Comprehensive Biology Notes – Forms 4–5 (OBE 2024)
MODULE BIOSL 1 – Continuity & Diversity of Life
1. Microscopy (PC 1.1.1 – 1.1.2)
• Purposes ↠ visualise cells, study microbiology, examine cell structures
• Two core families ↠ Light microscopes (5 types) & Electron microscopes (2 types)
• Light microscopy sub-types: Bright-field, Dark-field, Phase-contrast, Differential-Interference-Contrast (DIC), Fluorescence
• Electron microscopy sub-types : Transmission (TEM) & Scanning (SEM)
• Compound light microscope ↠ uses visible light; two lenses (objective & ocular)
• Total\,magnification = M{objective}\times M{ocular} (max ≈ 2000\times)
• Resolution ↠ ability to distinguish adjacent points; limited by light wavelength; LM ≈ 0.2\,\mu m (EM much finer)
• Improving contrast ↠ staining (methylene blue, safranin, crystal-violet), Gram-stain (positive ⇢ purple, negative ⇢ red)
• Phase-contrast/Dark-field ➡ enhance image without stains; Fluorescence uses natural or dye-tagged fluorophores (e.g., DAPI)
• Electron microscopes use electron beams, electromagnetic lenses, vacuum; TEM requires ultrathin sections & heavy-metal stains; SEM coats specimen (e.g., gold) to view surface relief
2. Prokaryotic vs. Eukaryotic Cells (PC 1.1.3)
• Prokaryotes: 1st life, unicellular, no nuclear membrane, circular DNA, no membrane organelles, small, appeared \sim4 billion yr ago
• Eukaryotes: later, linear DNA inside nucleus, membrane organelles, complex & larger, uni-/multicellular, \sim1 billion yr ago
• Shared features: plasma membrane, ribosomes, DNA, cytoplasm
3. Cell Components (PC 1.1.4 – 1.1.6)
• Cell wall (plants) – cellulose, protection, turgor
• Cell surface membrane – selectively permeable lipid bilayer
• Cytoplasm – aqueous medium; metabolic site
• Nucleus – DNA, genes, control centre, cell division
• Vacuoles – permanent (plant, sap: ions, sugars, pigments); temporary (animal)
• Chloroplasts – chlorophyll, photosynthesis
• Mitochondria – aerobic respiration
• Ribosomes – protein synthesis
• Golgi apparatus – package/store lipids & proteins
• Lysosomes – single-membrane sacs with digestive enzymes (autophagy)
• Plant vs Animal summary: cell wall, chloroplast, vacuole, food stores, shape/size
4. Cell Division (PC 1.1.7 – 1.1.8)
• Mitosis – body cells; produces 2 identical daughter cells (N → N or 2N → 2N) through Pro-, Meta-, Ana-, Telophase (interphase = resting)
• Meiosis – reproductive cells; 2 divisions; 4 haploid gametes; crossing-over in Prophase I; independent assortment at Metaphase I; reduction to n chromosomes
• Key contrasts: duplicative vs reductive, one vs two divisions, homologous pairing only in meiosis, 2 vs 4 cells, growth vs reproduction
5. Cell Specialisation (PC 1.1.9)
• Animals: erythrocytes (biconcave, Hb), neurones (long axon), muscles (contractile proteins), sperm (flagellum, acrosome), WBC – phagocytes & lymphocytes (antibodies)
• Plants: root-hair (large vacuole, mitochondria), xylem (dead, lignified), phloem (sieve tubes & companion cells), palisade (many chloroplasts), guard cells (stomatal control)
6. Movement of Substances (PC 1.1.10–1.1.11)
• Diffusion – random molecular motion down gradient; affected by temp, size, gradient
• Osmosis – water diffusion across partially permeable membrane; isotonic, hyper-, hypo-tonic effects; plant ≈ turgid/plasmolysed, animal ≈ lysed/crenated
• Active transport – \text{low} \to \text{high} conc.; needs ATP; crucial for mineral ion uptake
MODULE BIOSL 1.2 – Classification
• Taxonomy = orderly grouping; major criteria: feeding, structure, reproduction
• 5 Kingdoms: Monera, Protista, Fungi, Plantae, Animalia
• Viruses: acellular, DNA or RNA (never both), replication only in host; classes – animal, plant, bacteriophage; shapes: helical (TMV), polyhedral (adenovirus), enveloped (corona)
• Bacteria: prokaryotic; shapes – cocci, bacilli, spirilla; nutrition saprophytic/parasitic/photosynthetic/chemo-autotrophic; reproduction binary fission, conjugation
• Fungi: chitin cell walls; mycelial hyphae; heterotrophic (saprophyte, parasite, mutualist); reproduce by spores/budding/sexual hyphal fusion
