Relate the structure of chloroplasts to the events in photosynthesis Section Objectives Relate the structure of chloroplasts to the events in photosynthesis Describe light-dependent reactions. Explain the reactions and products of the light-independent Calvin cycle.

Photosynthesis: Life from Light and Air 2006-2007

Trapping Energy from Sunlight The process that uses the sun’s energy to make simple sugars is called photosynthesis.

AN OVERVIEW OF PHOTOSYNTHESIS Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water PHOTOSYNTHESIS

Plants are energy producers Like animals, plants need energy to live unlike animals, plants don’t need to eat food to make that energy Plants make both FOOD & ENERGY animals are heterotrophs(consumers) plants are autotrophs (producers)

How do plants make energy & food? Plants use the energy from the sun to make ATP energy to make sugars glucose, sucrose, cellulose, starch, & more sun ATP sugars

Building plants from sunlight & air Photosynthesis 2 separate processes ENERGY building reactions collect sun energy use it to make ATP SUGAR building reactions take the ATP energy collect CO2 from air & H2O from ground use all to build sugars ATP H2O + CO2 sugars carbon dioxide CO2 water H2O sugars C6H12O6 +

What do plants need to grow? The “factory” for trapping energy & making sugars chloroplast Fuels sunlight carbon dioxide water The Products - Oxygen & Glucose The Helpers Enzymes sun CO2 O2 enzymes sugars H2O

So what does a plant need? Bring In light CO2 H2O Let Out O2 Move Around sugars leaves shoot roots 6CO2 6H2O C6H12O6 6O2 light energy  +

Photosynthesis ATP ADP ENERGY building reactions sun Photosynthesis ENERGY building reactions ADP ATP SUGAR building reactions used immediately to synthesize sugars H2O sugar CO2

Chloroplasts absorb sunlight & CO2 Leaf Leaves CO2 Chloroplasts in cell Chloroplast Chloroplast Chloroplasts contain Chlorophyll make ENERGY & SUGAR

Stomates & Guard Cells in the leaf Function of stomates CO2 in O2 out H2O out gets to leaves for photosynthesis Function of guard cells open & close stomates guard cell stomate

An overview of photosynthesis Chloroplast Light CO2 H2O NADP+ ADP +P LIGHT REACTIONS (in grana CALVIN CYCLE (in stroma ATP NADPH O2 O2 Sugar

Trapping Energy from Sunlight Photosynthesis happens in two phases. The light-dependent reactions convert light energy into chemical energy. (ATP) 2. The molecules of ATP produced in the light-dependent reactions are then used to fuel the Calvin Cycle or light-independent reactions that produce simple sugars. The general equation for photosynthesis is written as 6CO2 + 6H2O→C6H12O6 + 6O2

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Visible radiation drives the light reactions Certain wavelengths of visible light drive the light reactions of photosynthesis X-rays Micro- waves Radio waves Gamma rays UV Infrared Visible light Wavelength (nm)

pigments in the chloroplast To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight. Wavelengths that are NOT absorbed are reflected (bounce off) or transmitted (pass through) So the material in which the pigment is found appears to be the color of the wavelengths that are NOT absorbed Photosynthetic pigments: can absorb light energy & make it available for conversion to chemical energy . Light Reflected light Chloroplast Absorbed light

pigments in the chloroplast Chlorophyll a: most common pigment in chloroplast (absorbs blue &red light and reflects green light thus giving the chloroplast a green color)(chloro = green phylla + leaf) Accessory pigments: additional pigments that absorb different wavelengths (carotene, chlorophyll b, & xanthophyll)

Light-Dependent Reactions absorption of light energy by chlorophyll As sunlight strikes the chlorophyll molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons. These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane. At each step along the transport chain, the electrons lose energy.

Energy from the energized electrons pump H+ ions and change NAPD+ to NADPH. The H+ ions move from high to low and turn the ATP synthase and change ADP + P to ATP Energized electrons Oxygen by-product Photolysis

Light-Dependent Reactions Chemiosmosis: This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc. .

Light-Dependent Reactions The electrons are transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP is used. NADP can combine with two excited electrons and a hydrogen ion (H+) to become NADPH. NADPH will play an important role in the light-independent reactions.

Restoring electrons To replace the lost electrons, molecules of water are split in the first photosystem. This reaction is called photolysis. The O2 liberated by photosynthesis is made from the oxygen in water Chlorophyll O2 + 2H+ 2 2e- H2O H2O ®2H+ + O2 + 2e-

Restoring electrons The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. The electrons are returned to chlorophyll. The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration.

Light Dependent Reactions: Summary Absorptions of light energy by chlorophyll-takes place in thylakoid 1. Split water molecule (PHOTOLYSIS) Oxygen combines with other oxygen to produce O2 which is given off as a by-product 2. Hydrogen produced by splitting of water is attached to hydrogen carrier NADP -> NADPH (energy in this molecule) 3. Then energy from “excited electrons”is used to take ADP + P ->ATP

Light Independent Reactions or The Calvin Cycle CO2 put into organic molecules called Carbon fixation Does not require light but must have ATP and NADPH which are produced by light dependent reactions Called Calvin Cycle (Melvin Calvin won Nobel prize in chemistry) Takes place in stroma of chloroplast

Light Independent Reactions or The Calvin Cycle The Calvin cycle constructs G3P (a sugar) using carbon from atmospheric CO2 electrons and H+ from NADPH energy from ATP Energy-rich sugar (G3P) is then converted into glucose INPUT CALVIN CYCLE OUTPUT:

So what does a plant need? Bring In light CO2 H2O Let Out O2 Move Around sugars leaves shoot roots 6CO2 6H2O C6H12O6 6O2 light energy  +

An overview of photosynthesis Chloroplast Light CO2 H2O NADP+ ADP +P LIGHT REACTIONS (in grana CALVIN CYCLE (in stroma ATP NADPH O2 Sugar

Factors Affecting Rate of Photosynthesis Temperature: increases rate up to a certain point Light Intensity: increases rate up to a certain point CO2 level: Increases rate up to a certain point Water: decrease water, decrease photosynthesis Minerals; Ex. Magnesium, Nitrogen