BIO/100 · Formula & Notes Sheet — Expanded Study Edition

20 chapters · tick ✓ as you go

Unit One · Chapters 01–04

Cells & Chemistry of Life

Microscopes, molecules, membranes — and the two engines that power every living thing.

Unit I · Cells & Chemistry

Cells & Microscopy

Everything alive is cells. Measure one correctly and the rest of biology scales from there.

EQ 01·AMagnification

M = image size ÷ actual size

Rearrange: actual = image ÷ M. Units: 1 mm = 1 000 µm = 10⁶ nm — always convert first.

EQ 01·BSA : V constraint

SA ∝ L² · V ∝ L³ ⇒ SA/V falls as a cell grows

Why cells stay microscopic: diffusion can't service a growing volume. Big organisms add cells, not cell size.

PLATE Ithe generalized animal cell

Field Notes

Cell theory (1839–55): all organisms are made of cells; the cell is the smallest unit of life; all cells arise from pre-existing cells.
Prokaryotes — no nucleus, circular DNA, 1–10 µm (bacteria, archaea). Eukaryotes — nucleus + membrane organelles, 10–100 µm.
Power pairs: nucleus = archive · ribosomes = protein factories · mitochondria = ATP by respiration.
Endomembrane route: rough ER → vesicle → Golgi (modify & pack) → vesicle → membrane or outside.
Plant extras: cell wall (cellulose), chloroplasts, one large central vacuole for turgor pressure.
Lysosomes digest; cytoskeleton (microtubules, actin) gives shape and moves cargo.
Limits: light microscope ≈ ×1 500, resolution ≈ 200 nm; electron microscopes resolve ≈ 0.1 nm.

Why are cells so small?

As size grows, volume outpaces surface area (L³ vs L²), so diffusion can't supply the interior fast enough.

Resolution of a light microscope? What can't it show?

≈ 200 nm — ribosomes, membranes and viruses are below that limit; use electron microscopy.

⚠ EXAM TRAPConvert units before dividing: 2 mm image of a 100 µm cell is 2 000 µm ÷ 100 µm = ×20, not ×0.02.

🧠 MNEMONICmilli → micro → nano: ×1 000 at each step. “M-M-N: Multiply by a thousaNd.”

Unit I · Cells & Chemistry

Biochemistry & Enzymes

Water, four families of molecules, and the catalysts that make life fast enough.

EQ 02·ApH scale

pH = −log₁₀[H⁺]

pH 7 ⇒ [H⁺] = 10⁻⁷ M. One unit = ×10 change. Blood is buffered to 7.35–7.45 — no negotiation.

EQ 02·BEnzyme rate (extension)

v = V_max[S] ÷ (K_m + [S])

Rate rises with substrate then plateaus when every active site is busy. K_m = [S] at ½V_max; low K_m = tight binding.

Field Notes

Water's toolkit: cohesion & adhesion, high specific heat, superb solvent, ice floats (density anomaly).
Dehydration synthesis builds polymers (−H₂O); hydrolysis breaks them (+H₂O).
Four families: carbohydrates (CH₂O, 1:2:1) · lipids (fats, membranes, steroids) · proteins (20 amino acids) · nucleic acids (DNA, RNA).
Enzymes lower activation energy; unchanged and reusable; named substrate + “-ase”.
Lock-and-key → induced fit: the active site moulds around the substrate.
Optimum ≈ 37 °C in humans; heat & extreme pH denature the 3-D shape → activity lost.
Competitive inhibitors occupy the active site; non-competitive bind elsewhere and distort it.

What happens to a human enzyme at 80 °C?

It denatures — the 3-D shape (and active site) is destroyed, usually irreversibly.

pH 5 vs pH 7 — how different is [H⁺]?

100× more H⁺ at pH 5 (two units lower = 10 × 10).

⚠ EXAM TRAPA pH drop of one unit means H⁺ ×10 (multiplication), not +10. From pH 8 to pH 5 is a ×1 000 increase.

🧠 MNEMONICEnzyme names end in -ase: lactase, lipase, malthase… if it ends in -ase, it's an enzyme.

Unit I · Cells & Chemistry

Membranes & Transport

What crosses, what can't, and the physics deciding where water goes.

EQ 03·AWater potential

ψ = ψ_s + ψ_p

Water moves high ψ → low ψ. Pure water ψ = 0; solutes make ψ_s negative; turgor makes ψ_p positive.

EQ 03·BFick's law (concept)

rate ∝ (SA × ΔC) ÷ distance

Big area + steep gradient + thin barrier = fast exchange. Explains alveoli, villi, gills, root hairs.

