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Biology notes - Chapter 7

by: Megan Smith

Biology notes - Chapter 7 Biol 1103k

Marketplace > Georgia State University > Biology > Biol 1103k > Biology notes Chapter 7
Megan Smith
GPA 3.6

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About this Document

these notes are directly from the book chapter 7
Introductory biology I
David blaustein
Class Notes
Biology, Biology 1103K
25 ?




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This 6 page Class Notes was uploaded by Megan Smith on Sunday February 14, 2016. The Class Notes belongs to Biol 1103k at Georgia State University taught by David blaustein in Summer 2015. Since its upload, it has received 27 views. For similar materials see Introductory biology I in Biology at Georgia State University.


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Date Created: 02/14/16
Date CAPTURING SOLAR ENER GY: PHOTOSYNTHESIS 1. WHAT IS PHOTOSYNTHSI S i. Photosynthesis • The process by which light energy is captured and stored as chemical energy in the bods of organic molecules B. Leaves and Chloroplast are adaptations for photosynthesis i. Epidermis • Protects the inner parts of the lead while allowing light to penetrate ii. Cuticle • A transparent, waxy, waterproof covering that reduces the evaporation of water from the leaf iii. Stoma • Adjustable pores in the epidermis • How the leaf obtains CO2 (necessar y for photosynthesis)? iv. Mesophyll • Most chloroplasts are located v. Vascular bundles • Form veins in the leaf, supply water and minerals to the leaf’s cells and carry the sugars produced during photosynthesis vi. Bundle sheath cells • Cells that surround the vascular b undles • Lack chloroplast in most plants vii. Chloroplasts • Photosynthesis in plants takes place within the chloroplasts • Most contained within mesophyll cells viii. Stroma • Chloroplasts are organelles that consist of a double outer membrane enclosing a semifluid substan ce ix. Thylakoids • Embedded in the stroma • Disk-shaped, interconnected membranous sacs • Each of these sacs encloses a fluid -filled region called the thylakoid space C. Photosynthesis consists of the light reactions and the Calvin Cycle i. Photosynthesis reaction • 6 CO2 + 6 H2O + light energy = C6H12O6 (sugar) + 6 O2 ii. photosynthesis actually occurs in dozens of individual reactions • two distinct stages a. Calvin Cycle b. The light reactions iii. Light reactions • Chlorophyll and other molecules embedded in the membranes of the chloroplast thylakoids capture sunlight energy and convert some of it into chemical energy stored in the energy -carrier molecule ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) • Water is split apart, and oxygen gas is released a s a by-product iv. Calvin Cycle • Enzymes in the fluid stroma that surrounds the thylakoids use CO2 from the atmosphere and chemical energy from the energy -carrier molecules to drive the synthesis of a three carbon sugar that will be used to make glucose v. Photosynthesis • “photo” refers to the part that captures light energy by the light reactions in the thylakoid membranes • “synthesis” refers to the Calvin Cycle , which captures carbon and uses it to synthesize sugar, powered by energy provided by ATP and NADPH 2. THE LIGHT REACTION: HO W IS LIGHT ENERGY CO NVERTED TO CEMICAL ENERGY i. The light reactions capture the energy of sunlight, sotring it as chemical energy in two different energy-carrier molecules a. ATP b. NADPH B. Light is captured by pigments in chloroplasts i. Electromagnetic spectrum • Ranges from short-wavelength gamma rays, through ultra -violet, visible, and infared light, to very long wavelength radio waves. 2 ii. Photons • Light and other electromagnietic waves are composed of individual packets of energy called photons • Energy corresponds to its wave length a. Short-wavelength – very energetic b. Long-wavelengths – low energy iii. Chlorophyll a • The key light capturing pigment molecule in chloroplasts strongly absorbs violet, blue, and red light, but reflects green, thus giving leae s their green color iv. Accessory pigment • Absorb addistional wave lengths of light energy and trasger their energy to chlorophyll a. • Include chorophyll b o Slights different form of cholorphyll that absorbs some of the blue and redorange wavelengths of light th at are missed by chlorophyll a and reflects yellow-gren light v. Carotenoids • Accessory pigments found in all chloroplasts • Absorb blue and green light and appear mostly yellow or oranage because they reflect these wavelengths C. The light reactions occur in as sociation wirh the thylakoid membrane i. Photosystmes • Each consisting of a cluster of chlorophyll and accessory pigment molecules surrounded by various proteins • Two photosystems – photosystem I and photosystem II – work together during light reaction ii. Electron transport chain • Consosts of a series of electron -carrier molecules embedded in the thylakoid membrane • Within the thylakoid chain a. Photosystem II b. Electron transport chain II c. Photosystem I d. Electron transport chain I e. NADP+ D. Photosystem II uses light energy to create a hydrogen