S2 Science Summary Notes
Chemistry · Physics · Biology | Created by Miss Clarissa Ng | www.clartutors.com
CHEMISTRY
Chemical Changes · Formulae & Equations · Acids & BasesCHEM 1Chemical Changes
Physical vs Chemical Change
| Physical Change | Chemical Change | |
|---|---|---|
| New substance? | No — same substance, different form | Yes — new substance(s) formed |
| Reversible? | Usually reversible (e.g. melting ice) | Usually irreversible (e.g. burning wood) |
| Energy | Small changes only | Often releases/absorbs noticeable heat or light |
Evidence of a Chemical Change
- Colour change — e.g. iron nail turns reddish-brown in copper sulphate solution.
- Gas production — bubbles/effervescence, e.g. zinc + dilute HCl → hydrogen gas (pops with a lighted splint).
- Precipitate formation — insoluble solid forms in solution.
- Temperature change — exothermic (releases heat) or endothermic (absorbs heat).
Common Reactions to Know
| Type | Example |
|---|---|
| Combustion | Methane + oxygen → carbon dioxide + water (flame = exothermic) |
| Oxidation of metals | Iron + oxygen + water → rust (hydrated iron oxide); copper → green patina |
| Cellular respiration (oxidation) | Glucose + oxygen → carbon dioxide + water + energy — happens in every living cell |
| Thermal decomposition | A compound breaks down when heated, e.g. calcium carbonate → calcium oxide + carbon dioxide (limestone heated) |
| Displacement | Zinc + CuSO₄ solution → zinc sulphate + copper (more reactive metal displaces less reactive one) |
| Acid + metal | Magnesium + dilute HCl → magnesium chloride + hydrogen gas |
Exam tip: A change of state (melting, boiling) is ALWAYS a physical change — no new substance is formed. If the question says "new substance", it's chemical.
CHEM 2Chemical Formulae & Equations
Valency — Common Ions
| Ion | Charge / Valency | Ion | Charge / Valency |
|---|---|---|---|
| H⁺, Na⁺, K⁺, Ag⁺ | +1 | O²⁻, S²⁻ | −2 |
| Mg²⁺, Ca²⁺, Zn²⁺ | +2 | N³⁻ (nitride) | −3 |
| Al³⁺ | +3 | HCO₃⁻ (hydrogen carbonate) | −1 |
| Cl⁻, Br⁻, I⁻ | −1 | SO₄²⁻ (sulphate) | −2 |
| NH₄⁺ (ammonium) | +1 | NO₃⁻ (nitrate) | −1 |
Other Important Polyatomic Anions (memorise!)
| Name | Formula | Charge |
|---|---|---|
| Hydroxide | OH⁻ | −1 |
| Ethanoate | CH₃COO⁻ | −1 |
| Carbonate | CO₃²⁻ | −2 |
| Phosphate | PO₄³⁻ | −3 |
Writing Formulae — Cross-Over Rule
- Cross the valencies: Mg²⁺ + O²⁻ → MgO (2 and 2 cancel); Al³⁺ + Cl⁻ → AlCl₃.
- Never change subscripts inside a polyatomic ion: Ca²⁺ + SO₄²⁻ → CaSO₄; Mg²⁺ + NO₃⁻ → Mg(NO₃)₂ — brackets when more than one of the same ion.
Balancing Equations
- Count atoms of each element on both sides.
- Add coefficients in front (never change subscripts — that changes the substance).
- Balance elements appearing in only one compound first; leave H and O to last.
Example: CH₄ + 2O₂ → CO₂ + 2H₂O (C:1=1, H:4=4, O:4=4 ✓)
Law of Conservation of Mass: Total mass of reactants = total mass of products. Atoms are neither created nor destroyed — only rearranged.
CHEM 3Acids, Bases & Salts
pH Scale (1–14)
| pH range | Nature | Examples |
|---|---|---|
| 0 – 6 | Acidic | Battery acid (≈0), stomach acid, lemon juice, vinegar |
| 7 | Neutral | Pure water |
| 8 – 14 | Basic (alkaline) | Baking soda solution, ammonia, drain cleaner (≈14) |
- Each pH unit is a 10× difference in H⁺ concentration — pH 3 has 10× more H⁺ than pH 4.
