Photosynthesis is the process a plant uses to make food and grow. A definition: Photosynthesis is the process a plant uses to make food and grow.

Four things are needed for photosynthesis: SUNLIGHT Gives the plant energy CHLOROPHYLL The green stuff where the chemical reactions happen WATER Travels up from the roots CARBON DIOXIDE Enters the leaf through small holes on the underneath

The word and chemical equations for photosynthesis: Sunlight Carbon dioxide + water glucose + oxygen 6CO2 + 6H20 C6H12O6 + 6O2 Chlorophyll Sunlight Chlorophyll

THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

THE BASICS OF PHOTOSYNTHESIS Almost all plants are photosynthetic autotrophs, as are some bacteria and protists Autotrophs generate their own organic matter through photosynthesis Sunlight energy is transformed to energy stored in the form of chemical bonds (c) Euglena (d) Cyanobacteria (b) Kelp (a) Mosses, ferns, and flowering plants

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 Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS

AN OVERVIEW OF PHOTOSYNTHESIS The light reactions convert solar energy to chemical energy Produce ATP & NADPH Light Chloroplast NADP ADP + P The Calvin cycle makes sugar from carbon dioxide ATP generated by the light reactions provides the energy for sugar synthesis The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Calvin cycle Light reactions

Light Energy Harvested by Plants & Other Photosynthetic Autotrophs 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

WHY ARE PLANTS GREEN? It has to do with sunlight! Sunlight is a form of electromagnetic energy, which travels in waves.

Electromagnetic Spectrum and Visible Light Gamma rays Infrared & Microwaves X-rays UV Radio waves Visible light Wavelength (nm): Distance between two waves

WHY ARE PLANTS GREEN? Different wavelengths of visible light are seen by the human eye as different colors. Gamma rays Micro- waves Radio waves X-rays UV Infrared Visible light Wavelength (nm)

The feathers of male cardinals are loaded with carotenoid pigments The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others. Reflected light Sunlight minus absorbed wavelengths or colors equals the apparent color of an object.

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED Chloroplasts absorb light energy and convert it to chemical energy Reflected light Light Absorbed light Transmitted light Chloroplast

Photosynthesis occurs in chloroplasts In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts A chloroplast contains: stroma, a fluid (site of Calvin Cycle) grana, stacks of thylakoids (site of Light reactions) The thylakoids contain chlorophyll Chlorophyll is the green pigment that captures light for photosynthesis

The location and structure of chloroplasts LEAF CROSS SECTION MESOPHYLL CELL LEAF Mesophyll CHLOROPLAST Intermembrane space Outer membrane Granum Inner membrane Grana Stroma Thylakoid compartment Stroma Thylakoid

Chloroplast Pigments Chloroplasts contain several pigments Chlorophyll a: absorbs mainly violet and red light the best Chlorophyll b: absorbs blue and orange light the best Carotenoids: absorbs blue and green best Figure 7.7

Different pigments absorb light differently

Paper Chromatography A laboratory test used to separate and analyze different pigments in a leaf. Example: https://www.pearsonsuccessnet.com/snpapp/iText/getTeacherHomepage.do?newServiceId=6000&newPageId=10100

Photosystems: Clusters of pigments in thylakoid membrane Photosystem I Traps light energy and transfers the light-excited electrons to an electron transport chain. Those excited electrons are replaced by splitting a molecule of water, which releases oxygen. The electron transport chain releases energy, which is used to make ATP Photosystem II Produces NADPH by transferring excited electrons and hydrogen ions to NADP+.

Light Reactions Photosystem I and Photosystem II SUMMARY: In the light reactions, electron transport chains generate ATP, NADPH, & O2 Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons The excited electrons are passed from the primary electron acceptor to electron transport chains The light reactions convert light energy to the chemical energy of ATP and NADPH Watch the following animation: http://www.youtube.com/watch?v=eY1ReqiYwYs

Two types of photosystems cooperate in the light reactions Inputs: Water Sunlight energy Outputs: Oxygen ATP NADPH Photon ATP mill Photon Water-splitting photosystem NADPH-producing photosystem

Plants produce O2 gas by splitting H2O The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

How the Light Reactions Generate ATP and NADPH Primary electron acceptor NADP Energy to make Primary electron acceptor 3 2 Light Electron transport chain Light Primary electron acceptor Reaction- center chlorophyll 1 NADPH-producing photosystem Water-splitting photosystem 2 H + 1/2

ELECTRON TRANSPORT CHAIN The production of ATP in photosynthesis Thylakoid compartment (high H+) Light Light Thylakoid membrane Antenna molecules Stroma (low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

A Photosynthesis Road Map Chloroplast Light Stroma NADP Stack of thylakoids ADP + P Light reactions Calvin cycle Sugar used for  Cellular respiration  Cellulose  Starch  Other organic compounds

Calvin Cycle Called a cycle because the starting material, RuBP, is regenerated. Uses carbon from carbon dioxide, the energy from ATP, and high energy electrons and hydrogen ions from NADPH to make a small sugar named G3P. The plant uses G3P to make glucose and other organic molecules. Overall input: CO2, ATP, NADPH Overall output: Glucose

Calvin Cycle Watch the following animation: http://www.youtube.com/watch?v=mHU27qYJNU0&NR=1

Review: Photosynthesis uses light energy to make food molecules Light reactions use water and produce oxygen. The Calvin Cycle uses ATP and NADPH created in the the light reactions to convert carbon dioxide to glucose. Chloroplast Light Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma Electrons Cellular respiration Cellulose Starch Other organic compounds LIGHT REACTIONS CALVIN CYCLE

Animation is of the Calvin Cycle Note what happens to the carbon dioxide and what the end product is. Second animation of the Calvin Cycle is very clear and even does the molecular bookkeeping for you.