🔬 Year 10 Science

Biology: Cell Biology

Eukaryotic vs Prokaryotic Cells

• Eukaryotic cells (plants and animals): have a nucleus enclosed in a membrane, membrane-bound organelles, and are larger (typically 10–100 μm)
• Prokaryotic cells (bacteria): no nucleus — DNA is in a loop in the cytoplasm; no membrane-bound organelles; smaller (typically 0.1–10 μm); may have a cell wall (different composition from plant cells), plasmids, pili, and flagellum

Cell Organelles

• Nucleus: contains DNA; controls cell activity
• Cell membrane: controls what enters and leaves the cell
• Cytoplasm: where chemical reactions take place
• Mitochondria: site of aerobic respiration; energy release
• Ribosomes: site of protein synthesis
• Cell wall (plant, fungal, bacterial): provides structural support
• Chloroplast (plant): site of photosynthesis; contains chlorophyll
• Permanent vacuole (plant): maintains cell turgidity; filled with cell sap

Specialised Cells

• Red blood cell: no nucleus → more space for haemoglobin; biconcave disc → large surface area for oxygen transport
• Sperm cell: long tail for swimming; many mitochondria for energy; acrosome (contains enzymes to penetrate the egg)
• Egg cell: large with food reserves; cell membrane changes after fertilisation to prevent further sperm entering
• Nerve cell (neurone): very long axon; insulating myelin sheath; dendrites for receiving signals
• Root hair cell: large surface area for water and mineral ion absorption
• Ciliated epithelial cell: cilia sweep mucus up the airway

Stem Cells

• Stem cells: undifferentiated cells capable of dividing to produce specialised cells
• Embryonic stem cells: pluripotent — can differentiate into almost any cell type
• Adult stem cells: multipotent — can differentiate into a limited range of cell types (e.g. bone marrow stem cells → blood cells)
• Medical uses: potentially treat Parkinson's, diabetes, spinal cord injuries, leukaemia
• Ethical issues: use of embryos; religion (some consider the embryo a person); vs potential to save lives
• Plant meristems: plant stem cells located at root and shoot tips and in the cambium — allow plants to grow throughout their lives

Transport across Membranes

• Diffusion: net movement of particles from high to low concentration along a concentration gradient. Passive (no energy required). Rate increased by: steeper gradient, higher temperature, larger surface area, thinner membrane, smaller particles.
• Osmosis: diffusion of water molecules through a partially permeable membrane from a dilute solution (high water potential) to a more concentrated solution (low water potential). Passive.
• Active transport: movement against the concentration gradient, from low to high concentration. Requires energy (ATP) and carrier proteins. Example: root hair cells absorbing mineral ions from soil.

Biology: Organisation

Levels of Organisation

• Cell → tissue → organ → organ system → organism
• Tissue: a group of similar cells working together. Muscle tissue, glandular tissue, epithelial tissue.
• Organ: a group of different tissues working together. The stomach (muscular, glandular, and epithelial tissue).
• Organ system: a group of organs working together. The digestive system, the circulatory system.

Enzymes

• Enzymes are biological catalysts — they speed up chemical reactions without being used up
• Lock and key model: the enzyme has an active site with a specific shape. Only a complementary substrate can fit — explaining enzyme specificity.
• Induced fit model: more accurate. The active site is flexible and changes shape slightly to fit the substrate.
• Temperature: increasing temperature increases reaction rate until the optimum. Above the optimum, the enzyme denatures (active site changes shape irreversibly). Human enzymes: optimum ~37°C.
• pH: each enzyme has an optimum pH. Pepsin (stomach): optimum pH 2. Amylase (mouth): optimum pH 7. Outside the optimum, the enzyme denatures.
• Digestive enzymes: amylase (carbohydrates → glucose, in mouth and small intestine), protease (proteins → amino acids, in stomach and small intestine), lipase (lipids → fatty acids + glycerol, in small intestine)