Ion Gradient and to split water 3 a. The energy hops from one pigment molecule to the next until it is funneled into the photosystem II reaction center b. the reaction center of each photosystem consists of a pair of specialized chlorophyll a molecules and a primary electronic acceptor molecule embedded in a complex of proteins i. when the energy from light reaches the reaction Center, it boosts an electron from one of the reception center chlorophylls to the primary electronic acceptor , whic h captures the energized electrons c. the reaction center of photosystem II must be supplied continuously with the electrons to replace those that are boosted out of it when energize by light i. these replacement electrons come from water d. water molecules are split buying enzyme associated with photosystem II, liberating electrons that will replace those lost by the reaction center chlorophyll molecules. i. Splitting water also releases two hydrogen ions (H+) that are used in forming the H+ gradient that drives A TP synthesis ii. for every two water molecules split, one molecule of O2 is produced iii. once the primary electronic acceptor in photosystem II captures the electron, it passes the electron to the first molecule electron transport chain II e. the electrons then t ravels from one electron carrier molecule to the next, losing energy as it goes. i. Some of this energy is harnessed to pump H+ across the thylakoid membrane into the thylakoid space, where it will be used to generate ATP f. finally, the energy depleted electr on leaves electron transport chain II and enters the reactions center of photosystem I, where it replaces the electronic injected when light strikes photosystem I E. photosystem I generates NADPH I. meanwhile, life has also been striking the pigment molecules of photosystem I. this light energy is passed to a chlorophyll a molecule and the reaction center. a. Here, it energizes an electron that is absorbed by the primary electron acceptor of photosystem I i. from the primary electron acceptor of photosystem I, t he energized electron is passed along electron transport chain I 4 b. until it reaches NADP+. i. When an NADP+ molecule ( dissolved in the fluid stroma) picks up two energetic electrons along with one hydrogen ion, the energy carrier molecule NADPH is formed F. The hydrogen ion gradient generates ATP by Chemiosmosis i. chemiosmosis • a process of how electrons move through the thylakoid membrane and use their energy to create and H+ gradient that drives ATP synthesis a. as an energized electron travels along the electron transport chain II, some of the energy of the electron liberates is used to pump H+ into the thylakoid space, creating a high concentration of H+ inside the space b. and a low concentration and the surrou nding stroma i. during chemiosmosis, H+ flows back down its concentration gradient through a special type of channel (ATP synthase) that spans the thylakoid membrane. ii. ATP synthase • Generates ATP from ADP and phosphate dissolved in the stroma as the H+ flows through the channel. 3. THE CAVIN CYCLE: HOW IS CHEMICAL ENERGY S TORED IN SUGAR MOLECULES i. Carbon fixation • Nearly all is performed by photosynthetic organisms • The carbon is captured from the atomospheric CO2 during the Calvin Cycle using energy from sunlight ha rnessed during the light reactions. • B. The Calvin cycle captures cabon dioxide i. Calvin cycle • Often referred to as the C3 pathway a. Carbon fixation b. The synthesis of G3P c. The regeneration of RuBP that allowed the cycle to continue ii. Carbon fixation • Carbon from CO2 is incorporated into larger organic molecules iii. Rubisco • This enzyme combines three CO2 molecules with three RuBP molecules to produce three unstable six -carbon molecules that immediately split in half, 5 forming six molecules of phosphoglyceric acid (PGA, a t hree carbon molecule iv. The synthesis of G3P • Occurs via a series of reactions using energy donated by ATP and NADPH (generated by the light reactions) • During these reactions, six 3 -carbon PGA molecules are rearranged to form six 3-carbon G3P molecules • Three molecules of RuBP are regenerated from five of the six G3P molecules; this regenerations is powered by ATP generated during the light reactions • The single remaining G3P molecule, the end product of photosynthesis, exits the Calvin Cycle v. Photorespiration • Prevents the Calvin Cycle from synthesizing sugar, effectively derailing photosynthesis vi. C4 Pathway and the Crassulacean Acid Metabolism (CAM) pathway • Small percentage of Earths terrestrial plants have evolved biochemical pathways that consume a bit more ener gy, but increase the efficiency of carbon fixation in hot dry climates C. Carbon Fixed during the Calvin Cycle is used to synthesize glucose i. In reactions that happen outside the calvin cycle, two G3P molecules can be combined to form one six-carbon glucose molecule. ii. Glucose can then be used to synthesize sucrose, a disaccharide storage molecule consisting of a glucose linked to fructose. iii. Glucose molecules are linked together in long chains to form starch 6


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