1. Photosynthesis Ch. 8 Biology Ms. Haut

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8-1 Energy and Life
Photo Credit: ©Stone
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3. Basics of Photosynthesis
All cells need energy to carry out their activities
All energy ultimately comes from the sun
Photosynthesis—process in which some of the solar energy is captured by plants (producers) and transformed into glucose molecules used by other organisms (consumers).
6CO2 + 6H2O C6H12O6 + 6O2
Light energy
enzymes

4. Basics of Photosynthesis
Glucose is the main source of energy for all life. The energy is stored in the chemical bonds.
Cellular Respiration—process in which a cell breaks down the glucose so that energy can be released. This energy will enable a cell to carry out its activities.
C6H12O6 + 6O CO2 + 6H2O + energy
enzymes

5. Autotrophs and Heterotrophs
Autotroph—organisms that synthesize organic molecules from inorganic materials (a.k.a. producers)
Photoautotrophs—use light as an energy source (plants, algae, some prokaryotes)
Heterotroph—organisms that acquire organic molecules from compounds produced by other organisms (a.k.a. consumers)

6. Chemical Energy and ATP
Energy comes in many forms including light, heat, and electricity.
Energy can be stored in chemical compounds, too.
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7. Chemical Energy and ATP
An important chemical compound that cells use to store and release energy is adenosine triphosphate, abbreviated ATP.
ATP is used by all types of cells as their basic energy source.
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8. Chemical Energy and ATP
ATP consists of:
adenine
ribose (a 5-carbon sugar)
3 phosphate groups
ATP is used by all types of cells as their basic energy source.
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9. Chemical Energy and ATP
The three phosphate groups are the key to ATP's ability to store and release energy.
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10. Chemical Energy and ATP
Storing Energy
ADP has two phosphate groups instead of three.
A cell can store small amounts of energy by adding a phosphate group to ADP.
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11. Chemical Energy and ATP
Releasing Energy
Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates.
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12. Chemical Energy and ATP
The energy from ATP is needed for many cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction.
ATP’s characteristics make it exceptionally useful as the basic energy source of all cells.
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13. Using Biochemical Energy
Most cells have only a small amount of ATP, because it is not a good way to store large amounts of energy.
Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose.
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Organisms that make their own food are called
autotrophs.
heterotrophs.
decomposers.
consumers.
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Most autotrophs obtain their energy from
chemicals in the environment.
sunlight.
carbon dioxide in the air.
other producers.
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How is energy released from ATP?
A phosphate is added.
An adenine is added.
A phosphate is removed.
A ribose is removed.
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How is it possible for most cells to function with only a small amount of ATP?
Cells do not require ATP for energy.
ATP can be quickly regenerated from ADP and P.
Cells use very small amounts of energy.
ATP stores large amounts of energy.
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Compared to the energy stored in a molecule of glucose, ATP stores
much more energy.
much less energy.
about the same amount of energy.
more energy sometimes and less at others.
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20. 8-2 Photosynthesis: An Overview
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21. Photosynthesis: An Overview
The key cellular process identified with energy production is photosynthesis.
Photosynthesis is the process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen.
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22. The Photosynthesis Equation
6CO2 + 6H2O C6H12O6 + 6O2
Light energy
enzymes
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23. The Photosynthesis Equation
Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.
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24. A Photosynthesis Road Map
Photosynthesis is composed of two processes:
The light reactions convert solar energy to chemical energy.
The Calvin cycle makes sugar from carbon dioxide.

25. Figure 7.4

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Light and Pigments
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll.
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Light and Pigments
Plants gather the sun's energy with light-absorbing molecules called pigments.
The main pigment in plants is chlorophyll.
There are two main types of chlorophyll:
chlorophyll a
chlorophyll b
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28. Light and Pigments
Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum.
Chlorophyll does not absorb light well in the green region of the spectrum.
Green light is reflected by leaves, which is why plants look green.
Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum.

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Light and Pigments
Light is a form of energy, so any compound that absorbs light also absorbs energy from that light.
When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons.
These high-energy electrons are what make photosynthesis work.
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8-2
Plants use the sugars produced in photosynthesis to make
oxygen.
starches.
carbon dioxide.
protein.
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8-2
The raw materials required for plants to carry out photosynthesis are
carbon dioxide and oxygen.
oxygen and sugars.
carbon dioxide and water.
oxygen and water.
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8-2
The principal pigment in plants is
chloroplast.
chlorophyll.
carotene.
carbohydrate.
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The colors of light that are absorbed by chlorophylls are
green and yellow.
green, blue, and violet.
blue, violet, and red.
red and yellow.
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35. 8-3 The Reactions of Photosynthesis
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36. Photosynthesis: redox process
Oxidation-reduction reaction:
Oxidation-loss of electrons from one substance
Reduction-addition of electrons to another substance

