THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

Energy can be transformed from one form to another FREE ENERGY (available for work) vs. HEAT (not available for work)

THE BASICS OF PHOTOSYNTHESIS Almost all plants are photosynthetic autotrophs, as are some bacteria and protists Phototrophs are autotrophs that generate their own organic matter through photosynthesis. Sunlight energy is transformed to energy stored in the form of chemical bonds (c) Euglena (d) Cyanobacteria (b) Kelp (a) Mosses, ferns, and flowering plants

Light Energy Harvested by Plants & Other Photosynthetic Autotrophs 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

Food Chain

THE FOOD WEB Photosynthesis provides a vital connection between the Sun and the energy needs of living organisms.

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

Electromagnetic Spectrum and Visible Light Gamma rays Infrared & Microwaves X-rays UV Radio waves Visible light Wavelength (nm)

WHY ARE PLANTS GREEN? Different wavelengths of visible light are seen by the human eye as different colors. Pigments are substances that absorb light of a certain wavelength Gamma rays Micro- waves Radio waves X-rays UV Infrared Visible light Wavelength (nm) Visible light has wavelengths from 3600 ◦A (violet) to 7600 ◦A (red).Light energy (photons) give energy to the electrons of the absorbing pigment

The feathers of male cardinals are loaded with carotenoid pigments The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others. Reflected light RED appears RED because the red wavelength is NOT being absorbed by the red pigment but is reflected into our eyes.

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).

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED Chloroplasts absorb light energy and convert it to chemical energy Chlorophylls- green-yellow is not absorbed, all other colors are. Chlorophylls receive energy from violet, blue, orange and red. Xanthophylls- yellow pigment Carotenes- orange pigments. Reflected light Light Absorbed light Transmitted light Chloroplast

AN OVERVIEW OF PHOTOSYNTHESIS Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water Carbon dioxide Water Glucose Oxygen gas PHOTOSYNTHESIS

AN OVERVIEW OF PHOTOSYNTHESIS The light reactions convert solar energy to chemical energy Produce ATP & NADPH Light Chloroplast NADP ADP + P The Calvin cycle makes sugar from carbon dioxide ATP generated by the light reactions provides the energy for sugar synthesis The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Calvin cycle Light reactions

Chloroplasts: Sites of Photosynthesis Occurs in chloroplasts, organelles in certain plants All green plant parts have chloroplasts and carry out photosynthesis The leaves have the most chloroplasts The green color comes from chlorophyll in the chloroplasts The pigments absorb light energy

Photosynthesis occurs in chloroplasts In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts A chloroplast contains: stroma, a fluid grana, stacks of thylakoids The thylakoids contain chlorophyll Chlorophyll is the green pigment that captures light for photosynthesis

The location and structure of chloroplasts LEAF CROSS SECTION MESOPHYLL CELL LEAF Mesophyll CHLOROPLAST Intermembrane space Outer membrane Granum Inner membrane Grana Stroma Thylakoid compartment Stroma Thylakoid

Chloroplast Pigments Chloroplasts contain several pigments Chlorophyll a Chlorophyll b Carotenoids Figure 7.7

Chlorophyll a & b Chl a has a methyl group Chl b has a carbonyl group Porphyrin ring delocalized e- Phytol tail

Different pigments absorb light differently

In the light reactions, ATP, NADPH, & O2 are Produced Light comes in, water is split- oxygen is given off to the atmosphere. Energy is given to electrons in chlorophyll and their energy ends up in ATP and NADPH. Hydrogen in water ends up in NADPH. Happens in the grana! Energy captured in the light reaction is used to power the Dark reaction

Plants produce O2 gas by splitting H2O

How the Light Reactions Generate ATP and NADPH Primary electron acceptor NADP Energy to make Primary electron acceptor 3 2 Light Electron transport chain Light Primary electron acceptor Reaction- center chlorophyll 1 NADPH-producing photosystem Water-splitting photosystem 2 H + 1/2

ELECTRON TRANSPORT CHAIN The production of ATP in the light reaction of photosynthesis Thylakoid compartment (high H+) Light Light Thylakoid membrane Antenna molecules Stroma (low H+) ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

A Photosynthesis Road Map Chloroplast Light Stroma NADP Stack of thylakoids ADP + P Light reactions Calvin cycle Sugar used for  Cellular respiration  Cellulose  Starch  Other organic compounds

The Calvin Cycle- Dark Reaction Occurs in the Stroma NADPH and ATP from the light reaction provide the hydrogen and the energy to power the dark reaction. Carbon Fixation- The Calvin Cycle “fixes” carbon dioxide from the atmosphere into an organic molecule- GLUCOSE

Review: Photosynthesis uses light energy to make food molecules A summary of the chemical processes of photosynthesis Photosynthesis happens only during the day when there is light. Chloroplast Light Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma Electrons Cellular respiration Cellulose Starch Other organic compounds LIGHT REACTIONS CALVIN CYCLE

Factors that Effect Photosynthesis Temperature- photosynthesis occurs best at 35◦ C Light intensity- photosynthesis occurs best at 1/3rd summer sunlight. Some leaves are shaded so photosynthesis works best for the whole plant at higher than 1/3rd summer sunlight.

Factors that Effect Photosynthesis Minerals- nitrogen, copper, magnesium, zinc iron, are necessary to make enzymes and pigments. Water- a certain level is necessary CO2 Level- X10 normal CO2 concentration in air

It's not that easy bein' green… but it is essential for life on earth!