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Chapter 1

BIOL 1000 Chapter 1 - Light and Life.docx

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BIOL 1000
Jennifer Steeves

Chapter 1 – Light and Life 1.1 – The Physical Nature of Light What is Light? • The portion of the electromagnetic spectrum that humans can detect with their eyes • Made up of waves and a stream of photons (energy particles) – Particle-wave duality Why is it important? • Energy  Photosynthesis (light dependant reactions)  Cellular Respiration (through photosynthesis)  Bacteriorhodopsin-driven ATP formation (Halobacteria) – Light driven H+ pump • Information Purposes – environment etc. 1.2 – Light as a Source of Energy • Light is absorbed by Pigments  A molecule that can absorb photons of light  Different pigments absorb diff. wavelengths of light • Pigments can absorb, transmit, or reflect wavelengths • Pigments have a conjugated system which allows photons to readily interact with electrons at those places • When a photon is absorbed you get a conformational change (shape change)  Ex: cis-retinal changes to trans-retinal (post-absorption)  This leads to a chain reaction of changes 1.3 – Light as a Source of Information • A photoreceptor (e.g. rhodopsin) consists of a pigment molecule (retinal) bound to a protein (opsin) • Chlamydomonas eyespot (contains rhodopsin)  Rhodopsin – The universal photoreceptor  Consists of a protein (opsin) that binds a pigment molecule (retinal)  Upon absorption of a photon of light, retinal changes shape  Triggers changes to the opsin molecule  Triggers signalling events; organism responds to the light  Senses light direction and intensity  Connected to mechanisms involved in swimming Eye • an organ used to detect light  Ocellus (pl. Ocelli) – found in planarians  Cup, used to detect light, sent to cerebral ganglion. Very simple  Senses light direction and intensity  Compound Eye – found in Arthropods  Insects have it, made up of ommatidium. They see a mosaic of vision.  Advantage, it permits visibility of motion incredibly well  Camera Eye  Human and Squid Vision • The interpretation by the brain of what the eye is detecting; the perception of our Sensation • Something used to detect what our eye is absorbing (the brain) Camera Eye Photoreceptors – receive light focused by the cornea and lens; send info to the brain through the optic nerve Two types of Photo receptors:  Rods  Cones  In the retina of the eye allow light of diff.
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