Biology — Essential Concepts (Quick Reference)
Cell biology, genetics, evolution, ecosystems — every Biology CBE essential summarized on one page for last-minute review.
Biology CBE quick-reference — every must-know concept across cells, genetics, evolution, and ecology.
Cell Structure
- Prokaryotic: no nucleus (bacteria, archaea)
- Eukaryotic: nucleus + membrane-bound organelles (plants, animals, fungi, protists)
- Mitochondria: ATP production (cellular respiration)
- Chloroplasts: photosynthesis (plants only)
- Ribosomes: protein synthesis
- Cell wall: plants (cellulose), fungi (chitin), bacteria (peptidoglycan)
Cell Cycle
- Mitosis: 1 diploid → 2 identical diploids (growth, repair)
- Stages: prophase → metaphase → anaphase → telophase
- Meiosis: 1 diploid → 4 haploids (gametes)
- Crossing over (prophase I) creates genetic variation
DNA & Protein Synthesis
- DNA bases: A-T, G-C; RNA: A-U, G-C
- Replication: semi-conservative (each new strand has one old, one new)
- Transcription: DNA → mRNA (in nucleus)
- Translation: mRNA → protein (at ribosome, using tRNA)
- Codon = 3 bases = 1 amino acid
Genetics
- Dominant (A) masks recessive (a)
- Homozygous: AA or aa; Heterozygous: Aa
- Punnett square predicts offspring ratios (e.g., Aa × Aa → 1 AA : 2 Aa : 1 aa)
- Sex-linked traits: more common in males (XY)
Evolution
- Natural selection: heritable variations that improve fitness become more common
- Evidence: fossils, homologous structures, DNA similarity, embryology
- Speciation: reproductive isolation → new species
- Genetic drift, gene flow, mutation also drive evolution
Ecosystems
- Producers (autotrophs) → Primary consumers (herbivores) → Secondary/tertiary consumers (carnivores) → Decomposers
- Only ~10% of energy transfers between trophic levels
- Carbon cycle: photosynthesis fixes CO₂; respiration + combustion release it
- Population growth: J-curve (exponential) vs S-curve (logistic, carrying capacity)
Human Body Systems (High Yield)
- Cardiovascular: heart → arteries → capillaries → veins; carries O₂, CO₂, nutrients
- Respiratory: alveoli exchange gases with blood
- Nervous: neurons; CNS (brain + spinal cord), PNS (everything else)
- Immune: innate (general) and adaptive (B cells, T cells, antibodies)
Common Test Mistakes
- Confusing mitosis (somatic, 2 cells) with meiosis (gametes, 4 cells)
- Mixing transcription (in nucleus) with translation (at ribosome)
- Saying "evolution has a goal" — it doesn't; it's selection on existing variation