- Acids turn blue litmus red; bases turn red litmus blue.
Indicators — Testing for Acid, Alkali or Neutral
| Indicator | In acid | In neutral (water) | In alkali |
|---|---|---|---|
| Litmus paper | Blue → red | No change (stays purple) | Red → blue |
| Universal Indicator | Red / orange | Green | Blue / purple |
| Natural indicator (red cabbage) | Pink / red | Purple | Green / yellow |
All Acid & Base Reactions (memorise the patterns)
| # | Reaction type | General equation | Example |
|---|---|---|---|
| 1 | Acid + reactive metal | acid + metal → salt + hydrogen (H₂ gas) | Mg + 2HCl → MgCl₂ + H₂ Zn + H₂SO₄ → ZnSO₄ + H₂ |
| 2 | Neutralisation: acid + alkali (soluble base) | acid + base → salt + water | HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l) H₂SO₄(aq) + 2KOH(aq) → K₂SO₄(aq) + 2H₂O(l) |
| 3 | Acid + metal oxide (insoluble base) | acid + metal oxide → salt + water | 2HCl(aq) + CuO(s) → CuCl₂(aq) + H₂O(l) H₂SO₄(aq) + MgO(s) → MgSO₄(aq) + H₂O(l) |
| 4 | Acid + metal hydroxide (insoluble base) | acid + metal hydroxide → salt + water | 2HNO₃(aq) + Cu(OH)₂(s) → Cu(NO₃)₂(aq) + 2H₂O(l) |
| 5 | Acid + metal carbonate | acid + carbonate → salt + water + CO₂ (fizzing!) | 2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g) H₂SO₄(aq) + Na₂CO₃(s) → Na₂SO₄(aq) + H₂O(l) + CO₂(g) |
| 6 | Alkali + ammonium salt (warmed) | alkali + ammonium compound → salt + ammonia + water | NaOH + NH₄Cl → NaCl + NH₃↑ + H₂O |
- Salt naming rule: metal part comes from the base; acid decides the ending — HCl → chloride, H₂SO₄ → sulphate, HNO₃ → nitrate.
- Less reactive metals (copper, silver, gold) do NOT react with dilute acids — no bubbles.
- Test for H₂: bring a lighted splint to the gas → squeaky "pop" sound confirms hydrogen.
- Test for CO₂: bubble gas into limewater → turns chalky (calcium carbonate forms). Fizzing = reliable test for carbonates.
- Test for NH₃: damp red litmus paper at the mouth of the tube turns blue; pungent smell.
- Uses of neutralisation: antacids (Mg(OH)₂, NaHCO₃) neutralise excess stomach acid; lime Ca(OH)₂ treats acidic soil; baking soda relieves bee stings (acidic), vinegar treats wasp stings (alkaline).
Exam tip: "Alkali" = a base that dissolves in water. All alkalis are bases, but not all bases are alkalis.
PHYSICS
Forces · Thermal Energy · Energy · ElectricityPHYS 1Forces
Key Formulas
Weight W = mg (g ≈ 10 N/kg)
Mass is constant everywhere; weight changes with gravity.
Mass is constant everywhere; weight changes with gravity.
What Is a Force?
- A force is a push or pull — it has both magnitude and direction (a vector), measured in newtons (N).
- Effects of forces: change an object's speed, direction, shape, or state of motion.
