Chapter 8 Photosynthesis

8.1 Objectives: Guiding Question: How do organisms store energy? 1. Describe the role of ATP in cellular activities. Explain where plants get the energy they need to produce food. (process of photosynthesis)

Chemical Energy and ATP To maintain homeostasis, all cells must: Grow Develop Move materials around Build new molecules Respond to environmental changes Requires lots of energy to maintain homeostasis Where does that power come from??

Chemical Energy and ATP Energy – ability to do work Nearly every activity in society depends on energy Examples??? Without ability to obtain and use energy, life would cease to exist

ATP Living things use chemical fuels Adenosine Triphosphate – ATP - One of most important compounds that cells use to store and release energy Adenine 5-carbon sugar (ribose) 3 phosphate groups

Storing Energy Adenosine Diphosphate – ADP – looks like ATP except it has 2 phosphate groups Cells can store small amounts of it by adding phosphate groups to ADP molecules  produces ATP

Releasing Energy Cells release energy stored in ATP by controlled breaking of chemical bonds b/w 2nd and 3rd phosphate groups A cell can store energy by adding a phosphate group

Using Biochemical Energy Cells use energy provided by ATP: Active Transport – sodium-potassium pumps Pump sodium out and potassium in ATP provides energy to keep pump working Maintains carefully regulated balance of ions on both sides of cell membrane ATP powers movement – energy for motor proteins to contract muscle and power wavelike movement of cilia and flagella

Using Biochemical Energy ATP energy used for: protein synthesis Responses to chemical signals at cell surface Produce light Blink from firefly

Using Biochemical Energy Most cells have only a small amount of ATP enough to last only a few seconds of activity ATP transfers energy well ATP does not store large amounts of energy well More efficient for cells to keep only a small supply of ATP on hand Cells can regenerate ATP from ADP as needed by using energy in foods like glucose

Heterotrophs Cells are not “born” with supply of ATP  must somehow produce it  from chemical compounds we call FOOD Heterotrophs – organisms that obtain food by consuming other living things Some eat only plants (herbivore) Some obtain food from plants indirectly by feeding on plant-eating animals (carnivore) Both plants and/or animals (omnivore) Some (mushrooms) obtain food by absorbing nutrients from decomposing organisms in the environment

Autotrophs Energy in nearly all food molecules comes from the sun Autotrophs – organisms that make their own food Plants, algae, and some bacteria are able to use light energy from the sun to produce food All life on earth depend on ability of autotrophs to capture the energy of sunlight and store it in the molecules that make up food

Photosynthesis Photosynthesis – process by which autotrophs use energy of sunlight to produce high-energy carbohydrates (sugars and starches) Photo = light Synthesis = putting together chemical energy stored in bonds of carbohydrates

Photosynthesis: An Overview Section 8.2 Photosynthesis: An Overview

Objectives: Guiding Question: What cellular structures and molecules are involved in photosynthesis? Explain the role of light and pigments in photosynthesis. Explain the role of electron carrier molecules in photosynthesis. State the overall equation for photosynthesis

How would you…. Design a system to capture the energy of sunlight and convert it into useful form?? Solution = insight to solar power energy source

Light Energy from sun travels to Earth in form of light White light – what our eyes perceive – mixture of different wavelengths What our eyes can see make up the visible spectrum Our eyes see different wavelengths as different colors: ROYGBIV

Pigments Pigments – light absorbing molecules plants use to gather the sun’s energy Chlorophyll – plants’ principal pigment 2 types: Chlorophyll a & Chlorophyll b Absorb light very well in blue-violet and red regions Do not absorb light well in green region of spectrum Plants look green b/c leaves reflect green light

Other Pigments Plants contain red and orange pigments (carotene) that absorb light in other regions of the spectrum Most of the time, the intense green color of chlorophyll overwhelms the accessory pigments, so we don’t notice them As temp drops late in year, chlorophyll molecules break down first, leaving reds and oranges

Chloroplasts Chloroplasts – organelle where photosynthesis takes place (plants and other photosynthetic eukaryotes) Thylakoids – abundance of saclike photosynthetic membranes found in chloroplasts Pigments (chlorophyll) located in thylakoid membranes Grana – stacks of interconnected thylakoids Stroma – fluid portion of chloroplast, outside thylakoids

