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CHAPTER 10 - Photosynthesis

CHAPTER 10 - Photosynthesis. Autotrophs vs. Heterotrophs. Autotrophs  can make their own food (by doing photosynthesis or chemosynthesis) Ex: Plants, algae, and some bacteria

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CHAPTER 10 - Photosynthesis

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  1. CHAPTER 10 - Photosynthesis

  2. Autotrophs vs. Heterotrophs • Autotrophs can make their own food (by doing photosynthesis or chemosynthesis) Ex: Plants, algae, and some bacteria • Heterotrophs  organisms that can NOT make their own food; they have to eat to get chemical energy Ex: Animals, humans • Oxidation  when you give an electron away; become more positive • Reduction  when you gain an electron; become more negative • Redox processes ALWAYS happen together! • Example: Photosynthesis Oxidation vs. Reduction

  3. Plant cells have chloroplasts. The structure of a leaf is to the left. • Structures to note: • Stoma (stomata) • Cuticle • Veins (xylem/ phloem) • Guard Cells • Epidermis • Palisades vs. Spongy Mesophyll • ***YOU WILL HAVE A SEPARATE SHEET FOR NOTES ON LEAF STRUCTURE Leaf Structure Xylem= carry water Phloem= carry food

  4. Add-on Leaf Structure Sheet • Stoma (plural = stomata) • The pore or pores surrounded by guard cells in the epidermis of a leaf. • When the stoma open, CO2enters the leaf and H20 and O2exit the leaf. • This is how plants conserve water. • Xylem (upper portion) – involved in H20 transport • Phloem (lower portion) – involved in sugar (food) transport

  5. Chloroplasts Chloroplasts are the organelles where photosynthesis takes place. Know the following structures: Stroma– inside of the chloroplast; clear liquid surrounding the thylakoids; Calvin cycle happens here Thylakoid– individual circles, light reactions happen here Grana– stacks of thylakoids Lumen - inside thylakoid ***Note the difference between stroma and stoma (stomata)

  6. Background of Photosynthesis • Definition: Process that converts sunlight (light energy) into food (chemical energy) • 6CO2 + 6 H2O + Light → C6H12O6 + 6O2 • Photosynthesis utilizes biochemical pathways, which is when the product of one pathway is the reactant of the next; a series of linked chemical reactions (pg. 110)

  7. Light can be transmitted, reflected, or absorbed. Whatever color wavelength is reflected is the color that the pigment appears to be. For Example: CHLOROPHYLL IS GREEN because it reflectsGREEN light! Best colors for Photosynthesis = red/blue Worst color = green PHOTONS= packets of radiant energy (light energy) that are absorbed by pigments to energize electrons Light The ultimate source of energy for all living things is the SUN! For the visible light spectrum, the shorter the wavelength, the more energy it contains!

  8. Chlorophyll and Accessory Pigments Chlorophyll A - MAIN light absorbing pigment for PS - Absorbs light energy - Reflects green light (so we see it as green) Accessory Pigments help Chlorophyll A absorb light - Ex:Chlorophyll B and carotenoids (appear orange and yellow usually; can give flower petals their color!)

  9. Part 1 – Light Reactions You need to be able to draw this picture!(pg 111/117)

  10. Light Reaction • Light Reaction makes ATP and NADPH and sends it to the Calvin Cycle • It occurs in the thylakoid (in chloroplast) • Makes ATP by chemiosmosis • Energy carrier = NADPH (reduced from NADP+) • Gets electrons from H2O and gives off O2 (the oxygen released is from water, not CO2) • Requires Light!!

  11. Reaction Center → made up of the special chlorophyll a molecule and a primary e- acceptor Photosystems clusters of light-absorbing pigments that energize e- by trapping energy from the sun; located on the thylakoid membranes Photosystem II → comes first in the ETC, but was discovered second; e- come from water splitting (more on this later) Photosystem I → comes second in the ETC, but was discovered first; gives e- to NADP+, the e- get replaced by e- from PSII Reaction Center Chlorophyll and Photosystems

  12. When a chlorophyll molecule absorbs a photon of light, some of the electrons are excited and raised to a higher energy level…where they are caught by a primary electron acceptor and enter the ETC (which is on the thylakoid membrane) • As e- go down the ETC, they lose energy. That energy is used to power proton pumps to pump H+ from the stromaINTO the lumen (also called thylakoid space)…this creates a concentration gradient • B/c of that concentration gradient, the H+ want to get back OUT of the lumen back into the stroma, and they can only do this by using the enzyme ATP Synthase • This enzyme creates ATP as H+ pass through it • This entire process is called CHEMIOSMOSIS.

  13. ATP Synthase ATP Synthase is an enzyme that is powered by the H+ gradient and converts ADP to ATP. This is how ATP is produced = CHEMIOSMOSIS

  14. Chemiosmosis Makes both ATP (via ATP Synthase) and NADPH (via NADP+ reductase) Chemiosmosis The process that uses the proton gradient and ATP synthase to make ATP

  15. Second part of PS • The CC “fixes” CO2 • Occurs in the stromaof the chloroplast • Carbon enters as CO2 and leaves as sugar • Produces a sugar (G3P) • Each turn “fixes” one molecule of carbon, so one G3P takes 3 turns of the Calvin Cycle Calvin Cycle

  16. Calvin Cycle: The enzyme that adds CO2 to RUBP is RUBISCO The “dark reaction” can occur with or without light Each Turn needs: 3 ATP 2 NADPH 1 CO2

  17. Rate of Photosynthesis • The rate of PS is affected by 3 things: • Light intensity • Amount of CO2 • Temperature • Why wouldn’t roots need chloroplasts? Root cells don't have chloroplasts, because chloroplasts catch sunlight! Since roots are underground, they are not exposed to the sun!

  18. Alternate Pathways • Sometimes if it is too hot out, the plant will close the stomata so that it doesn’t lose too much water and become dehydrated… however, this eliminates the gas exchange!! • SO  the levels of CO2 drop and the levels of O2 increase…which results in…. PHOTORESPIRATION - Adds oxygen to the Calvin Cycle instead of carbon dioxide - This makes NO sugar or ATP - This process wastes all of the plants resources!

  19. C4 Plants • - Fix the carbons into a 4C molecule instead of a 3C molecule • Uses a different enzyme that makes sure to add CO2 instead of O2 • Ex: Corn & Sugarcane

  20. CAM Plants • Open their stomata at night and store the CO2 in organic acids • During the day they break those acids down to use the CO2 • - Ex: Pineapples, cacti

  21. For the test, you will need to know these pictures: • Calvin Cycle • Light Reactions • Leaf Structure • All these can be found on the wiki!!

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