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Chapter 1

Chapter One Light and Life

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York University
BIOL 1000
Nicole Nivillac

Chapter One Light and Life Why it Matters? Because of light we are able to see colors. Reason being that the color is reflected off the object. The rest of the colors are absorbed by the object. For example green light is reflected off the leaf. The rest of the colors are absorbed by the leaf. 1.1 The Physical Nature of Light Two important functions of light:  A source of energy that sustains all organisms  Provides information about the physical world that surrounds organisms o Example: Chlamydomanas Reinhardtii  Single celled – Eukaryote  Ponds and lakes  One chloroplast that absorbs energy to do photosynthesis.  Light sensor in the eye allows the gathering of information (location and intensity of light) 1.1a What is Light?  Due to the exact distance between the earth and the sun, the sun is able to make energy off of matter in a matter of seconds. This helps life to sustain on earth.  Light is the most common part of the electromagnetic spectrum that humans are able to detect with their eyes.  Light has no mass  Light is composed of photons which is a stream of energy particles.  The longer the wavelength the lower the energy of photons it contains. 1.1b Light Interacts with Matter  Light is able to interact with matter and cause change which allows living things to use light  Light can do three actions o Reflect off the object o Transmit through the object o Absorbed the by the object  To be used as a source of energy light needs to be absorbed  If the energy of the photon matches the difference of the electrons ground state and excited state, only then the photon is able to give energy to the electron.  Once the energy is given to the electron it moves the electron moves from the ground state into the excited state.  Pigments also absorb photons very efficiently which. This is what allows us to see color.  The reason why pigments are able to absorb photons so efficiently is because they contain a conjugate system. Conjugated system is a system in which the carbon atoms are covalently bonded to one another with alternating single double bonds. 1.2Light as a Source of Energy  Light is a source of energy due to the process of photosynthesis. During photosynthesis a photon is absorbed by leaves which are then used to produce glucose.  This glucose is then used in cellular respiration to produce ATP. Because of ATP we are able to do action and bring about our day to day lives.  An archea halobacterium absorbs a photon of light which causes the archea to pump protons out of the cell creating a proton gradient. This proton gradient causes potential energy. This creates the energy to create ATP. 1.3Light as a Source of Information Light is used to provide organisms with the knowledge of what is around them. 1.3a Rhodopsin, the Universal Photoreceptor  The basic light seeing system is known as a photo receptor. The most common is rhodopsin.  Rhodopsin consists of a protein called opsin. Opsin forms a complex with retinal in the center of the retinal.  Once the rhodopsin absorbs light it the opsin changes shape. 1.3b Sensing light without eyes  There are many plants and living organisms that can sense light without the organ of the eye.  In reinhardtiis the eyespot is in the chloroplasts. It is composed of carotenoid rich lipid globules that help to direct the light toward the photoreceptors.  Eyespot does not play a role in photosynthesis.  Photoreceptors allow the cell to sense light direction and its intensity.  According to that, flagella either cause the light o move away from the cell or towards the cell. This allows the cell to stay in the maximum amount of light it needs.  Light absorption- swimming away or towards light- rapid changes in concentration ions which creates energy for the flagella to move.  In pants the photoreceptor phytochrome senses the light and sends signal to the nucleus for the development of a new leaf or to code for protein needed in the process of photosynthesis. 1.3c The eye  The eye is an organ in animal used to sense light.  To be able to see with the eye, the brain and the eye need to work together.  Ocellus(Ocelli) o is the simplest eye. o It consists of 100 photoreceptor cells. o Photoreceptor cells contain individual photoreceptor molecules. o The light hits the cerebral ganglion and orient them work away from the light towards darker areas.  Planaria (Planarians) o Organ can sense light and direction to a light o Objects and shapes can be seen as well  Compound Eyes  Common in an arthropods such as insects and crustaceans  In these insects there hundreds of eyes that are fitted closely to each other. The singular form is ommatidium  The photoreceptor cells detect light which helps the brain create a mosaic image of the world  Compound eyes cause it to easily detect motion.  Single Lens Eye  Light enters through the cornea. The lens concentrate the light and focus it on a layer of photoreceptor cells at the back of the eye, the retina. The retina sends the information to the brain through an optic nerve. 1.3d Darwin and the Evolution of the Eye  The eye has evolved into a single lens eye has guessed by Darwin. See page 11! 1.4 The Uniqueness of Light  Light is the narrowest band of the electromagnetic wavelength, yet it is used the most by humans  Wald reasoned that visible light is used mostly by organisms because it’s the most dominant form of electromagnetic radiation that reaches the earth.  The energy light contains is the right amount of energy for bonds to get bursts of energy and for life to be sustained on earth. Other wavelengths such
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