PLATE IIplant cells in three solutions

Field Notes

Membrane = fluid mosaic: phospholipid bilayer with proteins, cholesterol, glycoproteins.
Passive (no ATP): simple diffusion (O₂, CO₂), facilitated diffusion via channels/carriers, osmosis (water).
Active transport pumps against the gradient using ATP — e.g. Na⁺/K⁺ pump.
Tonicity: hypotonic → swell (plant: turgid ✓) · isotonic → no net flow · hypertonic → shrink; plant cells plasmolyse.
Animal cells burst (lyse) in pure water; plant cells don't — the wall holds.
Bulk traffic: exocytosis (out) and endocytosis (in — phago-/pinocytosis).
Carrier proteins are specific and saturable — they behave like enzymes.

A cell is placed in hypertonic solution — what happens?

Water leaves by osmosis: animal cells shrivel (crenation); plant membranes pull from the wall (plasmolysis).

Which movements cost ATP?

Active transport and bulk transport (endo-/exocytosis). Diffusion, facilitated diffusion and osmosis are free.

⚠ EXAM TRAPWater moves toward the more concentrated solution (lower ψ). Students flip this constantly.

🧠 MNEMONIC“Water follows salt.” Wherever solute goes, water flows after it.

Unit I · Cells & Chemistry

Bioenergetics — Photosynthesis & Respiration

Two equations that are each other's mirror — the whole carbon–oxygen economy of Earth.

EQ 04·APhotosynthesis

6CO₂ + 6H₂O light · chlorophyll→ C₆H₁₂O₆ + 6O₂

In chloroplasts. The O₂ released comes from split water, not CO₂ — proven with isotope tracers.

EQ 04·BAerobic respiration

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ≈30–32 ATP

Reverse the arrow and you get photosynthesis — inputs of one are outputs of the other.

Table 04·C — The ATP Ledger

Stage	Where	Net yield / glucose
Glycolysis	Cytoplasm	2 ATP + 2 NADH
Pyruvate oxidation	Matrix	2 NADH + 2 CO₂
Krebs cycle ×2	Matrix	2 ATP + 6 NADH + 2 FADH₂
Electron transport	Inner membrane	≈ 26–28 ATP

Field Notes

Chlorophyll a absorbs red (~680 nm) and blue light, reflects green — why leaves look green.
Light reactions (thylakoids): photolysis splits H₂O → O₂; charge up NADPH + ATP.
Calvin cycle (stroma): fixes CO₂ → G3P; each G3P costs 9 ATP + 6 NADPH; two G3P → glucose.
No O₂? Fermentation: lactate in muscle, ethanol + CO₂ in yeast — glycolysis-only, 2 ATP.
Compensation point: photosynthesis = respiration → no net gas exchange (dawn & dusk).
Limiting factors: light, CO₂, temperature — the lowest one caps the rate (Liebig's barrel).
Mnemonic logic: photosynthesis builds (stores energy); respiration splits (releases it).

Where does the O₂ released in photosynthesis come from?

Photolysis of water in the light reactions — not from CO₂.

Net ATP from glycolysis alone?

2 ATP (+ 2 NADH). Four made, two invested = net 2.

⚠ EXAM TRAPThe oxygen plants release comes from H₂O, not CO₂. Classic one-mark giveaway — don't lose it.

🧠 MNEMONICRespiration stages: Glycolysis → link → Krebs → ETC — “Good Kids Eat”.

Unit Two · Chapters 05–08

Continuity — Genetics & DNA

From dividing cells to pedigrees: how information is copied, shuffled, read and occasionally broken.

Unit II · Genetics & DNA

The Cell Cycle & Division

One genome, two strategies: photocopy exactly (mitosis) or shuffle and halve (meiosis).

EQ 05·AIndependent assortment

gamete variety = 2ⁿ ⇒ humans: 2²³ ≈ 8.4 × 10⁶

Per parent — before crossing over and random fertilization. Variation is effectively inexhaustible.

EQ 05·BDivision arithmetic

Mitosis: 2n → 2 × 2n · Meiosis: 2n → 4 × n

Humans: 2n = 46, n = 23. Mitosis for growth & repair; meiosis only in gonads.

PLATE IIIPMAT — mitosis at a glance

Field Notes

Cycle: Interphase G₁ → S (DNA replicates here) → G₂, then division. Division is only ~10% of the time.
PMAT: Prophase (condense) → Metaphase (align at equator) → Anaphase (pull apart) → Telophase (+ cytokinesis).
Checkpoints G₁/S, G₂/M and spindle — cancer is checkpoint failure plus evasion of apoptosis.
Meiosis I separates homologues (reduction); Meiosis II separates chromatids.
Variation engines: crossing over (prophase I) + independent assortment + random fertilization.
Karyotype 2n = 46: 22 autosome pairs + XX/XY; nondisjunction → trisomy (e.g. Down, chr 21).

What separates in meiosis I vs meiosis II?

Meiosis I: homologous chromosomes. Meiosis II: sister chromatids (like mitosis).

When exactly does DNA replicate?

S phase of interphase — before division ever begins, never during it.

⚠ EXAM TRAPCrossing over happens in prophase I of meiosis — not prophase II, not mitosis.

🧠 MNEMONICI Picked My Apples Today → Interphase, Prophase, Metaphase, Anaphase, Telophase.

