Instructions To help you navigate these slides, you should set your viewer to display thumbnails of these slides. On many viewers, this can be done by pressing the F4 key. The slides should be viewed in order because a slide may provide information that is needed to understand the next or subsequent slides. It is important that you understand each slide before advancing to the next because concepts build upon previous concepts. This slide presentation is intended to be a lecture. It might be helpful to take notes as you progress through the slides. 1
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. 6CO 2 + 6H 2 O + Energy C 6 H 12 O 6 + 6O 2 Glucose provides the energy and carbon needed to synthesize other plant material. 2
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. 6CO 2 + 6H 2 O + Energy C 6 H 12 O 6 + 6O 2 As can be seen from the equation for photosynthesis, the wood, bark, and root arose from water and carbon dioxide. 3
Wavelength Light travels in waves. The color of light is determined by its wavelength. The red light shown below has a wavelength of 700 nm. 700 nm Red Blue light has a shorter wavelength. Blue 4
Electromagnetic Spectrum Visible light is only part of the electromagnetic spectrum. Wavelength (meters): 10-14 10-12 10-8 10-6 10-5 10-3 10-2 1 Cosmic rays Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light 5
Electromagnetic Spectrum The numbers on this chart are wavelength (in meters). Wavelength (meters): 10-14 10-12 10-8 10-6 10-5 10-3 10-2 1 Cosmic rays Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light 6
Electromagnetic Spectrum Wavelength (meters): 10-14 10-12 10-8 10-6 10-5 10-3 10-2 1 Cosmic rays Gamma rays X-rays UV Infrared Microwaves Radio waves The spectrum shown below fits into the small space shown on the line. Visible light 7
Photosynthetic Pigments Light behaves as if it is composed of units or packets called photons. 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. 8
Photosynthetic Pigments Heat, light or excite another atom The energized molecule can transfer the energy to another atom or molecule or release it in the form of heat or light. 9
Photosynthetic Pigments Heat or light When the energy is released, the electron returns to a location closer to the nucleus. 10
What color is best? In this experiment by Engelmann in 1883, a microscope was used to view a photosynthetic alga and some bacteria. A prism device underneath the microscope produced a gradient of light that ranged from red to blue. The large horizontal cells in the photograph are part of a green alga. The dots represent bacteria that are able to move towards areas with higher oxygen concentration. Photosynthesis produces oxygen and the bacteria congregated in areas where the most oxygen was produced, thus, where the rate of photosynthesis was highest. Blue and red light therefore resulted in the highest rate of photosynthesis. Green algal cells Colors produced by a prism Bacteria 11
Chlorophyll a Absorption Spectra of Some Photosynthetic Pigments Chlorophyll b This graph shows the color of light absorbed by three different kinds of photosynthetic pigments. Notice that they do not absorb light that is in the green to yellow range. Absorption Carotenoids 400 500 600 700 Wavelength 12
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). [Be sure that you know what is meant by reduced before you go on.] The electrons needed for this reduction come from water. The energy needed for this reduction comes from light. The equation is: Energy + 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 13
light Light Reactions light reactions ATP NADPH During photosynthesis, CO 2 will be reduced (gain electrons) to form glucose. The electrons needed to reduce CO 2 are temporarily carried by NADPH. 14
H 2 O O 2 light Light Reactions light reactions ATP NADPH Recall that hydrogen atoms carry electrons. NADPH gets its electrons from water. The oxygen is not used. 15
H 2 O O 2 light Light-Independent Reactions light reactions ATP NADPH C0 2 light-independent reactions (Calvin cycle) C 6 H 12 O 6 The reduction of CO 2 to glucose occurs in the light-independent reactions. 16
H 2 O O 2 This slide summarizes photosynthesis. 6CO 2 + 6H 2 O + E C 6 H 12 O 6 + 6O 2 light Summary of Photosynthesis light reactions ATP NADPH ADP C0 2 light-independent reactions (Calvin cycle) NADP + C 6 H 12 O 6 17
Elodea leaf X 400 The small green structures within the cells of this plant are chloroplasts. 18
Chloroplast Structure Photosynthesis in plants occurs in organelles called chloroplasts. The chloroplasts contain disk-shaped structures called thylakoids. The area outside the thylakoids is called the stroma Prokaryotic cells do not have chloroplasts. Their thylakoids are extensions of the plasma membrane. Stroma Double membrane Thylakoids 19
H 2 O O 2 The next several slides will examine the light reactions of photosynthesis. light Summary of Photosynthesis light reactions ATP NADPH ADP C0 2 light-independent reactions (Calvin cycle) NADP + C 6 H 12 O 6 20
