Chapter 8 Photosynthesis

8.1 Energy and Life SC.912.L.18.7 SC.912.L.18.10 Chemical Energy and ATP: Why is ATP useful to cells? -Without the ability to obtain energy life would cease to exist -One of the most important compounds that cells use to store and release chemicals is ATP -ATP (adenosine triphosphate) consists of 5-carbon sugar called ribose, three phosphate groups, and adenosine.

8.1 Energy and Life SC.912.L.18.7 SC.912.L.18.10 Storing Energy: -Adenosine diphosphate (ADP) is a compound that looks like ATP. -The difference between ATP and ADP is that ATP holds three phosphate groups while ADP only holds two phosphate groups. -When a cell has energy available, it can store small amounts of it by adding phosphate groups to ADP creating ATP.

8.1 Energy and Life SC.912.L.18.7 SC.912.L.18.10 Releasing Energy: -Cells can release energy stored in ATP by the controlled breaking of chemical bonds between the third and second phosphate group of ATP. -Cells efficiently store and release energy this way. -ATP can easily release and store energy by breaking ad re-forming the bonds between its phosphate groups. This characteristic of ATP makes it exceptionally useful as a basic energy source for all cells.

8.1 Energy and Life SC.912.L.18.7 SC.912.L.18.10 Using Biochemical Energy: -Cells use the energy provided by ATP to carry out active transport. -Energy from ATP also powers protein synthesis and responses to chemical signals at the cell surface. -ATP is not good for storing large amounts of energy. -Cells can regenerate ATP and ADP as needed by using the energy in foods like glucose.

8.1 Energy and Life SC.912.L.18.7 SC.912.L.18.10 Heterotrophs and Autotrophs: What happens during the process of photosynthesis? -Cells are not born with a supply of ATP: they must produce it. -The ATP all comes from chemical compounds that we know as food. -Organisms that make their own food are called autotrophs. Heterotrophs are organisms that obtain food by consuming or even absorbing. -The process by which autotrophs use the energy of sunlight to produce high-energy carbohydrates, sugars and starches, that can be used as food is known as photosynthesis. Photo meaning light, synthesis meaning put together. -In photosynthesis plants convert the energy of sunlight into chemical energy stored in the bonds of carbohydrates.

8.2 Photsynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Chlorophyll and Chloroplasts: What role do pigment play in the process of photosynthesis? -Our lives are made possible by the energy we obtain from the sun. -This energy helps us maintain everyday life and continue to carry out everyday functions. -Without it we would die.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Light: -Energy from the sun travels to Earth in the form of light. -Sunlight is a mixture of different wavelengths known as white light.\ -Many wavelengths are visible to our eyes and are known as the visibe spectrum. -The visible spectrum consists of red, orange, yellow, green, blue, indigo, and violet.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Pigments: -Plants absorb the light-absorbing molecules called pigments. -Photosynthetic organisms capture energy from sunlight with pigments. -A plants principal pigment is chlorophyll. -Chlorophyll A and B are found in plants. -They absorb light well in the blue-violet and red regions of the visible spectrum but not green as it is just reflected.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Chloroplasts: -Photosynthesis takes lace in organelles known as chloroplasts. -Chloroplasts contain an abundance of saclike membranes called thylakoids. -Thylakoids are interconnected and arranged in stacks know as grana. Pigments such as chloroplast are located in thylakoid membranes. -The fluid portion is known as stroma.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Energy Collection: -Light is a from of energy. -Any compound that absorbs light absorb energy. -Chlorophyll absorbs visible light well. -When chlorophyll absorbs light, a large fraction of that light is transferred directly to electrons in the chloroplast itself. -By raising the energy levels of electrons , light energy can produce a steady supply of high-energy electrons, which is what makes photosynthesis work.

8.2 Photsynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 High-Energy Electrons: What are electron carrier molecules? -An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule. -One carrier molecule is known as NADP(nicotinamide adenine dinucleotide phosphate) -NADP holds 2-high energy electrons along with hydrogen ion to help with photosynthesis which converts to NADPH.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 An Overview of Photosynthesis: What are the reactants and products of photosynthesis? -Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high energy sugars and oxygen. -Because photosynthesis usually produces 6-carbon sugars the rreaction can be shown as follows.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Light-Dependent Reactions: -These reactions require direct involvement of light pigments. -These are used to create energy rich compounds such as ATP. -These reactions take place in thylakoid and thylakoid membranes, -Water is required in these reactions as a source of electrons and hydrogen ions. Oxygen is released as a byproduct.

8.2 Photosynthesis: An Overview SC.912.L.18.7 SC.912.N.1.1 Light-Independent Reactions: -Plants absorb carbon dioxide from the atmosphere and complete the process of photosynthesis by producing carbon-containing sugars and other carbohydrates. -During these reactions ATP and NADPH molecules produced in the light –dependent reactions are used to produce high-energy sugars from carbon dioxide. -No light is required for these reactions.

