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8–1 Energy and LifeA. Autotrophs and HeterotrophsB. Chemical Energy and ATP

1.Storing Energy2.Releasing Energy

C.Using Biochemical Energy

Section 8-1

Section Outline

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What is energy?•The ability to do work.•Cells require energy for any “work” they do:

– Cell reproduction– Manufacturing proteins– Movement of materials between cells– To allow tissues in muscles to move (animals)

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Autotrophs and Heterotrophs

•Autotrophs– Have the ability to generate their own food.– Base of many food chains– Plants, bacteria, etc.

•Heterotrophs– Must obtain food from other source– Typically the autotrophs

•All organisms must obtain/make food in the form of sugars to ultimately be used to create energy.

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8–2 Photosynthesis: An OverviewA. Investigating Photosynthesis

1.Van Helmont’s Experiment2.Priestley’s Experiment3.Jan Ingenhousz

B. The Photosynthesis EquationC. Light and Pigments

Section 8-2

Section Outline

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•Photosynthesis– the process of using light energy to convert

CO2 and H2O into high energy glucose

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Light Energy

Chloroplast

CO2 + H2O Sugars + O2

Section 8-2

Photosynthesis: Reactants and Products

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Early discoveries

•Jan Van Helmont– 1643 – discovered plants take in water

•Joseph Priestly– 1771 – plants release O2

•Jan Igenhousz– Plants only produce O2 in the presence of light.

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The Photosynthesis Equation

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ChloroplastLight

O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPHATP

ADP + PNADP+Chloroplast

Section 8-3

Figure 8-7 Photosynthesis: An Overview

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Absorption of Light byChlorophyll a and Chlorophyll b

V B G YO R

Chlorophyll b

Chlorophyll a

Section 8-2

Figure 8-5 Chlorophyll Light Absorption

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Light Used in Photosynthesis

• During Photosynthesis, the chlorophyll pigments can absorb only some wavelengths of the visible light from the electromagnetic spectrum.

• Visible light consists of the following colors or wavelengths in order of increasing wavelengths / decreasing energy:– Violet, Indigo, Blue, Green, Yellow, Orange and

Red.• The grana of the chloroplasts absorb mainly blue-

violet and red-orange lights.• Green light is reflected and transmitted by green

plants – hence, they appear green.

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Light• Photon = a discrete packet of light energy. • The shorter the wavelength, the greater the energy….and vice-

versa.

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Pigments

• Chlorophyll – “More like Borophyll”…..Billy Madison

– Main pigments absorbing light for photosynthesis– Two types:

1. Chlorophyll a – light green2. Chlorophyll b – dark green

• Accessory pigments– Found in much smaller quantities– Xanthophyll - yellow– Carotene - orange

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8–3 The Reactions of PhotosynthesisA. Inside a ChloroplastB. Electron CarriersC.Light-Dependent ReactionsD.The Calvin CycleE. Factors Affecting Photosynthesis

Section 8-3

Section Outline

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Inside the chloroplast

-Contain thylakoid- Site of light reaction- Stacks are called grana

-Space in between is known as stroma

- Site of Calvin cycle

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Electron carriers

•NADPH– Electrons are typically carried by molecules, especially when

they are energized– Because they are negatively charged they are attracted to

positive “things”– Electrons will combine with NADP+ and H+ to form NADPH

• Called a reduction reaction (NADP+ is reduced)

NADP+ + H+ +2e- NADPH

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Light Reaction overview

• Light reaction – is dependent on light and occurs only during the day in nature. – It takes place in the thylakoid membrane of the

chloroplast.• Light reactions involve a) Splitting of water to produce oxygen, b) Energy production (ATP) andc) Reduction of NADP+ to NADPH.

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Light reaction….in detail (now the party begins)•Chlorophyll's role

– Provide electrons to be “energized”

– Specific wavelengths of light strikes chlorophyll and energize electrons to enter into electron transport chain of light reaction. e-

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•Water’s role– Can chlorophyll run out of electrons?– Theoretically, yes.– Water replenishes the supply to chlorophyll so they

can donate electrons to the electron transport chain– Water is split into H+ (Hey, that looks familiar!) and

O2 (sort of important stuff – wonder where that goes?!?)

