Physics Light and Photography Biology Genes and Environmental Chemistry Revision

Transverse Waves: Vibrations move up and down while waves move side to side (e.g., light).
Longitudinal Waves: Vibrations move back and forward (e.g., sound).
Wave Components:
- Peak: Top of the wave.
- Trough: Bottom of the wave.
- Amplitude: The height of the wave.
- Wavelength: The distance from one crest to another.

Reflection: Light bounces off surfaces. Rule: Angle of incidence $=$ angle of reflection.
Refraction: Light bends when passing through different materials like air to water or air to glass.
Diffraction: Waves spread after passing through a gap; a smaller gap results in bigger diffraction.
Color of Light: White light consists of orange, red, yellow, green, blue, indigo, and violet. Prisms split white light.
Pinhole Cameras: Use a tiny hole to project an image that is upside down and smaller.
Convex Lenses: Curve upward and focus light together; used in cameras and magnifying lenses.
Concave Lenses: Curve inward and spread light out.
Digital Photography: Modern cameras use sensors to turn light into pixels instead of film.

DNA: Genetic material with a double helix shape carrying growth and reproduction instructions.
Genes: Small segments of DNA containing specific information (e.g., eye color).
Chromosomes: Long strands of DNA in the cell nucleus. Humans typically have $23$ pairs ( $23$ from each parent).
Sex Cells: Female (egg cell) and male (sperm cell).
Inherited Diseases: Conditions passed via genes, including cystic fibrosis, sickle cell disease, and haemophilia.
Environmental Factors: Inheritance is influenced by diet, sunlight, smoking, and exercise.

Genetic Engineering: Scientists modify genetic material to provide organisms with better characteristics.
Evolution: A process occurring over millions of years to adapt organisms to habitats.
Mutations: Changes in DNA that can be harmful, good, or neutral.

Pollutants: Harmful substances like chemical waste, plastic, smoke, and oil spills.
Water Quality (pH): Measured on a scale where $0\text{--}6$ is acidic, $7$ is neutral, and $8\text{--}14$ is alkaline.
Dissolved Oxygen: Required by fish; levels decrease due to pollution, algae, or warm temperatures.
Acid Rain: Caused when sulfur dioxide and nitrogen oxides mix with atmospheric water.
Greenhouse Gases: Trap heat leading to global warming; includes carbon dioxide, methane, water vapour, and nitrous oxide.
Ocean Acidification: Occurs when oceans absorb too much carbon dioxide, dissolving animal shells and damaging coral reefs.
Catalytic Converters: Devices in cars that convert toxic gases (e.g., carbon monoxide) into less harmful ones (e.g., carbon dioxide).
Water Treatment: The process of making water safe through screening, filtration, sedimentation, and chlorination.