Photosynthesis Ch. 8 Biology Ms. Haut

8-1 Energy and Life Copyright Pearson Prentice Hall

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). 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Light energy enzymes 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. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy enzymes Basics of Photosynthesis

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)

Chemical Energy and ATP Energy comes in many forms including light, heat, and electricity. Energy can be stored in chemical compounds, too. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Chemical Energy and ATP ATP consists of: –adenine –ribose (a 5-carbon sugar) –3 phosphate groups Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Chemical Energy and ATP The three phosphate groups are the key to ATP's ability to store and release energy. u/biotutorials/energy/images/

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. Copyright Pearson Prentice Hall

Chemical Energy and ATP Releasing Energy –Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

8-1 Organisms that make their own food are called a)autotrophs. b)heterotrophs. c)decomposers. d)consumers.

Copyright Pearson Prentice Hall 8-1 Most autotrophs obtain their energy from a)chemicals in the environment. b)sunlight. c)carbon dioxide in the air. d)other producers.

Copyright Pearson Prentice Hall 8-1 How is energy released from ATP? a)A phosphate is added. b)An adenine is added. c)A phosphate is removed. d)A ribose is removed.

Copyright Pearson Prentice Hall 8-1 How is it possible for most cells to function with only a small amount of ATP? a)Cells do not require ATP for energy. b)ATP can be quickly regenerated from ADP and P. c)Cells use very small amounts of energy. d)ATP stores large amounts of energy.

Copyright Pearson Prentice Hall 8-1 Compared to the energy stored in a molecule of glucose, ATP stores a)much more energy. b)much less energy. c)about the same amount of energy. d)more energy sometimes and less at others.

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8-2 Photosynthesis: An Overview Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

The Photosynthesis Equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Copyright Pearson Prentice Hall Light energy enzymes

The Photosynthesis Equation Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high- energy sugars and oxygen. Copyright Pearson Prentice Hall

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.

Figure 7.4

Light and Pigments In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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

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.

Copyright Pearson Prentice Hall 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.

Copyright Pearson Prentice Hall 8-2 Plants use the sugars produced in photosynthesis to make a)oxygen. b)starches. c)carbon dioxide. d)protein.

Copyright Pearson Prentice Hall 8-2 The raw materials required for plants to carry out photosynthesis are a)carbon dioxide and oxygen. b)oxygen and sugars. c)carbon dioxide and water. d)oxygen and water.

Copyright Pearson Prentice Hall 8-2 The principal pigment in plants is a)chloroplast. b)chlorophyll. c)carotene. d)carbohydrate.

Copyright Pearson Prentice Hall 8-2 The colors of light that are absorbed by chlorophylls are a)green and yellow. b)green, blue, and violet. c)blue, violet, and red. d)red and yellow.

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8-3 The Reactions of Photosynthesis Copyright Pearson Prentice Hall

Inside a Chloroplast In plants, photosynthesis takes place inside chloroplasts.

Copyright Pearson Prentice Hall Inside a Chloroplast Chloroplasts contain thylakoids—saclike photosynthetic membranes.

Copyright Pearson Prentice Hall Inside a Chloroplast Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.

Copyright Pearson Prentice Hall 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.

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. Copyright Pearson Prentice Hall

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.

Copyright Pearson Prentice Hall 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.

Copyright Pearson Prentice Hall 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.

Copyright Pearson Prentice Hall 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.

Copyright Pearson Prentice Hall 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.

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

The Calvin Cycle Factors Affecting Photosynthesis –Many factors affect the rate of photosynthesis, including: Temperature: enzymes fxs best 0 C- 35 C, temp above or below, slow down enzyme activity : slows down photsynthesis Intensity of light: high light, increases photosynthesis Water: shortage of water can slow, stop photosynthesis Copyright Pearson Prentice Hall

How Photosynthesis Moderates Global Warming Photosynthesis has an enormous impact on the atmosphere. –It swaps O 2 for CO 2.

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 CO 2.

Global Warming Greenhouse gases (CO 2, CH 4, 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

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

Copyright Pearson Prentice Hall 8-3 In plants, photosynthesis takes place inside the a)thylakoids. b)chloroplasts. c)photosystems. d)chlorophyll.

Copyright Pearson Prentice Hall 8-3 Energy to make ATP in the chloroplast comes most directly from a)hydrogen ions flowing through an enzyme in the thylakoid membrane. b)transfer of a phosphate from ADP. c)electrons moving through the electron transport chain. d)electrons transferred directly from NADPH.

Copyright Pearson Prentice Hall 8-3 NADPH is produced in light-dependent reactions and carries energy in the form of a)ATP. b)high-energy electrons. c)low-energy electrons. d)ADP.

Copyright Pearson Prentice Hall 8-3 What is another name for the Calvin cycle? a)light-dependent reactions b)light-independent reactions c)electron transport chain d)photosynthesis

Copyright Pearson Prentice Hall 8-3 Which of the following factors does NOT directly affect photosynthesis? a)wind b)water supply c)temperature d)light intensity

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