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

Chapter 8 Photosynthesis

8.1 Energy and LifeSC.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.


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.


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• 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.


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• 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.


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• 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.

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8.2 Photsynthesis: An OverviewSC.912.L.18.7SC.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 OverviewSC.912.L.18.7SC.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.


• 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.


• 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.


• 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 OverviewSC.912.L.18.7SC.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.


• 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.


• 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.


• 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 PhotosynthesisSC.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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.


• 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.

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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