codon; the codon is on the mRNA, and the anticodon is on the tRNA. At a stop codon, a release factor lets the finished polypeptide go.
  • One base can matter. In the beta-globin gene, GAG (glutamic acid, Glu) becomes GUG (valine, Val) in sickle cell disease: one base, one amino acid.
  • Predictable mistakes → cures. Writing a T into the mRNA: RNA uses U. Swapping transcription and translation: write the message in the nucleus, read it in the cytoplasm. Reading codons from anywhere: start at AUG and read in threes. Putting the anticodon on the mRNA: it is on the tRNA.
  • Deeper review: the Week 14 chapter and the Transcribe & Translate a Gene lab.

Unit 10 — Gene regulation, mutation, and biotechnology (Week 15)

  • Key idea. Every cell carries the same DNA but switches on different genes, a typo can change a protein, and people can now copy, sort, and edit DNA.
  • Gene regulation. Gene regulation is a cell's control over which genes are switched on and how much product each makes; it saves energy and lets cell types specialize. The lac operon is the classroom model: with no lactose, a repressor sits on the DNA and blocks the lactose-digesting genes; when lactose arrives, allolactose pulls the repressor off and the genes turn on. Full expression also needs glucose to be low.
  • Mutation. A mutation is a change in the DNA sequence, the ultimate source of new genetic variation. A substitution swaps one base: silent if the amino acid stays the same, missense if a different amino acid results, nonsense if the codon becomes a stop. A frameshift mutation is an insertion or deletion, not in a multiple of three, that shifts every codon after it. Effects range from neutral to harmful to beneficial.
  • PCR copies. Each round runs denature, anneal, extend, with a heat-stable polymerase from Thermus aquaticus.
  • A gel sorts. In gel electrophoresis negatively charged DNA runs toward the positive end, and smaller fragments travel farther. In DNA profiling, a band that differs rules a person out more firmly than a matching pattern rules them in.
  • Cut and paste, and edit. Restriction enzymes cut DNA at specific sequences, ligase joins the pieces, and a plasmid carries the new gene into a cell, as when bacteria make human insulin. In CRISPR-Cas9, a guide RNA is made to match the target DNA sequence; it leads the Cas9 protein to that spot, where Cas9 cuts the DNA.
  • The ethics, as questions. Somatic editing changes only the person treated; germline editing changes reproductive cells or an embryo, so the change can pass to future generations. The case for editing is preventing devastating heritable disease. The case for caution includes off-target cuts, the consent of future generations, therapy sliding into enhancement, and who gets access. The course gives no verdict.
  • Predictable mistakes → cures. "All mutations are harmful": effects range from neutral to beneficial. Swapping missense and nonsense: a different amino acid against a stop. "Bigger fragments travel farther": smaller ones do. "PCR and a gel are the same thing": PCR copies; a gel sorts.
  • Deeper review: the Week 15 chapter and the virtual-gel lab.

Representative practice

These are fresh variants, not the exam's questions. Every dataset here is illustrative, constructed for this guide, unless it names a course dataset. Work each one, then check it.

Worked example 1 — seedlings, salt, and soil (Units 1 and 2)

An illustrative garden test asks whether watering radish seedlings with salty water changes how tall they grow. Three plain-water pots reach 6, 7, and 8 cm; three salty-water pots reach 2, 3, and 4 cm.

  1. Averages: 6 + 7 + 8 = 21, and 21 ÷ 3 = 7 cm; 2 + 3 + 4 = 9, and 9 ÷ 3 = 3 cm.
  2. Gap: 7 − 3 = 4 cm, and 4 ÷ 7 ≈ 0.57, so the salty pots grew about 57% less.
  3. Variables: the independent variable is plain versus salty water; the dependent variable is seedling height; the plain-water pots are the control group.
  4. The cell's view: salty water is hypertonic to the root cells, so water moves out of them.
  5. A soil comparison: an illustrative soil at about pH 5 against one at about pH 8 is three steps, so 10³ = 1,000 times more hydrogen ions in the pH 5 soil.

Why it matters: the evidence supports the hypothesis without proving it, and a cell-level rule explains a whole-plant result.

Worked example 2 — one carbon atom's trip (Unit 3)

Follow one carbon atom from the air into a sandwich and back out of you, naming each stage and its place.

