Photosynthesis.

Photosynthesis

Jan Baptisa van Helmont (1648)
"...I took an earthenware vessel, placed in it 200 pounds of soil dried in an oven, soaked this with rainwater, and planted in it a willow branch weighing 5 pounds. At the end of five years, the tree grown from it weighed 169 pounds and about 3 ounces. Now, the earthenware vessel was always moistened (when necessary) only with rainwater or distilled water, and it was large enough and embedded in the ground, and, lest dust flying be mixed with the soil, an iron plate coated with tin and pierced by many holes covered the rim of the vessel. I did not compute the weight of the fallen leaves of the four autumns. Finally, I dried the soil in the vessel again, and the same 200 pounds were found, less about 2 ounces. Therefore 169 pounds of wood, bark, and root had arisen from water only.” 6CO2 + 6H2O + Energy ® C6H12O6 + 6O2 Glucose provides the energy and carbon needed to synthesize other plant material.

Jan Baptisa van Helmont (1648)
"...I took an earthenware vessel, placed in it 200 pounds of soil dried in an oven, soaked this with rainwater, and planted in it a willow branch weighing 5 pounds. At the end of five years, the tree grown from it weighed 169 pounds and about 3 ounces. Now, the earthenware vessel was always moistened (when necessary) only with rainwater or distilled water, and it was large enough and embedded in the ground, and, lest dust flying be mixed with the soil, an iron plate coated with tin and pierced by many holes covered the rim of the vessel. I did not compute the weight of the fallen leaves of the four autumns. Finally, I dried the soil in the vessel again, and the same 200 pounds were found, less about 2 ounces. Therefore 169 pounds of wood, bark, and root had arisen from water only.” 6CO2 + 6H2O + Energy ® C6H12O6 + 6O2 As can be seen from the equation for photosynthesis, the wood, bark, and root arose from water and carbon dioxide.

Electromagnetic Spectrum
Visible light is only a part of the electromagnetic spectrum. nanometers 10-5 10-3 1 103 106 1 m 103 m Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light

The numbers on this chart are wavelength. nanometers 10-5 10-3 1 103 106 1 m 103 m Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light

nanometers 10-5 10-3 1 103 106 1 m 103 m Gamma rays X-rays UV Infrared Microwaves Radio waves The spectrum shown below fits into the small space shown on the line. Visible light

Photosynthetic Pigments
Light behaves as if it is composed of units or packets called photons. Photon Plants have pigment molecules that contain atoms that become energized when they are struck by photons of light. Energized electrons move further from the nucleus.

Photosynthetic Pigments
When the energy is released, the electron returns to a location closer to the nucleus. Heat or light The energized molecule can transfer the energy to another atom or molecule or release it in the form of heat or light.

What color is best? In this experiment, a prism is used to produce a gradient of light that ranges from red to blue. The large cell is a photosynthetic alga called Spirogyra. The spiral-shaped green structure is its chloroplast. The bacteria (represented by dots) are aerobic, that is, they require oxygen. The slide was initially prepared so that there was no oxygen present in the water surrounding the alga. Photosynthesis produces oxygen and the bacteria congregate in areas where the most oxygen is produced, thus, the rate of photosynthesis is highest. Blue and Red light therefore produce the highest rate of photosynthesis. Light | Pigments | Chloroplast | Overview | Photosystems | Photosystem II | Electron Transport System | Photosystem I | Calvin Cycle | Photorespiration | C4 plants | Review | Return

Two Kinds of Reactions The reactions of photosynthesis can be divided into two main categories: The light reactions require light. The light-independent reactions occur either in the light or in the dark. As you view the rest of these slides, keep in mind that the “goal” of photosynthesis is to synthesize glucose. Carbon dioxide is reduced to glucose (see equation below). The electrons needed for this reduction come from water. The energy needed for this reduction comes from light. The equation is: Energy + 6CO2 + 6H2O  C6H12O6 + 6O2

Chloroplast Structure
In order to understand the reactions of photosynthesis, it will be helpful to review the structure of a chloroplast. It contains disk-shaped structures called thylakoids. The area outside the disks is called the stroma. Stroma Double membrane Thylakoids

Photosystem I and II Light Absorption

This drawing shows a magnified view of a part of a thylakoid
This drawing shows a magnified view of a part of a thylakoid. The green area is the thylakoid and the blue area is the stroma of the chloroplast. Photosynthetic pigments embedded within the membrane form a unit called an antenna. Antenna Stroma Thylakoid membrane Photosynthetic pigments such as chlorophyll A, chlorophyll B and carotinoids. Light | Pigments | Overview | Chloroplast | Photosystem II | Electron Transport System | Photosystem I | Calvin Cycle | Photorespiration | C4 plants | Review | Return

