Chapter

Chapter

Chapter 8 Photosynthesis General Biology I BSC 2010 Caption: I can photosynthesis (c) Kelvinsond, Public domain All organisms (from bacteria to us) need energy to maintain life Remember: no energy input = chaos = death in biology Download for free at http://cnx.org/contents/[email protected]

Photosynthesis Powers Ecosystems* It converts light energy into food energy. Both plants and animals depend on the food it produces as parts of food chains or food webs. *99% of known ecosystems are powered by sunlight. Deep sea hydrothermal vent ecosystems are an example of the other 1%. Download for free at http://cnx.org/contents/[email protected]

Trophy = Feeding energy source photo- chemo- carbon source auto- carbon from carbon dioxide (CO2) gas hetero- energy from light photoautotrophs plants algae

cyanobacteria photoheterotrophs some types of bacteria carbon from solid molecules (food) energy from molecules (food) chemoautotrophs some bacteria and archaea chemoheterotrophs animals, fungi

some protists some prokaryotes 0.009% 0.09% 0.9% 9% 90% Caption: Ecological Pyramid (c) Swiggity Swag, Public domain The ultimate source of energy for Earth is the Sun However, living organisms are not able to use the

energy from the Sun directly, the energy must be transformed This happens through the process of photosynthesis Caption: Magnificent CME Erupts on the Sun with Earth to Scale (c) NASA, Public domain Photosynthesis is the only process that can capture energy that originates in outer space and convert it into energy stored as chemical compounds (food). During photosynthesis, the energy from the sun is converted and captured in the bonds of

carbohydrates which are now in the plant, that energy then makes its way up the food chain Caption: Photosynthesis (c) At09kg Public domain Photosynthesis: Global Distribution Where do you think majority of photosynthesis occurs? on the surface of the ocean or land? Photosynthesis a series of chemical reactions

results in production of food consumes carbon dioxide releases oxygen (stored water is oxidized) occurs in plants, green algae, some bacteria, and some protists Download for free at http://cnx.org/contents/[email protected] Photosynthesis uses solar energy, carbon dioxide, and water to produce energystoring carbohydrates. Oxygen is generated as a waste product of

photosynthesis. Download for free at http://cnx.org/contents/[email protected] Photosynthesis Locations Eukaryotes: occurs in chloroplasts Prokaryotes: occurs in association with cell membranes Chloroplasts arose by endosymbiosis of photosynthetic bacteria.

Download for free at http://cnx.org/contents/[email protected] Plant Leaf Structure (typical) Caption: Leaf Anatomy (c) Maksim Public domain Chloropl asts Download for free at http://cnx.org/contents/[email protected] outer membrane intermembrane space inner membrane stroma

thylakoid membrane thylakoid lumen thylakoid membrane thylakoid lumen thylakoid membrane stromal thylakoid mem. thylakoid lumen thylakoid membrane thylakoid lumen grana thylakoid membrane thylakoid lumen Photosynthesis Has Two Stages

The light-dependent reactions Generate ATP and NADPH from sunlight, ADP, and NADP+, from the oxidation of water to oxygen gas (~oxidative phosphorylation) The light-independent reactions (Calvin Cycle) ATP and NADPH used to build sugar molecules incorporate CO2 into glyceraldehyde-3P (glycolysis intermediate) Download for free at http://cnx.org/contents/[email protected] Visible Light is a form of electromagnetic radiation exists in different

wavelengths Different wavelengths correspond to different colors. Download for free at http://cnx.org/contents/[email protected] The Electromagnetic Spectrum Plants use this for photosynthesis Download for free at http://cnx.org/contents/[email protected] Absorption of Light When light waves hit a pigment, that pigment will either absorb

the energy or reflect it. Different pigments absorb different wavelengths, as seen in the absorption spectrum graph. Photosynthesis pigments include chlorophylls a and b and carotenoids. Download for free at http://cnx.org/contents/[email protected] Absorption of Light: Why are plants green? Chlorophyll reflects (does not absorb) green light. Plants with lots of chlorophyll reflect green light and appear

green. Thats why the main photosynthetic part of the plant appears greenish to us Carotenoids absorb some of the longer wavelengths. This is why they tend to look redder/bluer (red onions, blood oranges, red grapes, etc.) Download for free at http:// cnx.org/content/col11448/latest/ Accessory pigments

These pigments are found in lesser amounts in the leaf Caption: Fall Leaves (c) Sympohony 999 Public domain Might be more concentrated in other parts of the plant (seeds or fruit) or become more visible at certain times of year (autumnal