Unit II · Genetics & DNA

Mendelian Genetics

A monk, some peas, and the ratios that let you predict the next generation.

EQ 06·AMonohybrid cross

Aa × Aa → 1 AA : 2 Aa : 1 aa ⇒ 3 : 1

Test cross (Aa × aa) gives 1 : 1 and reveals an unknown genotype. Incomplete dominance → 1 : 2 : 1 phenotype.

EQ 06·BDihybrid + probability

AaBb × AaBb → 9 : 3 : 3 : 1 · P(A∧B) = P(A)·P(B)

Only for unlinked genes. “AND” multiplies, “OR” adds — the two rules that solve every genetics problem.

Field Notes

Vocabulary: gene vs allele · genotype vs phenotype · homozygous vs heterozygous · dominant masks recessive.
Law of segregation: alleles part into different gametes. Independent assortment: unlinked genes sort freely.
Incomplete dominance blends (red × white → pink, 1:2:1). Codominance: both show — blood type AB.
Sex-linked recessive (e.g. colour-blindness): far more males affected; carrier mothers pass to sons.
Pedigrees: □ male, ○ female, shaded = affected. Two unaffected parents + affected child ⇒ recessive.
Blood types: Iᴬ and Iᴮ codominant, both dominate i. O parent × O parent → only O children.

Two unaffected parents have an affected child — what inheritance pattern?

Autosomal recessive — both parents must be carriers (Aa × Aa).

What ratio does Aa × aa produce?

1 : 1 — the classic test cross.

⚠ EXAM TRAP9 : 3 : 3 : 1 requires both parents double-heterozygous and unlinked genes. Check both before quoting it.

🧠 MNEMONICTest cross = “reveal the mystery genotype” — always cross with the recessive.

Unit II · Genetics & DNA

DNA Structure & Replication

Structure explains mechanism: the double helix suggests exactly how it copies itself.

EQ 07·AChargaff's rules

A = T · G = C ⇒ purines (A+G) = pyrimidines (C+T)

A=T holds 2 H-bonds, G≡C holds 3 — GC-rich DNA is harder to melt.

EQ 07·BB-DNA dimensions

width 2 nm · 0.34 nm/bp · ≈10 bp per turn (3.4 nm)

Watson–Crick 1953, from Franklin's Photo 51. Antiparallel strands: 5′→3′ against 3′→5′.

PLATE IVthe replication fork

Field Notes

Nucleotide = deoxyribose + phosphate + base (A, T, G, C). Sugar–phosphate backbone outside, bases stacked inside.
Semi-conservative replication proven by Meselson–Stahl (1958): each daughter duplex keeps one old strand.
Machinery: helicase unwinds · primase lays RNA primer · DNA polymerase adds 5′→3′ only · ligase joins Okazaki fragments.
Lagging strand is built in short pieces because polymerase can only read 3′→5′ while writing 5′→3′.
Proofreading keeps errors at ≈ 1 per 10⁹ bases after repair.
Human genome: ≈ 3.2 billion bp, ~20 000 genes; any two people 99.9% identical.

Why is one new strand made in fragments?

DNA polymerase only adds 5′→3′, so the strand running “backwards” from the fork is built in Okazaki fragments, later joined by ligase.

If 20% of bases are adenine, what % is cytosine?

A = T = 20%, so G + C = 60%, hence C = 30%.

⚠ EXAM TRAPA ≠ C. If A = 20%, then T = 20% and C = G = 30% — the most-missed calculation in genetics.

🧠 MNEMONICG is for Glued — G≡C has three bonds, A=T only two.

Unit II · Genetics & DNA

Protein Synthesis & Mutation

The gene is a sentence; transcription photocopies it, translation reads it three letters at a time.

EQ 08·ACentral dogma

DNA →transcription→ mRNA →translation→ protein

RNA pairs A–U, G–C. Information flows outward; reverse transcriptase (viruses) is the rare exception.

EQ 08·BThe genetic code

4³ = 64 codons → 20 amino acids + 3 stops

Start = AUG (methionine); stops = UAA, UAG, UGA. Degenerate but unambiguous.

Field Notes

RNA polymerase binds the promoter, reads template 3′→5′, builds mRNA 5′→3′.
Eukaryotic editing: 5′ cap, introns spliced out, poly-A tail → mature mRNA exits the nucleus.
Translation: ribosome reads codons; tRNA anticodons deliver amino acids; peptide bond forms.
One mRNA + many ribosomes = polyribosome — mass production from one transcript.
Mutations: silent (same AA) · missense (new AA) · nonsense (early stop) · frameshift (indel) — frameshifts wreck everything downstream.
Regulation: the lac operon in bacteria; transcription factors & epigenetics in eukaryotes.

Which is usually worse — frameshift or missense?

Frameshift: every codon downstream changes, so nearly the whole protein is garbled.

What is tRNA's job?