Light energy 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. A light-harvesting complex contains photosynthetic pigments bound to a complex of proteins. A reaction center complex contains two special molecules of chlorophyll a and a primary electron acceptor. The entire structure- the light-harvesting complex and the reaction center complex- is a photosystem. These structures will be discussed in the next several slides. The photosystem is embedded within the thylakoid membrane. Light-harvesting complex Reaction center complex Primary electron acceptor Pigment molecule Chlorophyll a Thylakoid membrane Thylakoid Photosystem 21
During the light reactions, a pigment molecule absorbs a photon of light energy. The energy from that pigment molecule is passed to neighboring pigment molecules and eventually makes its way to chlorophyll a in the reaction center complex. The chlorophyll a molecules lose an electron to the primary electron acceptor. Light energy Reaction center complex Primary electron acceptor Light-harvesting complex Pigment molecule Chlorophyll a Thylakoid membrane Photosystem Thylakoid 22
As a result of gaining an electron (reduction), the primary electron acceptor becomes a high-energy molecule. Its energy originally came from light. To understand this transfer of energy, recall that oxidation is the loss of an electron and is associated with the loss of energy. Reduction is the gain of an electron and energy. Energy is transferred with the electron. Light energy Reaction center complex Primary electron acceptor Light-harvesting complex Pigment molecule Chlorophyll a Thylakoid membrane Photosystem Thylakoid 23
There are two kinds of photosystems in plants: photosystem I and photosystem II. Photosystem I is sometimes called P 700 and photosystem II is sometimes P 680. The 680 and 700 designations refer to the wavelength of light that the reaction center chlorophyll a absorbs best. Light energy Reaction center complex Primary electron acceptor Light-harvesting complex Pigment molecule Chlorophyll a Thylakoid membrane Photosystem Thylakoid 24
In the diagrams that follow, we will use less magnification so that the three thylakoids can be seen. The photosystem will be drawn as a green circle. A red dot within the photosystem represents the primary electron acceptor. Light energy Reaction center complex Primary electron acceptor Light-harvesting complex Pigment molecule Chlorophyll a Thylakoid membrane Photosystem Thylakoid 25
Light Energy The red circles represent the primary electron acceptors. In the previous slides, we saw that the primary electron acceptor of photosystem II was reduced with an electron from the reaction center. This electron must be replaced. Electron transport system Chloroplast Photosystem II Photosystem I Thylakoids Thylakoids Stroma 26
Light Energy Chloroplast H 2 O 2e - + 2 + ½ O 2 The electrons needed to replace those lost by chlorophyll a in the reaction center complex are obtained from water. A hydrogen atom contains one electron (e - ) and one proton ( ). The two hydrogen atoms in a water molecule can therefore be used to produce 2e - and 2. The oxygen is not used and is liberated. Thylakoids Stroma 27
Light Energy Chloroplast H 2 O 2e - + 2 + ½ O 2 The three blue circles represent the electron transport system. They are proteins embedded within the thylakoid membrane. The first protein receives the electron (and energy) from the electron acceptor in photosystem II. Thylakoids Stroma 28
Light Energy Chloroplast H 2 O 2e - + 2 + ½ O 2 As a result of gaining an electron (reduction), the first carrier of the electron transport system gains energy. It uses some of the energy to pump into the thylakoid. Thylakoids Stroma 29
Light Energy Chloroplast H 2 O 2e - + 2 + ½ O 2 The carrier then passes the electron to the next carrier. Thylakoids Stroma 30
Light Energy Chloroplast H 2 O 2e - + 2 + ½ O 2 This carrier uses some of the remainder of the energy to pump more into the thylakoid. Stroma 31
Light Energy Chloroplast H 2 O 2e - + 2 + ½ O 2 The electron is passed to the next carrier which also pumps. Thylakoids Stroma 32
Light Energy Chloroplast H + H 2 O 2e - + 2 + ½ O 2 The electron transport system creates a concentration gradient of inside the thylakoid. Stroma 33
Light Energy Chloroplast The concentration gradient of is used to synthesize ATP. ATP is produced from ADP and P i when hydrogen ions pass out of the thylakoid through ATP synthase. H + H 2 O 2e - + 2 + ½ O 2 ATP ADP + P i Thylakoids Stroma 34
Light Energy Chloroplast This method of synthesizing ATP by using a gradient in the thylakoid is chemiosmotic phosphorylation. It can also be called photophosphorylation. H + H 2 O 2e - + 2 + ½ O 2 ATP ADP + P i Thylakoids Stroma 35
