Photosynthesis Energy & Life

Overview of Photosynthesis

Autotrophs Plants and some other types of organisms that contain chlorophyll are able to use light energy from the sun to produce food.

Autotrophs Autotrophs include organisms that make their own food Autotrophs can use the sun’s energy directly Euglena

Heterotrophs Heterotrophs are organisms that can NOT make their own food Heterotrophs can NOT directly use the sun’s energy

Candles release energy as HEAT & LIGHT Energy Takes Many Forms such as light, heat, electrical, chemical, mechanical Energy can be changed from one form to another Energy can be stored in chemical bonds & then released later Candles release energy as HEAT & LIGHT

ATP – Cellular Energy Adenosine Triphosphate Contains two, high-energy phosphate bonds Also contains the nitrogen base adenine & a ribose sugar

One phosphate bond has been removed ADP Adenosine Diphosphate ATP releases energy, a free phosphate, & ADP when cells take energy from ATP One phosphate bond has been removed

Sugar in ADP & ATP Called ribose Pentose sugar Also found on RNA

Importance of ATP Principal Compound Used To Store Energy In Living Organisms

Releasing Energy From ATP ATP is constantly being used and remade by cells ATP provides all of the energy for cell activities The high energy phosphate bonds can be BROKEN to release energy The process of releasing ATP’s energy & reforming the molecule is called phosphorylation

Releasing Energy From ATP Adding A Phosphate Group To ADP stores Energy in ATP Removing A Phosphate Group From ATP Releases Energy & forms ADP Loose Gain

Cells Using Biochemical Energy Cells Use ATP For: Active transport Movement Photosynthesis Protein Synthesis Cellular respiration All other cellular reactions

More on ATP Cells Have Enough ATP To Last For A Few Seconds ATP must constantly be made ATP Transfers Energy Very Well ATP Is NOT Good At Energy Storage

Glucose Glucose is a monosaccharide C6H12O6 One Molecule of glucose Stores 90 Times More Chemical Energy Than One Molecule of ATP

History of Photosynthesis & Plant Pigments

Photosynthesis Involves the Use Of light Energy to convert Water (H20) and Carbon Dioxide (CO2) into Oxygen (O2) and High Energy Carbohydrates (sugars, e.g. Glucose) & Starches

Investigating Photosynthesis Many Scientists Have Contributed To Understanding Photosynthesis Early Research Focused On The Overall Process Later Researchers Investigated The Detailed Chemical Pathways

Early Questions on Plants Several Centuries Ago, The Question Was: Does the increase in mass of a plant come from the air? The soil? The Water?

Van Helmont’s Experiment 1643 Planted a seed into A pre-measured amount of soil and watered for 5 years Weighed Plant & Soil. Plant Was 75 kg, Soil The Same. Concluded Mass Came From Water

Priestley’s Experiment 1771 Burned Candle In Bell Jar Until It Went Out. Placed Sprig Of Mint In Bell Jar For A Few Days. Candle Could Be Relit And Burn. Concluded Plants Released Substance (O2) Necessary For burning.

Ingenhousz’s Experiment 1779 Repeated Priestly experiment with & without sunlight

Results of Ingenhousz’s Experiment Showed That Priestley’s Results Only Occurred In The Presence Of Sunlight. Light Was Necessary For Plants To Produce The “Burning Gas” or oxygen

Julius Robert Mayer 1845 Proposed That Plants can Convert Light Energy Into Chemical Energy

Samuel Ruben & Martin Kamen 1941 Used Isotopes To Determine That The Oxygen Liberated In Photosynthesis Comes From Water RUBIN KAMEN

Melvin Calvin 1948 Does NOT require sunlight First to trace the path that carbon (CO2) takes in forming Glucose Does NOT require sunlight Called the Calvin Cycle or Light Independent Reaction Also known as the Dark Reaction

Rudolph Marcus 1992 Studied the Light Independent Reactions First to describe the Electron transport Chain

