PHOTOSYNTHESIPHOTOSYNTHESISS

What is Photosynthesis?What is Photosynthesis?

• A chemical reaction powered by A chemical reaction powered by sunlight that uses sunlight that uses carbon carbon dioxide (COdioxide (CO22), and water (H), and water (H22O)O) to to produce produce glucose and oxygen.glucose and oxygen.

6CO2 + 6H2O C6H12O6 + 6O2glucoseglucose

SUN

How to read a chemical equation

light energy

6CO2 + 6H2O C6H12O6 + 6O2

Inputs are on the left = reactantsOutputs on the right = products(Energy is not considered a reactant so it is written

above: in this reaction energy is needed to break the bonds in H2O)

Why is there a 6 in front of the carbon dioxide, water, and oxygen molecules but not in front of the glucose molecule?

How to read a chemical equation

6CO2 + 6H2O C6H12O6 + 6O2

Chemical equations are like math: the stuff on one side of the arrow (or

equal sign) has to be equivalent to the stuff on the other side.

The number of atoms of each kind of element on one side has to match the

number of atoms on the other side.

We call that a balanced equation.

How many carbon atoms are on the reactant side? How many oxygen? How many hydrogen?

Does that match the product side?

Where does the plant get the CO2 and H2O?

• Water comes from the soil and travels in veins throughout plant including to the leaves, where photosynthesis takes place?

• CO2 is one of many gases in the air

But how does the CO2 get into the leaf?

Through small pores called stomata or guard cells

These guard cells can open and close.

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Where does Where does photosynthesiphotosynthesis take place?s take place?

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Mesophyll Cell of LeafMesophyll Cell of Leaf

Cell WallNucleusNucleus

Chloroplast

Central Vacuole

Photosynthesis occurs in these Photosynthesis occurs in these cells!cells!

ChloroplastChloroplast

OrganelleOrganelle where photosynthesisphotosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected Thylakoid stacks are connected togethertogether

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ThylakoidThylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Grana make up the inner Grana make up the inner membranemembrane

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How does How does the the

chloroplast chloroplast work?work?

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Chloroplasts contain chlorophyll Chloroplasts contain chlorophyll moleculesmolecules

• Chlorophyll is a pigment.Chlorophyll is a pigment.• It’s located in the thylakoid It’s located in the thylakoid

membranes.membranes.• Chlorophyll pigments harvest energyChlorophyll pigments harvest energy

from the sunfrom the sun by absorbing certain by absorbing certain wavelengths, especially wavelengths, especially blueblue and and red.red.

• Plants are Plants are greengreen because the because the green green wavelength is reflectedwavelength is reflected, not , not absorbedabsorbed.

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Absorption of Light by Absorption of Light by ChlorophyllChlorophyll

wavelengthwavelength

Absorption

violet blue green yellow orange red

Chlorophyll absorbs blue-violet & red Chlorophyll absorbs blue-violet & red light bestlight best

So chlorophyll is the molecule that captures the energy from the sun

And turns it into energy the plant can use: ATP

Plants are autotrophs

They take inorganic molecules (CO2 and H2O) and by harvesting the power of the sun, turn them into the organic molecule glucose (C6H12O6) with O2 as a byproduct.

Without this ability to turn inorganic to organic molecules, life could not exist.

So thank a plant today!

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Energy : from sunlight to ATPEnergy : from sunlight to ATP

•Sunlight is the ULTIMATE energy for all life on Earth

•Plants store energy in the chemical bonds of sugars

•When those bonds are broken (in our bodies or in the plant) energy is released as ATP.

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Structure of ATPStructure of ATP

• ATP stands for adenosine triphosphate

• It is composed of the nitrogen base ADENINE, the pentose (5C) sugar RIBOSE, and three PHOSPHATE groups

• The LAST phosphate group is bonded with a HIGH ENERGY chemical bond

• This bond can be BROKEN to release ENERGY for CELLS to use

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High Energy Phosphate High Energy Phosphate BondBond

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PhotosynthesisPhotosynthesisHas Two PartsHas Two Parts

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Two Parts of Two Parts of PhotosynthesisPhotosynthesis

First part:First part:

1.1.Light Reaction (or Light Light Reaction (or Light

Dependent Reaction)Dependent Reaction)

--Splits water into H+ and O --Splits water into H+ and O (which is expelled as O(which is expelled as O22))

--Converts energy from sun into --Converts energy from sun into chemical energy of ATP and chemical energy of ATP and NADPH (another energy carrier NADPH (another energy carrier molecule).molecule).

SUNSUN

Where does the light reaction take place?

• In the thylakoid membranes

So now we have hydrogen and energy—but not glucose yet

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Two Parts of Two Parts of PhotosynthesisPhotosynthesis

Second part:Second part:

2. 2. Calvin Cycle or Light Calvin Cycle or Light Independent Reaction Independent Reaction

• Uses energy (Uses energy (ATP and ATP and NADPHNADPH) from light reaction ) from light reaction along with the freed along with the freed hydrogen and the COhydrogen and the CO22 to to make sugar make sugar (glucose).(glucose).

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Where does the light Where does the light independent reaction take independent reaction take place?place?• In the In the stromastroma

• Called light independent because this Called light independent because this part does not need sunlight to occurpart does not need sunlight to occur

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Overall ReactionOverall Reaction

light energy

6CO2 + 6H2O C6H12O6 + 6O2