General Biology II — High-Yield Review

Highest-Yield Facts by Unit

Unit 1 — Evolution

• High yield: Natural selection requires variation, heritability, and differential reproductive success; it acts on populations over generations, not on individuals.
• Evidence for evolution: fossil record, homologous structures, embryology, biogeography, and molecular (DNA) similarities.
• High yield: Hardy–Weinberg equilibrium (p² + 2pq + q² = 1) holds only with no mutation, no gene flow, large population, random mating, and no selection.
• Mechanisms of microevolution: genetic drift, gene flow, mutation, non-random mating, natural selection.
• Selection types: stabilizing (favors intermediate), directional (favors one extreme), disruptive (favors both extremes), sexual (favors traits for mating).

Unit 2 — Diversity

• Phylogenies group organisms by shared ancestry; homologous traits share ancestry, analogous traits are similar by convergent evolution.
• High yield: The endosymbiotic theory explains mitochondria and chloroplasts as engulfed prokaryotes.
• Viruses are acellular; lytic cycle destroys the host, lysogenic cycle integrates into the genome.
• Bacteria reproduce by binary fission; antibiotic resistance evolves by natural selection.
• Fungi are heterotrophic decomposers with chitin cell walls; mycorrhizae aid plant nutrient uptake.

Unit 3 — Plants

• High yield: Plants alternate between haploid gametophyte and diploid sporophyte generations.
• Bryophytes are non-vascular; ferns are seedless vascular; gymnosperms have "naked" seeds; angiosperms have flowers and fruit.
• Xylem moves water up (cohesion–tension); phloem moves sugars (pressure–flow).

Unit 4 — Animals

• Animal body plans are described by symmetry, germ layers (diploblastic vs triploblastic), coelom presence, and protostome vs deuterostome development.
• High yield: Protostomes form the mouth first; deuterostomes form the anus first.
• Chordates have a notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail.

Unit 5 — Form & Function

• High yield: Homeostasis is maintained by negative feedback (e.g., thermoregulation).
• Neurons signal via action potentials; hormones signal via the bloodstream and feedback loops.
• Closed circulatory systems (vertebrates) keep blood in vessels; open systems (arthropods) bathe tissues directly.
• Adaptive immunity is specific and has memory; innate immunity is rapid and non-specific.

Unit 6 — Ecology

• High yield: Exponential growth (J-curve) is unlimited; logistic growth (S-curve) reaches carrying capacity (K).
• Keystone species have effects far larger than their abundance.
• High yield: Only about 10% of energy transfers between trophic levels (energy pyramid).
• Primary succession starts from bare rock; secondary succession follows a disturbance that leaves soil.

Comparison Tables

Cumulative Self-Check

1. What three conditions are required for natural selection to operate?
2. A population in Hardy–Weinberg equilibrium has a recessive-allele frequency q = 0.2. What fraction is heterozygous?
3. Name the two types of prezygotic and postzygotic barriers (one example each).
4. What is the difference between a homologous and an analogous trait?
5. What does the endosymbiotic theory explain, and what is its key evidence?
6. Contrast the lytic and lysogenic viral cycles.
7. Why does antibiotic resistance spread through a bacterial population?
8. What is alternation of generations, and which plant stages are haploid vs diploid?
9. Which plant tissue transports water, and by what mechanism?
10. Distinguish protostomes from deuterostomes.
11. List the four chordate characteristics.
12. What is homeostasis, and what type of feedback most commonly maintains it?
13. Contrast innate and adaptive immunity.
14. What is carrying capacity, and how does it shape logistic growth?
15. Why do energy pyramids rarely have more than four or five trophic levels?
16. Contrast primary and secondary succession.

Answers and Rationales

1. Variation, heritability, and differential reproductive success.
2. Heterozygotes = 2pq = 2(0.8)(0.2) = 0.32, or 32%.
3. Prezygotic (e.g., habitat isolation, behavioral isolation); postzygotic (e.g., hybrid sterility).
4. Homologous = shared ancestry (same origin); analogous = convergent evolution (similar function).
5. Mitochondria/chloroplasts originated as engulfed prokaryotes; evidence includes double membranes and their own DNA.
6. Lytic destroys the host cell; lysogenic integrates viral DNA and can stay dormant.
7. Resistant bacteria survive antibiotics and reproduce, so resistance alleles increase by natural selection.
8. Alternation of generations cycles between haploid gametophyte and diploid sporophyte stages.
9. Xylem transports water upward via cohesion–tension (transpiration pull).
10. Protostomes form the mouth first; deuterostomes form the anus first.
11. Notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail.
12. Homeostasis is maintenance of a stable internal state, usually by negative feedback.
13. Innate is rapid and non-specific with no memory; adaptive is specific, slower, and has memory.
14. Carrying capacity (K) is the maximum sustainable population; logistic growth slows near K.
15. Only ~10% of energy transfers between levels, so little remains after 4–5 levels.
16. Primary starts from bare rock (no soil); secondary follows a disturbance that leaves soil.

Last-Minute Review

• Core mechanisms: natural selection; genetic drift; speciation via reproductive isolation; endosymbiosis; alternation of generations; negative-feedback homeostasis; energy flow (10% rule).
• High-yield distinctions: micro vs macroevolution, allopatric vs sympatric, protostome vs deuterostome, innate vs adaptive immunity, exponential vs logistic growth, primary vs secondary succession, xylem vs phloem, lytic vs lysogenic.
• Key principles: evolution acts on populations, is not goal-directed, and is supported by multiple independent lines of evidence; biodiversity is organized by phylogeny; ecosystems move energy and cycle matter.

Links

• Subject overview
• Topic 01
• Topic 23