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Photosynthesis

Energy & Life

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Overview of Photosynthesis

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Autotrophs

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

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Autotrophs • Autotrophs include organisms that make their own food

• Autotrophs can use the sun’s energy directly Euglena

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Heterotrophs • Heterotrophs are organisms that can NOT make their own food

• Heterotrophs can NOT directly use the sun’s energy

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Energy • 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

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ATP – Cellular Energy • Adenosine Triphosphate • Contains two, high-energy phosphate

bonds • Also contains the nitrogen base adenine

& a ribose sugar

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ADP • Adenosine Diphosphate • ATP releases energy, a free phosphate, & ADP when cells take energy from ATP

One phosphate bond has been removed

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Sugar in ADP & ATP

• Called ribose • Pentose sugar

• Also found on RNA

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Importance of ATP

Principal Compound Used To Store Energy In Living Organisms

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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

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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

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

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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

Crash Course ATP • http://www.youtube.com/watch?v=00jbG_cfGuQ&sa

fe=active

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Glucose • Glucose is a monosaccharide

• C6H12O6 • One Molecule of glucose Stores 90 Times More Chemical Energy Than One Molecule of ATP

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History of Photosynthesis & Plant Pigments

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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

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Investigating Photosynthesis

• Many Scientists Have Contributed To Understanding Photosynthesis

• Early Research Focused On The Overall Process

• Later Researchers Investigated The Detailed Chemical Pathways

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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?

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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

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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.

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Ingenhousz’s Experiment 1779

Repeated Priestly experiment with & without sunlight

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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

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Julius Robert Mayer 1845

Proposed That Plants can Convert Light Energy Into Chemical Energy

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Samuel Ruben & Martin Kamen 1941

Used Isotopes To Determine That The Oxygen Liberated In Photosynthesis Comes From Water

KAMEN

RUBIN

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Melvin Calvin 1948 •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

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

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The Photosynthesis Equation

Crash Course – Photosynthesis • http://www.youtube.com/watch?v=sQK3Yr4Sc_k&s

afe=active

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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

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Light and Pigments • 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

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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

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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

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Chlorophyll a and b

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

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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

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The Biochemical Reactions

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It Begins with Sunlight!

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Photoautotrophs Absorb Light Energy

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Inside A Chloroplast

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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

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Function of the Stroma • Light Independent reactions occur here

• ATP used to make carbohydrates like glucose

• Location of the Calvin Cycle

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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

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Photosynthesis Overview

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Energy Carriers • 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

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NADPH

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• 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 Reactions

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Light Dependent Reaction

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Light Dependent Reaction

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

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Photosystem II

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

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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

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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+

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Phosphorylation

Enzyme in thylakoid membrane called ATP Synthase

As H+ ions passed through thylakoid membrane, enzyme binds them to ADP

Forms ATP for cellular respiration

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

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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

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The Calvin Cycle

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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

• A 3-carbon molecule called Ribulose Biphosphate (RuBP) is used to regenerate the Calvin cycle

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Factors Affecting the Rate of Photosynthesis

• Amount of available water

• Temperature • Amount of available light energy

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