Degree: Biomedical Sciences with Honours in Infectious Diseases (Bachelors) - Edinburgh University
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A greenhouse gas is one which absorbs infrared radiation from the Earth and re-radiates it, increasing the surface temperature of the Earth. Normally these molecules are non-symmetrical such as triflurometane. This is not the case as carbon dioxide is a linear symmetrical molecule. However in the case of carbon dioxide, it is made up of a single carbon atom covalently bonded by double bonds to 2 oxygen atoms. Carbon dioxide therefore is still able to absorb infrared radiation. It can do so because each carbon oxygen double bond can buy vibrate at a different time from the other, known as asymmetrical vibration. This asymmetrical vibration of the carbon oxygen double bonds is what allows carbon dioxide molecules to absorb infrared radiation and re-radiated back to Earth acting as a greenhouse gas.see more
The photoelectric effect describes the process by which surface electrons are emitted from a metal when light is shined on it. This occurs because the electrons are able to absorb the electromagnetic energy and escape the surface of the metal.
During the photoelectric effect we observe that electrons will not be emitted from the surface of the metal if the light intensity is increased unless the incident light is above a certain frequency known as the threshold frequency. Above this frequency, increasing the intensity of the light increases the number of electrons emitted. This tells us that light at a higher intensity must contain more quanta of energy, known as photons. These photons collide with the electrons and excite them out of the metal's surface.
Increasing the frequency of the light above the threshold frequency increases the maximum kinetic energy of the electrons released, proving that at a higher frequency each photon has more energy (Energy = Planck's constant * Frequency). Below the threshold frequency, the photons don't have enough energy to excite the electrons off the surface of the metal. This effect therefore illustrates light behaving as a particle, because if it was a wave, increasing the intensity of the light would result in electron emission, but it does not.see more
Allicin has antimicrobial properties and can therefore protect garlic from fungal and bacterial infections and is coded for in the DNA of the garlic by an allele.
The presence could have been the result of widespread microbial infections that infect garlic plants in the past. The change in the environment would apply a selection pressure onto the garlic plant population, and the plants that had the advantageous allele for Allicin would survive, making them more likely to reproduce and pass on the allele to the future garlic plant generations. These plants would also reproduce, and overtime, the allele frequency for the advantageous Allicin allele would increase, until it was present across the entire garlic plant population.see more