Carry one specific amino acid; its anticodon base-pairs with the matching mRNA codon at the ribosome.

⚠ EXAM TRAPCodon tables are written in mRNA. If given the DNA template strand, transcribe first (and flip T→U).

🧠 MNEMONICAUG = “Always U Go” — the start codon.

III

Unit Three · Chapters 09–11

Botany — Plant Life

Tissues, plumbing and hormones: how a rooted organism solves every problem it can't walk away from.

Unit III · Botany

Plant Structure & Tissues

Three organs, three tissue systems, and one very useful monocot/dicot cheat table.

Table 09·A — Monocot vs Eudicot

Feature	Monocot	Eudicot
Cotyledons	1	2
Leaf venation	Parallel	Net-like
Vascular bundles	Scattered	Ring
Floral parts	× 3	× 4 or × 5
Examples	Grasses, lilies, palms	Beans, roses, oaks

EQ 09·BThe vascular rule

xylem = water ↑ (dead) · phloem = sugar ⇅ (alive)

Xylem vessels are hollow dead tracheids; phloem sieve tubes are living, with companion cells.

PLATE Vcross-section of a leaf

Field Notes

Three organs (root, stem, leaf) from three tissue systems: dermal, ground, vascular.
Dermal: epidermis + waxy cuticle; guard cells operate stomata; root hairs multiply absorption.
Ground: parenchyma (photosynthesis & storage), collenchyma/sclerenchyma (support — celery strings, pear grit).
Meristems = plant stem cells: apical (length) and lateral cambium (girth → wood & bark).
Leaf: palisade mesophyll = chief photosynthesizer; spongy layer = gas exchange; stomata mostly underneath.
Roots: root cap protects the tip; root hairs sit just behind it; mycorrhizal fungi boost uptake.

Which transport tissue is dead at maturity?

Xylem — hollow tubes of dead cells; water flows through the empty lumen.

What do meristems do?

Supply new undifferentiated cells: apical meristems lengthen, lateral cambium widens.

⚠ EXAM TRAPPhloem is alive (sieve tubes + companion cells); xylem is dead. Don't swap them.

🧠 MNEMONIC“Xylem up, phloem fills” — xylem lifts water; phloem fills sinks with sugar.

Unit III · Botany

Plant Transport & Water Potential

A 90-metre redwood lifts water with no heart and no pump — only physics.

EQ 10·AWater potential

ψ = ψ_s + ψ_p · ψ_s = −iCRT

Soil (≈ −0.03 MPa) → root → leaf (≈ −1.5) → air (very negative). Water falls down the ψ gradient.

EQ 10·BCohesion–tension

evaporation → tension → cohesion ⇒ column rises

Hydrogen bonds hold the column together; transpiration at the leaf pulls it up — zero ATP.

PLATE VIthe stem's two pipelines

Field Notes

Xylem: one-way, upward, passive. Phloem: pressure-flow, source → sink, both directions, uses ATP.
Guard cells pump K⁺ in → water follows → turgid → stomata open. K⁺ out closes them.
Transpiration drivers: light, warmth, wind, low humidity. Wilting = ψ collapse.
Root pressure and capillarity help seedlings; cohesion–tension lifts tall trees.
Girdling (removing a phloem ring) starves the roots first — proof sugar travels in phloem.
Potometer measures transpiration rate; bubble speed ∝ water uptake.

What pulls water up a tall tree?

Cohesion–tension: evaporation at leaves creates tension, hydrogen-bonded water is dragged up — no ATP.

How do stomata open?

Guard cells actively take up K⁺, water follows by osmosis, cells swell turgid and bow apart.

⚠ EXAM TRAPψ of pure water is 0 and every solution is negative. Water goes from −0.2 toward −1.0, i.e. “more negative”.

🧠 MNEMONICWater “falls down” the ψ ladder — always toward the most negative value.

Unit III · Botany

Plant Hormones & Growth Responses

No nerves, no muscles — plants steer with five chemicals and a light switch.

Table 11·A — The Big Five Hormones

Hormone	Made in	Key jobs
Auxin	Shoot tips	Elongation, phototropism, apical dominance
Gibberellin	Young leaves, seeds	Stem elongation, germination
Cytokinin	Roots	Cell division, delays ageing
Ethylene (gas)	Ripening tissue	Fruit ripening, leaf fall
Abscisic acid	Leaves, stems	Closes stomata, dormancy

EQ 11·BPhotoperiodism

flowering ⇐ night length · Pr ⇌ Pfr

“Long-day” plants are really short-night (spinach); “short-day” = long-night (poinsettia). A night-flash of light flips the switch.

Field Notes

Phototropism: auxin migrates to the shaded side → those cells elongate → stem bends toward light (Darwin & Went).
Gravitropism: statoliths settle → auxin pools below; shoots bend up, roots bend down.
Thigmotropism = touch response (tendrils); jasmonates coordinate anti-herbivore defence.
One ripe banana spoils the bunch: ethylene is airborne and autocatalytic.
ABA is the drought hormone — closes stomata, keeps seeds dormant.
Auxin/cytokinin balance in tissue culture decides roots vs shoots.