The Circulatory System

• Double circulatory system: blood travels through the heart twice per circuit — once to the lungs (pulmonary circuit), once around the body (systemic circuit)
• The heart: 4 chambers — right and left atria (receive blood), right and left ventricles (pump blood). The left ventricle has a thicker wall — it pumps blood further (around the body).
• Blood vessels: arteries (thick muscular walls, carry blood away from heart at high pressure), veins (thinner walls, valves to prevent backflow, carry blood to the heart at low pressure), capillaries (one cell thick wall, site of exchange with tissues)
• Coronary heart disease: fatty deposits (atheroma/plaque) narrow the coronary arteries → reduced blood flow to heart muscle → angina or heart attack. Risk factors: high LDL cholesterol, high blood pressure, smoking, obesity, lack of exercise, family history.
• Treatments: lifestyle changes, statins (lower cholesterol), stents (metal mesh inserted to keep artery open), bypass surgery (a vein/artery from elsewhere is grafted to bypass the blockage)

Biology: Infection & Response

Pathogens and Disease

• Pathogen: a microorganism that causes disease. Types: bacteria, viruses, fungi, protists.
• Bacteria: living cells; damage host by producing toxins. Treated with antibiotics.
• Viruses: not living; replicate inside host cells, destroying them. NOT treated with antibiotics. Antiviral drugs target specific viruses. Vaccines prevent.
• Spread: direct contact, droplets (coughing/sneezing), contaminated food/water, vectors (mosquitoes → malaria)
• Measles (virus), HIV (virus), tobacco mosaic virus (plants), salmonella (bacteria), gonorrhoea (bacteria), malaria (protist — Plasmodium, spread by Anopheles mosquitoes), rose black spot (fungus)

The Immune System

• Non-specific defences: skin (barrier), mucus and cilia (respiratory tract), stomach acid (kills pathogens in food), tears (lysozyme enzyme)
• Phagocytes: white blood cells that engulf and destroy pathogens (phagocytosis). Non-specific — attack any pathogen.
• Lymphocytes: white blood cells that produce antibodies. Each lymphocyte makes one specific type of antibody complementary to a specific antigen on the pathogen. Antibodies cause: agglutination (clumping), marking for destruction, neutralising toxins.
• Memory cells: long-lived lymphocytes that remain after an infection. If the same pathogen is encountered again, the response is much faster and larger — producing immunity.
• Vaccines: introduce a harmless version (weakened pathogen, dead pathogen, antigen, mRNA) of the pathogen → immune system produces antibodies and memory cells → if real pathogen encountered, quickly destroyed before causing disease
• Herd immunity: if enough people are vaccinated, the pathogen cannot spread — protecting those who cannot be vaccinated (newborns, immunocompromised)

Biology: Bioenergetics

Photosynthesis

• Light-dependent reactions (in the thylakoid): light energy splits water (photolysis). Oxygen is released. ATP and NADPH are produced.
• Light-independent reactions / Calvin cycle (in the stroma): CO₂ is fixed using ATP and NADPH to produce glucose.
• Factors limiting photosynthesis: light intensity, CO₂ concentration, temperature (affects enzyme activity). The factor in shortest supply is the limiting factor.
• Glucose is used for: respiration (energy), cellulose (cell walls), starch (storage), proteins (with nitrate ions from the soil), lipids (seeds, cell membranes)

Aerobic Respiration

Anaerobic Respiration

• In animals: glucose → lactic acid (+ small amount of ATP). Occurs in muscle cells during intense exercise when oxygen supply is insufficient.
• In plants and yeast: glucose → ethanol + carbon dioxide (fermentation). Used in bread-making and brewing.
• Oxygen debt: after anaerobic respiration, extra oxygen is needed to break down lactic acid → oxidised to CO₂ and water. This is why we keep breathing heavily after exercise stops.

