Photosynthesis

Where does all of our energy come from?

How do plants get food? Photosynthesis- Process by which green plants or organism with chlorophyll convert light energy into chemical energy in the bonds of carbohydrates Autotrophic – Can transfer energy to produce food – can synthesize food Heterotrophic – Must obtain energy from preformed food – gotta eat food!

What is needed for autotrophs to photosynthesize? Carbon dioxide (atmospheric) Water (in the soil or air) Sunlight (or artificial light source) Chlorophyll (present in leaves and sometimes stems) Enzymes (to regulate the rate of the reaction)

Who helped us figure this out? Van Helmont (1600s)—experiment with potted plant to determine what a plant uses to grow.

Conclusion: mass of tree comes from water He got it only half right: there is also CO2!

Who helped us figure this out? Joseph Priestly (1770s) experiment with candle, sprig of mint and a jar

Who helped us figure this out? Ingen-Housz—repeated Priestley’s experiment but put the sprig of mint in the dark Candle would not burn for as long in the dark, so LIGHT is important for plants

Putting it all together The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen

THE FORMULA 6CO2 + 12 H2O → C6H12O6 + 6O2 + 6H2O Seems simple, huh? chlorophyll enzymes Seems simple, huh? Takes EIGHTY different chemical reactions from start to finish

Where does Photosynthesis happen? In the chloroplasts! Chloroplasts are oval structure consisting of stacks called grana (photosynthetic membranes) and a liquid called stroma. Chlorophyll is found in the stacked grana

What are the pigments Two main ones Other accessory pigments Chlorophyll a and Chlorophyll b Other accessory pigments Absorb other wavelengths of light Carotenoids, xylophylls, anthocyanin

Light White light is a mixture of all the wavelengths of visible light Color is all about the reflection of light

Absorption and Reflection Chlorophyll absorbs red/blue light the best It mostly reflects green light THIS IS WHY PLANTS ARE GREEN!

Why do the leaves change? When [water] is low, plant pigments break down Mostly green pigment, that goes away first

ATP When chlorophyll absorbs light, it is absorbing energy It stores it in the bonds of Adenosine Triphosphate (ATP)

ATP ATP ADP AMP Made of This is temporary storage Adenine (nitrogenous base) Ribose (5 carbon sugar) 3 phosphate groups This is temporary storage ATP ADP AMP

ATP Is constantly made and broken down Think of ATP like cash in your pocket Glucose like an ATM card Glycogen like your savings account

ATP v ADP

2 Main steps of Photosynthesis Light reactions—occurs only in the presence of light Occurs in the grana (thylakoids) of the chloroplasts Also known as Photolysis because light is used to split water molecules into hydrogen and oxygen

2 Main steps of Photosynthesis Dark Reactions—can occur in light or darkness. Follows light reactions Occurs in the stroma of the chloroplasts Also known as Carbon fixation because CO2 will get “fixed up” with the hydrogen’s and energy from the light reaction

Photosynthesis Overview

Light Reactions The light energy strikes the leaf, passes into the leaf and hits a chloroplast inside an individual cell. The light energy, upon entering the chloroplasts, is captured by the chlorophyll inside a granum. Inside the grana some of the energy is used to split water into hydrogen and oxygen. The oxygen is released into the air.

The Dark Reactions The hydrogen is taken to the stroma along with the grana's remaining light energy. Carbon dioxide enters the leaf and passes into the chloroplast. In the stroma the remaining light energy is used to combine hydrogen and carbon dioxide to make carbohydrates. This occurs during the Calvin Cycle The energy­-rich carbohydrates are carried to the plant's cells. The energy-­rich carbohydrates are used by the cells to drive the plant's life processes.

What are the inputs of light dependent reactions What are the inputs of light dependent reactions? What are the outputs of the light dependent reactions? What are the inputs of light independent reactions? What are the outputs of the light independent reactions? LIGHT: Inputs – light, NADP+, ADP+Pi, water Outputs – ATP, NADPH, Oxygen DARK: Inputs – ATP, NADPH, carbon dioxide Outputs – NADP+, ADP+Pi, 1 glucose molecule