1. Chapter 8 Photosynthesis

2. 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.

3. 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.

4. 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.

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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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

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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.

15. 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.

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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.

17. 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.

18. 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.

19. 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.

20. 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.

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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.

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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.

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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.

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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.

25. 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.

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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.

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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.

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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.