Chemistry: Atomic Structure & Periodic Table

Atomic Structure

• Atom: nucleus (protons + neutrons) + electrons in shells/energy levels
• Proton: charge +1, relative mass 1. Neutron: charge 0, relative mass 1. Electron: charge −1, relative mass ~0 (1/1836 of a proton)
• Atomic number (Z) = number of protons = number of electrons (in a neutral atom)
• Mass number (A) = protons + neutrons
• Electron configuration: 1st shell max 2; 2nd shell max 8; 3rd shell max 8 (for first 20 elements). e.g. Na (11 electrons): 2, 8, 1
• The outer electrons determine chemical properties. All elements in the same group have the same number of outer electrons.

The Periodic Table

• Dmitri Mendeleev (1869): arranged elements by atomic mass, leaving gaps for undiscovered elements. Modern table is ordered by atomic number.
• Groups: vertical columns. Elements in the same group have the same number of outer electrons → similar chemical properties.
• Periods: horizontal rows. Going across a period, one proton (and one electron) is added each time. Properties change dramatically across a period.
• Group 1 (Alkali metals): 1 outer electron. React vigorously with water → metal hydroxide + hydrogen gas. Reactivity increases down the group (outer electron is further from nucleus, less strongly attracted).
• Group 7 (Halogens): 7 outer electrons. Diatomic molecules (Cl₂, Br₂, I₂). Reactivity decreases down the group. More reactive halogen displaces a less reactive one from solution.
• Group 0 (Noble gases): full outer shells → very stable → unreactive. Used in: light bulbs, neon signs, helium balloons.
• Transition metals: middle of the periodic table. Hard, dense, high melting points, good conductors. Form coloured ions (Fe²⁺ green, Fe³⁺ yellow-orange, Cu²⁺ blue). Good catalysts (iron in Haber process, manganese dioxide in hydrogen peroxide decomposition).

Chemistry: Bonding & Properties

Ionic Bonding

• Metal + non-metal → electrons transferred. Metals lose electrons (form +ve ions); non-metals gain electrons (form −ve ions).
• Giant ionic lattice: strong electrostatic forces in all directions. High melting/boiling points. Conduct when molten or dissolved (ions free to move). Often soluble. Brittle.

Covalent Bonding

• Non-metal + non-metal → electrons shared
• Simple molecules (H₂O, CO₂, CH₄, NH₃): low melting/boiling points (weak intermolecular forces). Poor conductors (no charged particles free to move).
• Giant covalent (diamond, graphite, SiO₂): very high melting/boiling points (many strong covalent bonds). Diamond: does not conduct; each C bonded to 4 others. Graphite: conducts; each C bonded to 3 others with one delocalised electron; layers slide easily (lubricant). SiO₂: does not conduct; used in glass.
• Fullerenes: C₆₀ (buckminsterfullerene — "buckyball"), carbon nanotubes. High strength-to-weight ratio, electrical conductivity, potential medical and material applications.

Metallic Bonding

• Sea of delocalised electrons surrounding positive metal ions. Strong attraction between ions and electron sea.
• Properties: good conductors of heat and electricity (delocalised electrons), malleable/ductile (layers slide), high melting points (strong forces)

Chemistry: Quantitative Chemistry

Relative Atomic Mass and Relative Formula Mass

• Relative atomic mass (Aᵣ): the average mass of an atom of an element relative to 1/12 the mass of carbon-12. Given in the periodic table. For carbon: Aᵣ = 12.
• Relative formula mass (Mᵣ): sum of all Aᵣ values of atoms in the formula. H₂O: 2(1) + 16 = 18. NaCl: 23 + 35.5 = 58.5

The Mole

• One mole of any substance contains 6.02 × 10²³ particles (Avogadro's constant)
• Mass of 1 mole (molar mass) of a substance in grams = Mᵣ in grams
• Number of moles = mass (g) ÷ molar mass (g/mol)
• Concentration: n = c × V (moles = concentration (mol/dm³) × volume (dm³))

