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Chapter 1

BIOL 1000- LIGHT AND LIFE (chap#1)

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BIOL 1000
Julie Clark

Tanya Sivamanoharan Fri, Sept, 09/11 Biology- Chap# 1 Notes LIGHT AND LIFE 1.1- The Physical Nature of Light Light serves 2 import. functions for life on earth  it is a source of energy sustaining all life  light provides info. to organisms about physical world chloroplast site of photosynthesis in plant cells 1.1a- What is Light? -life on earth exists b/c of light energy from the sun -the energy from the sun is given off as electromagnetic radiation, which travels in the speed of light (1 079 353 848 km/h) -electromagnetic radiation travels in 2 diff. waves (electric and magnetic) -electromagnetic radiation is distinguished by its wavelength -wavelength distance of a wave from peak to peak -light portion of the electromagnetic spectrum visible by humans -light is a wave but also a line of energy particles called photons -photons unlike atoms, they have no mass, but contains spec. amount of energy -amount of energy in photon is related to its wavelength (ex: blue light with shorter wavelength has more energy and red light with longer wavelength has less energy 1.1b- Light Interacts With Matter -light has no mass but can interact with matter and is used by living things -when photons hit an object there are 3 possibilities:  reflected off the object  transmitted through the object  absorbed by the object -in order for light to benefit an organism it must be absorbed by the organism -pigment molecule that can absorb photons of light -each pigment differs in wavelengths of light they can absorb (green, blue) -chlorophyll is a type of pigment used by plants in photosynthesis -pigments have conjugated system of bonds where carbon atoms are covalently bonded with double and single bonds making it easier to interact with photons 1.1c- Why Chlorophyll is Green -absorption of light occurs when the energy from photons are transferred to pigment -chlorophyllmolecule of green pigment that absorbs photons of light in photosynthesis -an electron in ground state moves to an excited state after absorbing photon of light -light absorption by pigments have 2 principles  a single photon excite 1 and only 1 electron in the pigment molecule  in order for photon of light to be absorbed, the energy of the photon must match the energy difference between the ground state and the excited state -The colour of the pigment represents the colour of wavelength that it cannot absorb (ex: chlorophyll is green and therefore cannot absorb green light) -chlorophyll does not have an energy level matching a green photon so green light is reflected or transmitted 1.2- Light as a Source of Energy -when a photon of light is absorbed an electron goes from ground state to excited state, this electron in excited state is an energy source that can be used to do work (in electron transport chain-ETC ) -organisms use light as a source of energy in other processes (ex: in prokaryote called Halobacterium, there is a protein complex called bacteriorhodopsin, which is a light dependent proton pump 1.3- Light as a Source of Information -organisms use light to sense their environment -the ability to sense light is critical in many forms of life 1.3a- Rhodopsin, a Highly Conserved Photoreceptor -photoreceptor the light sensing system found in most organisms -rhodopsin the most common photoreceptor and is the basis of vision -opsin a protein found in each rhodopsin molecule binding a pigment molecule called retinal opsin proteins span a membrane many times and becomes a complex with the retinal in the middle -absopriton of light causes the shape of a retina the chnge, which then forces the opsin protein to cause electrical signals -the electrical signals are sent to the brain -eyes require almost 125 million photoreceptor cells (rods+ cones) in order to capture light -these photoreceptor cells are aligned along the retina and each indiv. cell contains 1000’s of rhodopsin molecules -rhodhopsin is the most common phtoreceptor but plants and animals use various other photoreceptors to absorb diff. wavelngths. of light 1.3b-Sensing Light Without Eyes -many organisms can sense light or feel the presence of light evn without eyes (plants, fungi, algae, and some prokaryotes) -these organisms without eyes have something called an eyespot -eyespot does not interfere with photosynthesis but contains photoreceptors which can sense light direction and intensity -phototaxis the process of an organisms using flagella to swim away/toward light source -phototaxis allows organisms to stay near light and makes it easier to absorb photons for photosynthesis -light absorp. by eyespot is connected to the movement of flagella which is altered by changes in the concentration of ions -there is a transductional pathway that occurs when the organism swims -plants use a diff. photoreceptor called the phytochrome -phytochrome senses the light environment among plant cells, located in the cytosol of all plant cells -photomorphogenesis the developmental process that occurs when seeds are exposed to light -phytochrome initiates a signal transduction pathway that hits the nucleus - the nucleus then actives several genes which code for proteins involved in photosynthesis and development 1.3c- The Eye -organ used to sense light -the eye also requires a brain or nervous system to activate signals from the eye for visual processing to occur -simplest eye is called the ocellus -ocellus contains 100 photoreceptor cells lining a cup -the eye of planaria and the eyespot of C.Reinhardtii are just used to sense light intensity and direction to a light source -then came image forming eyes showing image of environment -two types of image forming eye 1)compound eyes and 2) single-lens eyes 1.3d- Darwin and the Evolution of the Eye -Charles Darwin theory of evolution predicted a problem in “organs of extreme perfection” such as the eye -he is saying that human and other animal eyes were not always complex but they evolved overtime through mutations -he believes that today’s human eyes evolved by variations and natural selection from simple eyes -there has been found, animals from 500m yrs ago with primitive eyes -therefore a predictions has been made that the human eye has been evolved over 1000 times -in order for the eye to have been evolved so has the brain, for it has to be able to read the neu
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