Balanced & Unbalanced Forces
| Balanced forces | Unbalanced forces | |
|---|---|---|
| Resultant force | Zero — the forces cancel each other out | Not zero — one direction "wins" |
| Motion | No change: an object at rest stays at rest; a moving object keeps going at constant speed in a straight line | The object speeds up, slows down, or changes direction |
| Example | A book resting on a desk — weight and normal reaction balance; two teams pulling equally in a tug-of-war | Kicking a stationary ball; a car accelerating from the traffic lights |
Types of Forces
| Force | What it does | Example |
|---|---|---|
| Weight (gravity) | Pulls objects towards Earth's centre — W = mg | A 60 kg student weighs about 600 N; a dropped pen falls down |
| Normal reaction | Support force from a surface, perpendicular to it | The desk pushing up on the book; the floor under your feet |
| Tension | Pulling force transmitted through a rope or string | Lifting a bucket with a rope; a tug-of-war rope |
| Friction | Opposes motion between surfaces in contact — rougher surface → more friction. Useful (walking, brakes, writing) but causes wear and wasted heat; reduced by lubricants, rollers/ball bearings, and streamlining | Brake pads slowing a bicycle wheel; shoes gripping the ground |
| Air resistance (drag) | Friction from air opposing a moving object — larger area → more drag | A parachute slows a falling skydiver |
Contact vs Non-Contact Forces
| Type | How it acts | Examples |
|---|---|---|
| Contact force | Objects must be touching | Friction, tension (rope), normal reaction, air resistance |
| Non-contact force | Acts at a distance — no touching needed | Gravitational force (weight), magnetic force |
Turning Effects of Forces
- A force can also produce a turning effect — e.g. using a spanner to loosen a nut, or a lever to open a tin.
- The longer the handle (greater distance from the pivot), the easier it is to turn — that's why long-handled spanners are used for tight nuts.
Pressure in Solids & Liquids
- P = F/A (Pa = N/m²) — smaller area → larger pressure. Sharp knife, nail point, high heels concentrate force on a small area.
- Liquid pressure: P = ρgh — increases with depth and liquid density; acts equally in all directions at a point.
- Dam walls are thicker at the bottom because water pressure is greatest at depth. Submarines have depth limits for the same reason.
- Atmospheric pressure: air pushes on everything around us — suction cups stick and we can drink through a straw because our mouth lowers the air pressure inside, so higher outside air pressure pushes the liquid up.
Exam tip: Pressure is a scalar (no direction); force is a vector. Always state units: N, Pa, J.
PHYS 2Thermal Energy & Processes
Three Modes of Heat Transfer
| Mode | How it works | Needs medium? | Example |
|---|---|---|---|
| Conduction | Vibrations passed between particles in contact; free electrons carry heat fast in metals | Yes (solid) | Spoon hot in soup; copper pan handle gets warm |
| Convection | Warmer, less dense fluid rises; cooler denser fluid sinks → convection current | Yes (fluid) | Boiling water circulation; sea breeze; hot-air balloon |
| Radiation | Infrared waves travel through empty space | No | Sun's heat reaching Earth; feeling a fire from a distance |
Good & Bad Conductors / Insulators
- Metals = good conductors (copper, aluminium) — used in cookware bases.
- Insulators: wood, plastic, rubber, air — used for pan handles, thermos flask walls (vacuum eliminates conduction & convection).
- Shiny/silvered surfaces reflect heat radiation — thermos flask, emergency blanket.
Melting & Boiling Points of Water
| Process | Temperature (at 1 atm) | Key point |
|---|---|---|
| Melting / freezing | 0 °C | Temp stays constant during change of state — energy goes into breaking bonds, not raising temp |
| Boiling / condensing | 100 °C | Boiling happens throughout the liquid at a fixed temperature; evaporation happens at any temperature at the surface only |
Thermal Expansion & Contraction
- Solids, liquids and gases expand when heated and contract when cooled.
- Gases expand the most, then liquids, then solids — which is why a hot-air balloon rises (hot air = less dense).
- Expansion changes volume → so the density of the substance also changes (same mass, bigger volume = lower density).
- Everyday applications: gaps left between railway rails and bridge sections; a small amount of mercury left in a thermometer bulb when filling it; electric wires sag more on hot days; a tight jar lid loosens after pouring hot water over it.
Radiation — What Affects the Rate?
- Colour & texture: dull black surfaces are good absorbers AND good emitters of heat radiation; shiny/silvered surfaces are poor absorbers and poor emitters (good reflectors).
- Surface temperature: the hotter the surface, the faster it emits radiation.
- Applications: radiant heaters have shiny curved backs (reflect heat forward); solar water heaters are painted black to absorb more; thermos flasks use silvered walls to reflect heat back in.
Temperature Units
- The SI unit of temperature is the kelvin (K). K = °C + 273, so 0 °C = 273 K and 100 °C = 373 K.
Evaporation cools: faster with higher temp, lower humidity, more air movement, larger surface area. This is why sweating cools us and wet clothes dry faster on a windy day. | Climate change: burning fossil fuels releases CO₂ (a greenhouse gas) — man-made causes include vehicles and industry; natural ones include volcanic eruptions.
