ap biology 2007-2008 ap biology 2007-2008 photosynthesis: life from light and air

2007-2008 AP Biology


Photosynthesis:Life from Light and Air

AP Biology

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

Heterotrophs (Animals) get their energy from “eating others”

eat food = other organisms = organic molecules

make energy through respiration Autotrophs (Plants)

produce their own energy (from “self”) convert energy of sunlight build organic molecules (CHO) from CO2

Synthesize sugars through photosynthesis energy through respiration

consumers

producers

AP Biology

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

Where’s the ATP?

oxidation = exergonic

reduction = endergonic

AP Biology

Chloroplasts

chloroplastsin plant cell

cross sectionof leafleaves

chloroplast

absorbsunlight & CO2

makeenergy & sugar

chloroplastscontain

chlorophyll

CO2

AP Biology

Chloroplasts double membrane stroma

fluid-filled interior Stacks of thylakoids

Stack = Granum (pl. grana) Thylakoid membrane contains

chlorophyll molecules electron transport chain ATP synthase

H+ gradient built up within thylakoid sac

Plant structure H+ H+

H+

H+

H+H+

H+ H+

H+H+

H+

outer membrane inner membrane

thylakoidgranum

stroma

thylakoid

chloroplast

ATP

AP Biology

Photosynthesis

Equation:

6CO2 + 6H2O + Light Energy C6H12O6 + 6O2 Carbon Dioxide + Water + Light Energy Glucose + Oxygen

2 chemical reactions (two biochemical pathways) to make a sugar molecule Light Reaction and Calvin Cycle

OR Light-dependent Reaction and Light-independent

Reaction

AP Biology

Photosynthesis

Where do they OCCUR?

AP Biology

Photosynthesis

Light reaction Need Light energy conversion reactions

convert solar energy to chemical energy (ATP & NADPH)

Calvin cycle Does not need light

(needs products from light reaction) sugar building reactions

uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

It’s not theDark Reactions!

AP Biology

Pigments of photosynthesis

Chlorophylls & other pigments embedded in thylakoid membrane arranged in a “photosystem”

collection of molecules structure-function relationship

How does thismolecular structurefit its function?

AP Biology

A Look at Light The spectrum of color

ROYGBIV

AP Biology

Light: absorption spectra Photosynthesis gets energy by absorbing

wavelengths of light chlorophyll a

absorbs best in red & blue wavelengths & least in green accessory pigments with different structures

absorb light of different wavelengths chlorophyll b, carotenoids, xanthophylls

Why areplants green?

AP Biology

Photosystems of photosynthesis 2 photosystems in thylakoid membrane

collections of chlorophyll molecules act as light-gathering molecules Photosystem II

chlorophyll a P680 = absorbs 680nm

wavelength red light Photosystem I

chlorophyll b P700 = absorbs 700nm

wavelength red light

reactioncenter

antennapigments

AP Biology

Electron Transport Chain like in cellular respiration

proteins in organelle membrane electron acceptors

NADPH proton (H+)

gradient across inner membrane find the double membrane!

ATP synthase enzyme

Light reactionsH+H+

H+H+

H+H+

H+H+

H+H+

H+

H+H+

H+H+

H+H+

H+H+

H+H+

H+ATP

thylakoidchloroplast

AP Biology

The ATP that “Jack” built

moves the electrons Which pumps the protons in builds the gradient Diffusion drives the

flow of protons through ATP synthase

bonds Pi to ADP

generates the ATP

… that evolution built

sunlight breakdown of C6H12O6

respirationphotosynthesis

H+

ADP + Pi

H+H+

H+

H+ H+

H+H+

H+

ATP

AP Biology

ETC of Photosynthesis

Photosystem II

Photosystem I

chlorophyll a

chlorophyll b

AP Biology


Light Reactions: Non Cyclic Electron Flow – Step 1

Photon strikes antenna complex of Photosystem II (P680)

Energy is bounced on molecules in antenna complex until they land on chlorophyll a in the reaction center

Electrons of reaction center chlorophyll a are excited to a higher energy level and CAUGHT by the primary electron acceptor

AP Biology

1


ee

sun

Photosystem IIP680

chlorophyll a

AP Biology

ETC of PhotosynthesisLight Reactions: Non Cyclic Electron Flow – Step 2

An electron “hole” is left behind in the chlorophyll a in the reaction center of Photosystem II

An enzyme extracts electrons from water found in the chloroplast (stroma) and supplies these electrons to the chlorophyll a molecule so that it can work again.