The Photosynthesis Equation

Pigments In addition to water, carbon dioxide, and light energy, photosynthesis requires Pigments Chlorophyll is the primary light-absorbing pigment in autotrophs Chlorophyll is found inside chloroplasts

Light and Pigments Photon = Light Energy Unit Energy From The Sun Enters Earth’s Biosphere As Photons Photon = Light Energy Unit Light Contains A Mixture Of Wavelengths Different Wavelengths Have Different Colors

Light & Pigments Different pigments absorb different wavelengths of light Photons of light “excite” electrons in the plant’s pigments Excited electrons carry the absorbed energy Excited electrons move to HIGHER energy levels

Magnesium atom at the center of chlorophyll There are 2 main types of chlorophyll molecules: Chlorophyll a Chlorophyll b A third type, chlorophyll c, is found in dinoflagellates Magnesium atom at the center of chlorophyll

Chlorophyll a Found in all plants, algae, & cyanobacteria Makes photosynthesis possible Participates directly in the Light Reactions Can accept energy from chlorophyll b

Chlorophyll b Chlorophyll b is an accessory pigment Chlorophyll b acts indirectly in photosynthesis by transferring the light it absorbs to chlorophyll a Like chlorophyll a, it absorbs red & blue light and REFLECTS GREEN

The Biochemical Reactions

It Begins with Sunlight!

Photoautotrophs Absorb Light Energy

Inside A Chloroplast

Structure of the Chloroplast Double membrane organelle Outer membrane smooth Inner membrane forms stacks of connected sacs called thylakoids Thylakoid stack is called the granun (grana-plural) Gel-like material around grana called stroma

Function of the Stroma Light Independent reactions occur here ATP used to make carbohydrates like glucose Location of the Calvin Cycle

Thylakoid membranes Light Dependent reactions occur here Photosystems are made up of clusters of chlorophyll molecules Photosystems are embedded in the thylakoid membranes The two photosystems are: Photosytem I Photosystem II

Photosynthesis Overview

Energy Carriers NADP+ = Reduced Form Nicotinamide Adenine Dinucleotide Phosphate (NADP+) NADP+ = Reduced Form Picks Up 2 high-energy electrons and H+ from the Light Reaction to form NADPH NADPH carries energy to be passed on to another molecule

Light Dependent Reactions Occurs across the thylakoid membranes Uses light energy Produce Oxygen from water Convert ADP to ATP Also convert NADP+ into the energy carrier NADPH

Light Dependent Reaction

Light Dependent Reaction

Photosystem I Discovered First Active in the final stage of the Light Dependent Reaction Made of 300 molecules of Chlorophyll Almost completely chlorophyll “a”

Photosystem II Discovered Second Active in the beginning stage Of the Light Dependent Reaction Contains about equal amounts of chlorophyll a and chlorophyll b

Photosynthesis Begins Photosystem II absorbs light energy Electrons are energized and passed to the Electron Transport Chain Lost electrons are replaced from the splitting of water into 2H+, free electrons, and Oxygen 2H+ pumped across thylakoid membrane

Photosystem I High-energy electrons are moved to Photosystem I through the Electron Transport Chain Energy is used to transport H+ from stroma to inner thylakoid membrane NADP+ converted to NADPH when it picks up 2 electrons & H+

Phosphorylation Enzyme in thylakoid membrane called ATP Synthase As H+ ions passed through thylakoid membrane, enzyme binds them to ADP Forms ATP for cellular

Light Reaction Summary Reactants: H2O Light Energy Energy Products: ATP NADPH

Light Independent Reaction ATP & NADPH from light reactions used as energy Atmospheric C02 is used to make sugars like glucose and fructose Six-carbon Sugars made during the Calvin Cycle Occurs in the stroma

The Calvin Cycle

The Calvin Cycle Two turns of the Calvin Cycle are required to make one molecule of glucose 3-CO2 molecules enter the cycle to form several intermediate compounds (PGA) A 3-carbon molecule called Ribulose Biphosphate (RuBP) is used to regenerate the Calvin cycle

Factors Affecting the Rate of Photosynthesis Amount of available water Temperature Amount of available light energy