Energy Collection Light is a form of energy Any compound that absorbs light  absorbs energy Chlorophyll absorbs visible light a large fraction of that light energy is transferred directly to electrons in the chlorophyll molecules itself light energy can produce a steady supply of high-energy electrons, which is what makes photosynthesis work

High Energy Electrons High-energy electrons produced by chlorophyll are highly reactive and require a special “carrier” High energy electron = hot potato Must use an oven mitt to transport it Oven mitt = electron carrier – to transport high-energy electrons from chlorophyll to other molecules electron carrier - compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule

Electron Carrier = NADP+ NADP+ (nicotinamide adenine dinucleotide phosphate) – one type of electron carrier molecule accepts and holds 2 high-energy electrons, along with a hydrogen ion (H+) converts NADP+ into NADPH One way in which some of energy from sunlight can be trapped in chemical form NADPH carry electrons chemical reactions elsewhere in the cell Used to help build variety of molecule the cell needs (glucose)

Overview of Photosynthesis Involves many steps Photosynthesis uses energy of sunlight to convert water and carbon dioxide (reactants) into high-energy sugars and oxygen (products) Plants use sugars to produce complex carbs (starches) to provide energy for synthesis of other compounds (proteins & lipids)

Overview of Photosynthesis Usually produces 6-carbon sugars (C6H12O6) as final product Reaction in Symbols: 6CO2 + 6H2O (light)  C6H12O6 + 6O2 Reaction in Words: Carbon dioxide + Water + (light)  Sugars + Oxygen

Light-Dependent Reactions Light-dependent reactions – require direct involvement of light and light-absorbing pigments Use energy from sunlight to produce energy-rich compounds (ATP) Occurs in thylakoids (membranes) in chloroplast Water is source of electrons and hydrogen ions in reactions Oxygen released as a byproduct

Light-independent Reactions Plants absorb carbon dioxide from atmosphere Produce carbon-containing sugars (carbohydrates) ATP and NADPH molecules produced in light dependent reactions used to produce high-energy sugars from carbon dioxide No light is required to power the light independent reactions Occur outside thylakoids (in the stroma)

Relationship between reactions diagram

The Process of Photosynthesis Section 8.3 The Process of Photosynthesis

Objectives: Guiding Question: How do photosynthetic organisms convert the sun’s energy into chemical energy? Describe what happens during light-dependent reactions Describe what happens during light-independent reactions Identify factors that affect the rate at which photosynthesis occurs

Light-Dependent Reactions The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Movie? 35

Light-Dependent Reactions Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level. Photosystem II The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. 36

Light-Dependent Reactions These high-energy electrons are passed on to the electron transport chain. Photosystem II Electron carriers High-energy electron 37

Light-Dependent Reactions Enzymes on the thylakoid membrane break water molecules into: Photosystem II 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall 38

Light-Dependent Reactions hydrogen ions oxygen atoms energized electrons Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron 39

Light-Dependent Reactions The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron 40

Light-Dependent Reactions As plants remove electrons from water, oxygen is left behind and is released into the air. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. High-energy electron 41

Light-Dependent Reactions The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron 42

Light-Dependent Reactions Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 43

Light-Dependent Reactions High-energy electrons move through the electron transport chain from photosystem II to photosystem I. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Photosystem I 44

Light-Dependent Reactions Pigments in photosystem I use energy from light to re-energize the electrons. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Photosystem I 45

Light-Dependent Reactions NADP+ then picks up these high-energy electrons, along with H+ ions, and becomes NADPH. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 46

Light-Dependent Reactions As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 47

Light-Dependent Reactions Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 48

Light-Dependent Reactions The difference in charges across the membrane provides the energy to make ATP. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 49

Light-Dependent Reactions H+ ions cannot cross the membrane directly. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 50

Light-Dependent Reactions The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 51

Light-Dependent Reactions As H+ ions pass through ATP synthase, the protein rotates. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH 52

Light-Dependent Reactions As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH 53

Light-Dependent Reactions Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH 54

