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Chapter 8

Chapter 8 bio 102

9 Pages

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BIOL 102
Wayne Snedden

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Chapter 8: Photosynthesis o Write the general equations that represent the process of photosynthesis. The general equation is: CO 2 2H A 2 light energy  CH O +22 + H O 2 Where A is either oxygen or sulfur and CH O i2 the general formula for a carbohydrate (H A is 2 being oxidized and CO is2being reduced. In green plants the A is always going to be oxygen. In order for green plants to make 1 glucose molecule, the equation must be multiplied by 6: 6CO + 12H O + light energy  C H O +6O + 6H O 2 2 6 12 6 2 2 CO is being reduced to form glucose, and H O is being oxidized to form O2 gas 2 2 - Like we learned earlier on, endergonic reactions are driven forward by coupling the reaction with an exergonic process  in this case with plants, the energy from light ultimately drives the synthesis of glucose o Outline how photosynthesis powers the biosphere. In the biosphere we have many different types of organisms. Heterotroph – these animals must consume organic molecules (food) to sustain life (most species of bacteria and protists, and all fungi and animals) Autotroph – these animals sustain themselves by producing organic molecules from inorganic sources like CO2 and H2O Photoautotroph – type of autotroph that uses light as a source of energy to make organic molecules (green plants, algae, and some bacteria – cyanobacteria) - All types of animals work together and basically form a cycle that benefits all the different types of organisms o Describe the general structure of chloroplasts. - Outer and inner membrane - Intermembrane space - Thylakoid membrane – contains pigment molecules (chlorophyll and maybe others) - Thylakoids – the thylakoid membrane forms many flattened, fluid-filled tubules called thylakoids and they enclose a single convoluted compartment - Thylakoid lumen – enclosed compartment made - Granum – stacks of thylakoids - Stroma – fluid filled regions between thylakoid membrane and inner membrane o Explain how photosynthesis occurs in two phases: the light reactions and carbon fixation. 2 stages are the light reaction (occur in the thylakoid membrane) and the Calvin cycle (carbon fixation) (occurs in the stroma) - photo – refers to the light reactions that capture the energy needed for the… - synthesis – of carbohydrates in the Calvin cycle Light reactions – start with light energy and end with chemical energy in the form of covalent bonds (produces ATP, NADPH and O2, which help drive the Calvin cycle) NADPH – an electron carrier similar to NADH but has an additional phosphate group O2 – super important product because nearly all the oxygen in the atmosphere is produced by photosynthesis o Define the general properties of light. - Light is a form of energy known as electromagnetic energy or electromagnetic radiation: it has properties of both particles and wavelengths - Wavelength – the distance between peaks in a wave pattern (crest to crest on a wave) (wavelength X frequency = speed of light) - The electromagnetic spectrum shows all the possible wavelengths of electromagnetic information, and it is important to know that visible light is in the range of 380 – 740 nm. - Light also behaves as though it consists of discrete particles called photons: massless particles each travelling in a wavelike pattern and moving at the speed of light o Describe how pigments absorb light energy, and describe the types of pigments found in plants and green algae. Pigment – used to describe a molecule that can absorb light energy. When light strikes a pigment, some of the wavelengths of light energy are absorbed and some are reflected (leaves are green because they reflect radiant energy of the green wavelength) - light energy is usually absorbed by boosting electrons to higher energy levels - for an electron to absorb light energy and be boosted to and orbital with higher energy, it must overcome the difference in energy between the orbital it is in and the orbital to which it is going - Once a photon comes in and excites the electron, to goes into an unstable state and it can release energy by heat or light; transfer energy; or cause a reaction If we look first as the absorption spectrum of chlorophyll a, it suggests that blue and red light work best for photosynthesis, while green is the least effective colour - Chlorophyll a is a blue-green, whereas chlorophyll b is a yellow-green - Chlorophylls in general contain a porphyrin ring and a phytol tail – a magnesium ion is bound to the porphyrin ring Other accessory pigments include the carotenoids, hydrocarbons that are various shades of yellow and orange - These compounds absorb and dissipate excessive light energy that would otherwise damage chlorophyll o Absorption vs. action spectrum Absorption spectrum – Wavelengths that are absorbed by different pigments in the plant Action Spectrum – the rate of photosynthesis by a whole plant plotted as a function of different wavelengths of light – having different pigments allows plants to absorb light at many different wavelengths so this shows the efficiency of that. o Outline the steps in which photosystem II and I capture light energy and produce O , 2 ATP, and NADPH. The thylakoid membranes of a chloroplast contain two distinct complexes, photosystem II (PSII) and photosystem I (PSI). – NON-CYCLIC ELECTRON FLOW Photosystems – a collection of pigment proteins that include chlorophyll a and absorb either light at the 700nm wavelength or 680nm wavelength according to if the photon is exciting P680 or P700. - Photosystem II contains P680 - Photosystem I contains P700 - A photon of light strikes the antenna complex, its absorbed and energy is transferred to P680, and one of its electrons changes from ground state to an excited state, resulting in energized molecule P680+. - the excited electron is then transferred to the primary accepter molecule, which then becomes negatively charged, while P680 is positive - The positive P680+ ion is now extremely electronegative and can exert forces so strong that it can remove an electron from a molecule of water (oxidizes water by the water- splitting complex, which passes an electron to P680+ to make it neutral again) - high energy electron is transferred from the reaction centre to the carrier molecule PQ - This process releases both oxygen gas and protons into the lumen - must occur twice for each water molecule that is completely oxidized (bc only ½ an oxygen is made for one electron) - each photoexcited electron passes from the primary electron acceptor of PSII to PSI via the electron
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