CO 7 Photosynthesis Name a plant you have seen recently.

Photosynthesis

Brainstorm... What are some careers or college majors related to plants? U of I - College of Agriculture

What is a plant anyway? Photosynthetic Organisms A. Photosynthesis transforms solar energy into organic molecules. B. Organic molecules built by photosynthesis provide both the building blocks and energy for cells.

Figure 7.1b C. The raw materials are carbon dioxide and water. D. Chloroplasts carry out photosynthesis.

Figure 7.1c E. Chlorophylls and other pigments involved in absorption of solar energy reside within thylakoid membranes of chloroplasts

Figure 7.2 Two words that sound alike but are not at all similar: Stroma Stoma

Quick Check 1. Plant 2. Thylakoid 3. Photosynthesis 4. Organic Molecules

Plants as Solar Energy Converters A. Solar Radiation - Only ~50% of solar radiation that hits Earth’s atmosphere reaches surface; most is visible light.

B. Photosynthetic Pigments - Pigments found in chlorophyll absorb various portions of visible light; absorption spectrum. 1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b. 2. Both chlorophylls absorb violet, blue, and red wavelengths best. 3. Most green is reflected back; this is why leaves appear green.

4. Carotenoids are yellow-orange pigments which absorb light in violet, blue, and green regions. 5. When chlorophyll breaks down in fall, the yellow-orange pigments in leaves show through.

Fall Foliage Slideshow

C. Absorption and action spectrum – A spectrophotometer measures the amount of light that passes through a substance (pigment) by wavelength. 1) As different wavelengths are passed through, some are absorbed. 2) Graph of percent of light absorbed at each wavelength is absorption spectrum.

3) Photosynthesis produces oxygen; production of oxygen is used to measure the rate of photosynthesis. 4) Oxygen production and, therefore, photosynthetic activity is measured for plants under each specific wavelength; plotted on a graph, this produces an action spectrum. 5) Since the action spectrum resembles absorption spectrum, this indicates…what?  chlorophylls and carotenoids contribute to photosynthesis.

Checkpoint 1. What is the relationship between the absorption spectrum and the action spectrum? 2. How can we measure the rate of photosynthesis? 3. How is the wavelength of light related to the rate of photosynthesis? 4. A radish plant is grown using lights of different colors. Explain the data.

E. Two Sets of Reactions in Photosynthesis 1. Light reactions cannot take place unless light is present. They are the energy-capturing reactions.

b. Chlorophyll within thylakoid membranes absorbs solar energy and energizes electrons. c. Energized electrons move down an electron transport system; the energy is captured and used for ATP production. d. Energized electrons are taken up by NADP+, becoming NADPH.

2. Calvin Cycle Reactions a. These reactions take place in the stroma; can occur in either light or dark conditions. b. These are synthesis reactions that use NADPH and ATP to reduce CO2 (add an e- to it). -- and make a carbohydrate, sugar

D. Photosynthetic Reaction 1.In 1930 a Dutch-American microbiologist (Cornelius Bernardus Van Niel) showed that O 2 given off by photosynthesis comes from water and not from CO 2. 2.The net equation reads:

What you should know by now.. 1. The equation for photosynthesis. Write it! 2. The structure of a chloroplast. Sketch it! 3. The two reactions of photosynthesis. **Things are about to get much more difficult**

7.3 The Light Reactions 1. Two electron paths operate between two photosystems within the thylakoid membrane linear electron flow, and cyclic electron flow 2. Both paths use ATP, but only the noncyclic also produces NADPH to be used in the Calvin Cycle 3. PHOTOPHOSPHORYLATION = ATP production by sunlight Due to the movement of ions (H+) across a selectively permeable membrane, down their electrochemical gradient (CHEMIOSMOSIS).

1. Light hits photosystem II and excites an electron in the pigment (chlorophyll, etc.)…initial electron supplied by splitting water (photolysis  energy from photons, assisted by enzymes) 2. The primary electron acceptor passes the electron down the ETC and generates ATP via chemiosmosis 3. Light is required for PSI, but not water, it generates NADPH

Something trivial.... Photosystem I and Photosystem II are named based on when they were discovered, PSI was established first.

Cyclic Electron Flow: - many prokaryotes, including purple-sulfur bacteria, and mutant plants - Avoids both photosystem II, release of O2, and donation of electrons to NADP + --> diverts more capture photons to produce ATP - Fd = ferrodoxin protein, & Pc = plastocyanin protein Q: Can you think of the environmental conditions in which this would be a major advantage?

