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Chapter 1

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York University
BIOL 1000
Nicole Nivillac

Bio notes What is light (Chapter 1) - Each cell contains a single chloroplast which transforms light energy in and uses it to make energy rich molecules thru the process of photosynthesis (eg. ATP) - Light is the portion of the electromagnetic spectrum that human can detect with their eyes. - Light behaves as a stream of energy particles, protons - Light interacts with matter, by going thru them, reflecting off the object, or being absorbed by the object - Molecule that can absorb photons of light is called a pigment, different pigments can absorb different lights - A single photon must be able to excite one electron in the electron molecule otherwise the photon would not be absorbed(eg. Green light with chlorophyll is not absorbed because the energy provided doesn’t excite the electron to an excited state but blue and red light does) - Color of pigment is determined by the wavelengths of light it cannot absorb - Action spectrum- graph showing the effectiveness of light at each wavelength for photosynthesis Light as a source of energy - Photon is absorbed, electron inside pigment molecule is excited. Excited electron energy is used in photosynthesis to create NADPH, and ATP. - Energy is then used to create other biological molecules - Prokaryotes called halobacterium use light to power their proton pumps along the membrane. Light as a source of information - Organisms use light to sense their environment. - Rhodopsin is the most common photoreceptor in nature - Each Rhodopsin molecule contains opsin that binds a single pigment molecule called retinal - Absorption of light causes retinal pigment molecule to change shape, causes changes in opsin and causes other events like electrical signals. - Eyespot = structure located in the chloroplast allows cell to sense light direction. Phototaxis - Positive phototaxis – move towards light / negative phototaxis- move away from light - When photoreceptor cal
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