Photosynthesis Ch. 8 Biology Ms. Haut. 8-1 Energy and Life Copyright Pearson Prentice Hall.

PhotosynthesisCh. 8

BiologyMs. 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).

6CO2 + 6H2O C6H12O6 + 6O2

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.

C6H12O6 + 6O2 6CO2 + 6H2O + energyenzymes

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)

http://www.flatrock.org.nz/topics/animals/assets/conscious_animal.jpg

Chemical Energy and ATP

• Energy comes in many forms including light, heat, and electricity.

• Energy can be stored in chemical compounds, too.


http://www.green-the-world.net/images/forms_of_energy.jpg


• 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.


http://www.accessexcellence.org/RC/VL/GG/ecb/ecb_images/03_32_ATP_and_ADP_cycle.jpg


• ATP consists of:

– adenine

– ribose (a 5-carbon sugar)

– 3 phosphate groups


http://dm.ncl.ac.uk/helencollard/blogger/wp-content/uploads/2009/04/atp.gif



• The three phosphate groups are the key to ATP's ability to store and release energy.

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• 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.


http://zymes.com/wordpress/wp-content/uploads/2007/04/atp_sr.jpg


• Releasing Energy– Energy stored in ATP is released by breaking

the chemical bond between the second and third phosphates.


http://zymes.com/wordpress/wp-content/uploads/2007/04/atp_sr.jpg


• 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.


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.



8-1

Organisms that make their own food are calleda) autotrophs.b) heterotrophs.c) decomposers.d) consumers.


8-1

Most autotrophs obtain their energy froma) chemicals in the environment.b) sunlight.c) carbon dioxide in the air.d) other producers.


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.


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.


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.

END OF SECTION

8-2 Photosynthesis: An Overview


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.


The Photosynthesis Equation

• The Photosynthesis Equation

6CO2 + 6H2O C6H12O6 + 6O2

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Light energy

enzymes

http://www.biologycorner.com/resources/photosynthesis.jpg

The Photosynthesis Equation

• Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.


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 Hallhttp://www.biologycorner.com/resources/photosynthesis.jpg


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.


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.


8-2

Plants use the sugars produced in photosynthesis to makea) oxygen.b) starches.c) carbon dioxide.d) protein.


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.


8-2

The principal pigment in plants isa) chloroplast.b) chlorophyll.c) carotene.d) carbohydrate.


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.

END OF SECTION

8-3 The Reactions of Photosynthesis


Photosynthesis: redox process

• Oxidation-reduction reaction: – Oxidation-loss of electrons from one

substance– Reduction-addition of electrons to another

substance

6CO2 + 6H2O C6H12O6 + 6O2

Light energy

enzymes

oxidation

reduction

Releases e- (and H+ ions)

gains e- (and H+ ions)

6CO2 + 6H2O C6H12O6 + 6O2

Light energy

enzymes

oxidation

reduction



Light energy

enzymes

Light energy

enzymes

oxidation

reduction

oxidation

reduction




Inside a Chloroplast

• In plants, photosynthesis takes place inside chloroplasts.



• Chloroplasts contain thylakoids—saclike photosynthetic membranes.



• Thylakoids are arranged in stacks known as grana. A singular stack is called a granum.



• Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the 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.



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.


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.


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.

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html

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

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html


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.


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.

•

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.


The Calvin Cycle

• Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules.


The Calvin Cycle

• The result is twelve 3-carbon molecules, which are then converted into higher-energy forms.


The Calvin Cycle

• The energy for this conversion comes from ATP and high-energy electrons from NADPH.


The Calvin Cycle

• Two of twelve 3-carbon molecules are removed from the cycle.


The Calvin Cycle

• The molecules are used to produce sugars, lipids, amino acids and other compounds.

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

• 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.


The Calvin Cycle

• Factors Affecting Photosynthesis – Many factors affect the rate of photosynthesis,

including:• Water• Temperature• Intensity of light


How Photosynthesis Moderates Global Warming

• Photosynthesis has an enormous impact on the atmosphere.– It swaps O2 for CO2.

http://www.destination360.com/asia/malaysia/images/s/borneo-rainforest.jpg

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.

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

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 waterhttp://i.treehugger.com/images/2007/10/24/melting%20ice-jj-002.jpg


8-3

In plants, photosynthesis takes place inside thea) thylakoids.b) chloroplasts.c) photosystems.d) chlorophyll.


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.


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.


8-3

What is another name for the Calvin cycle?a) light-dependent reactionsb) light-independent reactionsc) electron transport chaind) photosynthesis


8-3

Which of the following factors does NOT directly affect photosynthesis?

a) windb) water supplyc) temperatured) light intensity

END OF SECTION

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Photosynthesis Ch. 8 Biology Ms. Haut. 8-1 Energy and Life Copyright Pearson Prentice Hall.

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