A pigment molecule within the antenna absorbs a photon of light energy.
The energy from that pigment molecule is passed to neighboring pigment molecules and eventually makes its way to pigment molecule called the reaction center. When the reaction center molecule becomes excited (energized), it loses an electron to an electron acceptor. Light energy Thylakoid membrane Electron acceptor Reaction center Light | Pigments | Overview | Chloroplast | Photosystem II | Electron Transport System | Photosystem I | Calvin Cycle | Photorespiration | C4 plants | Review | Return

The antenna and electron acceptor are called a photosystem.
There are two kinds of photosystems in plants called photosystem I and photosystem II. Photosystem I is sometimes called P700 and photosystem II is sometimes P680. The 680 and 700 designations refer to the wavelength of light that they absorb best. Photosystem Antenna Thylakoid membrane Electron acceptor Reaction center Light | Pigments | Overview | Chloroplast | Photosystem II | Electron Transport System | Photosystem I | Calvin Cycle | Photorespiration | C4 plants | Review | Return

Light Dependent Reaction Review
Light Energy Chloroplast NADP+ + H+ NADPH H+ H+ H+ H+ H+ H+ H+ ATP ADP + Pi H2O2e- + 2H+ + ½ O2 Light Dependent Reaction Review H+ A hydrogen atom contains one electron (e-) and one proton (H+). The two hydrogen atoms in a water molecule can therefore be used to produce 2e- and 2H+. Thylakoids Stroma Return

electron transport system
NADPH NADP+ light e- acceptor e- acceptor ATP This diagram traces the path followed by an electron during the light reactions. The path is indicated by red arrows and letters. The high-energy parts of the pathway are drawn near the top of the diagram. electron transport system P700 antenna complex P680 antenna complex H2O  2e- + 2H+ + O Light | Pigments | Chloroplast | Overview | Photosystem II | Electron Transport System | Photosystem I | Calvin Cycle | Photorespiration | C4 plants | Review | Return

CO2 Fixation CO2 fixation refers to bonding CO2 to an organic molecule to make a larger molecule. C5 + CO2  C6 “C5” is an abbreviation that means that this molecule has 5 carbon atoms. The oxygen and hydrogen atoms are not written.

Cross Section of a C3 Leaf
Stomata (singular stoma) are microscopic openings on the undersurface of leaves that allow gas exchange and water evaporation from inside the leaf. Because dehydration can be a serious problem, the stomata close when the plant is under water stress. When closed, CO2 needed for the Calvin cycle cannot enter. mesophyll cells bundle-sheath cells stoma vein

If CO2 is low CO2 6 CO2 6 C-C-C-C-C-C O2 RUBISCO RuBP 6 C-C-C-C-C
Evolutionary relic Rice, Wheat, Soybean When the concentration of CO2 is low (red above), oxygen will bind to the active site of RUBISCO. When oxygen is bound to RUBISCO, RuBP is broken down and CO2 is released. This wastes energy and is of no use to the plant. It is called photorespiration because oxygen is taken up and CO2 is released. Light | Pigments | Chloroplast | Overview | Photosystem II | Electron Transport System | Photosystem I | Calvin Cycle | Photorespiration | C4 plants | Review | Return

Photosynthesis occurs within the mesophyll cells in C3 plants, which form a dense layer on the upper surface of the leaf and a spongy layer on the lower surface. Bundle-sheath cells surrounding the veins are not photosynthetic. mesophyll cells bundle-sheath cells stoma vein

Sugar cane and Corn bundle-sheath cells mesophyll cells vein stoma

CO2 Fixation in C4 Plants bundle sheath cells CO2 C3 C4
Calvin cycle mesophyll cells bundle sheath cells CO2 fixation occurs in mesophyll cells

CO2 Fixation in C4 Plants CO2 C3 C4 Calvin cycle C3= PEP carboxylase
CO2 fixation occurs in mesophyll cells Calvin cycle occurs in bundle sheath cells C3= PEP carboxylase C4= Oxaloacetate then convert to Malate C3= Pyruvate

C4 Plants

CAM Plants vrs. C4

CAM Plants: Arid Conditions/succulent plants
CAM= crassulacean acid metabolism Crassulaceae are a family of plants where CAM was first discovered. Mesophyll stores organic acid during night in vacoules until morning Light Rxn supplies ATP and NADPH (for Calvin Cycle), CO2 released From organic acid in mesophyll.

Review Exercises

Identify components A through D.
ADP + Pi ATP Energy A B C D

NADP+ NADPH + H+ Energy + 2H A B C D

Identify each component.
G 6 B 6 A 6 C 12 D 10 F 12 H 12 I 12 J 12 K 6L 6M

Fill in the Boxes below. Light Reactions Light-Independent Reactions
Inputs Produced

light, ADP, NADP+, H2O Inputs Produced

light, ADP, NADP+, H2O Inputs ATP, NADPH, O2, H+ Produced

light, ADP, NADP+, H2O ATP, NADPH, CO2 Inputs ATP, NADPH, O2, H+ Produced

light, ADP, NADP+, H2O ATP, NADPH, CO2 Inputs glucose, ADP, NADP+ ATP, NADPH, O2, H+ Produced

The End

Photosynthesis.

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