Inheritance + Waves

• Light travels at different speeds depending on its colour, with violet being the fastest and red being the slowest.
• Wave speed = Frequency x Wavelength
• The speed of light is approximately 300 million metres per second (m/s).
• Inheritance is the transmission of genetic information from generation to generation.
• Chromosomes are thread-like structures made of DNA, carrying genetic information in the form of genes.
• Chromosomes are located in the nucleus of the cell.
• A gene is a length of DNA found on a chromosome with a sequence of bases that code for a specific protein, eg enzymes, collagen.
• Genes control our characteristics and are the code for protein.
• Alleles are forms of genes that differ in the nucleotide sequence of the DNA.
• Humans have 23 different chromosomes in each cell, 2 pairs of each meaning we have 46 chromosomes.
• In average body cell, we have 44 chromosomes, these are diploid cells.
• Gametes have half the number of normal chromosomes and are haploid (they have 23 chromosomes)
• Mitosis is used to repair broken tissue, replace cells, growth, and asexually reproduce.
• Meiosis is used to produce gametes with half the number of chromosomes
• During meiosis, homologous chromosome pair up and exchange genetic material through crossing over.
• Waves are periodic disturbances that transfer energy but not matter
• Transverse waves oscillate perpendicular to direction of wave travel
• Longitudinal waves oscillate parallel to direction of wave travel
• Longitudinal waves have compressions and rarefactions. Eg, sound and P-earthquake waves.
• Transverse waves have crests and troughs. Eg, Electromagnetic radiation, S-earthquake waves, vibration along a string.
• Only electromagnetic radiation does not rely on a medium.
• Wave equation: v=fλ
• v= velocity in ms^-1

  f= frequency in Hertz (s^-1)

  λ= wave length in m.
• If a wave speeds up when moving into another medium, it will bend away from the normal.
• refractive index , n = speed of light in a vacuum (2.998*10^8) / speed of light in material (perspex: 2.0*10^8)
• Snells law is that when light enters a denser medium it slows down and bends towards the normal.
• snells law is n = sin i / sin r
• Convex lenses make light rays converge to a real focal point (F)
• Concave lenses make light rays diverge out and make a virtual focus.
• Images created by lenses can be classified as

  * inverted or upright

  * diminished, magnified, same size

  * real, virtual
• Radio waves can travel long distance before being absorbed and reflect off the atmosphere. Therefore they are used for communication.
• Microwaves are absorbed easily by water, therefore are used to heat up food.
• All things easily absorb infrared waves, therefore they increase heat. They are used in ovens, toasters, and infrared cameras.
• Visible light waves have short wavelengths and high energy and are absorbed by human eyes. They are used in communication and sight.
• Ultraviolet waves have shorter wavelengths and higher energy and, therefore are used in energy-efficient lightbulbs and sun tanning.
• X ray waves are absorbed by bones but not tissue, so are used to print medical images and treat cancer.
• Gamma rays are the most penetrative rays, therefore are used to make medical images and treat cancer.