The function and Structure of Chloroplasts Photosynthesis

I. Introduction to Photosynthesis

A. Photosynthesis: capturing and transforming energy from sunlight into chemical energy (glucose) * A process utilized by green plants and blue-green algae, and some Protozoan. * These organisms are called Autotrophs meaning they can make their own food with light

Photosynthesis takes place in plants in the leaves only: Chloroplasts are here Cross- section of a leaf

B. Sunlight is a form of radiation or energy in the form of waves. This energy is absorbed by autotrophs in The chloroplasts

C. Structure of the Chloroplast Stroma Thylacoid Grana Transmission electron micrograph

a. Thylacoid – sacs of membranes with a coin-like shape. - location of chlorophyll - location of light reaction b. Grana – stacks of thylacoids c. Stroma – regions between the grana. -fluid-like region -location of dark reactions when organic molecules are made.

D. Pigments *substance that absorb light energy. * Pigments use visible light- light we can detect. * When we “see” a color, that wavelength of light is reflected from the object. Others are absorbed.

absorbed red reflected

What is the significance of plants Being green? Plant REFLECT green light and absorb others.

Plants contain several pigments, but the major pigment that absorbs energy is called Chlorophyll Polar- magnesium “head” Non –polar Lipid “tail”

The other pigments plants contain are called accessory pigments, pigments that assist in the reactions of photosynthesis. Beta Carotene- yellow orange Phycoerythrin- red Xanthophyll- yellow

Chromotography It is possible to extract, separate, and analyze pigment from a plant. This process is called Chromotography. * Pigments are separated on paper dependent on how soluble they are in a particular solvent. * Small molecules move fast, larger molecules slower. *Solvent moves across the paper due to capillary action.

Plant pigment placed on paper. Solvent moves through paper due To capillary action Separating pigments

Alcohols: isopropanol, methanol Organic acids: acetone, hexane What solvent would you use based on the composition of chlorophyll? Something non-polar: Alcohols: isopropanol, methanol Organic acids: acetone, hexane * Not water!

II. The reactions of Photosynthesis

A. General equation for photosynthesis 6 CO2 + 6 H2O C6H12O6 + 6O2 Sunlight enzymes ATP glucose oxygen water Carbon dioxide Many reactions are involved , this is the Overall outcome.

Quick Overview Two types of reactions in photosynthesis: Light and Dark Reactions

B. The Light reactions require light and are also called the Light Dependent Reactions * Need light and occur during the day *Take place in the grana of the chloroplast *Uses the energy from the sun to break apart water and ultimately produce organic compounds.

(this is splitting water!) 1. Part 1: Photosystem II *Light is absorbed and excites electrons *Electrons pass to the electron transport chain *Makes ATP *Takes electrons from H2O ( to replace those lost)and forms O2 which is released (this is splitting water!)

*ATP is adenosine triphosphate, a high energy molecule *Oxygen is released through the stomates ( openings on the under surface of leaves)

2. Part 2: Photosystem I *More light is absorbed *NADP forms NADPH2 (it is a protein that is a hydrogen/electron acceptor, like a shuttle to carry the excited electrons) * ATP and the “shuttle” move to the Dark reaction.

Summary of Light Reactions A. Electons are excited B. Break apart water C. Releases O2 D. Forms ATP and NADPH2

C. The second part of photosynthesis does not require light C. The second part of photosynthesis does not require light. This is called the Dark or Light Independent Rection. Electrons go through the Calvin Cycle: *It starts with RuBP, a five carbon sugar that takes in CO2. *Breaks ATP into ADP for energy *Changes NADPH2 into NADP- electrons dropped off the “shuttle”

*One glucose molecule is produced per 2 trips of the cycle Beginning ATP NADPH2 from light reaction Calvin cycle Summary of two trips

Summary of the Dark Reactions A. Use CO2 B. Change ATP into ADP C. Change NADPH2 to NADP D. Create glucose (stored as cellulose or starch) and other organic compounds

http://www.phschool.com/science/biology_place/biocoach/photosynth/quiz.html http://www.cnr.vt.edu/dendro/forestbiology/photosynthesis.swf

Location in chloroplast You do this: Reaction Location in chloroplast Reactants necessary Products produced Light dependent GRANA WATER OXYGEN ATP Light independent STROMA CARBON DIOXIDE C6H12O6