📊 Reasoning & Data
Observation vs inference
Observation = directly detected. Inference = interpretation drawn from data.
Anomaly — what to do
Identify → give reason → exclude from mean → state mean calculated from remaining readings.
Mean formula
Mean = sum of valid readings ÷ n
Precision vs accuracy
Precision: smallest readable division. Accuracy: closeness to true value.
Reliability ↑ by
Repeating ≥3× and taking the mean. Reduces random error.
Validity ↑ by
Controlling all variables except the IV.
Random vs systematic error
Random: varies each time, fixed by repeating. Systematic: constant offset, NOT fixed by repeating.
Graph trend description
Direction + nature (linear/curved) + specific values with units.
Correlation vs causation
Correlation ≠ causation. A confounding variable may explain both. Need a controlled experiment for causation.
⚠ Trap: Never average an anomaly without identifying and justifying it first.
♻️ Matter & Cycles
Water cycle processes
Evaporation · Transpiration · Condensation · Precipitation · Runoff · Infiltration
Carbon IN atmosphere
Respiration · Combustion · Decomposition
Carbon OUT atmosphere
Photosynthesis · Ocean absorption
Photosynthesis equation
CO₂ + H₂O → glucose + O₂ (light energy)
Aerobic respiration
glucose + O₂ → CO₂ + H₂O + energy
Role of decomposers
Break down dead matter → return CO₂ to atmosphere + minerals to soil. Essential for nutrient cycling.
Energy vs matter in ecosystems
Energy FLOWS (lost as heat). Matter is RECYCLED between organisms and environment.
Deforestation effects
↑CO₂ · soil erosion · ↑runoff · ↓biodiversity · local temperature ↑
⚠ Trap: Photosynthesis removes CO₂; respiration adds CO₂. They are opposite in direction.
🧬 Living Systems
Enzyme specificity
Active site shape fits only one substrate (lock and key model).
High temperature → enzyme
Denatures — active site permanently changes shape. Irreversible.
Low temperature → enzyme
Slows activity (less KE). NOT denatured — reversible.
Artery vs vein
Artery: away from heart, thick walls, no valves. Vein: to heart, thin walls, has valves.
Alveoli adaptations
Large number · walls 1 cell thick · moist lining · good blood supply
Reflex arc sequence
Stimulus → Receptor → Sensory → Relay → Motor → Effector → Response
Insulin / glucagon
Insulin: lowers blood glucose. Glucagon: raises blood glucose. Negative feedback.
Nervous vs hormonal
Nervous: fast, electrical, short-lived. Hormonal: slower, chemical, longer-lasting.
⚠ Trap: Cold temperatures SLOW enzymes — they do NOT denature them.
⚡ Physical Systems
Ohm's Law
V = I × R (V in volts, I in amps, R in ohms)
Power
P = V × I (watts = V × A)
Series circuit rules
Same current throughout. Voltage shared. Total R = R₁ + R₂ + …
Parallel circuit rules
Same voltage across each branch. Current splits. Adding branches ↓ total R.
Pressure
P = F ÷ A (Pa = N ÷ m²)
Moments
Moment = F × d (N m) Clockwise = anticlockwise for equilibrium.
Wave equation
v = f × λ (m/s = Hz × m)
Transverse vs longitudinal
Transverse: vibration ⊥ travel (light, water). Longitudinal: vibration ∥ travel (sound).
Efficiency
Efficiency = useful out ÷ total in × 100%
⚠ Trap: Current is NOT "used up" — energy is transferred. Same current in series throughout.
🌍 Environment
Energy transfer rule
Only ~10% of energy passes to the next trophic level. ~90% lost as heat.
Food web arrows
Show direction of energy transfer — from food source → consumer.
Eutrophication chain
Fertiliser run-off → algal bloom → plants die (no light) → bacteria decompose → O₂ depleted → fish die.
Acid rain cause
SO₂ and NOₓ from burning fossil fuels dissolve in water vapour → sulfuric/nitric acid.
Enhanced greenhouse effect
Human activities ↑ CO₂/methane → more infrared trapped → global temperature rises.
Biodiversity importance
High biodiversity = more resilient ecosystem. If one species declines, others fill its role.
Renewable vs non-renewable
Renewable: no direct CO₂, intermittent. Non-renewable: reliable, high energy, emits CO₂.
Sustainability answer structure
Benefit → Limitation → Conclusion. Never one-sided.
⚠ Trap: Sustainability answers must include trade-offs — one-sided answers lose marks.