Baltimore Polytechnic Institute Unit 4: Energy; Photosynthesis Honor’s Biology January 7th, Monday Unit 4: Energy; Photosynthesis Insong James Lee, Ph.D.

Unit 4: Energy; Photosynthesis January 7th, Monday Learning objectives: Describe the overall process of photosynthesis, including the inputs, outputs, and the organelle and molecules that are involved. Describe the light reaction part of the photosynthesis. Describe the Calvin Cycle part of the photosynthesis. Unit 4: Energy; Photosynthesis

Unit 4: Energy; Photosynthesis Topic slides Review of energy. 4 Overview of photosynthesis. 5-12 The light cycle of photosynthesis. 13-22 The Calvin cycle of photsynthesis. 23-32

Review Respiration Photosynthesis Carbon is (Redox) Location (in Eukaryotes) Energy is Types of organisms (‘trophs)

Overview of photosynthesis slides 6-12

Photosynthesis Happens in Two Main Steps 1) The light reactions of photosynthesis are responsible for capturing the energy of light, and storing it in chemicals like ATP. Water is split, producing O2. 2)Those chemicals and CO2 from the atmosphere are then used by the Calvin Cycle to build sugars the plant needs to grow and survive.

Photosynthesis as a Process

The Carbon Cycle of Life C6H12O6 Photo-synthesis Respiration ATP Energy Produced CO2 Light Energy

Photosynthesis Happens in Chloroplasts Thylakoid Stroma

Chlorophyll is the green pigment that green plants use to capture light energy

Photosynthesis as a Process

The light reaction part of photosynthesis slides 14-22

Overview of the light reaction of Photosynthesis

Step1: Chlorophyll in the chloroplast captures light energy Light strikes chlorophyll which is located near Photosystem 2. Electrons (from H2O) are knocked out of chlorophyll and move through photosystem 2 and then to other proteins nearby. Light electrons Chlorophyll 2 H+ + O H2O

Step 2: Electrons are Transferred to Photosystem II The high-energy electrons taken from chlorophyll (which came from water) are transferred to the electron transport chain of Photosystem II by an electron carrier protein called plastoquinone. Stroma

Step 3: The Electron Transport Chain of PSII Makes a Hydrogen Gradient Stroma H+ H+ H+ H+ Inside Thylakoid (Lumen) H+ H+ Electrical energy allows ACTIVE transport from low concentration to high.

H+ is at a high concentration in the inside of thylakoids (called thylakoid lumen)

Step 4: ATP is made by the enzyme ATP synthase Inside Thylakoid The energy to make ATP from ADP + P comes from the concentration gradient of hydrogen ions across the thylakoid membrane. This is called oxidative phosphorylation ATP synthase is a key enzyme that makes ATP Stroma

Step 5: Electrons are Transferred to Photosystem I The electrons move to Photosystem I through a protein called plastocyanin and additional sunlight is used to form NADPH which is used for the Calvin cycle. Stroma

Light Reaction Summary Light energy is captured by chlorophyll in the chloroplast. Light energy is stored in ATP and NADPH. The electrons used in the process come from the splitting of water. This is why plants make oxygen.

Light Reactions Recap Use light energy to oxidize H2O, producing O2. PS II produces ATP by oxidative phosphorylation. PS I produces NADPH, a reduced electron carrier. Overall function of the light reactions is to provide the energy (ATP) and electrons (NADPH) needed for the Calvin Cycle.

The Calvin cycle part of photosynthesis slides 24-32

The Calvin Cycle The Calvin Cycle builds sugars from CO2. (Carbon Fixation) The energy for the process comes from ATP and NADPH made during the light reaction. This process also happens in the chloroplast (specifically, the stroma).

Calvin Cycle… it’s complicated What you need to know FOR NOW: CO2 molecules are combined to make sugar (C6H12O6) Requires lots of ATP

Calvin Cycle = Carbon Fixation Carbon fixation is the process of turning inorganic carbon (like CO2) into organic carbon (like C6H12O6) Carbon fixation is the source of ALL CARBON BIOMASS ON EARTH. Thank you, autotrophs!

The Calvin Cycle is an Energy Hog To make 2 molecules of G3P required for a single glucose molecule, the cell must use 18 ATP molecules and 12 NADPH molecules. (NADPHNADP+ releases more energy than converting 7 ATPs to ADP!) Bottom line: it takes a lot of energy to turn CO2 and water into glucose! The process is about 75% efficient

Calvin Cycle Recap The Calvin Cycle (aka “light-independent reactions”) BUILDS CARBOHYDRATE RuBisCo catalyzes carbon fixation RuBisCo: (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is an enzyme involved in the first major step of carbon fixation Energy from ATP and NADPH (made in the light reactions) provide the energy to reduce carbon.

Photosynthesis Happens in Two Main Steps: The light reactions of photosynthesis are responsible for capturing the energy of light, and storing it in chemicals like ATP. Water is split, producing O2. Those chemicals and CO2 from the atmosphere are then used by the Calvin Cycle to build sugars the plant needs to grow and survive.