CHAPTER 10 - Photosynthesis

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 to Leaf Structure Sheet • Stoma(plural = stomata) • The pore \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 photosynthesistakes place! • Know the following structures: • Stroma– inside of the chloroplast; clear liquid surrounding the thylakoids; Calvin Cycle happens here • Thylakoid– individual sacs inside chloroplast, light reactions happen here • Grana– stacks of thylakoids • Lumen- inside thylakoid CHLOROPLAST ***Note the difference between stroma and stoma (stomata)

6. Photosynthesis • Occurs in the chloroplast • Divided into 2 sets of reactions: - Light Dependent Reaction - Calvin Cycle (Dark Reaction) Photosynthesis

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

8. 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 GREENbecause 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!

9. 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:ChlorophyllBand carotenoids - Often appear orange and yellow - Can give flower petals their color!

10. Part 1 – Light Reactions You need to be able to draw this picture!(pg 111/117) Photosystem II Photosystem I H2O Splits 

11. Light Reaction • During the “light reaction,” ETC makes ATP and NADPH 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!!

12. Reaction Center Chlorophyll & Photosystems • Photosystems • Located on the thylakoid membranes • Clusters of light-absorbing pigments trap energy from the sun  energize e- • This energy is passed from molecule to molecule until it reaches the rxn center • Reaction Center → • Surrounded by photosystems • Made up of the special chlorophyll a molecule and a primary e- acceptor • Primary e- acceptor passes the e- to the electron transport chain (ETC) • 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+ • Electrons get replaced by e- from PS II

13. CHEMIOSMOSIS • When a chlorophyll molecule absorbs a photon of light, some of the electrons are excited and raised to a higher energy level • The primary electron acceptor catches them & they enter the ETC(on the thylakoid membrane) • As e- go down the ETC, they lose energy • That energy is used to power protonpumpsthat pump H+ from the stromaINTO the lumen (aka - thylakoid space) • This creates a concentration gradient

14. ATP Synthase • B/c of that concentration gradient, the H+ ionswant to get backOUTof the lumenand into the stroma • These ions can only do this by using the enzyme ATPSynthase • ATP Synthaseis an enzyme that is powered by the H+ gradient and converts ADP into ATP • Summary : ATP Synthase creates ATP as H+ pass through it

15. CHEMIOSMOSIS… • Summary: • Chemiosmosis The process that uses the proton gradient and ATP synthase to make ATP • Both ATP(via ATP Synthase) and NADPH(by reducing NADP+) are produced during the light reaction  these then enter the Calvin Cycle • e- travel from PSII  PSI  NADP+ • NADP+ is the finale-acceptorin photosynthesis

16. Calvin Cycle! INPUT: Each Turn needs: - 3 ATP - 2 NADPH - 1 CO2 • Second part of PS • AKA – “The Dark Reaction” • Occurs in the stromaof the chloroplast • - Can occur withorwithoutlight • Main job: • Incorporate CO2 and rearrange C’s to form sugar using the energy (ATP/NADPH) from the Light Rxn • - The CC “fixes” CO2 • Carbon enters as CO2 and leaves as sugar • Goal is to produce a sugar (G3P) • Each turn “fixes” one molecule of carbon, so one G3P takes 3 turns of the Calvin Cycle Three turns shown above

17. Calvin Cycle Steps: Enzyme Rubiscoattaches CO2 to RuBP creates 6 x 3-PGA 6 x PGA are reducedto = 6 x G3P (sugar) via ATP/NADPH 1 x G3P exits as glucose 5 x G3P remain in the cycle . ATP rearranges the atoms  3 x RuBP

18. 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!

19. 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 • Photorespiration adds oxygen to the Calvin Cycle instead of carbon dioxide - This makes NO sugar or ATP - This wastes all of the plants resources!

20. C4 Plants • Fixes 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

21. 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

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