Why do stems bend toward light?

Auxin shifts to the shaded side; those cells elongate faster, curving the stem toward the light.

What do plants actually measure to time flowering?

Unbroken night length — a brief light flash at night can block or trigger flowering depending on type.

⚠ EXAM TRAP“Long-day” is a historical misnomer — these plants flower when nights are short.

🧠 MNEMONICThe five hormones: “All Gardeners Care Enormously, Always” — Auxin, Gibberellin, Cytokinin, Ethylene, ABA.

Unit Four · Chapters 12–18

Human Physiology

Seven systems, one theme: every organ is an exchange surface, a pump, or a feedback loop.

Unit IV · Human Physiology

Digestion & Nutrition

A nine-metre disassembly line where pH decides which enzyme works where.

Table 12·A — Stations, Juices & pH

Station	Enzyme / juice	Substrate → product	pH
Mouth	Salivary amylase	Starch → maltose	≈ 6.8
Stomach	Pepsin + HCl	Protein → peptides	≈ 2.0
Small intestine	Amylase, trypsin, lipase	Starch / protein / fat	≈ 8.0

EQ 12·BThe digestion rule

digestion = mechanical + enzymatic · absorption ∝ SA

Every adaptation — teeth, churning, villi, microvilli — exists to multiply surface area.

PLATE VIIthe alimentary canal, schematically

Field Notes

Alimentary canal ≈ 9 m; four processes: ingestion, digestion, absorption, egestion.
Bile (liver → gall bladder) emulsifies fat into droplets — it is not an enzyme.
Villi + microvilli ≈ 250 m²; glucose & amino acids → blood; fatty acids → lacteals (lymph).
Everything absorbed heads to the liver first via the hepatic portal vein.
Enzymes mind their pH: pepsin works at 2 and quits in the intestine; trypsin needs ≈ 8 (bicarbonate neutralizes acid).
Peristalsis moves food even upside-down; the epiglottis guards the trachea while swallowing.

Why does pepsin stop working in the small intestine?

Bicarbonate raises pH toward 8 — far from pepsin's optimum of ~2, so it denatures/stops.

Is bile an enzyme?

No — it physically emulsifies fat into small droplets, giving lipase more surface to attack.

⚠ EXAM TRAPBile emulsifies; it never “digests”. Only enzymes digest.

🧠 MNEMONICStomach = Super Acid (pH 2, pepsin); intestine = Basic (pH 8). “SA-B”.

Unit IV · Human Physiology

Circulation & Blood

Four chambers, two circuits, and a pump that turns over its own volume every minute.

EQ 13·ACardiac output

CO = HR × SV ≈ 70 bpm × 70 mL ≈ 4.9 L/min

Your ≈ 5 L blood volume completes one lap per minute at rest — ×5 during hard exercise.

EQ 13·BBlood pressure

BP = CO × TPR · MAP ≈ DBP + ⅓(SBP − DBP)

120/80 mmHg: systolic = contraction, diastolic = filling.

PLATE VIIIthe heart · oxygenated side shaded red

Field Notes

Double circulation: pulmonary (heart ⇄ lungs, low pressure) + systemic (heart ⇄ body, high pressure).
Valves enforce one-way flow (AV + semilunar); “lub-dub” is valves snapping shut.
Conduction: SA node (pacemaker ≈ 70 bpm) → AV node → bundle of His → Purkinje fibres.
Vessels: arteries thick & elastic (high pressure) · veins valved (low pressure) · capillaries one cell thick.
Blood ≈ 55% plasma, ≈ 45% RBCs (haemoglobin, no nucleus, ~120-day life), <1% WBCs + platelets.
ABO: A and B codominant, O recessive — O = universal donor, AB = universal recipient; Rh matters in pregnancy.

If HR doubles but SV halves, what happens to CO?

Nothing — CO = HR × SV stays the same. The two factors trade off.

Why do veins have valves but arteries don't?

Venous pressure is too low to prevent backflow; valves keep blood moving toward the heart.

⚠ EXAM TRAPArteries carry blood away — but the pulmonary artery carries deoxygenated blood. Artery ≠ oxygenated.

🧠 MNEMONICArtery = Away from the heart.

Unit IV · Human Physiology

Respiration & Gas Exchange

You breathe because of CO₂, not oxygen — and gases only ever move downhill.

EQ 14·APulmonary ventilation

V̇ = tidal volume × rate ≈ 500 mL × 14 ≈ 7 L/min

Only ~350 mL of each breath reaches alveoli; the rest fills airway “dead space”.

EQ 14·BPartial-pressure gradients

O₂: 104 → 40 mmHg · CO₂: 45 → 40 mmHg

No pumps for gases — pure diffusion across ~0.5 µm of tissue, in under a second.

