PhotosynthesisCapturing and using solar energy

• Does photosynthesis:

• create energy?

• use energy?

• “store” energy?

• release energy?

No

Yes

Yes

No

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• Plants do photosynthesis but not cellular respiration.

• Photosynthesis is a plant’s way of creating ATP for its cells.

• Plants make sugar and other carbon compounds so that animals can eat.

False

False

False

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Photosynthesis

• What photosynthesis does:

• Converts sunlight into stored chemical energy.

• Makes carbon compounds that can be broken down for energy or used to build tissue.

Photosynthesis is an ___ process.

1 2

0%

100%

1. Endergonic2. Exergonic

Photosynthesis is endergonic because:

1 2 3

80%

20%

0%

1. Energy is consumed by the process.

2. Energy is given off by the process.

3. Energy is made by the process.

Remember this?energyinput

C6H12O6(glucose)

O2(oxygen)

6 CO2(carbondioxide)

6 H2O(water)

+

+

Photosynthesis is an endergonic process.Photosynthesis takes in energy and uses it to build

carbon compounds.

Inorganic mineral nutrients(nitrate, phosphate) areabsorbed from soil andused in plant tissues.

Energy iscapturedfromsunlight.

Oxygen isreleased.

Sugar issynthesizedand used inplant tissues.

planttissues,growth

Carbon dioxideis absorbedfrom the air.

Water is absorbedfrom soil, used inphotosynthesis, andstored in cells.

photosynthesis

This diagram shows that photosynthesis is

an endergonic reaction because it takes in energy.Carbon for making carbon compounds

(such as sugar) comes from the atmosphere.

Oxygen, hydrogen, and minerals are needed also.

Oxygen and hydrogen come from water.

Minerals comes from the soil

photosynthesis

cellularrespiration

(mitochondrion)

O2ATP sugar CO2H2O

(chloroplast)

Plants make carbon-based molecules from raw inorganic compounds.

Plants use the organic carbon compounds as “food” and to build cell parts.

Organic molecules are:

1 2 3 4

20% 20%

40%

20%

1. Natural, not man-made.

2. Molecules that contain carbon.

3. Molecules that contain carbon AND hydrogen.

4. Any molecule from a living organism.

Internal leaf structure

cuticleupperepidermis

mesophyllcells

lowerepidermis

chloroplastsstoma

bundlesheath

vascular bundle(vein)

Chloroplast

channelinterconnectingthylakoids

stroma

thylakoid

outer membrane

inner membrane

The function of the chloroplast is to:

1 2 3

0% 0%

100%

1. Produce energy.2. Gather light

energy and convert it to chemical energy.

3. Break sugars down for energy.

O2

energy fromsunlight

chloroplast

Light-independentreactions(C3 cycle) occurin stroma.

Light-dependentreactions areassociated withthylakoids.

CO2

NADP+

G3P

NADPH

ADP

ATP

H2O

Light energy is “captured” by

chlorophyl, which is embedded in the

thylakoid membranes.

Energy from the light-dependent reactions drives

the reactions where carbon

compounds are produced.

CO2

LIGHT-DEPENDENTREACTIONS(in thylakoids)

LIGHT-INDEPENDENTREACTIONS(in stroma)

DEPLETEDCARRIERS

(ADP, NADP+)

ENERGIZEDCARRIERS

(ATP, NADPH)

H2O

G3P

O2

ATP and NADPH are used to move energy from one

part of the chloroplast to

another.

ATP made in the chloroplast is ONLY

used to power production of carbon compounds. It is not available to the rest

of the cell.

Overall, the light-dependent reactions do what?

1 2 3 4

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20%

80%

1. Make energy.2. Capture energy.3. Make carbon

compounds.4. Break down

carbon compounds.

Overall, the light-independent reactions do what?

1 2 3 4

20% 20%

60%

0%

1. Make energy.2. Capture energy.3. Make carbon

compounds.4. Break down carbon

compounds.

• Suppose for a moment that the ATP made in the chloroplast was available to the cell, and was the ONLY source of ATP for the cell. Could the plant survive? (Remember that ATP is an unstable molecule that cannot be stored longer than a few minutes.)

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NADPH

H2O2e–

2H+

reactioncenter

photosystem II

electron transport chain

energy to driveATP synthesis

ener

gy le

vel o

f ele

ctro

ns

photosystem I

sunlight

electrontransport chain

2e–

1/2 O2

H+

NADP+

2e–

2e–

2e–

9

Light-dependent reactions convert light energy into temporary chemical energy.

The electron transport chain produces NADPH and drives ATP synthesis.

C3cycle

PSII PSIETCstroma

ETC

thylakoid space

Energy fromenergizedelectrons powersNADPH synthesis.

Flow of H+ downconcentration gradientpowers ATP synthesis.

Energy from energizedelectrons powers activetransport of H+ by ETC.