8.3 The Process of Photosynthesis SC.912.L.18.7 The Light-Dependent Reaction: Generating ATP and NADPH: What happens during the light-dependent reactions? -The light dependent reactions use energy from sunlight to produce oxygen and convert ADP and NADP into the energy carriers ATP and NADPH. -Thylakoids contain clusters of chlorophyll and proteins know as photosystems. -The photosystems are surrounded by accessory pigments and are essential to the light-dependent reactions. -Photosystems absorb sunlight and generate high-energy electrons that are then passed to a series of electron carriers embedded in the thylakoid membrane.

8.3 The Process of Photosynthesis SC.912.L.18.7 Photosystem II: -Light dependent reactions begin when pigments in photosystem II absorb light. -Light energy is absorbed by electrons in the pigments found within photosystem II, increasing electron energy level. -An electron transport chain is a series of electron carrier proteins that shuttle high energy electrons during ATP-generating reactions. -The thylakoid membrane contains a system that provides new electrons to chlorophyll to replace the ones it has lost.

8.3 The Process of Photosynthesis SC.912.L.18.7 Electron Transport Chain: -Energy from electrons is used by the proteins in the chain to pump hydrogen ions from stroma to the thylakoid space. -At the end of electron transport electrons pass themselves to a second photosystem called photosystem I.

8.3 The Process of Photosynthesis SC.912.L.18.7 Photosystem I: -Because some energy is used to transport form photosystem II to photosystem I some electrons do not contain as much energy. -Pigments in photosystem I use energy from light to reenergize the electrons. -At the end NADP picks up the extra hydrogen bond to become NADPH. -The NADPH is very important as it is part of the light dependent reactions.

8.3 The Process of Photosynthesis SC.912.L.18.7 Hydrogen Ion Movement and ATP Formation: -Other than being added to NADP some hydrogen ions are pumped in from the stroma. -The buildup makes the stroma negatively charged relative to the space within the thylakoids. -This difference provides the energy to make ATP so that it can help carry out photosynthesis. -ATP synthase allows hydrogen ions to pass through the stroma.

8.3 The Process of Photosynthesis SC.912.L.18.7 Summary of Light Dependent Reactions: -The light dependent reactions produce oxygen gas and convert ADP and NADP into ATP and NADPH. -These play important roles in starting photosynthesis and completing the processes carried out in photosystems. -They provide energy needed to build high-energy sugars from low-energy carbon dioxide.

8.3 The Process of Photosynthesis SC.912.L.18.7 The Light-Independent Reactions Producing Sugars: What happens during the light independent reactions? -The ATP and NADPH store much energy but cannot store the high amount for more than a few minutes. -During the Calvin Cycle plants use energy that ATP and NADPH contain to build stable high energy carbohydrate compounds that can be stored for a long time. -During the light independent reactions ATP and NADPH from the light dependent reactions are used to produce high energy sugars. -The Calvin Cycle is named after Melvin Calvin who founded it.

8.3 The Process of Photosynthesis SC.912.L.18.7 Carbon Dioxide that Enters the Cycle: -Carbon dioxide enter the Calvin cycle through the atmosphere. -An enzyme in the stroma of the chloroplast combines these carbon dioxide molecules with 5-carbon compounds that are already present in the organelle, producing 3 carbon compounds that continue in the cycle. -For every 6 molecules that enter the cycle a total of twelve 3 compounds are produced. -Enzymes in the chloroplast convert these compounds into higher energy forms.

8.3 The Process of Photosynthesis SC.912.L.18.7 Sugar Production: -Two of the twelve 3 carbon molecules are removed from the cycle -These molecules become building blocks that the plants use to produce the sugar which becomes the product of photosynthesis. -In this phase molecules separate and combine as photosynthesis is completing.

8.3 The Process of Photosynthesis SC.912.L.18.7 Summary of Calvin Cycle/End Results: -As photosynthesis proceeds the Calvin cycle moves steadily. Carbon dioxide is removed from the atmosphere as energy rich sugars are created. -The two sets of photosynthetic reactions work together. -Stable sugars and high energy is produced. -We get oxygen and food in change for carbon dioxide.

8.3 The Process of Photosynthesis SC.912.L.18.7 Factors Affecting Photosynthesis: What factors affect photosynthesis? Temperature Sunlight and Water: -Among the most important factors that affect photosynthesis are temperature, light intensity, and availability of water. -Temperatures help from 0C to 35C. -Light intensity affects it by increasing the activation level. -Water is also a factor. A shortage of water can slow or even stop photosynthesis.

8.3 The Process of Photosynthesis SC.912.L.18.7 Photosynthesis Under Extreme Conditions: -C4 plants have a specialized chemical pathway that allows them to capture even very low levels of carbon dioxide through the Calvin cycle. -The name C4 comes from the amount of carbon molecules. (4 molecules of carbon) -C4 includes organisms like corn, sugar cane, and sorghum. -CAM plants are those that adapt to dry environments. -CAM plants store their water supply and use very little to carry out photosynthesis.