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GPSTR & HSTR Science Study Notes — 2026

1. Scientific Method

• Independent variable: the factor deliberately changed.
• Dependent variable: the factor measured.
• Control variables: factors kept constant.
• Accuracy: closeness to the true value.
• Precision: closeness of repeated measurements.
• Validity: whether the experiment measures what it should.
• Reliability: whether repeated results are consistent.

Question → Hypothesis → Fair test → Results → Analysis → Conclusion
    ↑                                                        ↓
    └──────────── Improved question or method ───────────────┘

Important graph rules:

• Independent variable on the x-axis.
• Dependent variable on the y-axis.
• Include units.
• Use a suitable scale.
• Draw a line of best fit.

2. Biology

Cell structures

Plant cell                         Animal cell
┌────────────────────┐             ┌───────────────┐
│ Cell wall          │             │ Cell membrane │
│ ┌────────────────┐ │             │ Nucleus       │
│ │ Cell membrane  │ │             │ Mitochondria  │
│ │ Nucleus        │ │             └───────────────┘
│ │ Chloroplasts   │ │
│ │ Large vacuole  │ │
│ └────────────────┘ │
└────────────────────┘

• Nucleus: controls cell activities and contains genetic material.
• Cell membrane: controls movement into and out of the cell.
• Mitochondria: site of aerobic respiration.
• Chloroplasts: absorb light for photosynthesis.
• Cell wall: provides support in plant cells.
• Vacuole: contains cell sap and maintains turgor.

Transport

• Diffusion: movement from high concentration to low concentration.
• Osmosis: movement of water through a partially permeable membrane.
• Active transport: movement against the concentration gradient using energy.

Key equations

Carbon dioxide + water → glucose + oxygen
                 photosynthesis

Glucose + oxygen → carbon dioxide + water + energy
                 aerobic respiration

Human systems

Air → trachea → bronchi → bronchioles → alveoli ⇄ blood
Food → stomach → small intestine → blood → body cells

Alveoli are efficient because they have:

• a large surface area;
• thin walls;
• a good blood supply;
• a moist surface.

3. Chemistry

Particle model

Solid              Liquid              Gas
● ● ●              ●  ● ●              ●       ●
● ● ●              ● ●  ●                 ●
● ● ●               ●   ●              ●          ●
Fixed positions    Close and moving    Far apart and fast

• Heating increases particle kinetic energy.
• A change of state is a physical change.
• No new substance is formed during melting, freezing, boiling, or condensation.

Atomic structure

• Proton: positive charge.
• Neutron: no charge.
• Electron: negative charge.
• Atomic number = number of protons.
• Mass number = protons + neutrons.

Chemical bonding

• Ionic bonding: electrons are transferred between atoms.
• Covalent bonding: atoms share electrons.
• Metallic bonding: positive ions are surrounded by delocalised electrons.

Acids and bases

• pH below 7: acidic.
• pH 7: neutral.
• pH above 7: alkaline.

Acid + base → salt + water
Acid + carbonate → salt + water + carbon dioxide

Reaction rates

A reaction becomes faster when:

• temperature increases;
• concentration increases;
• pressure increases for gases;
• surface area increases;
• a catalyst is added.

A catalyst lowers activation energy and is not used up.

4. Physics

Motion and forces

             Normal reaction
                   ↑
Friction ← [ block ] → Applied force
                   ↓
                 Weight

Formulas:

• speed = distance ÷ time
• acceleration = change in velocity ÷ time
• force = mass × acceleration
• weight = mass × gravitational field strength
• work done = force × distance
• power = energy transferred ÷ time
• efficiency = useful output ÷ total input × 100

A resultant force of zero means that an object is stationary or moving at constant velocity.

Waves

       crest              crest
         ▲                  ▲
         │ amplitude        │
─────────┼───────╱╲──────────┼── equilibrium
              ╱    ╲
             trough

        ←── wavelength ──→

• Transverse wave: vibrations are perpendicular to the direction of travel.
• Longitudinal wave: vibrations are parallel to the direction of travel.
• wave speed = frequency × wavelength
• Frequency is measured in hertz (Hz).

Electricity

        ┌──────[ resistor ]──────┐
        │                       │
      (+) Battery               │
        │                       │
        └───────────────────────┘

• current = charge ÷ time
• potential difference = energy ÷ charge
• resistance = voltage ÷ current
• power = voltage × current

Series circuits:

• same current throughout;
• voltage is shared.

Parallel circuits:

• same voltage across each branch;
• current is divided between branches.

5. Earth and Environment

Water cycle

                 Condensation
                     ↓
Evaporation → Clouds → Precipitation
     ↑                    ↓
 Oceans/Lakes ← Runoff ← Land
                     ↓
              Groundwater

• Photosynthesis removes carbon dioxide from the atmosphere.
• Respiration, decomposition, and combustion release carbon dioxide.
• The greenhouse effect occurs when gases absorb outgoing infrared radiation.
• Renewable resources include solar, wind, hydroelectric, geothermal, and biomass.
• Non-renewable resources include coal, oil, gas, and many minerals.

6. Exam Skills

• State: give a short fact.
• Define: give the exact meaning.
• Describe: state what happens or what a graph shows.
• Explain: give a reason using scientific principles.
• Compare: give similarities and differences.
• Evaluate: discuss evidence, strengths, limitations, and judgement.

For calculation questions:

1. Write the formula.
2. Substitute the values.
3. Show the unit.
4. Round sensibly.
5. Check whether the answer is realistic.

Model explanation:

The rate increases as temperature rises because particles have more kinetic energy. Therefore, collisions occur more frequently and more particles have enough energy to react.

7. Final Revision Checklist

• I can explain accuracy, precision, validity, and reliability.
• I can label plant and animal cells.
• I can explain diffusion, osmosis, and active transport.
• I can write the equations for photosynthesis and respiration.
• I can calculate speed, force, work, power, density, and efficiency.
• I can explain acids, bases, bonding, and reaction rates.
• I can interpret graphs and identify anomalies.
• I can explain the water cycle, carbon cycle, and greenhouse effect.
• I can plan a safe and fair scientific investigation.
• I can answer “explain” questions using: because → scientific principle → result.