• Protists: unicellular; locomotion via flagella, cilia, pseudopodia; nutrition autotroph (euglena) or heterotroph (paramecium); binary or multiple fission, conjugation
• Green algae: filamentous or unicellular; chlorophyll; store starch; cell wall cellulose; reproduce sexually (gametes) & asexually (fragmentation)
• Arthropods: exoskeleton chitin, jointed limbs, segmented body; classes – insects, arachnids, myriapods, crustaceans; heterotrophic; sexual reproduction + ecdysis
• Chordates: vertebral column, dorsal nerve cord, closed circulation, lungs/gills; heterotrophic
• Plants – Angiosperms (flowers, seeds in fruit) & Gymnosperms (cones, naked seeds, evergreen, resin)
• Dichotomous Keys: paired contrasting statements; binomial nomenclature rules (Genus capitalised, species lowercase, italic/underline)
MODULE BIOSL 1.3 – Reproduction
Asexual in Plants
• Vegetative organs: tubers, rhizomes, runners, suckers, bulbs; artificial – grafting, cuttings, layering
• Pros: rapid, preserves genotype; Cons: no variation, transmits disease
Sexual in Plants
• Flower structure: sepals, petals (insect vs wind traits), stamens, carpels
• Pollination – self vs cross; agents: wind, insects, birds, water, rodents
• Fertilisation → ovule↦seed, ovary↦fruit
• Seed/fruit dispersal: wind (sycamore), animals (tomato, burr), water, self
• Germination needs water, oxygen, suitable temp
Human Reproduction
• Male: testes (sperm, testosterone), epididymis, vas deferens, prostate, seminal vesicle, penis; spermatogenesis → haploid, motile
• Female: ovaries (ova, oestrogen, progesterone), oviducts, uterus, cervix, vagina; oogenesis → non-motile ovum
• Fertilisation in oviduct → zygote; implantation in uterus; placenta (exchange), amnion & fluid (shock absorber); umbilical cord (artery & vein)
• Menstrual cycle (≈28 d): menstruation (days 1–5, ↓progesterone), repair (6-13, FSH↑, oestrogen ↑), ovulation (day 14, LH surge), luteal (15-28, corpus luteum, progesterone)
• Contraception: barrier, hormonal, surgical, natural
• STIs: syphilis (bacteria, antibiotics), gonorrhoea, HIV/AIDS (virus, no cure, ARVs)
MODULE BIOSL 1.4 – Heredity & Genetics
• Key terms: gene, allele, locus, genotype vs phenotype, homozygous/heterozygous, autosome, diploid (2n), haploid (n)
• Monohybrid crosses (complete, incomplete, co-dominance)
• e.g. sickle-cell Hb^A Hb^S heterozygote
• Test/back cross (unknown \times homozygous recessive)
• Pedigree charts
• Mutation: gene vs chromosomal; mutagens (radiation, chemicals); good/bad; e.g. Down syndrome (trisomy 21)
• Sex determination: XY ♂, XX ♀; sex linkage (haemophilia, colour-blindness)
• Variation: continuous (polygenes + environment) vs discontinuous (single gene)
• Natural selection (Darwin/Wallace): overproduction, constancy, struggle, variation, survival of fittest, inheritance, speciation; artificial selection in agriculture
MODULE BIOSL 2 – Energy Flow in Ecosystems
Ecology Basics (PC 2.1.1 – 2.1.15)
• Definitions: habitat, population, community, ecosystem, species, food chain, trophic level, producer, consumer, decomposer, pyramid of numbers
• Adaptations – structural, physiological, behavioural; dry vs wet conditions; human impacts (fencing, dams, overgrazing, deforestation, fossil fuels)
• Energy flow: \approx10\% transfer per trophic step; 4-level limit
• Nutrient cycles: Carbon (photosynthesis \leftrightarrow respiration, combustion, decay); Nitrogen (N$2$ fixation, nitrification, assimilation, ammonification, denitrification) • Human impacts: monoculture, over-stocking, fertiliser eutrophication, pesticides bioaccumulation, pollution (air SO$2$, CO$_2$, water sewage/heavy metals, land litter)
• Conservation, recycling (glass, metals, paper, biogas)
Nutrition (Animal & Plant)
• Balanced diet: carbs, lipids, proteins, vitamins (A,B,C,D,K), minerals (Fe,I,Ca,P), fibre, water
• Food tests: iodine (starch → blue-black), Benedict (glucose → brick-red), Biuret (protein → purple), ethanol (emulsion → milky)
• Enzymes: protein catalysts, optima pH & temp (\sim37^\circ\text{C}), substrate-specific (lock & key), denaturation >50^\circ\text{C}
