Review Where does photosynthesis occur? Where does the energy from photosynthesis come from? What pigment is responsible for the green color in most plants? What is ATP used for?

Photosynthesis occurs in the leaves of green plants More specifically the chloroplasts

Energy for almost all living things starts with the Sun

Chlorophyll is responsible for the green color in plants

ATP is used as energy inside of cells Turning ATP into ADP releases energy cells can use

Objectives Learn the difference between light and dark reactions in photosynthesis Learn the reactants and products of photosynthesis Learn where the mass of plants come from Learn where oxygen comes from in photosynthesis

Photosynthesis takes place in three stages: 1. Capture energy from sunlight 2. Use energy from sun to make ATP and reduce the compound NADP + to NADPH 3. Use ATP and NADPH to make glucose from CO 2

Light-Dependent Reactions The first two stages require light

Light-Independent Reactions The third stage does not require light Happens in the presence or absence of light

Light Independent Reactions As long as ATP and NADPH are available the third step will occur

Photosynthesis Equation

Discovery of Photosynthesis* From the time of the Greeks, plants were thought to obtain their food from the soil Just sucking up soil with their roots caused them to grow

Jan Baptista van Helmont thought of a way to test this idea. He weighed a small willow tree and planted it in a pot of soil. He allowed the tree to grow several years during which he only added water The weight of the tree increased by 74.4 kg. (1kg =2.2lbs) The mass of the soil only decreased by 54 g. (1000g = 1kg) He concluded that the water he added must have been adding the mass to the plant

Joseph Priestly provided further insight to the understanding of where plants get their mass He placed a small plant into air which was full of CO 2 (he blew out a candle) He came back 10 days later and was able to light the candle in the same environment. His conclusion: Living vegetation adds something to the air

Jan Ingenhousz determined how this works He demonstrated air was only restored in the presence of sunlight. The specifics of how this works was worked out in the past 50 years.

Conclusion A lot of the plants mass comes from the gases that it uses and creates during photosynthesis. Only a very small portion is water and soil.

Oxygen comes from water, not CO 2 Hydrogen sulfide photosynthesis equation vs Water photosynthesis* Water Sulfide

Light-Dependent Reactions 4 steps 1. Primary photoevent – sunlight is captured 2. Charge separation – energy is transferred to reaction center 3. Electron Transport Chain – Electrons are shuttled around the cell and eventually reduce NADP + into NADPH 4. Chemiosmosis – Protons move around and ATP is made

Products of Light Dependent Reactions ATP NADPH O 2

Light Independent Reactions Use the products of light dependent reactions to make sugar /glucose Glucose

Light Independent Reactions ATP provides the energy NADPH provides protons and electrons CO 2 provides carbon

Calvin Cycle* The Calvin Cycle is technically the final step in photosynthesis. The cycle explains how Glucose is made.

Light Independent Reactions Sometimes called Dark Reactions I don’t like this because it suggests the reaction can only happen when there is no light, which is not correct