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Photosynthesis

Energy & Life

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Photosynthesis• Plants use the Energy of

sunlight to convert Water (H20) and Carbon Dioxide (CO2) into Oxygen (O2) and High Energy Carbohydrates (sugars, e.g. Glucose) & Starches

The Photosynthesis Equation

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[Waste product]

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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

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Early Questions on Plants

Several Centuries Ago, The Question Was:

Does the increase in plant mass come from the air? The soil? The

water?

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Van Helmont’s Experiment

1643• Planted a seedling

into A pre-measured amount of soil and watered for 5 years.

• Weighed Plant & Soil. Plant- gained 75 kg, Soil- same weight.

• Concluded increase in Mass Came From Water

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Priestley’s Experiment• Burned candle in Bell

Jar until it went out.• If 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.

1771

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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

Used Isotopes to determine that the Oxygen liberated[released] in Photosynthesis comes from water KAMEN

RUBIN

1941

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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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Autotrophs

Organisms that contain chlorophyll and are able to use light energy from the sun to produce their own food.

Plant

Euglena

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Heterotrophs• Heterotroph

s are organisms that can NOT make their own food

• Heterotrophs can NOT directly use the sun’s energy

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Importance of ATP

Principal Compound Used To Store Energy In Living Organisms

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Cells Using Biochemical Energy

Cells Use ATP For:• Active transport• Movement• Photosynthesis• Protein Synthesis• Cellular

respiration• All other cellular

reactions

EVERYTHING!

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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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Sugar in ADP & ATP• Called ribose• Pentose sugar• Also found in

RNA

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Releasing Energy From ATP

• ATP provides all of the energy for cell activities

• The high energy phosphate bonds are BROKEN to release energy

• ATP is constantly being used and remade by cells

• The process of releasing ATP’s energy & reforming the molecule is called phosphorylation

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PhosphorylationEnzyme in thylakoid

membrane called ATP Synthase

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

Forms ATP for cellular

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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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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

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Plant Pigments & Cell Structure

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Light and Pigments

• Energy From The Sun Enters Earth’s Biosphere As Photons, a light energy unit.

• Visible or ‘White’ Light contains a mixture Of different wavelengths

• Different wavelengths are seen as Different Colors

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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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ChlorophyllThere are 2 main

types of chlorophyll molecules:

Chlorophyll aChlorophyll b

A third type, chlorophyll c, is found in dinoflagellates

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Light wavelength absorbed by pigments

Chlorophyll a absorbsBlue = bestRed = 2nd best

Chlorophyllreflects green

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Chlorophyll

• Absorbs blue wavelength best and red wavelength 2nd best.

• Does NOT absorb green wavelength, but reflects green wavelength.

• This is why plants look green.

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Carotenoids

• Plant pigment • Absorbs light energy

best in the yellow, orange and red wavelengths.

• Chlorophyll masks these pigments

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Color Note

• pigments that absorb all wavelengths of light are black.

• pigments that reflect all wavelengths of light are white.

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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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Leaf Structures• Cuticle- Waxy outer layer• Epidermal Cells – Waxy and rigid

outer cell layer.• Stomata - Openings in the

epidermis that allow gas and water exchange.

• Mesophyll layer- spongy layer of cells within leaf where photosynthesis takes place.

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Leaf Structure

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Structure of the Chloroplast

• Double membrane organelle

• Thylakoids – flattened sac that contains photosynthesis pigments. Where light dependent reactions occur.

• Granun (grana-plural) Stack of connected Thylakoid sacks.

• Stroma- Gel-like material around grana.

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Inside A Chloroplast

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Light & Pigments• Pigments absorb different

wavelengths of light which “excite” electrons in the plant’s pigments.

• Excited electrons carry the absorbed energy

• Electrons are transported by an electron carrier called NADP+

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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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Energy Carrier• NADP+ =Nicotinamide

adenine dinucleotide phosphate

• Accepts 2 high energy electrons and a H+ from the Light Reaction which convert NADP+ into NADPH.

• High energy electrons used to build molecules cell needs like glucose.

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NADPH

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Light Dependent Reaction

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Light Reaction SummaryReactants:• H2O• Light EnergyProducts:• OxygenEnergy to drive Dark Reaction• ATP• NADPH

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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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Light Independent Reaction• Also known as the Calvin

Cycle OR Dark Reaction.• Does not require light.• Occurs in the stroma• Uses ATP and NADPH from

the light-dependent reactions to produce high-energy sugars.

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Light Independent Reaction

• Uses: ATP & NADPH from light reactions used as energy source

• 6 Atmospheric C02 are used to make sugars like glucose and fructose

• Six-carbon Sugars made during the Calvin Cycle

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The Calvin Cycle

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Light Independent Reaction Summary

Reactants:• CO2

• Energy from ATP & NADPHProducts:• ADP • NADP+

• Sugars

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Factors Affecting the Rate of Photosynthesis

• Amount of available water

• Temperature• Amount of

available light energy

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Photosynthesis Overview