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Lecture 7

BSC 108 Lecture 7: Biology Chapter 7 Notes

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Biological Sciences
BSC 108
Christina Yates

Biology Chapter 7 Notes The Basics of Photosynthesis • Almost all plants are photosynthetic autotrophs, as are some bacteria and protists ➢ They generate their own organic matter through photosynthesis Chloroplasts: Sites of Photosynthesis • Photosynthesis ➢ Occurs in chloroplasts ➢ Energized electrons are added to carbon dioxide to make sugar ➢ Sunlight provides the energy • Chloroplasts ➢ Are found in the cells of the mesophyll ➢ Contains stroma, a thick fluid ➢ Contain thylakoids, membranous sacs Photosynthesis Road Map • Photosynthesis is a two-step process ➢ The light reactions convert solar energy to chemical energy ➢ The Calvin cycle makes sugar from carbon dioxide The Light Reactions: Converting Solar Energy to Chemical Energy • Sunlight is a type of energy called radiation, or electromagnetic energy • The full range of radiation is called the electromagnetic spectrum ➢ Gamma rays, x-rays, UV, visible light, infrared, microwaves, radio waves (smallest to biggest) Chloroplast pigments • Chloroplasts contain several pigments ➢ Chlorophyll a ➢ Chlorophyll b ➢ Carotenoids How Photosystems Harvest Light Energy • Light behaves as photons, discrete packets of energy • Chlorophyll molecules absorb photons ➢ Electrons in the pigment gain energy ➢ As the electrons fall back to their ground state, energy is released as heat or light • A photosystem is a group of chlorophyll and other molecules that function as a light-gathering antenna. How the Light Reactions Generate ATP and NADPH • Two types of photosystems cooperate in the light reactions: ➢ The water splitting photosystem ➢ The NADPH-producing photosystem • An electron transport chain: ➢ Connects the two photosynthesis ➢ Releases energy that the chloroplast uses to make ATP The Calvin Cycle: Making Sugar From Carbon Dioxide • For the dark cycle • The Calvin cycle: ➢ Functions like a sugar factory within a chloroplast ➢ Regenerates the starting material with each turn Water-Saving Adaption of C4 and CAM Plants • C3 plants ➢ Use CO2 directly from air ➢ Are very common and widely distributed • C4 plants ➢ Close their stomata to save water during hot and dry weather ➢ Can still carry out photosynthesis • CAM plants ➢ Open their stomata only at night to conserve water Review • The metabolic pathway of cellular respiration ➢ C6H1206 + 602  6C02 + 6H20 + ATP ➢ Glucose + oxygen  6 carbon + water + energy • The overall equation for photosynthesis ➢ 6CO2 + 6H20 (Light energy  photosynthesis) C6H1206 + 602 ➢ Carbon dioxide + water (light energy  photosynthesis) glucose + oxygen gas • Oxygen, glucose, carbon dioxide and water cycle through cellular respiration and photosynthesis Photosynthesis • Photosynthesis has an enormous impact on the atmosphere ➢ It swaps 02 for CO2 How Photosynthesis Moderates the Greenhouse Effect • Old growth forests ➢ Are important for lumber ➢ Are important for moderating world climates • The Greenhouse effect ➢ Warms the atmosphere ➢ Is caused by atmospheric CO2 • Greenhouse gases are the most likely cause of global warming, a slow but steady rise in the Earth’s surface temperature ➢ Destruction of forests may be increasing this effect Key Terms • Chloroplasts: an organelle found in plants and photosynthetic protists. Enclosed by two concentric membranes, a chloroplast absorbs sunlight and uses it to power the synthesis of organic food molecules (sugars). • Chlorophyll: a light-absorbing pigment in chloroplasts that plays a central role in convertin
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