🔬 Year 7 Science

Biology – Cells & Life Processes

The Seven Life Processes (MRS GREN)

• Movement – ability to move
• Respiration – releasing energy from food
• Sensitivity – responding to the environment (stimuli)
• Growth – increasing in size and complexity
• Reproduction – producing offspring
• Excretion – removing waste products
• Nutrition – taking in food/energy

Animal Cell vs Plant Cell

• Both have: cell membrane, nucleus, cytoplasm, ribosomes, mitochondria
• Only plant cells have: cell wall (cellulose), chloroplasts, large permanent vacuole
• Cell membrane: controls what enters and leaves the cell
• Nucleus: contains DNA; controls the cell's activities
• Cytoplasm: jelly-like fluid where chemical reactions occur
• Mitochondria: site of aerobic respiration; releases energy
• Chloroplasts: contain chlorophyll; where photosynthesis occurs (plant only)
• Cell wall: made of cellulose; supports and strengthens the plant cell
• Vacuole: stores cell sap; keeps cells firm (turgid)

Specialised Cells

• Red blood cells: no nucleus (more room for haemoglobin); biconcave shape (large surface area)
• Sperm cell: long tail (flagellum) for swimming; lots of mitochondria for energy
• Egg cell (ovum): large with nutrients to feed the developing embryo
• Root hair cell: long hair-like extension to increase surface area for absorbing water
• Nerve cell (neurone): very long with branches to carry signals across the body
• Muscle cell: contains protein fibres that can contract

From Cells to Organisms

• Cell → Tissue → Organ → Organ system → Organism
• e.g. Muscle cells → Muscle tissue → Heart → Circulatory system → Human body

Microscopes

• Light microscopes magnify up to ~1000×; used in school labs
• Electron microscopes magnify up to 1,000,000×; reveal sub-cellular structures
• Total magnification = eyepiece lens × objective lens (e.g. 10× × 40× = 400× magnification)

Biology – Reproduction

Sexual vs Asexual Reproduction

• Sexual reproduction: requires two parents; produces genetically unique offspring; involves gametes (sex cells)
• Asexual reproduction: one parent; offspring are genetically identical (clones); examples: bacteria dividing, runners in strawberries, bulbs

Human Reproductive System

• Gametes: sperm (male) and egg/ovum (female); each contain half the normal number of chromosomes
• Fertilisation: sperm and egg fuse → forms a zygote with a full set of chromosomes
• Gestation: 9 months (approximately 40 weeks) in humans
• Placenta: supplies the foetus with nutrients and oxygen from the mother's blood
• Umbilical cord: connects foetus to placenta

Puberty

• Puberty is triggered by hormones (oestrogen in females, testosterone in males)
• In females: ovulation begins, menstrual cycle starts, breasts develop, growth spurt, body hair
• In males: sperm production begins, voice breaks, muscles develop, body hair
• Menstrual cycle: approximately 28 days; ovulation occurs around day 14

Plant Reproduction

• Parts of a flower: stamen (anther + filament) = male; carpel (stigma + style + ovary) = female; petals; sepals
• Pollination: transfer of pollen from anther to stigma — by insects (bright colours/scent) or wind (light pollen/feathery stigma)
• Fertilisation: pollen tube grows to ovary; male gamete fuses with ovule → seed
• Seed dispersal: wind, water, animals (eaten or carried), explosion
• Germination: needs warmth, water, and oxygen (not light at first)

Biology – Ecosystems & Food Chains

Key Vocabulary

• Ecosystem: all living things in an area plus the non-living environment
• Habitat: the place where an organism lives
• Population: all individuals of one species in an area
• Community: all populations of different species living in the same area
• Producer: a plant that makes its own food via photosynthesis
• Consumer: an organism that eats other organisms
• Herbivore: eats only plants; Carnivore: eats only animals; Omnivore: eats both
• Predator: hunts and eats prey
• Decomposer: breaks down dead material (e.g. bacteria, fungi)

Food Chains & Food Webs

• Food chain shows the direction of energy flow: Producer → Primary consumer → Secondary consumer → Tertiary consumer
• Arrows show where energy goes (not what eats what!): grass → rabbit → fox
• Food web: several interconnected food chains in an ecosystem
• If one species is removed from a food web, it can affect all others (predator–prey relationships)

Adaptation

• Organisms have features (adaptations) that help them survive in their habitat
• Polar bear adaptations: white fur (camouflage), thick fur and fat layer (insulation), large paws (spread weight on ice)
• Cactus adaptations: thick waxy stem (stores water), spines (protection, less surface area), deep roots (reach water)

