PHOTOSYNTHESIS

Photosynthesis – Making Sugar from

Sunlight

“Life is woven out of air by light “

Jacob Moleschott Dutch

It’s a Fundamental process

–Photosynthesis

And just in caseyou didn’t catch all the words… …..One more time!

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Photosynthesis• Endergonic reaction (stores energy) that uses light energy , Carbon

dioxide (CO2), and water (H2O) to produce organic molecules (glucose).

6CO2 + 6H2O C6H12O6 + 6O2

SUN

Carbon dioxide

water glucose oxygen

So what then is the main source of energy on earth????

THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON

EARTH

Light Energy Harvested by Plants & Other Photosynthetic Autotrophs

6 CO2 + 6 H2O + light energy → C6H12O6 +6 O2

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Plants• Autotrophs – produce their own

food (glucose)• Process called photosynthesis• Mainly occurs in the leaves:

a. stoma - poresb. mesophyll cells

StomaMesophyllCell

Chloroplast

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Stomata (stoma)Pores in a plant’s cuticle through

which water vapor and gases (CO2 & O2) are exchanged between the plant and the atmosphere.

Guard Cell

Guard CellCarbon Dioxide

(CO2)

Oxygen (O2)

Found on the underside of leaves

Stoma

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Mesophyll Cell of Leaf

Cell Wall

Nucleus

Chloroplast

Central Vacuole

Photosynthesis occurs in these cells!

ChloroplastOrganelle where

photosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected together

WHY ARE PLANTS GREEN?

It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that…

Kermit the Frog

Different wavelengths of visible light are seen by the human eye as different colors.

WHY ARE PLANTS GREEN?

Gammarays

X-rays UV Infrared

Micro-waves

Radiowaves

Visible light

Wavelength (nm)

The wavelength that is not absorbed but is reflected back equals the apparent color of an object.

The feathers of male cardinals are loaded with pigments. These pigments absorb some wavelengths of light and reflect others.

Reflected light

Why are plants green?

Reflected

light

WHY ARE PLANTS GREEN?

Plant Cells have Green Chloroplasts

The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

• Chloroplasts absorb all light energy except the green light and convert it to chemical energy

LightReflected

light

Absorbedlight

Chloroplast

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

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Question:

During the fall, what causes the leaves to

change colors?

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Fall Colors

• In addition to the chlorophyll pigments, there are other pigments present

• During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments

• Carotenoids are pigments that are either red, orange, or yellow

• Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water

A REVIEW OF PHOTOSYNTHESIS

Carbondioxide

Water Glucose Oxygengas

PHOTOSYNTHESIS

The location and structure of chloroplasts

LEAF CROSS SECTION MESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outermembrane

Innermembrane

ThylakoidcompartmentThylakoidStroma

Granum

StromaGrana

2 Major Reactions of photosynthesis

• Light-dependent Reactions-

• use light to produce ATP and NADPH

• Light-independent (dark) Reactions (Calvin Cycle)

• use ATP and NADPH to produce sugars

A Photosynthesis Road Map

Chloroplast

Light

Stack ofthylakoids ADP

+ P

NADP

Stroma

Lightreactions

Calvincycle

Sugar used for

Cellular respiration Cellulose Starch

Other organic compounds

• The Calvin cycle makes sugar from carbon dioxide– ATP and NADPH

generated by the light reactions provides the energy and electrons for sugar synthesis

LightChloroplast

Lightreactions

Calvincycle

NADP

ADP+ P

• The light reactions convert solar energy to chemical energy– Produce ATP &

NADPH

AN OVERVIEW OF PHOTOSYNTHESIS

• Happens in thylakoids• Stacks of membranes in chloroplasts called thylakoids contain chlorophyll and membrane proteins• Chlorophyll absorbs light

Light Reactions

• Called Calvin cycle• Happens in stroma• Uses ATP and NADPH from light reactions to produce stable sugars

Light-independent Reactions

Review: Photosynthesis uses light energy to make food molecules

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Energy for Life on Earth• Sunlight is the ULTIMATE

energy for all life on Earth• Plants store energy in the

chemical bonds of sugars through photosynthesis

• Chemical energy is released as ATP during cellular respiration