Photosynthesis

Energy & Life1

Autotrophs

Plants, algae, and cyanobacteria contain chlorophyll. This pigment trapslight 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 5

ATP – Cellular Energy

• Adenosine Triphosphate• The energy is stored in the 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 7

Importance of ATP

Principal Compound Used To Transfer 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

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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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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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The Photosynthesis Equation

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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 aChlorophyll b

A third type, chlorophyll c, is found in dinoflagellates

Magnesium atom at the center of chlorophyll19

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 indirectlyin 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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Photosynthesis Begins with Sunlight!

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Autotrophs Absorb Light Energy

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Inside A Chloroplast

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Structure of the Chloroplast

• Double membrane organelle• Outer membrane smooth

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Structure of the Chloroplast

• Inner membraneforms stacks of connected sacs called thylakoids

• Thylakoid stack is called the granum(grana-plural)

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Structure of the Chloroplast

•Gel-like material around grana called stroma

Function of the Stroma

• Light Independentreactions 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:Photosystem IPhotosystem II 29

Photosynthesis Overview

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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 and II

Photosystem IMade of 300 molecules of Chlorophyll…mostly chlorophyll a

Photosystem IIContains about equal amounts of chlorophyll a and chlorophyll b 34

Photosystem IHigh-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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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 stroma38

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 (PGA)

• 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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