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Chapter 5

Chapter 5 bio

7 Pages

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Holly Smith

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Chapter 1: Light and Life Light: Serves 2 important functions [1] source of energy that directly or indirectly sustains all organisms. [2] light provides organisms with information about the physical world that surrounds them. - single celled photosynthetic eukaryotic cell - each cell contains 1 chloroplast that harvests light energy (photosynthesis) - contains light censor called eyespot (allows cells to gather location and intensity of a light source) electromagnetic radiation: energy given off by converting hydrogen to helium 38 [3.4x10 hydrogen nuclei/second] - light is the portion of electromagnetic spectrum humans can detect with their eyes. - light has no mass - light is composed of a stream of energy particles called photons (particle wave duality) - the relationship between the wavelength of light and the energy of photons in carries is an inverse one: the longer the wavelength, the lower the energy of the photons it contains. - small portion of spectrum is essential for life [400-700 nm] - longer wave lengths: tend not to reach Earth’s surface, not too concerned about longer wavelengths because they don’t have enough electrons to excite photons - shorter wave lengths: do not reach Earth and can damage biological molecules. [DNA can be damaged--> cancer] - organisms have protective and repair mechanisms to prevent and repair damage in DNA and in proteins. - photosystems involved in photosynthesis. - strange relationship [light is essential in life yet shorter wavelengths are damaging. organisms need to have a balance between harmful waves and beneficial/essential waves] wavelength: distance between 2 successive peaks photons: when a photon hits an object, the photon has 3 fates: [1] reflected off the object [2]transmitted through the object [3]absorbed by the object Absorption: must take place in order for an organism to use energy as a source of energy or information - occurs when the energy of the photon is transferred to an electron within a molecule. this excites the electron, moving it from its ground state to a higher energy level that is referred to as the “excited state” - a photon can only be absorbed by an electron of a molecule only if the photon energy equals the energy difference between the electrons ground state and the excited state. if the energies don’t match then the photon is transmitted through or reflected off the molecule. Pigments: major class of molecules that are very efficient in absorbing photons chlorophyll a- involved in photosynthesis retinal- vision indigo- used to dye blue jeans - Most pigments absorb light at distinctly different wavelengths. this is because they differ in the number of excited states available to the excitable electrons - photon absorption is related to the concept of color - a pigment’s color is the result of photons of light that it doesn’t absorb. instead of being absorbed, these photons are reflected off the pigment or transmitted through the pigment to reach your eyes. conjugated system: Bonding arrangement, a region where carbon atoms are covalently bonded to each other with alternating single and double bonds [common feature critical to light absorption] results in delocalization light as a source of energy: - energy from the sun enters the biosphere through photosynthesis. [plants and organisms convert CO t2 sugars] - after light absorption, the potential energy of excited electrons within pigment molecules such as chlorophyll are used in photosynthetic electron transport to synthesize NADPH and ATP - In turn these molecules are consumed in the calvin cycle during photosynthesis. - Photosynthesis sustains virtually all life on Earth Cellular respiration: process that breaks down carbohydrates and other molecules trapping the released energy as ATP halo-bacterium: one of the organisms that uses light as energy but is not classified as a photosynthetic organism [doesn’t use light to convert CO to 2ugars] - live in areas with very high salt levels - contain a pigment protein complex called bacteriorhodopsin [functions as a light driven proton pump] the pigment of bacteriorhodopsin captures photons of light that provide the energy supply needed to pump protons out of the cell - as a result ATP--> ADP Photoreceptor: basic light sensing unit of the eyespot found almost universally in all organisms - most common photoreceptor is rhodopsin - used by animals and other organisms - serves as light sensing unit of the eyespot (in the eye and in other organisms) - each rhodopsin molecule consists of a protein called opsin that binds a single pigment molecule called retinal - the photoreceptor cell is actually a modified nerve cell that contains thousands of individual photoreceptor molecules - Bacteriorhodopsin uses light as a source of energy whereas the photoreceptor rhodopsin uses light as a light sensor Opsin: membrane proteins that span a membrane multiple times and form a complex with the retinal molecule at the center. - Absorption of a photon of light causes the retinal pigment molecule to change shape. Eyespot: light sensitive structure approximately 1micrometer in diameter and is found with the chloroplast of the cell [region closely associated with the cell membrane] - composed of two layers of carotenoid rich lipid globules that play a role in focusing and directing incoming light towards the photoreceptors - eyespot is in chloroplast but doesn’t take part of photosynthesis [instead helps sense light] - organisms sense light without actually having eyes - rhodopsin is very abundant in the eyespot Phototaxis: cells respond to light by swimming towards or away from light - this allows the light to stay in the optimum light environment to maximize light capture for photosynthesis Eye: defined as the organ animals use to sense light - process of vision requires not only an eye to focus and absorb incoming light but also a brain signal. - vision: requires a brain to interpret signals send
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