Photosynthesis

• Chlorophyll in chloroplasts absorbs light (mostly red and blue wavelengths)
• Glucose is used for: respiration, growth, making starch for storage, making cellulose
• Factors that increase the rate: more light, higher CO₂ concentration, higher temperature (up to a point)

Chemistry – Particles & States of Matter

The Three States of Matter

• Solid: particles close together in fixed positions, vibrate; definite shape and volume; cannot be compressed
• Liquid: particles close together but can move and slide past each other; definite volume but no fixed shape; flows
• Gas: particles far apart, moving randomly and fast; no fixed shape or volume; easily compressed

Changes of State

• Melting: solid → liquid (heating)
• Freezing: liquid → solid (cooling)
• Evaporation/Boiling: liquid → gas (heating)
• Condensation: gas → liquid (cooling)
• Sublimation: solid → gas directly (e.g. dry ice)
• Changes of state are physical changes — the substance is not altered, just rearranged

Melting Points and Boiling Points

• Melting point: temperature at which a substance changes from solid to liquid
• Boiling point: temperature at which a substance changes from liquid to gas throughout
• Water: melts at 0°C, boils at 100°C (at standard pressure)
• Pure substances have sharp melting/boiling points; mixtures melt/boil over a range of temperatures

Diffusion

• Movement of particles from an area of high concentration to an area of low concentration
• Occurs in gases and liquids (not solids — particles can't move freely)
• Increases with: higher temperature, smaller particles

Chemistry – Elements, Compounds & Mixtures

Elements

• An element is a substance made of only one type of atom; cannot be broken down further by chemical means
• 118 known elements; each has a chemical symbol (1–2 letters)
• e.g. O = oxygen, C = carbon, Na = sodium (from Latin "Natrium"), Fe = iron (from "Ferrum")

Compounds

• A compound is a substance made of two or more different elements chemically joined
• Properties are different from the elements it contains
• e.g. H₂O (water) = hydrogen + oxygen bonded together
• NaCl (table salt) = sodium + chlorine bonded together
• Compounds can only be separated by chemical reactions

Mixtures

• A mixture contains two or more substances that are NOT chemically joined
• The substances keep their own properties and can be separated by physical means
• Examples: air (gas mixture), seawater (salt dissolved in water), sand and water

Separating Mixtures

• Filtration: separates an insoluble solid from a liquid (e.g. sand from water)
• Evaporation: removes a liquid from a dissolved solid (e.g. getting salt from saltwater)
• Distillation: separates liquids with different boiling points; the liquid evaporates, cools, and condenses
• Chromatography: separates different coloured dyes (pigments) in a mixture (e.g. inks in felt-tip pens)
• Magnetic separation: uses a magnet to remove magnetic materials (e.g. iron filings from sand)

Chemistry – The Periodic Table

• Arranged by increasing atomic number (number of protons)
• Period: horizontal row — elements have the same number of electron shells
• Group: vertical column — elements have the same number of outer electrons and similar properties
• Metals are on the left and middle; non-metals are on the right; metalloids on the dividing line
• Over 75% of elements are metals

Key Groups

• Group 1 (Alkali metals): Li, Na, K — very reactive, soft, shiny, react violently with water; reactivity increases down the group
• Group 7 (Halogens): F, Cl, Br, I — non-metals, diatomic molecules (Cl₂, Br₂); reactivity decreases down the group
• Group 0 (Noble gases): He, Ne, Ar — very unreactive because they have a full outer shell
• Transition metals: middle block — denser, harder, higher melting points, less reactive than Group 1

Atomic Structure

• Protons (positive charge) and neutrons (no charge) are in the nucleus
• Electrons (negative charge) orbit the nucleus in shells
• Shell capacities: 1st = 2, 2nd = 8, 3rd = 8
• e.g. Sodium (Na): 11 protons, 11 electrons, configuration = 2, 8, 1

Chemistry – Chemical Reactions

Signs of a Chemical Reaction

• Production of a gas (effervescence/bubbling)
• Formation of a precipitate (solid forms in a liquid)
• Change in colour
• Temperature change (exothermic = heat released; endothermic = heat absorbed)
• Irreversible change (often hard to reverse)

Word Equations

• Reactants → Products
• e.g. Magnesium + Oxygen → Magnesium oxide
• e.g. Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water

