Photosynthesis http://www.brainpop.com/science/cellularlifeandgenetics/photosynthesis/

Life on Earth is largely solar powered Photosynthesis produces 160 billion metric tons of carbohydrates each year

Life in the Sun -Photosynthesis provides food for most organisms. (Some autotrophic bacteria use chemosynthesis, which makes food from inorganic compounds) Light is central to the life of a plant, It provides food for virtually all organisms

Examples of photosynthetic autotrophs: plants, some protists (algae) and some bacteria photosynthetic autotrophs = They generate their own organic matter through photosynthesis (c) Euglena (d) Cyanobacteria (b) Kelp Mosses, ferns, and flowering plants

In aquatic environments, algae and photosynthetic bacteria are the main food producers.

Each square millimeter of a leaf contains about 500,000 photosynthesis factories called chloroplasts

Chloroplasts: Sites of Photosynthesis Are found in the cells of the mesophyll Enclosed by two membranes Contain stroma, a thick fluid Contain thylakoids, membranous sacs, that are stacked together http://www.youtube.com/watch?v=-P-IUyAjqYc&feature=fvw

Vein Chloroplast Outer membrane Inner membrane Stomata Mesophyll Inner membrane Stomata Leaf cross section Mesophyll cell Thylakoid Stroma Thylakoid space Grana

The Overall Equation for Photosynthesis Light energy Photosynthesis Water Glucose Carbon dioxide Oxygen gas

Plants produce O2 gas by splitting water The O2 released by photosynthesis is made from the oxygen in water

Photosynthesis occurs in two parts Light reactions: Solar energy is converted into chemical energy (NADPH and ATP) when H2O splits. Oxygen is released. 2) Calvin Cycle: CO2 combines with NADPH and ATP (from the light reactions) to make organic compounds (sugars). http://www.youtube.com/watch?v=m8v7prlscM0&feature=related

An overview of photosynthesis CO2 Chloroplast Light NADP+ ADP +P CALVIN CYCLE (in stroma) LIGHT REACTIONS (in grana) Photosynthesis is a two-step process 1. The light reactions convert solar energy to chemical energy 2. The Calvin cycle makes sugar from carbon dioxide ATP Electrons NADPH O2 Sugar

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Sunlight is a type of energy called radiation, or electromagnetic energy

The full range of radiation is called the electro-magnetic spectrum Increasing energy The full range of radiation is called the electro-magnetic spectrum Gamma rays Micro- waves Radio waves X-rays UV Infrared Visible light Wavelength (nm) 600 nm

Chloroplast Pigments Chloroplasts contain several pigments Chlorophyll a Chlorophyll b Carotenoids Xanthophyll

Chlorophyll: Occurs in two forms, chlorophyll a and b Absorbs light in the blue-violet and orange-red regions, thus appears green Occurs in two forms, chlorophyll a and b Chlorin ring Mg Chlorophyll a, b and other associated pigments are assembled in clusters in the thylakoid membrane Hydrocarbon tail

Chloroplasts absorb light energy and convert it to chemical energy Reflected light Light Absorbed light Transmitted light Chloroplast

Harvesting Light Energy Light behaves as photons, discrete packets of energy Chlorophyll molecules absorb photons - Electrons in the pigment gain energy - The energy is released and used

Absorption of a photon (light energy) Excited state 2 1 Heat Light Light (fluores- cence) Photon Ground state Chlorophyll molecule Absorption of a photon (light energy)

A photosystem Is an organized group of chlorophyll and other pigment molecules Is a light-gathering antenna Cluster of pigment molecules embedded in membrane Chloroplast Primary electron acceptor Photon Electron transfer Granum (stack of thylakoids) Reaction center A chlorophyll a molecule located at the center of the pigment cluster receives light energy from the pigment of cluster and forms part of the reaction center Each of the many light-harvesting photosystems consists of: an “antenna” of chlorophyll and other pigment molecules (carotenoids, phycobilins, phycocyanins) that absorb light a primary electron acceptor that receives excited electrons from the reaction-center chlorophyll Reaction- center chlorophyll a Transfer of energy Thylakoid membrane Antenna pigment molecules Photosystem

Primary electron acceptor PHOTOSYSTEM Photon Chlorophyll a Pigment molecules of antenna

I. LIGHT REACTIONS: Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons The excited electrons are passed from down the electron transport chains Their energy ends up in ATP and NADPH

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

Electron Transport Chains (ETC) Connect the two photosystems Release energy that the chloroplast uses to make ATP

II. THE CALVIN CYCLE Functions like a sugar factory within a chloroplast Regenerates the starting material with each turn

ATP and NADPH power sugar synthesis in the Calvin cycle The Calvin cycle occurs in the chloroplast’s stroma The carbon atoms from CO2 are used to make organic compounds like sugar. INPUT CALVIN CYCLE OUTPUT:

Most plants make more sugar than they need The excess is stored in roots, tubers, and fruits and seeds These are a major source of food for animals

A review of photosynthesis Light Chloroplast NADP RuBP ADP + P 3-PGA Calvin cycle Light reactions Electrons G3P Cellular respiration Cellulose Starch Other organic compounds

Photosynthesis & the Greenhouse Effect

The Greenhouse effect: Warms the atmosphere Is caused by atmospheric CO2 Sunlight Atmosphere Radiant heat trapped by CO2

Photosynthesis has an enormous impact on the atmosphere It swaps O2 for CO2

Because photosynthesis removes CO2 from the atmosphere, it moderates the greenhouse effect Unfortunately, deforestation may cause a decline in global photosynthesis