Field Notes

Route: nose → pharynx → larynx → trachea → bronchi → bronchioles → ≈ 300 million alveoli (≈ 70 m²).
Boyle's law: diaphragm contracts → volume ↑ → pressure ↓ → air rushes in. Exhalation is passive at rest.
O₂: ≈ 98% on haemoglobin. CO₂: ≈ 70% as HCO₃⁻, ≈ 23% carbaminohaemoglobin, ≈ 7% dissolved.
Breathing pace is set by blood CO₂ / pH via medulla chemoreceptors — not by O₂.
Bohr effect: low pH + high CO₂ make haemoglobin release O₂ — working muscles get priority.
Alveoli are thin, moist, capillary-wrapped — Fick's law (ch. 03) at work again.

What drives breathing rate up during exercise?

Rising CO₂ (falling pH) detected by chemoreceptors — not falling O₂.

How is most CO₂ carried in blood?

As bicarbonate ions HCO₃⁻ — about 70% of the total.

⚠ EXAM TRAPBreathing responds to CO₂, not O₂. Holding your breath hurts from CO₂ build-up.

🧠 MNEMONIC“Boyle = Breathing”: volume up → pressure down → air in.

Unit IV · Human Physiology

Excretion & Osmoregulation

The kidneys filter a bathtub of fluid every day and take back 99% of it.

EQ 15·AThe kidney equation

urine = filtrate − reabsorbed + secreted

GFR ≈ 125 mL/min → ≈ 180 L/day filtered, only ≈ 1.5 L excreted. ~99% reclaimed.

PLATE IXthe nephron — one of ~1 million

Field Notes

Nephron = functional unit, ≈ 1 million/kidney: glomerulus → Bowman's → PCT → loop of Henle → DCT → collecting duct.
Glomerulus: leaky, high-pressure sieve — water, glucose, urea, salts pass; cells and proteins stay.
PCT reclaims 100% of glucose + most water/salts; loop of Henle runs a counter-current multiplier.
Hormonal taps: ADH ↑ water reabsorption (concentrated urine) · aldosterone ↑ Na⁺ → water follows.
Protein waste: amino acids → ammonia (toxic) → urea in the liver → out via kidney.
Kidneys multitask: pH balance, blood pressure (renin), RBC production (EPO), vitamin D activation.

Where is glucose reclaimed, and how much?

Proximal convoluted tubule — 100% (glucose in urine signals diabetes).

What does ADH do?

Makes collecting ducts permeable to water → more reabsorption → small volume of concentrated urine.

⚠ EXAM TRAP180 L filtered ≠ 180 L urine. ~99% returns to blood; only ~1.5 L leaves.

🧠 MNEMONICNephron order: “Good Boys Play Loud Drums” — Glomerulus, Bowman's, PCT, Loop, DCT.

Unit IV · Human Physiology

Nervous System & Senses

An electrical alphabet written in millivolts — same voltage every time, meaning carried by frequency.

−70 mVresting −55 mVthreshold +35 mVpeak 3 : 2Na⁺ out : K⁺ in 120 m/smax speed

EQ 16·AThe action potential

stimulus ≥ threshold → Na⁺ in → K⁺ out → refractory

All-or-nothing: a stronger stimulus fires more often, never harder. Na⁺/K⁺-ATPase restores rest.

PLATE Xthe motor neuron

Field Notes

Neuron route: dendrite → soma → axon → terminal. Myelin insulates; impulses leap node-to-node (saltatory).
Synapse: Ca²⁺ entry → vesicles fuse → neurotransmitter crosses cleft → receptors fire; reuptake resets it.
Reflex arc: receptor → sensory → interneuron (cord) → motor → effector — the brain isn't consulted.
CNS = brain + spinal cord. PNS = somatic + autonomic: sympathetic (fight-or-flight) vs parasympathetic (rest-and-digest).
Senses: rods (~120 M, dim) & cones (~6 M, colour); cochlear hair cells → sound; semicircular canals → balance.

Why does a strong stimulus feel stronger?

Impulses fire more frequently — amplitude is always the same (all-or-nothing).

What's the advantage of myelin?

Saltatory conduction — the impulse jumps between nodes, up to ~120 m/s vs ~1 m/s unmyelinated.

⚠ EXAM TRAPImpulse size never changes. Strength is coded by frequency and by how many neurons fire.

🧠 MNEMONICReflex arc: Really Simple, Instant Movement — Receptor, Sensory, Interneuron, Motor, Effector.

Unit IV · Human Physiology

Endocrine System & Homeostasis

Slow mail, precise addresses: hormones in the blood, receptors only where they matter.

Table 17·A — Core Hormones

Hormone	Source	Effect
Insulin	Pancreas β	Glucose → glycogen; sugar ↓
Glucagon	Pancreas α	Glycogen → glucose; sugar ↑
Adrenaline	Adrenal medulla	Fight-or-flight: HR ↑, bronchi dilate
Thyroxine	Thyroid	Metabolic rate
Growth hormone	Anterior pituitary	Growth, protein synthesis
ADH	Posterior pituitary	Kidney retains water (ch. 15)

EQ 17·BNegative feedback

deviation → receptor → control → effector → reversal

Thermostat logic: the response always opposes the change. Positive feedback is rare (birth contractions).

