Biology Specification

• Diffusion: Passive movement down concentration gradient
• Osmosis: Water movement driven by water potential differences
• Active transport: Energy-requiring movement against gradient

• Mitosis:
  • Interphase (growth, DNA replication)
  • Mitosis → two genetically identical daughter cells
  • Roles: growth, tissue repair, asexual reproduction
  • Cancer = uncontrolled mitotic division due to mutations
• Meiosis: Interphase + two successive divisions → four haploid gametes; generates genetic diversity; essential for sexual reproduction
• Asexual vs. Sexual reproduction:
  • Asexual: one parent, offspring genetically identical (absent mutation)
  • Sexual: two parents, offspring genetically distinct
• Sex determination (humans): Females = XX, Males = XY

• Genetic material housed in nucleus (eukaryotes)
• Key terms: Gene, allele, dominant, recessive, heterozygous, homozygous, phenotype, genotype, chromosome, autosome
• Monohybrid crosses: Use Punnett squares, pedigree charts; express results as ratios, percentages, probabilities
• Recognise that most traits are polygenic; single-gene traits are exceptions

• Genome: Complete DNA set of an organism; organized into chromosomes
• DNA structure:
  • ssDNA = polymer of nucleotides (single strand)
  • dsDNA = double helix of two complementary strands
  • Nucleotide = sugar + phosphate + nitrogenous base (A, T, C, G)
  • Base pairing: A↔T, C↔G
• Protein synthesis: Genes → mRNA (triplet codons) → polypeptide chain → functional protein; amino-acid sequence determines 3-D protein shape
• Mutations: Change nucleotide sequence; may be neutral, minor, or phenotypically significant

• Genetic engineering: Isolate gene from donor DNA → insert into recipient genome using restriction enzymes & ligases → express in new organism
• Stem cells:
  • Totipotent (early embryonic) → full organism
  • Pluripotent (embryonic) → any cell type
  • Multipotent (adult) → limited lineages
  • Benefits: regenerative medicine; Risks: ethical concerns, tumorigenicity
• Selective breeding vs. natural selection: Both alter population genetics; selective breeding is human-directed

• Natural selection & evolution: Genetic variation → differential survival → allele frequency change → new species possible (e.g., antibiotic resistance in bacteria)
• Sources of variation:
  • Genetic (inheritance)
  • Environmental (affects phenotype)

• Enzymes: Protein catalysts; active site binds substrate → lowers activation energy
• Specificity determined by active-site shape
• Factors: temperature & pH affect rate (optimum conditions)
• Digestive enzymes: Amylases (carbohydrates), proteases (proteins), lipases (fats)

Respiration

• Cellular respiration: Glucose + O₂ → CO₂ + H₂O + ATP (aerobic)
• Anaerobic respiration: Glucose → lactic acid + ATP (less efficient, e.g., in muscles)

Organ Systems

• Nervous system:
  • Central nervous system = brain + spinal cord
  • Neurone types: sensory, relay, motor
  • Synapse & reflex arc convey signals
• Respiratory system:
  • Structures: lungs, thoracic cavity
  • Functions: ventilation (air movement) & gas exchange (diffusion)
  • High surface-area:volume ratio vital for diffusion
• Circulatory system:
  • Heart structure, heart rate, ECG basics
  • Vessels: arteries (high pressure), veins (low pressure), capillaries (exchange)
  • Blood components: RBCs (O₂ transport), WBCs (immune), platelets (clotting), plasma (transport, heat distribution)
• Digestive system: Peristalsis (movement), digestion (breakdown), absorption (nutrient uptake), egestion (waste removal)
• Excretory system: Kidneys & nephron structure; role in homeostasis (filtration, reabsorption, secretion)

Homeostasis

• Maintains stable internal environment; negative feedback loops
• Blood glucose regulation: Insulin (lowers) vs. glucagon (raises)
• Diabetes:
  • Type 1 = autoimmune destruction of insulin-producing cells (treated with insulin)
  • Type 2 = insulin resistance (managed with lifestyle, medication)
• Water balance: Antidiuretic hormone (ADH) controls renal water reabsorption
• Temperature regulation: Sweating, vasodilation/vasoconstriction

Hormones

• Endocrine glands release hormones into blood to target organs
• Adrenaline: "Fight-or-flight" response (increases heart rate, bronchodilation)
• Reproductive hormones: FSH, LH, oestrogen, progesterone → regulate menstrual cycle
• Contraception: Hormonal (e.g., pill) vs. non-hormonal methods

Disease and Body Defence

• Communicable diseases: Caused by bacteria, viruses, protists, fungi
  • Transmission of STIs; HIV → AIDS (immune system collapse)
  • Treatments: antibiotics (bacterial), vaccines (stimulate immunity, memory cells)
  • Drug/vaccine development: pre-clinical → clinical trials
• Non-communicable diseases: Cardiovascular disease, many cancers, lung/liver disease, type 2 diabetes
  • Management: lifelong medication (statins, anticoagulants, antihypertensives), surgery (stents, bypass), lifestyle changes (diet, exercise, smoking cessation)

• Levels of organisation: Individual → population → community → ecosystem
• Biotic & abiotic influences affect community structure
• Population dynamics: Factors causing size changes (birth, death, immigration, emigration)
• Interactions: Predation, mutualism, parasitism, competition
• Primary producers: Photosynthetic organisms → source of biomass

Material Cycling

• Carbon cycle: Photosynthesis ↔ respiration ↔ combustion ↔ decomposition
• Water cycle: Evaporation, condensation, precipitation, runoff, uptake

Biodiversity

• Sampling methods: Quadrats & belt transects to sample organism distribution & abundance
• Human impacts: Fish farming, acid rain, eutrophication → affect biodiversity

• Photosynthesis (endothermic): 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₆
• Limiting factors: Temperature, light intensity, CO₂ concentration
• Transport in plants:
  • Xylem – lignified dead cells → transport water/minerals (upward)
  • Phloem – living sieve-tube elements → transport sugars (downward/upward)

Plant Transport

• Mineral ion transport (xylem):
  • Xylem is a vascular tissue that conducts mineral ions and water from roots to shoots
  • Root hair cells increase surface area → facilitate diffusion of water/minerals
  • Uptake mechanism: diffusion of water into root hair cells (osmosis); active transport of mineral ions into the root cortex (against concentration gradient)
  • Cohesion–tension theory: a continuous water column pulled upward by transpiration
• Sugar transport (phloem):
  • Phloem transports dissolved sugars (mainly sucrose) from source (leaves) to sink (growing tissues, storage organs)
  • Loading: Sucrose actively transported into sieve-tube elements → increase osmotic pressure
  • Pressure-flow mechanism: high turgor pressure at source pushes sap toward lower pressure at sink; energy supplied by active loading/unloading of sugars
• Transpiration: Loss of water vapour from stomata on leaf surfaces; drives the upward movement of water in the xylem
• Stomatal structure: Pairs of guard cells that swell/shrink to open/close the pore
• Translocation: Movement of solutes (mainly sugars) in the phloem, governed by pressure differences

Environmental Factors Affecting Transpiration Rate

Factor	Effect on transpiration
Light intensity	↑ Light → ↑ stomatal opening → ↑ transpiration
Air movement (wind)	↑ wind → ↑ water-vapour gradient → ↑ transpiration
Relative humidity	↑ humidity → ↓ gradient → ↓ transpiration
Temperature	↑ temperature → ↑ kinetic energy → ↑ transpiration