AP Biology

Photosynthesis: Life from Light

AP Biology

Energy needs of life All life needs a constant input of energy

Heterotrophs get their energy from “eating others” consumers of other organisms consume organic molecules

Autotrophs get their energy from “self” get their energy from sunlight use light energy to synthesize organic

molecules

AP Biology 2005-2006

How are they connected?

glucose + oxygen carbon + water + energydioxide

C6H12O6 6O2 6CO2 6H2O ATP+ + +

Heterotrophs

+ water + energy glucose + oxygencarbondioxide

6CO2 6H2O C6H12O6 6O2light

energy + ++

Autotrophsmaking energy & organic molecules from light energy

making energy & organic molecules from ingesting organic molecules

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Energy cycle

Photosynthesis

Cellular Respiration

glucose O2H2OCO2

ATP

sun

The Great Circleof Life!

Where’s Mufasa?

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What does it mean to be a plant Need to…

collect light energy transform it into chemical energy

store light energy in a stable form to be moved around the plant

& also saved for a rainy day need to get building block atoms from

the environment C,H,O,N,P,S

produce all organic molecules needed for growth carbohydrates, proteins, lipids, nucleic acids

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Plant structure Obtaining raw materials

sunlight leaves = solar collectors

CO2

stomates = gas exchange regulation

Found under leaves

H2O uptake from roots

nutrients uptake from roots

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Chloroplasts double membrane stroma thylakoid sacs grana stacks

Chlorophyll & ETC in thylakoid membrane H+ gradient built up

within thylakoid sac

Plant structure

H+ H+

H+

H+

H+H+

H+ H+

H+H+

H+

AP Biology 2005-2006

Pigments of photosynthesis

chlorophyll & accessory pigments “photosystem” embedded in thylakoid

membrane structure function

Why does this structure make sense?

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Light: absorption spectra Photosynthesis performs work only with

absorbed wavelengths of light chlorophyll a — the dominant pigment —

absorbs best in red & blue wavelengths & least in green

other pigments with different structures have different absorption spectra

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Photosystems Photosystems

collections of chlorophyll molecules

2 photosystems in thylakoid membrane act as light-gathering “antenna complex” Photosystem II

chlorophyll a P680 = absorbs 680nm

wavelength red light Photosystem I

chlorophyll b P700 = absorbs 700nm

wavelength red light

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Transfer of Electrons in PSII & PSI In both PSII and PSI, the energy from the

excited e- pumps H+ into the thylakoid as it moves through the ETC.

Electrons from PSII are transferred to PSI. After electrons have moved through PSI,

an intermediary molecule (embedded in the membrane and adjacent to PSI) transfers the e- to NADP+. A H+ is attracted to this molecule and NADPH is formed.

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Chemiosmosis in Photosynthesis**(similar in Cell Respiration)

proton (H+) gradient across inner membrane

drive ATP formation ATP synthase

enzyme

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Summary of the LDR PS II absorbs light

excited electron passes from chlorophyll to “primary electron acceptor” at the REACTION CENTER. splits H2O (Photolysis!!) O2 released to atmosphere

PS I absorbs light Produces NADPH (stored energy) which will be

used by the Calvin cycle Chemiosmosis produces ATP from light

energy ATP will be used by the Calvin Cycle

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ETC of Photosynthesis Chloroplasts transform light

energy into chemical energy of ATP

use electron carrier NADPH

split H2O

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2 Photosystems Light reactions

elevate electrons in 2 steps (PS II & PS I) PS II helps generate

energy as ATP (H+ pumps)

PS I generates reducing power as NADPH

This shows Noncyclic photophosphorylation.

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ETC of Photosynthesis

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ETC of Photosynthesis

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Cyclic photophosphorylation If PS I can’t pass

electron to NADP, it cycles back to PS II & makes more ATP, but no NADPH coordinates light

reactions to Calvin cycle

Calvin cycle uses more ATP than NADPH

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Do Now: Light Reactions Summary Questions

Where did the energy come from?Where did the H2O come from?Where did the electrons come from?Where did the O2 come from?Where did the H+ come from?Where did the ATP come from?Where did the O2 go?What will the ATP be used for?What will the NADPH be used for?

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Calvin Cycle Overview Calvin cycle

uses chemical energy

(NADPH & ATP)

to reduce CO2 to

build C6H12O6 (sugars)

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From Light reactions to Calvin cycle Calvin cycle

Occurs in the stroma of the chloroplast

Need products of light reactions to drive synthesis reactions ATP NADPH

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From CO2 C6H12O6

CO2 has very little chemical energy fully oxidized

C6H12O6 contains a lot of chemical energy reduced endergonic

Reduction of CO2 C6H12O6 proceeds in many small uphill steps each catalyzed by specific enzyme using energy stored in ATP & NADPH

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PGALto make glucose

6Cunstable

intermediate

1C CO2

Calvin cycle

5CRuBP

3C2xPGA

6 ADP

6 ATP

3C2x

3C x2PGAL

6 NADP

6 NADPH

3 ADP

3 ATPRubisco

1. Carbon fixation

2. Reduction

3. Regeneration

ribulose bisphosphate

ribulose bisphosphatecarboxylase

sucrosecellulose

etc.

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Rubisco Enzyme which fixes carbon from

atmosphere ribulose bisphosphate carboxylase the most important enzyme in the world!

it makes life out of air! definitely the most abundant enzyme

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Calvin cycle PGAL

end product of Calvin cycle energy rich sugar 3 carbon compound “C3 photosynthesis”

PGAL important intermediatePGAL glucose carbohydrates

lipids

amino acids

nucleic acids

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Photosynthesis summary Light reactions

produced ATP produced NADPH consumed H2O produced O2 as byproduct

Calvin cycle consumed CO2

produced PGAL regenerated ADP regenerated NADP

AP Biology 2005-2006

Summary of photosynthesis

Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the H2O go? Where did the energy come from? What’s the energy used for? What will the C6H12O6 be used for? Where did the O2 come from? Where will the O2 go? What else is involved that is not listed in this

equation?

6CO2 6H2O C6H12O6 6O2light

energy + ++