Field Notes

Hormones travel in blood but act only on target cells bearing the matching receptor.
Glucose loop: high sugar → insulin → glycogen storage; low sugar → glucagon → glucose release. Failure ⇒ diabetes.
Steroid hormones enter cells and switch genes; peptide hormones bind membrane receptors → second messengers.
Hypothalamus bridges nervous and endocrine systems, conducting the pituitary (“master gland”).
Thermoregulation: too hot → vasodilation + sweating; too cold → vasoconstriction + shivering + piloerection.
Endocrine = slow & long-lasting; nervous = fast & brief. Adrenaline is the hybrid exception.

Blood sugar rises after a meal — what's released and why?

Insulin from pancreas β cells → liver & muscle store glucose as glycogen → sugar falls back to set point.

Steroid vs peptide hormones — how do they differ mechanistically?

Steroids (lipid) cross the membrane and regulate genes directly; peptides can't enter, so they bind surface receptors triggering second messengers.

⚠ EXAM TRAPInsulin lowers blood sugar; glucagon raises it. Swapping these two loses easy marks.

🧠 MNEMONICInsuLin Lowers; Glucagon Gains.

Unit IV · Human Physiology

The Immune System

Three lines of defence: a wall, a patrol, and an intelligence service with a memory.

EQ 18·AImmune memory

1°: slow (~1 wk) → memory cells ⇒ 2°: fast & huge

Vaccines are the first exposure, rehearsed safely. This curve is why you (mostly) get measles once.

EQ 18·BSelf-recognition

self vs non-self ⇐ MHC markers

Every nucleated cell displays MHC “ID tags”; cytotoxic T cells check them. Transplant rejection is this system working.

Field Notes

Line 1 — barriers: skin, mucus, stomach acid (pH ≈ 2), lysozyme in tears. Non-specific, instant.
Line 2 — innate: phagocytes (macrophages, neutrophils), NK cells, inflammation (histamine), fever, complement.
Line 3 — adaptive: B cells → antibodies (humoral); T cells: helper CD4 coordinate, cytotoxic CD8 kill infected cells.
Antibodies are Y-shaped, one antigen each; clonal selection amplifies the winning clone.
Active immunity (infection/vaccine — lasting) vs passive (mother's milk/antiserum — temporary).
Failure modes: autoimmunity (attacks self) · allergy (IgE overreacts) · HIV destroys CD4⁺ helpers.

Why don't you usually catch the same viral strain twice?

Memory B and T cells from the primary response mount a faster, larger secondary response before symptoms develop.

Which cells does HIV destroy, and why is that fatal?

Helper T cells (CD4⁺) — without them, neither B cells nor cytotoxic T cells can be properly activated; opportunistic infections follow.

⚠ EXAM TRAPAntibodies don't kill pathogens directly — they tag them for phagocytes and complement.

🧠 MNEMONICThree lines: Wall (barriers) → Patrol (innate) → Intelligence (adaptive, with memory).

Unit Five · Chapters 19–20

Evolution & Ecology

Populations change over generations; energy flows and matter cycles through everything they touch.

Unit V · Evolution & Ecology

Evolution & Population Genetics

Darwin supplied the mechanism; Hardy and Weinberg supplied the null hypothesis to detect it.

EQ 19·AHardy–Weinberg

p + q = 1 · p² + 2pq + q² = 1

Holds only with huge population, random mating, no mutation/migration/selection — i.e. never. Deviation = evolution detected.

EQ 19·BWorked example

q² = 0.09 → q = 0.30 → p = 0.70
carriers = 2pq = 2(0.7)(0.3) = 0.42

A recessive condition affecting 9% means 42% are carriers. Always start from q².

PLATE XIthree shapes of natural selection

Field Notes

Darwin (1859): variation + heritability + overproduction → differential survival. Selection acts on phenotypes; populations evolve, individuals don't.
Fitness = reproductive success, not strength.
Evidence: fossils · homologous structures (same plan, different job) · embryology · molecular (universal code).
Selection shapes: directional (mean shifts) · stabilizing (middle wins — e.g. birth weight) · disruptive (extremes win).
Genetic drift (bottleneck, founder effect) rules small populations; gene flow blends populations.
Speciation: allopatric (geographic barrier) vs sympatric (same place — often polyploidy in plants).
Homo sapiens: ≈ 300 000 years old, African origin; antibiotic resistance is evolution in real time.

What does deviation from Hardy–Weinberg mean?

Evolution is occurring — at least one assumption (no selection, drift, migration, mutation, non-random mating) is broken.

A recessive condition affects 16% of a population. Carrier frequency?

q² = 0.16 → q = 0.4, p = 0.6 → 2pq = 0.48 = 48% carriers.

