Cell Structure
Cell Theory
- All living things are made of cells
- Cells are the basic unit of life
- All cells come from pre-existing cells
Prokaryotic Cells
- No membrane-bound nucleus
- No membrane-bound organelles
- Smaller (1-10 Ξm)
- Examples: Bacteria, Archaea
Eukaryotic Cells
- True nucleus with membrane
- Membrane-bound organelles
- Larger (10-100 Ξm)
- Examples: Plants, Animals, Fungi
Key Organelles
Nucleus: Contains DNA, controls cell
Mitochondria: ATP production (powerhouse)
Ribosome: Protein synthesis
ER: Protein (rough) / Lipid (smooth) synthesis
Golgi: Modifies & packages proteins
Lysosome: Digestion & recycling
Chloroplast: Photosynthesis (plants)
Cell Wall: Support (plants, fungi, bacteria)
Cell Division
Mitosis (PMAT)
Division of somatic cells. Results in 2 identical diploid (2n) cells.
Prophase
Chromatin condenses, nuclear envelope breaks
Metaphase
Chromosomes align at cell equator
Anaphase
Sister chromatids separate
Telophase
Nuclear envelope reforms
Meiosis
Division of sex cells. Results in 4 unique haploid (n) cells.
Meiosis I:
- Homologous pairs separate
- Crossing over occurs
- Results in 2 haploid cells
Meiosis II:
- Similar to mitosis
- Sister chromatids separate
- Results in 4 haploid cells
Comparison
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair | Gamete production |
| Divisions | 1 | 2 |
| Daughter cells | 2 (2n) | 4 (n) |
| Genetic variation | No | Yes |
Genetics
Key Terms
- Gene: Segment of DNA that codes for a trait
- Allele: Different versions of a gene
- Genotype: Genetic makeup (AA, Aa, aa)
- Phenotype: Physical expression of genes
- Dominant: Expressed when present (A)
- Recessive: Only expressed when homozygous (aa)
Mendel's Laws
- Law of Segregation: Allele pairs separate during gamete formation
- Law of Independent Assortment: Genes for different traits sort independently
Punnett Square
Tool for predicting offspring genotypes.
Monohybrid cross (Aa à Aa): 25% AA, 50% Aa, 25% aa â 3:1 phenotypic ratio
DNA Structure
- Double helix structure (Watson & Crick)
- Sugar-phosphate backbone
- Nitrogenous bases: A-T, G-C (complementary pairs)
- DNA â RNA â Protein (Central Dogma)
Evolution
Darwin's Theory of Natural Selection
- Variation exists within populations
- More offspring are produced than can survive
- Individuals with favorable traits survive and reproduce
- Favorable traits become more common over time
Evidence for Evolution
- Fossil record
- Homologous structures
- Embryology
- DNA/molecular evidence
- Biogeography
Types of Selection
- Stabilizing: Favors average
- Directional: Favors one extreme
- Disruptive: Favors both extremes
Speciation
Formation of new species through reproductive isolation. Can occur through geographic separation (allopatric) or within the same location (sympatric).
Ecology
Levels of Organization
Organism â Population â Community â Ecosystem â Biome â Biosphere
Energy Flow
- Producers: Make own food (photosynthesis)
- Consumers: Eat other organisms
- Decomposers: Break down dead matter
- Energy decreases ~10% at each trophic level
Biogeochemical Cycles
Carbon: Photosynthesis â Respiration
Nitrogen: Fixation â Nitrification â Denitrification
Water: Evaporation â Condensation â Precipitation
Phosphorus: Rocks â Soil â Organisms
Ecological Relationships
- Mutualism: Both benefit (+/+)
- Commensalism: One benefits, other unaffected (+/0)
- Parasitism: One benefits at expense of other (+/-)
- Predation: One kills and eats another (+/-)
- Competition: Both harmed by resource sharing (-/-)