  1. Into the plant: carbon dioxide enters a wheat leaf, and the Calvin cycle in the stroma fixes it into G3P, using ATP and NADPH from the light-dependent reactions in the thylakoid membrane.
  2. Turn count: three turns export one G3P, and two G3P make one glucose. Twelve turns fix 12 carbon dioxide molecules: 12 ÷ 3 = 4 G3P, and 4 ÷ 2 = 2 glucose.
  3. Into your cell: the glucose is split in glycolysis in the cytoplasm, netting 2 ATP.
  4. Out again: pyruvate oxidation in the mitochondrion and the citric acid cycle in the matrix release the carbon as carbon dioxide. The electron transport chain on the inner membrane makes the most ATP.

Why it matters: the order-and-location habit turns two long pathways into two short, checkable chains.

Worked example 3 — a mitotic index from a fresh count (Unit 4)

An illustrative microscope slide of a growing bean root tip is scored: 340 cells in interphase, 28 in prophase, 14 in metaphase, 7 in anaphase, and 11 in telophase.

  1. Total: 340 + 28 + 14 + 7 + 11 = 400 cells.
  2. In mitosis: 28 + 14 + 7 + 11 = 60 cells.
  3. Index: (60 ÷ 400) × 100 = 15%, so about 15 of every 100 cells are dividing.
  4. Wrong-total trap: 60 ÷ 340 ≈ 0.176 gives about 17.6%, which divides by the interphase count instead of the total.
  5. Hours on a 24-hour cycle: mitosis ≈ 0.15 × 24 = 3.6 hours, and interphase ≈ 0.85 × 24 = 20.4 hours; 3.6 + 20.4 = 24.

Why it matters: the denominator is always every cell you counted.

Worked example 4 — meiosis in a species with 14 chromosomes (Unit 5)

An illustrative plant species has 14 chromosomes in its body cells.

  1. Sets: 2n = 14, so n = 14 ÷ 2 = 7 pairs.
  2. After the S phase: 14 chromosomes, each two chromatids, so 14 × 2 = 28 chromatids.
  3. After meiosis I: 2 cells, each with 7 chromosomes that are still doubled.
  4. After meiosis II: 2 × 2 = 4 haploid cells, each with 7 single chromosomes.
  5. Gametes from independent assortment: 2⁷ = 128 kinds.
  6. Random fertilization: two such parents can pair their gametes 128 × 128 = 16,384 ways, before crossing over adds more.
  7. Mitosis for contrast: a body cell of this species divides into 2 identical cells with 14 chromosomes each.

Why it matters: each pair doubles the count, so the count is 2ⁿ, never n or 2n.

Worked example 5 — rabbit crosses by box and by rule (Unit 6)

In an illustrative rabbit breed, B (black coat) is dominant to b (brown coat), and E (long ears) is dominant to e (short ears).

  1. Test cross: Bb × bb fills the boxes Bb, Bb, bb, bb, so 2 : 2 reduces to 1:1, and P(brown) = 1⁄2.
  2. Monohybrid: Bb × Bb gives 1 BB : 2 Bb : 1 bb, so P(black) = 3⁄4. Among 48 offspring, expect 48 × 3⁄4 = 36 black and 48 × 1⁄4 = 12 brown.
  3. Three in a row: P(three black kits in a row) = 3⁄4 × 3⁄4 × 3⁄4 = 27⁄64 ≈ 0.42, so a litter of three that is all black is common.
  4. Dihybrid: BbEe × BbEe gives 9 : 3 : 3 : 1. Among 160 offspring, expect 160 × 9⁄16 = 90 black with long ears, 30 black with short ears, 30 brown with long ears, and 160 × 1⁄16 = 10 brown with short ears.
  5. Product rule check: P(brown with long ears) = 1⁄4 × 3⁄4 = 3⁄16.

Why it matters: the boxes and the product rule must agree, and a ratio is odds over many offspring.

Worked example 6 — blood types, a carrier cross, and a family chart (Unit 7)

  1. ABO: a type AB parent (IᴬIᴮ) and a type O parent (ii) fill the boxes Iᴬi, Iᴬi, Iᴮi, Iᴮi. P(type A) = 1⁄2, P(type B) = 1⁄2, and P(type AB) = P(type O) = 0. No child shows either parent's type.
  2. Two type O parents: ii × ii gives ii in every box, so every child is type O.
  3. X-linked: a carrier mother (XᴬXᵃ) and an affected father (XᵃY) fill the boxes XᴬXᵃ (carrier daughter), XᵃXᵃ (affected daughter), XᴬY (unaffected son), and XᵃY (affected son). Half of the daughters and half of the sons are affected, so 2 of 4 boxes, or 1⁄2 of all children.
  4. A family chart: in generation I, an unaffected couple, I‑1 and I‑2. In generation II, two affected sons and one unaffected daughter. Decision one: unaffected parents with affected children, so recessive. Decision two: only sons are affected, consistent with X-linked recessive, and I‑2 would then be an obligate carrier.