PHYS 3Energy, Work & Power
Key Formulas
KE = ½mv² (J) |
GPE = mgh (J) |
Work = F × d (J, distance in direction of force)
Power = Work ÷ time (W = J/s) | Efficiency = useful output ÷ total input × 100%
Power = Work ÷ time (W = J/s) | Efficiency = useful output ÷ total input × 100%
Common Forms of Energy
| Form | Stored in / carried by | Example |
|---|---|---|
| Kinetic energy (KE) | Moving objects — KE = ½mv² | A rolling ball, flowing water |
| Gravitational potential energy (GPE) | Raised objects — GPE = mgh | Water held behind a dam, a book on a shelf |
| Chemical energy | Bonds in food, fuels, batteries | Petrol in a car, the food you eat |
| Electrical energy | Moving charges (current) | Current flowing through a lamp |
| Light (radiant) energy | Light waves, including infrared | Sunlight, torch beam |
| Sound energy | Vibrations travelling through a medium | A ringing bell |
| Thermal (internal) energy | Particles of hot substances | Hot soup, the Sun's core |
Energy Conversions (memorise these chains)
- Torch: chemical → electrical → light + thermal.
- Falling object: GPE → KE (+ a little sound and heat on impact).
- Photosynthesis: light energy → chemical energy stored in glucose.
- Car engine: chemical (petrol) → thermal + kinetic; most is "wasted" as heat and sound — that's why efficiency < 100%.
Law of Conservation of Energy
- Energy cannot be created or destroyed — only transferred (from one object to another) or converted (from one form to another).
- Falling object: GPE → KE (higher up = more GPE, less KE; just before impact = max KE).
- Trolley down a slope: some GPE becomes thermal energy in the wheels/track due to friction — that's why it never reaches the same height on the other side.
Energy Resources
| Type | Examples | Note |
|---|---|---|
| Renewable | Solar, wind, hydro, geothermal, biomass | Replenished naturally; low carbon emissions |
| Non-renewable | Coal, oil, natural gas, uranium | Finite; fossil fuels release CO₂ → greenhouse effect |
Exam tip: Efficiency is ALWAYS below 100% — some energy is "wasted" as heat and sound in every transfer.
PHYS 4Electricity & Circuits
Key Formulas (Ohm's Law)
V = IR (V in volts, I in amperes, R in ohms)
P = VI (power in watts)
P = VI (power in watts)
Circuit Components
| Component | What it does |
|---|---|
| Cell / battery | The energy source — pushes current around the circuit |
| Switch | Opens (breaks) or closes (completes) the circuit |
| Lamp | Converts electrical energy to light + heat |
| Fixed resistor | Opposes the flow of current — limits it |
| Variable resistor (rheostat) | Changes resistance → changes the current in the circuit |
| Ammeter | Measures current (A) — connected IN SERIES |
| Voltmeter | Measures potential difference (V) — connected IN PARALLEL |
Current, Potential Difference & Resistance
- Current (I) — the rate of flow of charge. SI unit: ampere (A).
- Potential difference (V) — the "push" that drives current between two points. SI unit: volt (V).
- Resistance (R) — how much a component opposes current flow. SI unit: ohm (Ω).
- More resistance → less current; more potential difference → more current.
Effects of an Electric Current
| Effect | What happens | Application |
|---|---|---|
| Heating effect | Current through a resistor makes it hot (electrical → thermal energy) | Electric kettle, iron, toaster, filament lamp |
| Magnetic effect | A current-carrying wire produces a magnetic field around it; coiling the wire makes an electromagnet | Bell, relay, electric motor, loudspeaker |
| Chemical effect | Current through a solution can cause chemical changes (e.g. plating metal onto objects) | Electroplating — e.g. chromium-plated taps |
Power & Electrical Energy Cost
- Power (P) = how fast an appliance converts energy. P = VI, SI unit: watt (W). A 100 W lamp converts energy faster than a 40 W one.
- The electricity bill is based on the kilowatt-hour (kWh): cost = power in kW × time in hours × rate per kWh. Example: a 2 kW heater running for 3 h uses 6 kWh.