Figure 7.5

Indicate which system (PS1 or PS2 or BOTH) ____1. Splits water ____2. Produces NADPH ____3. Has an electron transport chain ____4. Requires light ____5. Utilizes a primary electron acceptor ____6. Occurs in the thylakoid ____7. Requires the input of H20 ____8. The cyclic path ____9. Uses chlorophyll ____10. Releases oxygen

Are you still confused? This is pretty hard to visualize, but through the magic of technology, we can watch these processes as animations McGraw Hill Animation Forest Biology - The Light Reactions DB Post Assignment: Summarize the 8 Steps of Linear Electron Flow (pg. 194)

7.3 Light Reactions A. Two Pathways B. Noncyclic C. Cyclic D. ATP Production --> Photophosphorylation (CHEMIOSMOSIS) When H20 is split, two H+ remain These H+ are pumped from the stroma into the thylakoid This creates a gradient used to produce ATP from ADP ATP is the whole point of Photosystem II and will be used to power the Light Independent Reactions (Calvin Cycle)

Figure 7.7

Chemiosmosis is difficult to visualize. So... you get to color it!

The Calvin Cycle Also called *The Light Independent Reactions *The Dark Reactions *Named after Melvin Calvin, who used a radioactive isotope of carbon to trace the reactions.

The Calvin Cycle is a series of reactions producing carbohydrates. carbon dioxide fixation, carbon dioxide reduction, and regeneration of RuBP. FIXATION REDUCTION REGENERATION

B. Fixation of Carbon Dioxide 1. CO 2 fixation is the attachment of CO 2 to an organic compound called RuBP. 2. RuBP (ribulose bisphosphate) is a five-carbon molecule that combines with carbon dioxide.

3. The enzyme RuBP carboxylase (rubisco) speeds this reaction; this enzyme comprises 20–50% of the protein content of chloroplasts Calvin Cycle Animation Mainly this is a reshuffling of carbons using ATP and NADPH as energy

G3P can be converted into other things

Fortunately.... Summary Statements: What is the purpose of the Calvin Cycle? Where does the cell get its energy to perform these reactions? What is the final product? AP Biology no longer requires the memorization of every step of the Calvin Cycle, but you should understand the beginning and the end and what it's purpose is.

What factors affect photosynthesis? 1. Light Quality (color) 2. Light intensity 3. Light Period 4. Carbon Dioxide Availability 5. Water Availability *Design an experiment to test ONE of the above factors* Photosynthesis Simulation Waterweed Simulator

In order for photosynthesis to occur, plants must open tiny pores on their leaves called STOMATA. Opening these pores can lead to loss of water. Some Plant Taxonomy

Alternative Pathways The Calvin Cycle is the MOST Common Pathway for Carbon Fixation. Plant Species that fix Carbon EXCLUSIVELY through the Calvin Cycle are known as C3 PLANTS. Plants in hot and/or dry environments have a problem with water loss, so they keep their stomata partly closed... …this results in a CO 2 DEFICIT (Used in Calvin Cycle), and the level of O 2 RISES (as Light reactions Split Water Molecules).

Figure 7.10 In the presence of high O2, Rubisco combines O2 with RuBP instead of CO2.  only one molecule of G3P is produced and a toxic 2C molecule called phosphoglycolate is produced. C4 plants and CAM plants bypass this by using an alternate pathway to FIX carbon dioxide from the air. C4 PATHWAY uses PEP carboxylase to transfer CO 2 to bundle sheath cells where there is little to no O 2.

Figure 7.11 THE CAM PATHWAY - Plants that use the CAM Pathway open their stomata at night and close during the day. At night, CAM plants take in and use PEPC to fix CO 2 into organic compounds. During the day, CO 2 is released from these compounds and enters the Calvin Cycle. Because they have their stomata open only at night, they grow slow. C ARBON F IXER : C4/Cam  PEP Carboxylase C3  RuBisCo

Quick Practice

thylakoid O2O2 stroma granum

Pg 129b Light & H 2 O O2O2 CO 2 glucose ATP NADPH ADP NADP

A = photosystem II B = photosystem I C = H20 D = Electron Transport Chain E = ATP Synthase AB = ATP AC = phospholipids AD = light (energy)

Finito

Photosynthesis Activities 1. Elodea photosynthesis rate (lab) 2. Photosynthesis alphabet book 3. Chromatography of a spinach leaf 4. Viewing elodea cells chloroplasts 5. Fall colors observation