Photosynthesis

Objectives:1. Describe the structure of a chloroplast

2. Explain who ATP releases energy3. Explain the steps to photosynthesis

Energy• Energy is stored in chemical bonds and released at a later date. • Cellular energy is stored by ATP• Adenosine Triphosphate• Contains 2 high energy phosphate bonds• Also contains nitrogen base adenine and a ribose sugar

ADP

• Adenosine diphosphate• What is formed when ATP loses 1 phosphate• ATP releases energy and a free phosphate. This forms ADP • When ATP turns to ADP….energy is released• Energy is used to make ATP again

Importance of ATP

• Main compound used to store energy in living things

• Provides all of the energy for cell activities• Adding a phosphate group to ADP stores

energy• Removing a phosphate group from ATP

releases energy and makes ADP

Pigments and Chloroplasts

• Chlorophyll—primary light-absorbing pigment in autotrophs

• Found inside chloroplasts• Chlorophyll a– Found in all plants– Participates directly in light reactions

• Chlorophyll b– Accessory pigment– Indirectly works in photosynthesis– Both a and b absorb red and blue light

Structure of a Chloroplast

Structure of a Chloroplast

• Smooth outer membrane• Inside: stacks of connected sacs called

thylakoids• One thylakoid stack—granum (grana plural)• Gel-like material around the grana--stroma

Function of Stroma

• Light independent reaction• ATP makes glucose• Calvin cycle

Function of Thylakoid Membrane

• Light dependent reaction• Made up of chlorophyll molecules

Photosynthesis Equation

Photosynthesis Overview

Light Dependent Reactions

• Occurs across the thylakoid membranes• Uses light energy• Produces oxygen from water• Converts ADP to ATP• Converts NADP+ to energy carrier NADPH

Steps of the Light Dependent Reaction

• Photosystem II absorbs light energy• Electrons are energized and passed to the

Electron Transport Chain (ETC)• Lost electrons are replaced from the splitting

of water into 2 H+ , free electrons and oxygen• 2 H+ pumped across the thylakoid membrane

More..

• High energy electrons move to photosystem I through the electron transport chain

• Energy is used to transport H+ from stroma to inner thylakoid membrane

• NADP picks up 2 electrons from the ETC and a H+ to form NADPH

• As H+ ions pass through the thylakoid, ATP synthase binds them to ADP to form ATP

Summary

• Reactants:– Water, light

• Products– ATP, NADPH—energy for dark reaction– Oxygen—by product for cellular respiration

Light Independent Reaction

• ATP and NADPH from light reaction are used for energy of this reaction

• CO2 from the atmosphere is used to make sugars (glucose)

• Six carbon sugars made in calvin cycle• Occurs in stroma

The Calvin Cycle

• Two turns of the Calvin Cycle are required to make one molecule of glucose

• 3-carbon dioxide molecules enter the Calvin Cycle to form PGA

• Two molecules of PGA form 1 molecule of glucose

DONE!