- Reducing consumption: switch off lights and appliances when not in use, unplug standby devices, use energy-saving (LED) bulbs, run full loads only.
Series vs Parallel Circuits
| Series | Parallel | |
|---|---|---|
| Current | Same through all components | Splits between branches (I_total = I₁ + I₂) |
| Voltage | Shared: V_total = V₁ + V₂ | Same across each branch |
| If one bulb fails | All go out (circuit broken) | Others stay lit |
| Adding components | Bulbs get dimmer (R↑, I↓) | Total current increases (more paths) |
Conductors & Insulators
- Conductors: metals (copper wires) — free electrons move easily.
- Insulators: rubber, plastic, glass, wood — used to coat wires and plug casings.
- Ammeter in series; voltmeter in parallel with the component being measured.
Safety
- Fuse: thin wire that melts and breaks the circuit if current gets too high — protects appliances.
- Earth wire: third wire in plugs carries excess current to ground, preventing electric shock from metal casings.
Exam tip: Household appliances are wired in parallel so each gets the full 230 V and works independently.
BIOLOGY
Digestive System · Reproduction · Movement of Substances · Transport Systems · EcosystemsBIO 1Human Digestive System
Organs & Their Functions (in order)
| Organ | Function |
|---|---|
| Mouth | Mechanical breakdown (teeth) + amylase in saliva starts starch → maltose; tongue forms bolus |
| Oesophagus | Peristalsis pushes food to stomach (no digestion here) |
| Stomach | Pepsin digests protein; HCl kills bacteria & provides acidic pH for pepsin; churning forms chyme |
| Small intestine (duodenum) | Main digestion site — bile emulsifies fat; pancreatic amylase, trypsin, lipase finish the job |
| Ileum | Absorption of digested food into blood via villi (huge surface area) |
| Liver / Pancreas | Liver makes bile (stored in gall bladder); pancreas makes digestive enzymes + bicarbonate to neutralise acid |
| Large intestine | Absorbs water; bacteria make vitamins; faeces formed → rectum → anus |
Enzymes & Their Substrates (by location)
| Location | Food broken down | Enzyme(s) | End product |
|---|---|---|---|
| Mouth | Carbohydrates (starch) | Carbohydrase — amylase in saliva | Maltose (sugar) |
| Stomach | Proteins | Protease — pepsin (acidic pH ~2) | Peptides |
| Small intestine | Carbohydrates | Carbohydrases — amylase, maltase | Glucose |
| Proteins | Protease — trypsin (alkaline pH) | Amino acids | |
| Fats | Lipase (needs bile first to emulsify fat) | Fatty acids + glycerol |
Enzyme Properties
- Lock-and-key model: enzyme's active site fits only its specific substrate.
- Rate increases with temperature up to ~40 °C, then the enzyme denatures (active site changes shape) — irreversible.
- Each enzyme works best at a specific pH; extremes of pH also denature it.
Villi: finger-like projections in the ileum — huge surface area, thin walls, rich blood supply → fast absorption. Classic "adaptation" answer: structure → function link.
What Happens to the End Products?
- Glucose + oxygen are carried by the blood to every cell, where they are used in respiration (releasing energy), and for growth and tissue repair.
- Amino acids are also used to build new proteins for growth.
Bacteria — helpful or harmful? Bacteria in the large intestine help digest food and make vitamins (beneficial), but bacteria can also cause infections. | Diabetes: a disease where blood sugar is not controlled properly — sensible food choices (less sugar, more fibre) and regular exercise help fight it.
BIO 2Human Reproduction
Male & Female Systems
| Male | Female | |
|---|---|---|
| Gamete | Sperm (testes) — small, motile, tail for swimming | Egg / ovum (ovaries) — large, stores food for early embryo |
| Hormone | Testosterone (testes) | Oestrogen & progesterone (ovaries) |
| Ducts | Vas deferens carries sperm | Fallopian tubes carry egg — site of fertilisation |
Puberty & Heredity
- Puberty: the period of physical changes in early adolescence, driven by hormones (testosterone in boys; oestrogen in girls) — e.g. growth spurt, voice deepening in boys, breast development and menstruation starting in girls.