High H+ concentrationgenerated by activetransport.

H+ channel coupledto ATP-synthesizingenzyme.

Energy-carriermolecules powerthe C3 cycle.

ATP synthase uses energy from the diffusion of H+ to drive ATP synthesis.

• The ETC uses light energy to produce NADPH.

• Energy from the ETC concentrates H+ ions. The energy released as they diffuse through ATP synthase makes ATP.

• ATP and NADPH are used to power the light-independent reactions.

What’s important in the light-dependent (“photo”) reactions:

In photosynthesis, water is split in order to:

1 2 3 4

40%

0%0%

60%

1. Release oxygen.2. Get protons and

electrons.3. Make energy.4. Make chlorophyll.

In photosynthesis, light energy is captured by:

1 2 3 4

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0%

80%

0%

1. Protons2. Oxygen3. Chlorophyll4. ATP

The membrane protein that makes ATP is:

1 2 3 4

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0%

20%20%

1. ATP synthase2. Chlorophyll3. ADP4. Oxygen

ATP

ADP

NADPH

NADP+

12

12

12

1212

G3PATP

ADP

6

6

66 RuBP

6 CO2

12PGA

2 G3Psynthesisuses energy.

C3 cycle(Calvin-Benson cycle)

glucose(or other molecules)

3 RuBPsynthesisuses energyand 10 G3P.

1 CarbonfixationcombinesCO2 withRuBP.

4 G3P available for synthesis of carbon compounds such as glucose.

Light-independent reactions. Notice where ATP and NADPH are used up.

• Energy carried by ATP and NADPH is used to power synthesis of G3P.

• G3P can be used to make glucose as well as other monomers.

• These monomers can be used to build polymers, or may be broken down to make ATP for the cell.

What’s important in the light-independent (“synthesis”) reactions:

The source of carbon to make carbon compounds in photosynthesis is:

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100%

0%

1. Glucose2. G3P3. Carbon dioxide4. Water

Which of these happens in the C3 cycle?

1 2 3

20% 20%

60%1. ATP is made from

ADP and P.2. ATP is broken down

to power molecule synthesis.

3. ATP becomes the monomer of other compounds.

Plant cells need ATP to run cell processes. Where does that ATP come

from?

1 2 3 4

20%

80%

0%0%

1. Sunlight.2. The light-dependent

reactions of photosynthesis.

3. The light-independent reactions of photosynthesis.

4. Cellular respiration

IMPORTANT!!!

• Photosynthesis does NOT supply energy to the cell. Photosynthesis USES light energy to make organic compounds.

• To get energy for the cell, plant cells must use cellular respiration to break down glucose and make ATP.

An analogy:• Photosynthesis is like going to the

grocery store and buying food to store in your cupboard. The food and the energy in it is stored.

• Cellular respiration is like eating the food when you are hungry and need energy. The energy in food is released only by eating the food.

photosynthesis

cellularrespiration

(mitochondrion)

O2ATP sugar CO2H2O

(chloroplast)

While animals can only do cellular respiration, plants make “food” using photosynthesis and break the “food” down for energy in cellular

respiration.

DayNight

PhotosynthesisCellular Respiration

Cellular Respiration

DayNight

Cellular Respiration

Cellular Respiration

Animals Plants

Photosynthesis supplies the “food” that plants need to carry out cellular respiration.

CO2

C3 plants use the C3 pathway

bundle-sheathcells

In a C3 plant, mesophyll cellscontain chloroplasts; bundle-sheath cells do not.

Much photorespirationoccurs under hot, dryconditions.

Little glucoseis synthesized.

rubisco

G3P

CO2

PGA

O2

RuBP

glucose

within mesophyll chloropaststoma

C3Cycle

C3 plants are at a disadvantage in hot, dry climates.

within mesophyllchloropast

within bundle-sheathchloropast

CO2rubisco

G3P

CO2

PGA

O2

RuBP

glucose

pyruvate

4-carbonmolecule

PEP

CO2

ATP

AMP

C4 plants use the C4 pathway

bundle-sheathcells

stoma

CO2 is captured witha highly specific enzyme.

In a C4 plant, both mesophylland bundle-sheath cells containchloroplasts.

Lots of glucose is synthesized.

Almost nophotorespirationoccurs in hot, dryconditions.

C3Cycle

C4Pathway

C4 plants essentially store carbon for hot times of the day. Guess what pathway many weeds use?

• Fill in the blanks in this generalized diagram showing what goes into and what comes out of the chloroplast.

Chloroplast

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Recap

• Think of photosynthesis as an energy “storing” process, not an energy-making or energy-releasing process.

• The products of photosynthesis can be:

• used to build cell parts.

• broken down to make ATP for the cell.

Photosynthesis animations

• Electron transport chains• Light-dependent and light-indepen

dent reactions