ATP synthase + O2 2H2O ADP 2 NADP+ 2 NADPH 2 The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH 55

Summary of Light-Dependent Reactions Produce oxygen gas Convert ADP and NADP+ into energy carriers ATP and NADPH These carriers provide energy needed to build high-energy sugars from low-energy carbon dioxide

The Calvin Cycle The Calvin Cycle ATP and NADPH formed by the light-dependent reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes. During the Calvin cycle plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time. 57

The Calvin Cycle The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. Because the Calvin cycle does not require light, these reactions are also called the light-independent reactions. 58

Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules. CO2 Enters the Cycle The Calvin cycle uses ATP and NADPH to produce high-energy sugars. The Calvin Cycle 59

The result is twelve 3-carbon molecules, which are then converted into higher-energy forms. The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 60

The energy for this conversion comes from ATP and high-energy electrons from NADPH. Energy Input 12 12 ADP 12 NADPH The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ The Calvin Cycle 61

Two of twelve 3-carbon molecules are removed from the cycle. Energy Input 12 12 ADP 12 NADPH The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ 62

The 2 removed molecules are used to produce sugars, lipids, amino acids and other compounds. 12 12 ADP 12 NADPH The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ 6-Carbon sugar produced Sugars and other compounds 63

The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12 12 ADP 6 ADP 12 NADPH 6 The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 12 NADP+ 5-Carbon Molecules Regenerated Sugars and other compounds 64

The Calvin Cycle The two sets of photosynthetic reactions work together. The light-dependent reactions trap sunlight energy in chemical form. The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water. 65

Mystery Clue Page 239 Add to your page I will check on your way out.

Factors Affecting Photosynthesis Temperature, Light, and Water Among most important factors that affect photosynthesis are temperature, light intensity, and availability of water. Reactions made possible by enzymes that function best b/w 0oC and 35oC Above or below these temps could slow down rate of photosynthesis Low temps, may stop entirely

Temperature, Light, and Water Intensity of light affects rate of photosynthesis High light intensity increases rate of photosynthesis After intensity reaches a certain level, plant reaches maximum rate of photosynthesis

Temperature, Light, and Water Water is one of raw materials of photosynthesis Shortage of water can slow or stop photosynthesis Water loss can damage plant tissues Plants that live in dry conditions often have waxy coatings on leaves to redue water loss May also have biochemical adaptations that make photosynthesis more efficient under dry conditions

Photosynthesis Under Extreme Conditions To conserve water  plants in bright, hot conditions  close small openings in leaves that normally admit carbon dioxide Keeps plants from drying out Causes carbon dioxide w/in leaves to fall to very low levels Photosynthesis slows down or stops

C4 Photosynthesis Specialized chemical pathway that allows them to capture very low levels of carbon dioxide to pass it on to Calvin cycle 1st compound formed in pathway contains 4 carbon atoms Enables photosynthesis to keep working under intense light and high temperatures Requires extra energy in form of ATP to function Examples: corn, sugar cane, sorghum

CAM Plants Carbon dioxide becomes incorporated into organic acids during photosynthesis Process called Crassulacean Acid Metabolism Admit air into leaves only at night In cool darkness, carbon dioxide is combined w/ existing molecules to produce organic acids, “trapping” carbon w/in leaves During daytime, leaves tightly sealed to prevent loss of water  compounds release carbon dioxide  enable carbohydrate production Examples: pineapple trees, cacti, “ice plants” (near freeways along west coast to retard brush fires and prevent erosion)

Solve the Chapter 8 Mystery Page 245 Although soil does not significantly contribute to plant mass, how might it help plants grow? If a scientist were able to measure the exact mass of carbon dioxide and water that entered a plant, and the exact mass of the sugars produced, would the masses be identical? Why or why not? What do plants do with all of the carbohydrates they produce by photosynthesis? Explain how the experiments carried out by van Helmont and Calvin contributed to our understanding of how nutrients cycle in the biosphere.

Homework Due on TEST day: All vocabulary from Chapter 8 Chapter 8 Packet Chapter 8 Mystery All notes from Chapter 8 Photosynthesis Flip Books Visual Quiz Worksheet