Conservation of Mass and Balancing Equations

• In a chemical reaction, atoms are rearranged — they are neither created nor destroyed. Total mass of products = total mass of reactants.
• A balanced equation has equal numbers of each type of atom on both sides: 2H₂ + O₂ → 2H₂O
• Empirical formula: the simplest whole-number ratio of atoms. e.g. C₂H₆ → empirical formula CH₃
• Percentage yield = (actual yield / theoretical yield) × 100. Always <100% due to: incomplete reactions, reversible reactions, loss of product during filtration/evaporation.
• Atom economy = (mass of desired products / total mass of products) × 100. Important for sustainable chemistry — minimising waste.

Physics: Energy

Energy Stores and Transfers

• Energy stores: kinetic, gravitational potential, elastic potential, chemical, thermal, magnetic, electrostatic, nuclear
• Energy is transferred between stores by: mechanical work (a force moving through a distance), electrical work, heating, radiation
• Conservation of energy: energy cannot be created or destroyed — it is transferred between stores. In any process, total energy of the system is conserved.
• Dissipation: in real systems, some energy is always transferred to thermal energy stores in the surroundings (friction, air resistance, electrical resistance). This energy is "wasted" — it cannot be usefully recovered.

Power and Efficiency

• Power = energy transferred / time. P = E/t. Unit: Watts (W) = Joules per second
• Efficiency = useful output energy transfer / total input energy transfer. Can be expressed as a fraction or percentage. Always ≤ 1 (or ≤ 100%).
• Specific heat capacity (c): the energy needed to raise the temperature of 1 kg of a substance by 1°C. Unit: J/kg°C
• E = mcΔT where ΔT is the temperature change

Physics: Electricity

Circuit Symbols and Basics

• Current (I): the rate of flow of charge. Unit: Ampere (A). I = Q/t (Q = charge in coulombs, t = time in seconds)
• Voltage/Potential difference (V): the energy transferred per unit charge. Unit: Volt (V)
• Resistance (R): how much a component opposes current flow. Unit: Ohm (Ω)
• Ohm's Law: V = IR. A component obeys Ohm's Law if the ratio V/I is constant (at constant temperature).
• Ohmic conductors: resistors at constant temperature — linear V-I graph
• Non-ohmic components: filament lamp (resistance increases as it heats up — non-linear graph); diode (only conducts in one direction — almost zero resistance in forward direction, very high in reverse)
• LDR (light-dependent resistor): resistance decreases as light intensity increases
• Thermistor: resistance decreases as temperature increases

Series and Parallel Circuits

• Series: all components in one loop. Current the same throughout. Voltage shared. Total resistance = R₁ + R₂ + R₃.
• Parallel: components in separate branches. Voltage the same across all branches. Current splits. 1/Rₜ = 1/R₁ + 1/R₂ (total resistance is always less than the smallest individual resistance).

Electrical Power

Physics: Particle Model of Matter

States of Matter

• Solid: particles in fixed positions, vibrating. Cannot flow. Definite shape and volume. Incompressible.
• Liquid: particles close together, free to move. Can flow. Takes the shape of the container but has fixed volume. Incompressible.
• Gas: particles far apart, moving rapidly in all directions. Can flow. No fixed shape or volume. Compressible. Low density.
• Changes of state: melting, freezing, evaporation, condensation, sublimation, deposition. During a change of state, temperature does not change — energy goes into breaking/forming intermolecular bonds.

Density

Specific Heat Capacity and Specific Latent Heat

• Specific heat capacity (c): energy needed to raise 1 kg of a substance by 1°C. E = mcΔT
• Specific latent heat (L): energy needed to change the state of 1 kg of a substance without changing its temperature. E = mL. Unit: J/kg.
• Latent heat of fusion: solid → liquid (or reverse)
• Latent heat of vaporisation: liquid → gas (or reverse). Much larger than latent heat of fusion (more bonds broken)