Acids and Alkalis

• pH scale: 0–14. Below 7 = acid; 7 = neutral; above 7 = alkali
• Indicators: litmus (red in acid, blue in alkali), universal indicator (range of colours)
• Neutralisation: acid + alkali → salt + water
• Common acids: hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃)
• Common alkalis: sodium hydroxide (NaOH), calcium hydroxide, ammonia solution

Combustion

• Combustion = burning; requires: fuel, oxygen, and heat (fire triangle)
• Complete combustion: fuel + oxygen → carbon dioxide + water (blue flame)
• Incomplete combustion: not enough oxygen → carbon monoxide (CO) produced (poisonous) + carbon (soot)
• Hydrocarbons burn in oxygen: e.g. methane + oxygen → carbon dioxide + water

Physics – Forces & Motion

Types of Force

• Contact forces: friction, air resistance, tension, normal force, upthrust
• Non-contact forces: gravity, magnetism, electrostatic force
• Forces are measured in Newtons (N)
• Forces have both size and direction — they are vectors

Effects of Forces

• Forces can: change speed, change direction, change shape, start or stop movement
• Balanced forces: forces are equal in opposite directions → object stays still or moves at constant speed
• Unbalanced forces: a net (resultant) force exists → the object accelerates in the direction of the larger force

Gravity and Weight

• Gravity is a non-contact force that attracts masses towards each other
• On Earth, gravity pulls objects towards the centre of Earth
• Mass: the amount of matter in an object (kg) — stays the same everywhere
• Weight: the gravitational force acting on a mass (N) — changes on different planets
Weight Formula Weight (N) = mass (kg) × gravitational field strength (N/kg) On Earth: g = 10 N/kg | On Moon: g ≈ 1.6 N/kg

Friction

• Friction opposes motion between surfaces
• Useful friction: brakes, tyres gripping road, walking (feet don't slip)
• Unhelpful friction: wears down machine parts, wastes energy as heat
• Reduce friction: lubricants (oil, grease), smooth surfaces, ball bearings, streamlining

Speed

• Average speed: total distance ÷ total time (used when speed varies during journey)
• Distance-time graph: gradient = speed. Horizontal line = stationary. Steeper gradient = faster

Physics – Energy

Stores of Energy

• Kinetic: energy of movement (moving objects)
• Gravitational potential: energy due to height (objects raised above ground)
• Elastic potential: stored in stretched or compressed objects (springs, elastic bands)
• Thermal: energy stored in the temperature of an object
• Chemical: stored in food, fuel, batteries
• Magnetic: energy in a magnetic field
• Electrostatic: energy in separated electric charges
• Nuclear: energy stored in the nucleus of atoms

Energy Transfers

• Energy cannot be created or destroyed — only transferred between stores (conservation of energy)
• Methods of transfer: mechanical (forces), electrical (current), radiation (waves), heating
• e.g. A battery torch: Chemical → Electrical → Light + Thermal

Renewable & Non-Renewable Energy

• Non-renewable: fossil fuels (coal, oil, natural gas), nuclear — will run out; release CO₂ (except nuclear)
• Renewable: solar, wind, hydroelectric, tidal, geothermal, biomass — will not run out; generally lower carbon
• Fossil fuels formed from decayed organisms over millions of years
• Nuclear: uses uranium; produces radioactive waste; no CO₂ during operation but waste disposal is an issue

Physics – Light & Sound

Light

• Light is a transverse wave that can travel through a vacuum (no medium needed)
• Light travels at approximately 300,000,000 m/s (3×10⁸ m/s) in a vacuum
• Luminous objects produce their own light (sun, light bulb, candle)
• Non-luminous objects reflect light (moon, mirror, this page)
• Reflection: angle of incidence = angle of reflection (measured from the normal)
• Refraction: light bends when it passes from one medium to another (e.g. air to glass) because its speed changes
• Dispersion: white light splits into a spectrum (ROY G BIV) when passed through a prism
• Colour: objects appear a colour because they reflect that wavelength and absorb others

Sound

• Sound is a longitudinal wave — particles vibrate in the same direction as the wave travels
• Sound needs a medium (cannot travel through a vacuum)
• Sound travels faster in solids > liquids > gases (particles closer together)
• Speed of sound in air: approximately 340 m/s
• Amplitude: the height of the wave — controls volume (loudness). Measured in decibels (dB)
• Frequency: the number of waves per second — controls pitch. Measured in Hertz (Hz)
• Human hearing range: approximately 20 Hz to 20,000 Hz
• Ultrasound (>20,000 Hz): used in medical imaging and by bats for echolocation