⚠ EXAM TRAPAlways start HW problems from q² (the observed recessive phenotype) — never from p.

🧠 MNEMONICp² = AA, 2pq = Aa, q² = aa — “squares are homozygotes, the mixed term is the hybrid”.

Unit V · Evolution & Ecology

Ecology & Ecosystem Dynamics

Energy flows one way and is lost as heat; matter goes round forever. Everything else follows.

EQ 20·ALogistic growth

dN/dt = rN(K − N)/K

Exponential (J) while N ≪ K; flattens to an S at carrying capacity K. r = intrinsic growth rate.

EQ 20·B10% rule & NPP

~10% transfer per level · NPP = GPP − R

Why food chains rarely exceed 4–5 links, and why eating lower on the chain feeds more people per hectare.

PLATE XIIenergy shrinks ~10× at every step

Field Notes

Hierarchy: organism → population → community → ecosystem → biosphere.
Interactions: predation (+/−) · competition (−/−) · mutualism (+/+) · commensalism (+/0) · parasitism (+/−).
Cycles: carbon (photosynthesis in, respiration/combustion out) · nitrogen — fixation → nitrification → assimilation → denitrification (bacteria do nearly all of it) · water.
Succession: primary (bare rock: lichen → moss → …) vs secondary (soil survives — much faster).
Biodiversity = richness + evenness; keystone species punch above their biomass (sea otters → kelp forests).
Biomagnification: DDT, mercury concentrate upward — top predators take the biggest dose.
Human impacts: eutrophication (N & P → algal blooms → dead zones), CO₂ ↑ → warming, habitat loss = #1 threat.

Why are food chains usually short?

~90% of energy is lost as heat/respiration at each level — after 4–5 steps there's too little left to support another level.

Primary vs secondary succession — the one-line difference?

Primary starts with no soil (rock, lava); secondary starts where soil already remains (after fire, flood).

⚠ EXAM TRAPEnergy flows and is lost; matter cycles. Never write “energy is recycled”.

🧠 MNEMONICThe pyramid: 100 → 10 → 1 → 0.1. Each step, lose a zero.

Flash Review

16 cards · click to flip

Master Formula Strip

scroll → · click to copy

Σ 01Magnification

M = image ÷ actual

Σ 02pH

pH = −log₁₀[H⁺]

Σ 03Water potential

ψ = ψ_s + ψ_p

Σ 04Photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Σ 05Respiration

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ≈30–32 ATP

Σ 06Assortment

gamete variety = 2ⁿ

Σ 07Mendel ratios

3 : 1 · 9 : 3 : 3 : 1

Σ 08Chargaff

A = T · G = C

Σ 09Codons

4³ = 64 codons

Σ 10Cardiac output

CO = HR × SV ≈ 5 L/min

Σ 11Blood pressure

BP = CO × TPR

Σ 12Ventilation

V̇ = TV × rate ≈ 7 L/min

Σ 13Kidney

urine = filt − reabs + sec

Σ 14Hardy–Weinberg

p² + 2pq + q² = 1

Σ 15Logistic growth

dN/dt = rN(K − N)/K

Σ 16Productivity

NPP = GPP − R

Symbol Legend

decode every equation

ψwater potential (MPa); ψs solute, ψp pressure

n / 2nhaploid / diploid chromosome number

p, qallele frequencies in a population

rintrinsic (per-capita) growth rate

Kcarrying capacity of the environment

Npopulation size

ΔCconcentration difference (gradient)

CO · HR · SVcardiac output · heart rate · stroke volume

BP · MAP · TPRblood pressure · mean arterial P · peripheral resistance

GFRglomerular filtration rate (≈125 mL/min)

ATP · NADH · FADH₂energy carriers of respiration

GPP · NPP · Rgross / net primary production · respiration

Km · VmaxMichaelis constant · maximum enzyme rate

ADH · MHCantidiuretic hormone · tissue ID markers

M · µ · mV · mmHgmolar · micro (10⁻⁶) · millivolt · pressure

→ ⇌ ∝ ⇒yields · equilibrium · proportional to · therefore

Biology 100

Contents

Cells & Chemistry of Life

Cells & Microscopy

Biochemistry & Enzymes

Membranes & Transport

Bioenergetics — Photosynthesis & Respiration

Continuity — Genetics & DNA

The Cell Cycle & Division

Mendelian Genetics

DNA Structure & Replication

Protein Synthesis & Mutation

Botany — Plant Life

Plant Structure & Tissues

Plant Transport & Water Potential

Plant Hormones & Growth Responses

Human Physiology

Digestion & Nutrition

Circulation & Blood

Respiration & Gas Exchange

Excretion & Osmoregulation

Nervous System & Senses

Endocrine System & Homeostasis

The Immune System

Evolution & Ecology

Evolution & Population Genetics

Ecology & Ecosystem Dynamics

Flash Review

Master Formula Strip

Symbol Legend