Why it matters: a daughter can show an X-linked recessive trait only when her father shows it too.

Worked example 7 — base percentages and a complement (Unit 8)

  1. Chargaff: an illustrative DNA sample is 18% thymine. Adenine matches thymine, so %A = 18%. Then A + T = 18 + 18 = 36%, so G + C = 100 − 36 = 64%, and 64 ÷ 2 = 32% each. Check: 18 + 18 + 32 + 32 = 100.
  2. Complement: the strand 5′-CTTAGC-3′ pairs with 3′-GAATCG-5′.
  3. Hydrogen bonds: that stretch has 3 A–T pairs and 3 G–C pairs, so 3 × 2 + 3 × 3 = 6 + 9 = 15 hydrogen bonds.
  4. Semiconservative count: one helix copied three times gives 2 × 2 × 2 = 8 helices. Only 2 of them still carry an original strand, so 2 ÷ 8 = 1⁄4.

Why it matters: one base's percent fixes the other three, and one strand fixes its partner.

Worked example 8 — a model gene from template to protein (Unit 9)

A model gene's template strand reads 3′-TAC CTC CGG AAA GGA ATC-5′. Codon key: AUG = Met (start); GAG = Glu; GCC = Ala; UUU = Phe; CCU = Pro; UAA, UAG, UGA = stop.

  1. Pair each base: TAC → AUG, CTC → GAG, CGG → GCC, AAA → UUU, GGA → CCU, ATC → UAG.
  2. mRNA: 5′-AUG GAG GCC UUU CCU UAG-3′, with no T anywhere.
  3. Coding strand: 5′-ATG GAG GCC TTT CCT TAG-3′, the mRNA with T in place of U.
  4. Count: 18 bases ÷ 3 = 6 codons, and 6 − 1 stop = 5 amino acids.
  5. Protein: Met–Glu–Ala–Phe–Pro, then stop.
  6. One anticodon: the tRNA that reads GAG carries the anticodon 3′-CUC-5′.

Why it matters: the template fixes the mRNA, and the mRNA read in frame from AUG fixes the protein.

Worked example 9 — sorting changes and reading a gel (Unit 10)

Use the mRNA from Worked example 8, 5′-AUG GAG GCC UUU CCU UAG-3′. Extra key: GCU = Ala; GUG = Val.

  1. Silent: GCC → GCU still codes for Ala, so the protein stays Met–Glu–Ala–Phe–Pro.
  2. Missense: GAG → GUG swaps Glu for Val, giving Met–Val–Ala–Phe–Pro.
  3. Nonsense: GAG → UAG makes an early stop, so the chain is Met alone: 1 amino acid instead of 5.
  4. Frameshift: deleting the first base after AUG leaves 18 − 1 = 17 bases, read as AUG AGG CCU UUC CUU plus 2 leftover bases. Every codon downstream of AUG is regrouped, and the UAG stop no longer sits in the frame.
  5. A crime-lab gel (illustrative): the sample from the scene shows bands at 350, 1,400, and 2,800 bp. Person X shows 700, 1,400, and 5,600 bp, so 1 of 3 bands lines up. Person Y shows 350, 700, and 2,800 bp, so 2 of 3 line up. Person Z shows 350, 1,400, and 2,800 bp, so 3 of 3 line up.
  6. The call: X and Y are each excluded, because one band that differs is enough. Z is not ruled out, but a match is weaker evidence than an exclusion.
  7. Distance: in the scene sample's lane the 350 bp band runs farthest from the wells, and 2,800 ÷ 350 = 8, so the slowest band is 8 times the size of the fastest.

Why it matters: one base can do nothing, swap one amino acid, or end the chain, and one mismatched band rules a person out.

