- Photosynthesis: Life from Light and Air

Photosynthesis most important chemical process on Earth It provides food for virtually all organisms Photos = light Synthesis= to put together Puts together a sugar molecule using energy from light

Autotrophs are the producers of the biosphere They are the ultimate producers of food consumed by virtually all organisms

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 PHOTOSYNTHESIS

H2OH2O Building plants from sunlight & air Photosynthesis – 2 separate processes – ENERGY building reactions collect sun energy use it to make ATP – SUGAR building reactions take the ATP energy collect CO 2 from air & H 2 O from ground use all to build sugars ATP sun sugars + carbon dioxide CO 2 sugars C 6 H 12 O 6 CO 2 water H 2 O +

Using light & air to grow plants 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 sun energy  +++  glucose + oxygen carbon dioxide sun energy + water + (ATP) = used to build the sugar Photosynthesis – using sun’s energy to make ATP – using CO 2 & water to make sugar – in chloroplasts – allows plants to grow – makes a waste product oxygen (O 2 )

What do plants need to grow? The “factory” for making energy & sugars – chloroplast Fuels – sunlight – carbon dioxide – water The Helpers – enzymes H2OH2O sugars ATP Make ATP! Make sugar! I can do it all… And no one even notices! enzymes CO 2 sun

H2OH2O Photosynthesis ENERGY building reactions SUGAR building reactions ATP ADP CO 2 sugar sun used immediately to synthesize sugars

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

Chloroplasts are only in plants animal cells plant cells

Chloroplasts Chloroplasts in cell Leaf Leaves Chloroplast absorb sunlight & CO 2 make ENERGY & SUGAR Chloroplasts contain Chlorophyll CO 2 Chloroplast sun

Bring In – light – CO 2 –H2O–H2O Let Out –O2–O2 Move Around – sugars So what does a plant need? 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ roots shoot leaves

Stomates & Guard Cells Function of stomates – CO 2 in – O 2 out – H 2 O out gets to leaves for photosynthesis Function of guard cells – open & close stomates guard cell stomate

Guard cells & Homeostasis Homeostasis – keeping the internal environment of the plant balanced Stomates open – let CO 2 in needed to make sugars – let H 2 O out needed for photosynthesis – let O 2 out get rid of waste product Stomates close – if too much H 2 O evaporating

Oxidation-Reduction Reactions Redox for short Oxidation= loss of electrons (or H + ) Reduction= gain of electrons (or H + ) OIL RIG: Oil = Oxidation is loss Rig = Reduction is gain ~chemical reaction which involve a partial or complete transfer of electrons form one reactant to another ~ a coupled reaction Photosynthesis is a redox process When water molecules are split apart to release O 2, they are actually oxidized, that is they loose electrons along with hydrogen ions. Meanwhile CO 2 is reduced to sugar as electrons and hydrogen ions are added to is

Photosynthesis is a redox process Water molecules are split apart and electrons and H + ions are removed, leaving O 2 gas – These electrons and H + ions are transferred to CO 2, producing sugar Reduction Oxidation

Hydrogen carriers such as NADP + shuttle electrons in redox reactions Enzymes remove electrons from glucose molecules and transfer them to a coenzyme / electron carrier[ NADPH]

Overview: Photosynthesis occurs in two stages linked by ATP and NADPH The complete process of photosynthesis consists of two linked sets of reactions: – the light reactions and the Calvin cycle #1 The light reactions convert light energy to chemical energy and produce O 2 ( occurs in thylakoid membranes) #2 The Calvin cycle assembles sugar molecules from CO 2 using the energy-carrying products of the light reactions (occurs in stroma)

An overview of photosynthesis Chloroplast Light LIGHT REACTIONS (in grana CALVIN CYCLE (in stroma H2OCO2 O2 Sugar ATP NADPH NADP+ ADP +P O2

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Visible radiation drives the light reactions Certain wavelengths of visible light drive the light reactions of photosynthesis Visiblel light Wavelength (nm) Gamma rays X-rays UVInfrared Micro- waves Radio waves

Pigments Pigment: a substance that absorbs light of a particular wavelength Wavelengths that are NOT absorbed are reflected (bounce off) or transmitted (pass through) So the material in which the pigment is found appears to be the color of the wavelengths that are NOT absorbed Photosynthetic pigments: can absorb light energy & make it available for conversion to chemical energy Chlorophyll a: most common pigment in chloroplast (absorbs blue &red light and reflects green light thus giving the chloroplast a green color) Accessory pigments: additional pigments that absorb different wavelengths (carotene, chlorophyll b, & xanthophyll) Reflected light Transmitted light Light Absorbed light Chloroplast

Photons Light not only acts like waves, also made of particles called photons~ each carries a definite amount of energy depending on its wavelength Atoms can absorb light by capturing a photon ~ energy of photon is transferred to an e- of the atom-> bouncing it up to a higher energy level Green plants & other photosynthetic autotrophs can store this energy in a chemical form-> inside high energy compounds

Light-Dependent Reactions absorption of light energy by chlorophyll As sunlight strikes the pigment molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons. These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane. At each step along the transport chain, the electrons lose energy.

Light-Dependent Reactions This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc..

Restoring electrons To replace the lost electrons, molecules of water are split. This reaction is called photolysis. The O 2 liberated by photosynthesis is made from the oxygen in water H 2 O    O 2 + 2e - Chlorophyll 2e - H2OH2O O 2 + 2H + 2

Plants produce O 2 gas by splitting water  The O 2 liberated by photosynthesis is made from the oxygen in water

Photolysis Energized electrons Energy from the energized electrons pump H + ions and change NAPD + to NADPH. The H + ions move from high to low and turn the ATP synthase and change ADP + P to ATP Oxygen by-product

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY  In the light reactions, electron transport chains generate ATP, NADPH, and O 2  Absorption of light energy by chlorophyll~ electrons “excited” as electrons drop back, energy released to do 3 things: as electrons drop back, energy released to do 3 things: 1. “ photolysis ” split H 2 0 molecule using light energy, O 2 given off as by-product 2. Hydrogen produced by splitting of water is attached to hydrogen carrier NADP -> NADPH 3. energy from “excited” electrons used to make ATP 3. energy from “excited” electrons used to make ATP (ADP +P→ATP) using the ATP synthase (ADP +P→ATP) using the ATP synthase

THE CALVIN CYCLE: CONVERTING CO 2 TO SUGARS ATP and NADPH power sugar synthesis in the Calvin cycle occurs in the chloroplast’s stroma carbon fixation takes place and sugar is manufactured The Calvin cycle constructs G3P (a sugar) using – carbon fro m atmospheric CO 2 – electrons and H + from NADPH – energy from ATP Energy-rich sugar is then converted into glucose CALVIN CYCLE INPUT OUTPUT:

Bring InBring In –light –CO 2 –H2O–H2O–H2O–H2O Let OutLet Out –O2–O2–O2–O2 Move AroundMove Around –sugars So what does a plant need? 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 light energy  +++ roots shoot leaves

Review: Photosynthesis uses light energy to make food molecules LIGHT REACTIONS CALVIN CYCLE

Factors Affecting Rate of Photosynthesis 1.Temperature: increases rate up to a certain point 2.Light Intensity: increases rate up to a certain point 3.CO2 level: Increases rate up to a certain point 4.Water: decrease water, decrease photosynthesis 5.Minerals; Ex. Magnesium, Nitrogen

Comparing Cellular Respiration & Photosynthesis Cell Respiration Photosynthesis