- Heredity: sexual reproduction passes genetic material from both parents to the offspring — each child receives a UNIQUE combination (half from mother via egg, half from father via sperm), which is why siblings look similar but not identical.
Birth Control & STIs
| Type | Examples | How it prevents conception |
|---|---|---|
| Temporary | Condom, oral pills (hormones), withdrawal | Pills stop ovulation; condom blocks sperm from reaching the egg — can be reversed when stopped |
| Permanent | Vasectomy (male: vas deferens cut), tubal ligation (female: fallopian tubes blocked) | Sperm or egg physically cannot meet — not easily reversible |
- STIs: syphilis & gonorrhoea are BACTERIAL → can be cured with antibiotics. AIDS (caused by HIV) is VIRAL → cannot be cured, only managed.
- Condoms are the ONLY method that also protects against STIs — they form a physical barrier.
Fertilisation & Development
- Fertilisation: sperm fuses with egg in the fallopian tube → zygote (23 pairs of chromosomes restored).
- Zygote divides repeatedly and implants in the uterine wall (~day 7) as a blastocyst.
- Placenta forms — exchanges oxygen, nutrients and waste between mother and foetus (blood does NOT mix directly).
- Pregnancy lasts ~40 weeks; the uterus grows to hold the baby.
Menstrual Cycle (~28 days)
| Phase | Days (approx.) | What happens |
|---|---|---|
| Menstruation | 1–5 | Uterine lining sheds — no egg fertilised last cycle |
| Follicle development | 6–13 | Oestrogen rises, rebuilding the uterine lining |
| Ovulation | ~14 | Ripe egg released from ovary (LH surge) (fertile period is day 10–15) |
| Luteal phase | 15–28 | Progesterone maintains lining; if no fertilisation, hormone levels fall → cycle repeats |
Exam tip: Fertilisation happens in the fallopian tube, NOT the uterus. Implantation happens in the uterus.
BIO 3Movement of Substances
Diffusion vs Osmosis
| Diffusion | Osmosis | |
|---|---|---|
| Moves | Any particles (gases, solutes) | Water only |
| Direction | High → low concentration | Dilute solution → concentrated solution (through a partially permeable membrane) |
| Example | Perfume spreading in a room; O₂ into alveoli | Water entering root hair cells; red blood cell swelling in pure water |
Active Transport
- Moves substances against the concentration gradient (low → high).
- Requires energy (ATP) from respiration.
- Example: root hair cells absorbing mineral salts when soil concentration is lower than inside the cell; reabsorption of glucose in kidney tubules / ileum.
Cell Response to Solutions
| Solution | Water movement | Animal cell | Plant cell |
|---|---|---|---|
| Hypotonic (dilute) | Into cell | Swells & bursts (haemolysis) | Turgid — firm, healthy |
| Iso-tonic | No net movement | Normal | Slightly flaccid |
| Hypertonic (concentrated) | Out of cell | Shrivels (crenation) | Plasmolysed — cytoplasm pulls away from wall |
Why plant cells don't burst: the rigid cell wall resists expansion, so turgor pressure builds instead. Turgid = ideal for support in non-woody plants.
BIO 4Transport Systems (Plants & Humans)
Plant Transport — Xylem vs Phloem
| Xylem | Phloem | |
|---|---|---|
| Transports | Water + dissolved mineral salts | Sucrose & amino acids (manufactured food) |
| Direction | Upward only (roots → leaves) | Bidirectional (source ↔ sink) |
| Cells | Dead, hollow tubes with lignin walls | Living sieve tubes + companion cells |
| Energy? | No — passive transpiration pull | Yes — active transport (ATP) |
Transpiration & Its Factors
- Loss of water vapour from leaves, mainly through stomata; creates the suction (transpiration pull) that draws water up the xylem.
- Cohesion–tension theory: water molecules stick to each other (cohesion) and to xylem walls (adhesion), forming an unbroken column from roots to leaves.
- Rate increases with: bright light, high temperature, low humidity, strong wind.
- Guard cells: turgid → stoma opens; flaccid → stoma closes. (Inner wall is thicker — it can't stretch as much.)
