Biology and Physics Concepts: Cell Structure to Forces
Characteristics of Living Organisms (MRS. GREN)
- Movement (change position)
- Respiration (convert nutrients) 呼吸
- Sensitivity (sense) 敏感
- Growth (permanent increase)
- Reproduction (gametes, fertilisation) 繁殖
- Excretion (waste products removed) 排泄
- Nutrition (taking of nutrients into the body)
Cell Structure
Animal Cells
- Cytoplasm: The jelly-like substance filling the cell.
- Cell Membrane: Controls substances entering and leaving the cell.
- Nucleus: Contains genetic material that controls how a cell grows and works.
- Mitochondria: The site of aerobic respiration (有氧呼吸).
- Ribosomes: Make protein.
Plant Cells
- Cell Wall: Outer layer providing support for its shape.
- Cell Membrane: Inner layer.
- Large Vacuole: Contains cell sap.
- Chloroplasts: Contain chlorophyll to absorb sunlight.
- Nucleus: Control center for genetic material.
Bacterial Cells (细菌细胞)
- No nucleus (single chromosome).
- Plasmids: Smaller circles of DNA.
Magnification Calculation
Magnification = Image length / Actual length.
Experimental Accuracy
We repeat experiments to improve the accuracy (准确) of the results and reduce sources of error.
We measure mass (not height) because the plant may not grow straight or might fall over.
States of Matter and Particle Arrangement
Solid
- Fixed position and fixed shape.
- Regular arrangement.
- Particles move very slowly.
- Cannot be compressed.
Liquid
- Particles are not in fixed positions; irregular arrangement.
- Fixed volume.
- Cannot be compressed.
Gas
- Random arrangement.
- No fixed shape or volume.
- Particles move quickly.
- Can be compressed due to weak forces between particles.
Phase Changes: Solid ↔ Liquid ↔ Gas
Atomic Structure and Bonding
Compounds and Atomic Particles
Compounds: Two or more different elements chemically combined.
Valence: Refers to the outermost electron shell.
- Electrons: Negative charge.
- Protons: Positive charge (atomic number).
- Neutrons: No charge.
In a neutral atom, the number of protons equals the number of electrons.
Nucleon (Mass Number) = Protons + Neutrons.
Electrons are dynamic (动态) particles, not static.
Ions
- Atoms: Neutral particles (can gain or lose electrons).
- Ions: Charged particles.
- Cations: Positively charged (lose electrons; Protons > Electrons).
- Anions: Negatively charged (gain electrons; Protons < Electrons).
Chemical Bonding Types
- Covalent: Between non-metal and non-metal.
- Ionic: Between metal and non-metal. (Note: Ionic bonding does not occur only between metals.)
Motion and Forces in Physics
Speed and Acceleration
Acceleration (加速) is the change in speed over time (positive gradient on a speed-time graph).
Acceleration = Change in speed / Time taken.
Deceleration (减速) is negative acceleration (negative gradient).
Distance: Area under the speed-time graph (triangle area).
Acceleration = (Final speed – Initial speed) / Time taken.
Weight and Density
Weight (N) = Mass (kg) × 9.8 (Gravitational field strength).
Density
Density (ρ) = Mass (g) / Volume (cm³).
- If Density < Water: Floats.
- If Density = Water: Suspended (在水中间).
- If Density > Water: Sinks.
Relationship: Mass increase $\rightarrow$ Density increase. Volume increase $\rightarrow$ Density decrease.
Forces
Force (Push or Pull): Measured in Newtons (N).
Resultant Force: Total of all forces added up.
Forces can: 1. Change speed of an object. 2. Change direction of movement. 3. Change shape.
Types: Contact Force (接触力量) and Non-contact Force (非接触力量).
Balanced Forces: No resultant force.
Newton’s Second Law: Force = Mass × Acceleration. (Greater force yields greater acceleration; greater mass requires more force for the same acceleration).
Energy and Work
Energy Types and Conservation
Energy Stored: Kinetic, Gravitational Potential, Chemical, Elastic, Nuclear, Electrostatic, Internal Energy.
Principle of Conservation of Energy (能量守恒定律): Energy cannot be created or destroyed, only transferred.
Energy Calculations
- Kinetic Energy (J) = ½ × Mass (kg) × Velocity² (m/s).
- Gravitational Potential Energy (J) = Mass (kg) × 9.8 × Height (m).
Energy Sources:
- Water energy: Dams.
- Wind energy: Windmills.
- Solar energy: Solar panels.
- Geothermal energy: Hot springs.
Work, Power, and Efficiency
Work Done (W): Equal to the amount of energy transferred. W (J) = Force (N) × Distance (m).
Power (P): Work done per unit time. P (W) = Work done (J) / Time Taken (s).
Efficiency: (Useful energy output / Total energy input) × 100%. (Energy is lost due to heat and friction).
Pressure
Pressure: Force per unit area. Pressure (Pa) = Force (N) / Area (m²).
Particle Movement: Diffusion and Osmosis
Diffusion: Net movement of particles from a region of higher concentration to lower concentration. All particles possess kinetic energy.
Function: Transport useful substances into cells and waste substances out.
Osmosis: Net movement of water molecules from a region of higher water potential to lower, through a partially permeable membrane.