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Inside a Chloroplast
In plants, photosynthesis takes place inside chloroplasts.
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Inside a Chloroplast
Chloroplasts contain thylakoids—saclike photosynthetic membranes.
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Inside a Chloroplast
Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.
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Inside a Chloroplast
Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast.
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Inside a Chloroplast
The light-dependent reactions take place within the thylakoid membranes.
The Calvin cycle takes place in the stroma, which is the region outside the thylakoid membranes.
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Electron Carriers
Electron Carriers
When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy.
Cells use electron carriers to transport these high-energy electrons from chlorophyll to other molecules.
One carrier molecule is NADP+.
Electron carriers, such as NADP+, transport electrons.
NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+). This converts the NADP+ into NADPH.
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Electron Carriers
The conversion of NADP+ into NADPH is one way some of the energy of sunlight can be trapped in chemical form.
The NADPH carries high-energy electrons to chemical reactions elsewhere in the cell.
These high-energy electrons are used to help build a variety of molecules the cell needs, including carbohydrates like glucose.
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44. Light-Dependent Reactions
The light-dependent reactions require light.
The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.
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45. When photosystem II absorbs light an e- is excited in the reaction center chlorophyll (P680) and gets captured by the primary e- acceptor.
This leaves a hole in the P680

46. To fill the hole left in P680, an enzyme extracts e- from water and supplies them to the reaction center
A water molecule is split into 2 H+ ions and an oxygen atom, which immediately combines with another oxygen to form O2

47. Each photoexcited e- passes from primary e- acceptor to photosystem I via an electron transport chain.
e- are transferred to e- carriers in the chain

48. As e- cascade down the e- transport chain, energy is released and harnessed by the thylakoid membrane to produce ATP
This ATP is used to make glucose during Calvin cycle

49. When e- reach the bottom of e- transport chain, it fills the hole in the reaction center P700 of photosystem I.
Pre-existing hole was left by former e- that was excited

50. When photosystem I absorbs light an e- is excited in the reaction center chlorophyll (P700) and gets captured by the primary e- acceptor.
e- are transferred by e- carrier to NADP+ (reduction reaction) forming NADPH
NADPH provides reducing power for making glucose in Calvin cycle

51. Chemiosmosis
Energy released from ETC is used to pump H+ ions (from the split water) from the stroma across the thylakoid membrane to the interior of the thylakoid.
Creates concentration gradient across thylakoid membrane
Process provides energy for chemisomostic production of ATP

52. Light-Dependent Reactions
The light-dependent reactions use water, ADP, and NADP+.
The light-dependent reactions produce oxygen, ATP, and NADPH.
These compounds provide the energy to build energy-containing sugars from low-energy compounds.
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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.
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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.
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The Calvin Cycle
Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules.
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
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The Calvin Cycle
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.
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The Calvin Cycle
The energy for this conversion comes from ATP and high-energy electrons from NADPH.
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
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The Calvin Cycle
Two of twelve 3-carbon molecules are removed from the cycle.
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.
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59. The Calvin Cycle
The molecules are used to produce sugars, lipids, amino acids and other compounds.
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.

60. The Calvin Cycle
The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle.
The Calvin cycle uses ATP and NADPH to produce high-energy sugars.

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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.
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The Calvin Cycle
Factors Affecting Photosynthesis
Many factors affect the rate of photosynthesis, including:
Water
Temperature
Intensity of light
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63. How Photosynthesis Moderates Global Warming
Photosynthesis has an enormous impact on the atmosphere.
It swaps O2 for CO2.

64. How Photosynthesis Moderates Global Warming
Greenhouses used to grow plant indoors
Trap sunlight that warms the air inside.
A similar process, the greenhouse effect,
Warms the atmosphere.
Is caused by atmospheric CO2.

65. Global Warming
Greenhouse gases (CO2, CH4, CFC’s) are the most likely cause of global warming, a slow but steady rise in the Earth’s surface temperature.
Destruction of forests may be increasing this effect.
Combustion of fossil fuels

66. Global Warming Consequences
Polar ice caps melting
Rise in sea level and flooding of current coastline
New York, Miami, Los Angeles underwater
Change in types of plants—more adapted to warmer temps. and less water

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8-3
In plants, photosynthesis takes place inside the
thylakoids.
chloroplasts.
photosystems.
chlorophyll.
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8-3
Energy to make ATP in the chloroplast comes most directly from
hydrogen ions flowing through an enzyme in the thylakoid membrane.
transfer of a phosphate from ADP.
electrons moving through the electron transport chain.
electrons transferred directly from NADPH.
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NADPH is produced in light-dependent reactions and carries energy in the form of
ATP.
high-energy electrons.
low-energy electrons.
ADP.
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8-3
What is another name for the Calvin cycle?
light-dependent reactions
light-independent reactions
electron transport chain
photosynthesis
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Which of the following factors does NOT directly affect photosynthesis?
wind
water supply
temperature
light intensity
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