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Explore the pivotal role light plays in plant life through photosynthesis, the crucial chemical process that sustains all living organisms. Learn how plants convert light into energy and discover the key components involved in photosynthesis, such as chloroplasts and carotenoids. Uncover the intricate stages of photosynthesis, from generating oxygen to producing glucose. Delve into the world of autotrophs and understand how they are integral food producers in various ecosystems. This comprehensive overview sheds light on the fascinating process that powers life on our planet.
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CHAPTER 7Photosynthesis:Using Light to Make Food Modules 7.1 – 7.5
Life in the Sun • Light is central to the life of a plant • Photosynthesis is the most important chemical process on Earth • It provides food for virtually all organisms • Plant cells convert light into chemical signals that affect a plant’s life cycle
Plants that get adequate light are often bushy, with deep green leaves • Without enough light, plants become tall and spindly with small pale leaves • Too much sunlight can damage a plant • Chloroplasts and carotenoids help to prevent such damage • Light can influence the architecture of a plant
AN OVERVIEW OF PHOTOSYNTHESIS • Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water Carbondioxide Water Glucose Oxygengas PHOTOSYNTHESIS
7.1 Autotrophs are the producers of the biosphere • Plants, some protists, and some bacteria are photosynthetic autotrophs • They are the ultimate producers of food consumed by virtually all organisms
On land, plants such as oak trees and cacti are the predominant producers Figure 7.1A Figure 7.1B
In aquatic environments, algae and photosynthetic bacteria are the main food producers Figure 7.1C Figure 7.1D
7.2 Photosynthesis occurs in chloroplasts • In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts • A chloroplast contains: • stroma, a fluid • grana, stacks of thylakoids • The thylakoids contain chlorophyll • Chlorophyll is the green pigment that captures light for photosynthesis
Chloroplast LEAF CROSS SECTION MESOPHYLL CELL LEAF • The location and structure of chloroplasts Mesophyll Intermembrane space CHLOROPLAST Outer membrane Granum Innermembrane Grana Stroma Thylakoidcompartment Stroma Thylakoid Figure 7.2
7.3 Plants produce O2 gas by splitting water • The O2 liberated by photosynthesis is made from the oxygen in water Figure 7.3A
Experiment 1 Notlabeled Experiment 2 Labeled Figure 7.3B Reactants: Products: Figure 7.3C
7.4 Photosynthesis is a redox process, as is cellular respiration • Water molecules are split apart and electrons and H+ ions are removed, leaving O2 gas • These electrons and H+ ions are transferred to CO2, producing sugar Reduction Oxidation Figure 7.4A Oxidation Reduction Figure 7.4B
7.5 Overview: Photosynthesis occurs in two stages linked by ATP and NADPH • The complete process of photosynthesis consists of two linked sets of reactions: • the light reactions and the Calvin cycle • The light reactions convert light energy to chemical energy and produce O2 • The Calvin cycle assembles sugar molecules from CO2 using the energy-carrying products of the light reactions
H2O CO2 Chloroplast • An overview of photosynthesis Light NADP+ ADP+ P LIGHTREACTIONS(in grana) CALVINCYCLE(in stroma) ATP Electrons NADPH O2 Sugar Figure 7.5
