Chapter 1-Exploring the Diversity of Life

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Biological Sciences
Zachariah Campbell

Biology Exploring the Diversity of LifeChapter 1 Light and Life11 The Physical Nature of LightLight serves two important functions for life on earthst o1 it is a source of energy that sustains all lifend o2 light provides organisms with information about the physical worldEach cell contains oA single large chloroplast that harvests light energy and uses it to make energy rich molecules through the process of photosynthesisoA light sensor called an eyespot that allows it to sense both light direction and light intensity Wavelength the distance between two successive peaks The wavelength of electromagnetic radiation ranges from less than one picometre for cosmic rays to more than a kilometer for radio wavesLight the portion of the electromagnetic spectrum that humans can detect with their eyesoLight is a narrow band of the electromagnetic spectrum spanning the wavelengths in nanometers from 400nm blue light to about 700nm red lightoWavelengths outside this range should not be referred to as light but rather as ultraviolet and infrared radiationoLight can be described as a wave but also behaves as a stream of energy particles These particles or packets of energy are referred to as photons oLight has no mass but it is able to interact with and change matter These changes allow light to be used by living things Photons particles or packets of energyoPhotons have no mass but each contains a precise amount of energy oThe amount of energy in a photon is inversely related to its wavelength This means that blue light with a shorter wavelength consists of photons that have higher energy than longer wavelength red light oWhen photons of light hit an object the photons have 3 possible fates1 Reflected off the object2 Transmitted through the object3 Absorbed by the objectPigment A molecule that can absorb photons of lightoIndividual pigments differ in the wavelengths of light they can absorb Ex some pigments absorb only blue light some only green and some can absorb light of a number of different wavelengthsoAll pigments share a common feature critical to light absorption a region where carbon atoms are covalently bonded with alternating single and double bonds This bonding arrangement is called a conjugated system and results in the delocalization of electrons Absorption of light occurs when the energy of a photon is transferred to an electron of the pigment molecule oBefore absorbing a photon of light an electron exists in the ground state at 0 oUpon absorption of a photon of light the energy is transferred to the electron moving it from the ground state to a higher energy excited stateoFor a chlorophyll molecule the electron involved in photon capture can exist in 2 and only 2 excited statesoThe lower excited state at 1 is reached by chlorophyll absorbing a photon of red light The higher excited state at 2 is reached by the absorption of an electron to a higher energy state than absorption of red light because blue photons contain more energy Two Important Principlesst o1 a single photon results in the excitation of one and only one election in a pigment moleculendo2the energy of the photon must match the energy difference between the ground state and one of the excited states in order for the photon to be absorbed If the energies do not match the photon is not absorbed
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