This enzyme splits a water molecule into TWO H+ ions and an oxygen atom that will combine with another oxygen atom to form O2. THIS IS WHY WATER IS NEED FOR

PHOTOSYNTHESIS THIS IS WHERE THE OXYGEN GAS COMES FROM

IN PHOTOSYNTHESIS

AP Biology

12


Photosystem IIP680

chlorophyll a

OH H

H

H

Inhale, baby!

e e

ee

e-

e-

H+H+

H+H+

H+H+

H+H+

H+H+

H+

H+H+

H+H+

H+H+

H+H+

H+H+

H+ATP


H+

+H

OO

Plants SPLIT water!

fill the e– vacancy

AP Biology



Electrons pass from the primary electron acceptor of Photosystem II to Photosystem I by way of an electron transport chain

This is VERY much like the ETC found in the mitochondrion

As electrons fall down the chain their energy is used to PUMP PROTONS from the stroma INTO the thylakoid space

This creates a PROTON GRADIENT HIGH inside the thylakoid; LOW outside in the stroma

ATP is made as protons flow WITH their concentration gradient THROUGH a molecule of ATP synthase

ATP is created as ADP and Pi are combined at ATP Synthase

AP Biology

12

H+

H+

3

4

H+

ADP + Pi

H+H+

H+

H+ H+

H+H+H+

ee

e e

ATP

to Calvin Cycle

energy to buildcarbohydrates

H+H+

H+H+

H+H+

H+H+

H+H+

H+

H+H+

H+H+

H+H+

H+H+

H+H+

H+ATP


Photosystem IIP680

chlorophyll a


ATP

AP Biology

ETC of PhotosynthesisLight Reactions: Non Cyclic Electron Flow – Step 4

When electrons reach the bottom of the ETC, they are passed to chlorophyll a of the reaction center of photosystem I (P700)

Here, these electrons fill an electron hole left in this reaction center when electrons of this reaction center’s chlorophyll a are excited by their own photon of light.

Just as in Photosystem II, the electrons here are also caught and passed on by the primary electron acceptor of photosystem I. This, again, leaves an electron hole to fill.

AP Biology

ee

e e

sun

5

Photosystem IIP680

chlorophyll a

Photosystem IP700

chlorophyll b

e e


e e fill th

e e– vacancy

AP Biology



Electrons from Photosystem I are passed from its primary electron acceptor to a compound called NADP+ Reductase

This enzyme passes electron to a coenzyme called NADP+

NADP+ will become NADPH when it picks up the electrons. (reduced form of NADP+)

NADPH takes the electrons (and their ENERGY!) to the Calvin Cycle (Dark Reactions) where this energy will be used to make sugar.

AP Biology

6

electron carrier

ee

e e

5sun

NADPH toCalvin Cycle

Photosystem IIP680

chlorophyll a

Photosystem IP700

chlorophyll b$$ in the bank…reducing power!


AP Biology

split H2O


O

ATP

to Calvin CycleH+

H+

H+

H+

H+

H+

H+

H+

H+H+

H+

e e

e e

sun sun

Animation Click Here or Here

AP Biology

ETC of Photosynthesis ETC uses light energy to produce

ATP & NADPH go to Calvin cycle

PS II absorbs light excited electron passes from chlorophyll to

“primary electron acceptor” need to replace electron in chlorophyll enzyme extracts electrons from H2O & supplies

them to chlorophyll splits H2O O combines with another O to form O2

O2 released to atmosphere and we breathe easier!

AP Biology


energy + ++

Experimental evidence Where did the O2 come from?

radioactive tracer = O18


energy + ++

Experiment 1


energy + ++

Experiment 2

Proved O2 came from H2O not CO2 = plants split H2O!

AP Biology

Noncyclic Photophosphorylation Light reactions elevate

electrons in 2 steps (PS II & PS I) PS II generates

energy as ATP PS I generates

reducing power as NADPH

ATP

AP Biology

Cyclic photophosphorylation If PS I can’t pass electron

to NADP…it cycles back to ETC & makes more ATP, and no NADPH coordinates light

reactions to Calvin cycle Calvin cycle uses more

ATP than NADPH

18 ATP +12 NADPH

1 C6H12O6

ATP

AP Biology

Photophosphorylation

NONcyclicphotophosphorylation

cyclicphotophosphorylation

ATP

NADP

AP Biology

Photosynthesis summary Where did the energy come from?

Where did the electrons come from?

Where did the H2O come from?

Where did the O2 come from?

Where did the O2 go?

Where did the H+ come from?

Where did the ATP come from?

What will the ATP be used for?

Where did the NADPH come from?

What will the NADPH be used for?…stay tuned for the Calvin cycle


You can grow if you Ask Questions!


Ghosts of Lectures Past(storage)

AP Biology

Stomates

AP Biology

NPK

…

H2O

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 or stored need to get building block atoms

from the environment C,H,O,N,P,K,S,Mg

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

ATP

glucose

CO2

AP Biology

Plant structure Obtaining raw materials

sunlight leaves = solar collectors

CO2

stomates = gas exchange

H2O uptake from roots

nutrients N, P, K, S, Mg, Fe… uptake from roots

AP Biology

stomate

transpirationgas exchange

AP Biology

ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP

use electron carrier NADPH

generates O2

AP Biology

Mitochondria transfer chemical energy from food molecules into chemical energy of ATP

use electron carrier NADH

ETC of Respiration

generates H2O

ap biology 2007-2008 ap biology 2007-2008 photosynthesis: life from light and air

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