Light Energy Chloroplast The final electron carrier has little reducing capability (little energy is left). The electron is passed to photosystem I. H + H 2 O 2e - + 2 + ½ O 2 ATP ADP + P i Thylakoids Stroma 36
Light Energy A pigment molecule in photosystem I absorbs a photon of light. The energy from that molecule is passed to neighboring Chloroplast molecules within the antenna. The energy is eventually passed to chlorophyll a in the reaction center complex of this photosystem. H + H 2 O 2e - + 2 + ½ O 2 Light Reactions (12) ATP ADP + P i Thylakoids Stroma 37
Light Energy Chloroplast As a result of being energized, the chlorophyll a loses the electron to a primary electron acceptor. H + H 2 O 2e - + 2 + ½ O 2 Light Reactions (12) ATP ADP + P i Thylakoids Stroma 38
Light Energy Chloroplast NADP + + NADPH H + H 2 O 2e - + 2 + ½ O 2 ATP ADP + P i The acceptor passes it to NADP +, which becomes reduced to NADPH. According to the following equation, NADP + has the capacity to carry two electrons. NADP + + 2e - + NADPH Thylakoids Stroma 39
H 2 O O 2 light Summary of Photosynthesis (3) light reactions ATP NADPH ADP NADP + 6 C0 2 light-independent reactions (Calvin cycle) C 6 H 12 O 6 40
light e - acceptor ATP electron transport system e - acceptor NADPH NADP + 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. P 700 antenna complex Summary of Light Reactions P 680 antenna complex H 2 O 2e - + 2 + O 41
Light Energy Chloroplast CO 2 H + H 2 O 2e - + 2 + ½ O 2 NADP + + NADPH ATP ADP + P i Calvin Cycle The next several slides show how the products of the light reactions (ATP and NADPH) are used to reduce CO 2 to carbohydrate in the Calvin cycle. glucose Thylakoids Stroma 42
Light Energy Chloroplast CO 2 H + H 2 O 2e - + 2 + ½ O 2 NADP + + NADPH ATP ADP + P i Calvin Cycle The reactions of the Calvin cycle occur in the stroma of the chloroplast. glucose Thylakoids Stroma 43
CO 2 Fixation CO 2 fixation refers to bonding CO 2 to an organic molecule to make a larger molecule. C 5 + C C 6 C 5 is an abbreviation that means that this molecule has 5 carbon atoms. The oxygen and hydrogen atoms are not shown. 44
CO 2 Fixation 6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C RuBP CO 2 fixation refers to bonding CO 2 to an organic molecule to make a larger molecule. Each CO 2 is bonded to ribulose bisphosphate (RuBP). C 5 + CO 2 C 6 The enzyme that catalyzes this reaction is ribulose bisphosphate carboxylase (rubisco). 45
6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C 12 C-C-C Each of these 6-carbon compounds splits to form two 3- carbon compounds. 46
6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C 12 C-C-C The three-carbon compound is reduced to form G3P (glyceraldehyde 3-phosphate). 12 ATP 12 C-C-C G3P 12 NADPH 12 ADP + P 12 NADP + 47
6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C 12 C-C-C Two of the G3P molecules are used to form glucose phosphate, then glucose. G3P molecules can also be used to form other organic compounds. 10 C-C-C 12 ATP 12 C-C-C G3P 12 NADPH 12 ADP + P C-C-C-C-C-C Glucose and other organic molecules 12 NADP + 48
6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C 12 C-C-C 6 ADP + P The remaining 10 G3P are rearranged to form 6 RuBP. 6 ATP 10 C-C-C 12 ATP 12 C-C-C G3P 12 NADPH 12 ADP + P C-C-C-C-C-C Glucose and other organic molecules 12 NADP + 49
6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C 10 C-C-C 6 ADP + P 6 ATP This process requires energy in the form of ATP. 12 C-C-C 12 ATP 12 C-C-C G3P 12 NADPH 12 ADP + P C-C-C-C-C-C Glucose and other organic molecules 12 NADP + 50
6 CO 2 6 C-C-C-C-C-C RuBP Carboxylase (rubisco) 6 C-C-C-C-C The 6 in front of the CO 2 indicates that for each glucose molecule produced, this cycle occurs six times, that is, six CO 2 molecules are used. 12 C-C-C 6 ADP + P 6 ATP 10 C-C-C 12 ATP 12 C-C-C G3P 12 NADPH 12 ADP + P C-C-C-C-C-C Glucose and other organic molecules 12 NADP + 51
H 2 O O 2 light Summary of Photosynthesis (3) light reactions ATP NADPH ADP NADP + 6 C0 2 light-independent Calvin cycle reactions (Calvin (Stroma) cycle) C 6 H 12 O 6 52
Summary Slide and Review Questions The next slide is a summary of photosynthesis and the remaining slides are a review. 53
Light Energy Chloroplast CO 2 H + H 2 O 2e - + 2 + ½ O 2 NADP + + NADPH ATP ADP + P i Calvin Cycle glucose Thylakoids Stroma 54
Identify: H I ADP + P i ATP Calvin cycle A light reactions CO 2 glucose phosphate light NADP + NADPH B C D E oxygen water F J G 55
Where do the light reactions occur in plant cells? Where do the light-independent reactions occur in plant cells? H 2 O O 2 light light reactions ATP NADPH ADP NADP + C0 2 light-independent reactions (Calvin cycle) C-C-C-C-C-C 56
How many carbon atoms? 6 A 6 C 6 B 12 D 10 F 12 E G 57
Fill in the boxes. The answers are on the next slide. Light Reactions Light-independent Reactions Inputs Produced
Light Reactions Light-independent Reactions Inputs light, ADP, NADP +, H 2 O ATP, NADPH, CO 2 Produced ATP, NADPH, O 2, glucose, ADP, NADP +