• Digestion: mouth (salivary amylase), stomach (pepsin, HCl, rennin), duodenum (bile, pancreatic amylase/lipase/trypsin), ileum (maltase, lipase, sucrase, lactase, peptidase), absorption via villi; liver functions (deamination, detox, glycogen storage, bile, urea formation), pancreas – insulin, glucagon
Respiration
• Aerobic: \text{C}6\text{H}{12}\text{O}6 + 6\text{O}2 \rightarrow 6\text{CO}2 + 6\text{H}2\text{O} + 38\text{ATP}
• Anaerobic (muscle): \text{Glucose}\rightarrow \text{Lactic acid} + 2\text{ATP}
Yeast: \text{Glucose}\rightarrow 2\text{CO}2 + 2\text{Eth!anol} + 2\text{ATP} • O$2$ debt, fermentation uses
MODULE BIOSL 3 – Transport
Plants (PC 3.1.1 – 3.1.5)
• Root-hair cell adaptations (large SA, thin wall, vacuole) – water by osmosis, ions by diffusion/active transport
• Xylem (dead, lignified, upward transpiration stream) vs Phloem (living, sieve plates, bidirectional translocation)
• Transpiration factors: temp ↑, wind ↑, humidity ↓, light (stomata); control – stomata, cuticle, hairs, sunken pits
• Special adaptations: xerophytes (thick cuticle, rolled leaves), hydrophytes (air spaces), halophytes (salt glands)
Human Transport (PC 3.2.1 – 3.2.7)
• Double circulation: pulmonary (right → lungs), systemic (left → body)
• Heart anatomy: atria thin, ventricles thick, left wall thickest; valves (AV, semilunar); coronary vessels
• Blood vessels: artery (thick elastic, small lumen), vein (thin, valves, large lumen), capillary (one-cell wall)
• Blood: plasma (water, proteins, nutrients, hormones, wastes); RBC (Hb, biconcave, no nucleus); WBC (phagocytes, lymphocytes); platelets (clotting)
• Immunity: innate vs acquired; antigens/antibodies; vaccination; blood groups (ABO, rhesus); clotting cascade (fibrin)
• Homeostasis of temperature (vasodilation, sweating vs vasoconstriction, shivering); glucose (insulin \downarrow, glucagon \uparrow); water (ADH, kidney nephron filtration → reabsorption → secretion)
MODULE BIOSL 4 – Regulation & Control
Hormonal Coordination
• Endocrine glands: pituitary (HGH, TSH, FSH, LH, ADH, oxytocin), thyroid (thyroxine), adrenals (adrenaline, cortisol), pancreas (insulin/glucagon), gonads
• Negative feedback loops (e.g., ADH on collecting ducts, thyroxine on TSH)
Nervous Coordination
• CNS (brain, spinal cord) & PNS; neurones: sensory, relay, motor; impulse conduction; synapse (neurotransmitter release \rightarrow receptor binding); reflex arc
• Brain regions: cerebrum (voluntary, memory), cerebellum (balance), medulla (involuntary reflexes), hypothalamus (homeostasis), pituitary (master gland)
• Drug action: stimulants (nicotine, caffeine), depressants (alcohol), hallucinogens (cannabis); dependence, tolerance; alcohol effects (cirrhosis, reaction time, foetal alcohol syndrome)
MODULE BIOSL 5 – Biotechnology & Gene Technology
Industrial Microbiology
• Bread (yeast fermentation \Rightarrow CO$_2$); Chibuku (sorghum → maltose + yeast), Madila & cheese (lactobacillus + streptococcus convert lactose \rightarrow lactic acid coagulating casein), fruit juice clarification (pectinase), lactose-free milk (lactase)
• Single-cell protein (mycoprotein), antibiotics (penicillin from Penicillium), vaccines, waste-oil digestion, sewage treatment, composting, biogas
Genetic Engineering
• Recombinant DNA: restriction enzyme cuts vector & gene, ligase joins, plasmid inserted into bacterium, cloning, protein harvest (e.g., insulin)
• Gene therapy: add dominant allele to treat recessive disorder
• Applications: GM crops (disease/pest resistance), livestock improvement, pharmaceutical proteins
• Ethical & biodiversity issues: gene flow, super-weeds, patenting life, food safety
Reproductive Technology
• Artificial insemination steps (hormone stimulation, semen collection/prep, uterine catheter insemination); pros – genetic gain, disease control; cons – labour, inbreeding
• Artificial pollination in crops (emasculation, bagging, hand-pollinate desired cross)
• Cloning effectiveness & bioethics (Dolly, therapeutic vs reproductive)
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