Chapter Eight- Photosynthesis

Copyright Pearson Prentice Hall

8-1 Energy and Life


Living things need energy to survive.

This energy comes from food. The energy in most food comes from the sun.

Plants are able to use light energy from the sun to produce food.


autotrophs –Organisms that make their own food, such as plants.

heterotrophs must get energy from the foods they consume. Ex. Animals

I can make my

own food!!

I will eat you!!


Chemical Energy and ATP

Energy comes in many forms including light, heat, and electricity. Energy can be stored in chemical compounds, too.


An important chemical compound that cells use to store and release energy is adenosine triphosphate, abbreviated ATP.

Adenosine triphosphate or ATP is used by all types of cells as their basic energy source.

ATPMovie

ATP consists of:•adenine•ribose (a 5-carbon sugar)•3 phosphate groups

Adenine

ATP

Ribose 3 Phosphate groups


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


Storing EnergyADP has two phosphate groups instead of three.A cell can store small amounts of energy by adding a phosphate group to ADP.

ADP ATP

Energy

Energy

Partiallycharged battery

Fullycharged battery

+

Adenosine Diphosphate (ADP) + Phosphate

Adenosine Triphosphate (ATP)



Releasing Energy

Energy stored in ATP is released by breaking off the third phosphate.

P

ADP

2 Phosphate groups



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

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 called

a. autotrophs.

b. heterotrophs.

c. decomposers.

d. consumers.


8-1

Most autotrophs obtain their energy from

a. 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.


8-2 Photosynthesis: An Overview


8-2 Photosynthesis:

An Overvie

w

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 sugar and oxygen.

Van Helmont’s Experiment

a. In the 1600s, Jan van Helmont wanted to find out if plants grew by taking material out of the soil.

b. He determined the mass of a pot of dry soil and a small seedling, planted the seedling in the pot, and watered it regularly.

c. After five years, the seedling was a small tree and had gained 75 kg, but the soil’s mass was almost unchanged.

Investigating PhotosynthesisResearch into photosynthesis began centuries ago.


Investigatin

g Photosynth

a.Van Helmont concluded that the gain in a plants’ mass comes from water because water was the only thing he had added.

b. His experiment accounts for the “hydrate,” or water, portion of the carbohydrate produced by photosynthesis.


Investigatin

g Photosynth a. Although van Helmont did not realize it,

carbon dioxide in the air also made a major contribution to the mass of his tree.

b. In photosynthesis, the carbon in carbon dioxide is used to make sugars and other carbohydrates.

c. Van Helmont had only part of the story, but he had made a major contribution to science.


Joseph Priestley discovered oxygen and that plants release it.More than 100 years after van Helmont’s experiment-- a. Priestley took a candle, placed a glass jar over

it, and watched as the flame gradually died out.

b. He reasoned that the flame needed something in the air to keep burning and when it was used up, the flame went out. That substance was oxygen.


a. Priestley then placed a live sprig of mint under the jar and allowed a few days to pass.

b. He found that the candle could be relighted and would remain lighted for a while.

c. The mint plant had produced the substance required for burning. In other words, it had released oxygen.


Jan Ingenhousz

a.Later, Jan Ingenhousz showed that the effect observed by Priestley occurred only when the plant was exposed to light.

b. The results of both Priestley’s and Ingenhousz’s experiments showed that light is necessary for plants to produce oxygen.


Investigatin

g Photosynth

The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that, in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen.

The equation for photosynthesis is

6CO2 + 6H2O C6H12O6 + 6O2carbon water sugars oxygendioxide

Light

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

Photosynthesis activity


O2

CO2+

H20Sugar

ADPNADP+

Light-Dependent Reactions

(thylakoids)

H2O

ATPNADPH

Calvin Cycle

(stroma)

Light energy


Light and

Pigments

In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll.


Plants gather the sun's energy with light-absorbing molecules called pigments.

The main light-absorbing pigment in plants is chlorophyll.

There are two main types of chlorophyll: chlorophyll a chlorophyll b


Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum.

Wavelength (nm)

100

80

60

40

20

0

400 450 500 550 600 650 700 750Wavelength (nm)

Estim

ated

Abs

orpt

ion

(%)


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.