Self-check questions

  1. A lab report says, "Our three trials prove that basil grows taller under a grow lamp." Which word should change? Self-check: "prove" should become "support." Why: evidence supports or fails to support a hypothesis; one small experiment never proves it.
  2. A cell has a nucleoid and no membrane-bound organelles. Which kind of cell is it? Self-check: prokaryotic. Why: a eukaryotic cell has a true nucleus.
  3. Which stage of cellular respiration makes the most ATP, and where does it run? Self-check: the electron transport chain, on the inner mitochondrial membrane. Why: glycolysis nets only 2 ATP per glucose.
  4. In which phase of mitosis do the chromosomes condense and the spindle form? Self-check: prophase. Why: metaphase lines them up, anaphase pulls sisters apart, and telophase rebuilds the envelopes.
  5. What does a mutated proto-oncogene become, and what does it do? Self-check: an oncogene, which pushes the cycle forward too hard. Why: a tumor-suppressor gene is the brake; a proto-oncogene is the accelerator.
  6. Which source of variation makes new combinations within one chromosome? Self-check: crossing over, in prophase I. Why: independent assortment makes new combinations between chromosomes.
  7. An animal's coat shows red hairs and white hairs side by side. Which pattern is that? Self-check: codominance. Why: both alleles are fully expressed side by side; a blend would be incomplete dominance.
  8. Can two type O parents have a type A child? Self-check: no. Why: both parents are ii, so every child is ii.
  9. Which enzyme unzips the double helix, and which one seals the backbone? Self-check: helicase unzips; DNA ligase seals. Why: DNA polymerase adds nucleotides and proofreads between them.
  10. An mRNA written by a chatbot reads AUG GTT. What is wrong? Self-check: it carries T. Why: RNA uses uracil, so no mRNA carries a T.
  11. A detective has a trace of DNA too small to run on a gel. Which tool comes first? Self-check: PCR. Why: PCR copies; the gel then sorts the copies by size.
  12. An edit is made to the DNA of an early embryo. Somatic or germline? Self-check: germline. Why: editing an embryo falls on the germline side, so the change can pass to future generations.

Check yourself — choose one. (a) Which unit in this guide felt least familiar, and which worked example would you redo first? (b) Pick one early habit, such as structure determines function or the order-and-location habit, and explain in two sentences how it changes the way you read one Weeks 9–15 topic. Either choice is a good use of ten minutes.

Study plan

A short countdown sized to a course that meets twice a week. Count backward from the day the final opens in Week 16.

  • Two weeks out: review Units 1–3 in one sitting and redo Worked examples 1 and 2 from scratch. These ideas return inside later questions.
  • Ten days out: review Units 4 and 5. Redo Worked examples 3 and 4 until each step comes with its reason. Cell division carries 10 of the 40 questions.
  • One week out: review Units 6 and 7. Redo Worked examples 5 and 6 without looking, filling every box before you count.
  • Five days out: take the paired practice exam once, closed-book and under exam-like conditions, then sort every miss by week. Remember that it leans on Weeks 1–7 far more than the final does.
  • Four days out: review Units 8–10 and redo Worked examples 7, 8, and 9. Weeks 13 and 15 carry 7 questions each.
  • Three days out: run the paired exam-prep tutorial (the copy/paste chatbot tutor, or its no-AI route) on the two units that felt weakest, with at least one from Units 4–10.
  • Two days out: answer the twelve self-check questions cold, then retake the practice exam.
  • The day before: skim the "Predictable mistakes → cures" lines in every unit and watch one video from the list below. Sleep.

Use the exam-prep tutorial and the practice exam for active recall; this guide is for review, and those two are where you rehearse. Rereading alone does less for you than retrieval practice does.

Watch before the exam

These videos come from the course's own weekly readings. Use them to retrieve what you already learned and to connect weeks, not for new material.

Exam format and scoring

The final is scored automatically, and all 40 questions count the same. The questions appear one at a time, and you cannot go back to an earlier question once you move on. You have one attempt and no time limit. AI tools are not permitted on the final.

Test-taking strategies for this material:

  • For any process, say the stages in order and the place each one runs before you choose.
  • For any cross, write the parents' gametes, fill every box, and count before you pick a ratio. Decide first whether the question wants genotypes or phenotypes.
  • For a base percentage, find the partner base first, subtract the pair from 100, then split the rest.
  • For a sequence, scan for a T in any mRNA, start at AUG, and read in threes.
  • For a pair of look-alike terms, name the one word that separates them: chromosome or chromatid, homologs or sisters, blend or both, codon or anticodon, missense or nonsense, copies or sorts.
  • For a model, such as the lac operon or a paper chromosome, remember that it is a classroom model and does not describe every real case.
  • Since you cannot go back, settle each question before you move on.

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