Watch this: http://youtu.be/g78utcLQrJ4 Photosynthesis Watch this: http://youtu.be/g78utcLQrJ4

D. Photosynthetic Reaction In 1930 C. B. van Niel showed that O2 given off by photosynthesis comes from water and not from CO2. Redox reactions ultimately transfer electrons from water to carbon dioxide 2. The net equation reads: Pg 119a

What is a plant anyway? 7.1 Photosynthetic Organisms A. Photosynthesis transforms solar energy B. Organic molecules built by photosynthesis provide both the building blocks and energy for cells. Figure 7.1a

D. Chloroplasts carry out photosynthesis Figure 7.1b C. Plants use the raw materials: carbon dioxide (from stoma) and water (from roots) D. Chloroplasts carry out photosynthesis Photosynthesis takes place in the chloroplasts! Figure 7.1b

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

Stoma (stomata pl.) allow for gas exchange Figure 7.2 Stoma (stomata pl.) allow for gas exchange Figure 7.2

Quick Check - 1.  Plant 2.  Thylakoid 3.  Photosynthesis 4.  Organic Molecules 5. Grana 6. Chloroplast

7. 2 Plants as Solar Energy Converters A 7.2 Plants as Solar Energy Converters A. Solar Radiation - Only 42% of solar radiation that hits the earth’s atmosphere reaches surface; most is visible light. Light is composed of packets of energy called photons.

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. Figure 7.3a

Color The color that we see when looking at a pigmented object is the wavelengths that are reflected or transmitted by the pigmented object. In other words, we see the reflected wavelengths. A green leaf reflects green. Green is not absorbed by the plant. Chlorophyll absorbs in the red, blue and violet wavelengths.

Fall Foliage Slideshow

Fall Leaves Why do leaves turn orange/red/brown in the fall? What are the major pigments which absorb light? Why do leaves appear green? The reason why there are accessory pigments in a leaf is to absorb energy in parts of the spectrum that chlorophyll can’t

E. Two Sets of Reactions in Photosynthesis 1 E. Two Sets of Reactions in Photosynthesis 1. Light reactions cannot take place unless light is present. They are the energy-capturing reactions. They convert light energy to chemical energy. When chlorophyll absorbs a photon, one of its electrons is raised to the excited state. Pg 119b

Excited Electrons When a photon hits a molecule, it releases energy as light, loss of an electron, fluorescence and heat Light reactions, and photosystems are located in the thylakoid membrane as well as the H+ ion gradient

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

2. Calvin Cycle Reactions a. These reactions take place in the stroma; can occur in either the light or the dark. b. These are synthesis reactions that use NADPH and ATP to reduce CO2. Figure 7.4 The products of the light reactions are ATP and NADPH

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

7.3 The Light Reactions (this is where we pick up electrons!) 1.  Two paths operate within the thylakoid membrane                          noncyclic              and                cyclic                           *straight line                       *in a circle 2.  Both paths use ATP, but the noncyclic also produces NADPH (this is where we pick up electrons!) 3.  PHOTOPHOSPHORYLATION = ATP production (phosphorylation means adding a P to ADP  ATP) 4. Photosystems are located in the thylakoid membrane which is where the light reactions occur.

1. Light hits photosystem II (yes, II comes before I)and exites an electron in H20 2.  The primary electron acceptor passes the electron down the ETC and generates ATP 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, PSII was established first.

Figure 7.5 Figure 7.5 We use these electrons to go to the Calvin Cycle We’ve used our electrons here to form ATP

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

D. ATP Production --> CHEMIOSMOSIS 7.3   Light Reactions        A.  Two Pathways    B.  Noncyclic    C.  Cyclic    D.   ATP Production  -->  CHEMIOSMOSIS            When H20 is split, two H+ remain, oxygen is released            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 Figure 7.7

Figure 7.6

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

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 FIXATION REDUCTION REGENERATION 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. CO2 fixation is the attachment of CO2 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, probably since it is a slow enzyme. Calvin Cycle Animation

C. Reduction of Carbon Dioxide 1. With reduction of carbon dioxide, a PGA  (3-phosphoglycerate [C3]) molecule forms.

D. Regeneration of RuBP 1. Every three turns of Calvin cycle, five molecules of PGAL are used to re-form three molecules of RuBP. 2. Every three turns of Calvin cycle, there is net gain of one PGAL molecule; five PGAL regenerate three molecules of RuBP.

Figure 7.8 Figure 7.8

E. The Importance of the Calvin Cycle 1. PGAL, the product of the Calvin Cycle can be converted into all sorts of other molecules. 2. Glucose phosphate is one result of PGAL metabolism; it is a common energy molecule.

Figure 7.9 Figure 7.9

Factors that Affect Photosynthesis   1. Light Quality (color) 2. Light intensity 3. Light Period 4. Carbon Dioxide Availability 5. Water Availability

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.

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 dry environments (C4 plants) have a problem with water loss, so they keep their stomata partly closed... this results in CO2  deficit (Used in Calvin Cycle), and the level of O2 RISES (as Light reactions Split Water Molecules). CAM plants conserve water by opening their stomata only at night

Figure 7.10 C4 plants and CAM (Crassulacean acid metabolism) plants use an alternate pathway to FIX carbon dioxide from the air. Figure 7.10

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 CO2 and fix into organic compounds. During the day, CO2 is released from these Compounds and enters the Calvin Cycle. Because they have their stomata open only at night, they grow slow. Figure 7.11

Quick Practice

Quick Practice grana thylakoid stroma O2

Pg 129b Light & H2O CO2 ADP NADP ATP Pg 129b NADPH O2 glucose

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