Human Circulatory System
| Artery | Vein | Capillary | |
|---|---|---|---|
| Walls | Thick, elastic | Thin, less elastic + valves | One cell thick |
| Pressure | High | Low | Very low |
| Direction | Away from heart | Towards heart | Exchange site with body cells |
The Heart & Double Circulation
- Four chambers: two atria (receive), two ventricles (pump). Left ventricle has the thickest wall — pumps to the whole body.
- Pulmonary circuit: right ventricle → lungs → left atrium. Systemic circuit: left ventricle → body → right atrium.
- Valves (tricuspid, bicuspid, semi-lunar) prevent backflow — the "lub-dub" sound is valves closing.
Blood Components
| Component | % of blood | Function |
|---|---|---|
| Plasma | 55% | Carries dissolved substances (nutrients, urea, hormones) |
| Red cells | 45% total | Biconcave, no nucleus — carry O₂ via haemoglobin; made in bone marrow |
| White cells | Fight infection: phagocytosis (engulf) & antibodies | |
| Platelets | Blood clotting to seal wounds |
Diffusion in Transport Systems
- In humans: digested food (glucose, amino acids) and oxygen diffuse from the blood into body tissues; carbon dioxide diffuses out. This happens at the capillaries — their one-cell-thick walls make diffusion fast.
- In plants: gases (CO₂ in, O₂ out) and mineral salts diffuse into and out of plant cells through the cell membrane.
Exceptions to remember: the pulmonary artery carries oxygen-POOR blood (to lungs); the pulmonary vein carries oxygen-RICH blood (from lungs). All other arteries = O₂-rich, veins = O₂-poor.
BIO 5Interactions Within Ecosystems
Levels of Organisation
- Population: all individuals of ONE species in an area (all the elephants).
- Community: all populations of different species living together.
- Ecosystem: community + its physical environment. Population density = number per unit area.
Biotic & Abiotic Factors
| Type | What it is | Examples — all needed for survival |
|---|---|---|
| Biotic (living) | The living parts of the ecosystem | Plants, animals, bacteria, fungi |
| Abiotic (non-living) | The physical environment | Air, water, temperature, light, minerals, acidity/alkalinity (pH) |
Types of Interactions
| Type | Species A | Species B | Example |
|---|---|---|---|
| Predation | + (predator) | − (prey) | Fox hunts mice |
| Mutualism | + | + | Oxpecker eats ticks off impala |
| Parasitism | + (parasite) | − (host) | Tick on dog; bracket fungus on tree |
| Commensalism | + (commensal) | 0 (unaffected host) | Barnacles on whale |
| Competition | − | − | Lions & hyenas competing for prey |
Predator–Prey Cycles
- Prey increases → more food for predators.
- Predators increase (lag behind prey).
- More predation → prey decreases.
- Fewer prey → predators decrease; cycle repeats. Predator peak ALWAYS lags prey peak.
Energy Flow & Food Chains / Webs
- Sun → producers (plants) → consumers (animals); decomposers recycle nutrients.
- A food chain is one straight path of "eaten by" arrows; a food web shows several linked food chains in the same ecosystem — more realistic, because most animals eat more than one thing.
- Photosynthesis (in producers) captures sunlight to make glucose; respiration (in all organisms) releases energy from that glucose. These two processes drive the whole food web.
- Energy flow is non-cyclical — lost as heat at every trophic level via respiration, excretion and radiation. Only ~10% passes to the next level.
- Nutrient flow IS cyclical — decomposers (bacteria & fungi) break down dead organisms and return minerals to the soil for plants to reuse.
Human Impact on Ecosystems
- Conserving the environment matters: deforestation, pollution and overhunting destroy habitats and reduce biodiversity.
- Motor vehicles and modern lifestyles release greenhouse gases → climate change → ecosystems (e.g. coral reefs, polar regions) are disrupted.
Adaptations
| Type | Definition | Examples |
|---|---|---|
| Structural | Physical body features | Cactus spines & fleshy stem (water storage); polar bear blubber; fish gills & streamlined body |
| Behavioural | Actions / responses | Bird migration; desert animals nocturnal; bears hibernate |
Extreme environments: polar = thick fur/blubber, small ears (reduce heat loss); desert = light colouring (reflect sun), large ears (fennec fox — dissipate heat), nocturnal habits. Match the adaptation to the problem it solves.