Wavelength (nm)

100

80

60

40

20

0

400 450 500 550 600 650 700 750Wavelength (nm)

Estim

ated

Abs

orpt

ion

(%)


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

In van Helmont's experiment, most of the added mass of the tree came from

a. soil and carbon dioxide.

b. water and carbon dioxide.

c. oxygen and carbon dioxide.

d. soil and oxygen.


8-2

Plants use the sugars produced in photosynthesis to make

a. 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 is

a. 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.


8-3 The Reactions of Photosynthesis


Inside a Chloroplast

In plants, photosynthesis takes place inside chloroplasts.

Plant

Plant cells

Chloroplast

Chloroplast movie


Chloroplasts contain thylakoids—saclike photosynthetic membranes.

Chloroplast

Singlethylakoid


Inside a

ChloroplastThylakoids are arranged in stacks known as

grana. A singular stack is called a granum.

Granum

Chloroplast


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

Chloroplast

Photosystems


The long chain of photosynthesis reactions is divided into two parts

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 HallPHOTOSYNTHESIS

Chloroplast

LightH2O

O2

CO2

Sugars

NADP+

ADP + PLight-

dependent reactions

Calvin cycle


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.


Electron

Carriers

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.


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.

Light-dependent

movie


Light-Depen

dent Reacti

onsPhotosystems I and II carry out the light-dependent reactions and are in the thylakoid membrane.


Photosystem II

Light-Depen

dent Reacti

onsPhotosynthesis begins when pigments in

photosystem II absorb light, increasing their energy level.

Photosystem II

These high-energy electrons are passed on to the electron transport chain.

Electroncarriers

High-energy electron


Photosystem II

2H2O

Enzymes on the thylakoid membrane break water molecules into:

Electroncarriers



Photosystem II

2H2O

hydrogen ionsoxygen atomsenergized electrons

+ O2

Electroncarriers



Photosystem II

2H2O+ O2

The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain.



Photosystem II

2H2O

As plants remove electrons from water, oxygen is left behind and is released into the air.

+ O2



Photosystem II

2H2O

The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane.

+ O2



Photosystem II

2H2O

Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space.

+ O2


Photosystem II

2H2O

High-energy electrons move through the electron transport chain from photosystem II to photosystem I.

+ O2

Photosystem I


2H2O

Pigments in photosystem I use energy from light to re-energize the electrons.

+ O2

Photosystem I


2H2O

NADP+ then picks up these high-energy electrons, along with H+ ions, and becomes NADPH.

+ O2

2 NADP+

2 NADPH2


2H2O

As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane.

+ O2

2 NADP+

2 NADPH2


2H2O

Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged.

+ O2

2 NADP+

2 NADPH2


2H2O

The difference in charges across the membrane provides the energy to make ATP

+ O2

2 NADP+

2 NADPH2


2H2O

H+ ions cannot cross the membrane directly.

+ O2

ATP synthase

2 NADP+

2 NADPH2


2H2O

The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it

+ O2

ATP synthase

2 NADP+

2 NADPH2


2H2O

As H+ ions pass through ATP synthase, the protein rotates.

+ O2

ATP synthase

2 NADP+

2 NADPH2


2H2O

As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP.

+ O2

2 NADP+

2 NADPH2

ATP synthase

ADP


2H2O

Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well.

+ O2

ATP synthase

ADP2 NADP+

2 NADPH2


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 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 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.

Calvin Cycle Movie


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

CO2 Enters the Cycle


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


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

Energy Input

12 NADPH

12

12 ADP

12 NADP+


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

Energy Input

12 NADPH

12

12 ADP

12 NADP+


The Calvin Cycle

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

6-Carbon sugar produced

Sugars and other compounds

12 NADPH

12

12 ADP

12 NADP+


The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle.

5-Carbon MoleculesRegenerated

Sugars and other compounds

6

6 ADP12 NADPH

12

12 ADP

12 NADP+


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.


Many factors affect the rate of photosynthesis, including:• Water• Temperature• Intensity of light

Photosynthesis overview movie


8-3

In plants, photosynthesis takes place inside the

a. 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 ofa. ATP. b. high-energy electrons. c. low-energy electrons. d. ADP.


8-3

What is another name for the Calvin cycle?

a. light-dependent reactions

b. light-independent reactions

c. electron transport chain

d. photosynthesis


8-3

Which of the following factors does NOT directly affect photosynthesis?

a. wind

b. water supply

c. temperature

d. light intensity

Education

Chapter Eight- Photosynthesis