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So what happens?

1. A specific wavelength of light (680 nm) strikes chlorophyll on the thylakoid membrane.

2. An electron gets “energized” and enters into the electron transport chain.

3. Electron “hops” from protein to protein “down hill.”

4. Energy is released, provides energy for:

ADP + P ATP

e-

e-

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So where does the electron go?

•Into another chlorophyll “center” that is losing electrons when 700 nm of light hits it.•Those electrons eventually must join up with NADP+ and H+ to form NADPH (also needed by Calvin cycle)

– Electron carriers!

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Untitled Document

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How is it made?

•Concentration gradients are established by “pumping” H+ into the inner thylakoid space (energy comes from the electron “bouncing down hill”)•H+ naturally tend to diffuse out

– This is kinetic energy – energy of motion– ATP synthase uses that energy to put ADP

together with P to make ATP

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HydrogenIon MovementPhotosystem II

InnerThylakoidSpace

ThylakoidMembrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Section 8-3

Figure 8-10 Light-Dependent Reactions

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So what if ATP is made?

•What is it used for?– To run the Calvin Cycle!

•So does light directly make food for the plant?– No! Makes the fuel to run the reaction that makes

food for the plant!

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Summary

•Light hits chlorophyll P680…..– Electrons energized enter electron transport chain

•Water split………– Replenishes lost electrons

•Electrons passed “downhill”………– Releases energy used to “pump” H+ uphill

•P700………..– Catches electron, 700 nm of light hits it and sends

electrons on down to be picked up by NADP•NADP…..

– Catches electrons, goes to Calvin Cycle•H+………

– “Fall” or diffuse through ATP synthase, provides energy to make ATP

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Calvin Cycle

•Series of reactions that require energy from ATP and electrons from NADPH•Starting reactant:

– CO2

•Finished product:– “G3P” – glyceraldehyde 3-phosphate

•G3P is then later processed into sugars, starches etc.

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http://ppdb.tc.cornell.edu/images/calvincycle9kj7.jpg

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(3) CO2 molecules enterRubisco attaches the CO2 to RuBP

CARBON FIXATION

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6 ATP and 6 NADPH used REDUCTION

1 G3P molecule produced

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Regenerate RuBPUse 3 more ATP

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•“PGA”– Three carbon molecules formed at the beginning

of Calvin•“G3P”

– Cell converts later to sugars and carbs•“RuBP”

– What combines with CO2, to keep Calvin going.

Click the image to play the video segment.

Video 5

Calvin Cycle

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Photosynthesis

includes

of

take place intakes place in uses

to produce to produce

use

Light-dependentreactions

Calvin cycle

Thylakoidmembranes Stroma NADPHATPEnergy from

sunlight

ATP NADPH O2 Chloroplasts High-energysugars

Section 8-3

Concept Map

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Now where???

•So what happens with this G3P??– Converted to sugar based molecules like….

• Glucose/fructose…. – maple syrup anyone?• Starch – French fries, cornbread, and pasta• Cellulose – cell wall material – 2 X 4’s, paper,

and Raisin BRAN– Depends on the needs of the cell at that instance

•Plants generate 200 billion tons of “Carbs” a year globally!

– Atkins would be mortified!

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Factors affecting photosynthesis•Water deficiencies

– Supplies chlorophyll with electrons for light reaction•Temperature

– Low temperatures minimize enzyme activity– Most reactions in photosynthesis enzyme driven

•Light– Amount of daylight– Why deciduous trees drop leaves and go dormant

for the winter

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Alternative methods of photosynthesis•Tropical plants temporarily fix CO2 by alternate method

– Corn, sugar cane, grasses– C4 plants (most plants are C3 –

remember PGA?)

•CO2 fixed forms a 4-carbon molecule instead of PGA, one of the carbons breaks off, saving an extra carbon dioxide for the regular Calvin Cycle •Why do they feel the need to do so?

– Generates lots of CO2 inside the leaf for Calvin

– Ok???, So what?

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Leaf anatomy of plants adapted for hot/arid conditions (C4 plants)… O2

C4 pathway

C3 pathway

Separate CO2 fixation and sugar making into two different cells