The Light-Dependent Reactions the first stage of photosynthesis harvest light energy to make NADPH and ATP* occurs in photosystems embedded in the thylakoid membrane include 2 types of photosystems (type II and type I) * Yes! ATP is made in chloroplasts. However, it is used only in the chloroplast to build sugars. * Chloroplasts are a sugar and lipid powerhouse, not an ATP powerhouse like mitochondria are. * Both plants and animals use mitochondria to generate ATP for cytosolic needs

Download for free at http://cnx.org/contents/[email protected] Photosystems are LightHarvesting, Water-Oxidizing Complexes structure includes an antenna complex made of proteins and pigment molecules pigment molecules pass energy to the reaction center as photons, or packets of light. pigments absorb photons and the molecule becomes excited in a highenergy state, donating electrons to the electron transport chain It ultimately strips electrons from water, forcing the production of oxygen gas (O2) and hydrogen ions

Download for free at http://cnx.org/contents/[email protected] Electron Capture: PhotoSystem II Occurs in the grana thylakoid The excited reaction center gives up an electron. This is an oxidation event. The electron is captured by the primary electron acceptor. (plastoquinone) The electron is sent through a cytochrome complex (and forces more H+ into lumen) to a final

electron acceptor (plastocyanin) Download for free at http://cnx.org/contents/[email protected] Electron Capture: PhotoSystem I Occurs in the stroma thylakoid PSI harvests more light energy, and with that energy, sends new electrons into a second ETC The PSI recovers its electrons by oxidizing plastocyanin (NOT water) The electrons go through an iron:sulfur complex called ferredoxin, then to NADP

reductase NADP+ is the final electron acceptor to become NADPH (in the stroma), that further reduces H+ in the lumen and helps build sugar molecules. ferredoxin NADPreductase NADP+ + H+ primary electron acceptor in PSII

NADPH to Calvin Cycle from plastocyanin Download for free at http://cnx.org/contents/[email protected] Light Reactions in the Thylakoid Water is split (oxidized) to recover the electrons lost from the light

harvesting. This releases oxygen, and hydrogen ions, that acidify the thylakoid lumen. Combined with absorption of H+ by NADP+ reductase, a H+ gradient is built up across the thylakoid membrane Guess what this H+ gradient will be used for????? Download for free at http://cnx.org/content/col11448/latest/

Light Reactions in the Thylakoid Thylakoid lumen The Light-Independent Reactions the second stage of photosynthesis NADPH and ATP built up during the days during first stage uses NADPH and ATP to build carbohydrate molecules (food) occurs in the stroma

accomplishes carbon fixation also known as the Calvin cycle Download for free at http://cnx.org/contents/[email protected] The Calvin Cycle Has Three Parts 1. Fixation: CO2 from air is fixed into solid ribulose-1,5bisphosphate to make two 3-phosphoglycerate (3-PGA)* molecules (before pyruvate in glycolysis). 2. Reduction: ATP energy and NADPH are used to reduce the 3-PGA to make glyceraldehyde-3-phosphate (GP3)*. 3. Regeneration: More ATP and a shell game are used to regenerate the starting material (ribulouse-1,5-bisphosphate.

*Where have you seen 3-PGA and GP3 before? In glycolysis, a 6-carbon glucose is first split into two 3-carbon G3P molecules; one is 3-phosphoglyceraldehyde. On the way to make pyruvate, 3-phosphoglycerate is formed 3-PGA = 3-phosphoglycerate * * * as carbon dioxide, or as carbonate from the soil or water

Out of the six G3P molecules made, one can leave the cycle and be used to generate glucose The rest of the GP3 is recycled back into RuBP by the shell game so the cycle can continue. GA3P = Glyceraldehyde-3-phosphate Note that only one of

the recently fixed carbons is part of the GA3P that goes into glucose production. The Shell Game to regenerate Ru-1,5-BP O O OP OH OH OH OH OP

OH aldehyde ketone isomerism ketone:aldehyde fusion OH OH OP OH Multiple instances of x3 OP

OP OP OP OP OP OH OP OH OP OH OP

ketone:aldehyde separtion) OH OP OP OH OP Dephosphorylation before fusion 3+3=6 OH OH OP

OH OP OH OH OP OH OP OH OH OH

OH OH OH OH OP OH OP 6+3=5+4 3+4=7 OH OH OH

OP OH OP OH OH OH OH OH OH OH OH OH OH OH OH

OP OH OP 7+3=5+5 OP OP OP Carboxylic acid Aldehyde/ketone Hydroxyl/alcohol

Phosphate Recall: Photosynthesis Has Two Stages The light-dependent reactions The light-independent reactions (Calvin Cycle) Download for free at http://cnx.org/contents/[email protected] Photosynthesis and aerobic respiration play important roles in the carbon cycle. Download for free at http://cnx.org/contents/[email protected]

Differentiate: Chloroplasts and Mitochondria O2 and glucose CO2 sunlight Download for free at http://cnx.org/contents/[email protected]

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