The Reaction of Photosynthesis Chapter 8.3 The Reaction of Photosynthesis

The Chloroplast  Site of photosynthesis

The Chloroplast Inner membrane  thylakoid Highly folded so there is an increased surface area for absorption of sunlight Stacks of thylakoids  grana Clusters of chlorophyll and other pigments  photosystems Liquid filling of chloroplast  stroma

Electron Carriers A carrier molecule is a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule Main electron carrier of photosynthesis  NADP+  Turns into NADPH when it is carrying electrons

Photosystems There are two different groupings of photosystems in photosynthesis  Light dependent reactions Happens on the  thylakoid membrane Has 2 photosystems (II and I)  Light independent reactions Happens in the  stroma Also known as the  Calvin cycle

Figure 8-7 Photosynthesis: An Overview Section 8-3 Light O2 Sugars CO2 Chloroplast Chloroplast NADP+ ADP + P Light- Dependent Reactions Calvin Cycle ATP NADPH

Concept Map Photosynthesis Light- dependent reactions Calvin cycle Section 8-3 Photosynthesis includes Light- dependent reactions Calvin cycle takes place in uses use take place in Thylakoid membranes Stroma NADPH ATP Energy from sunlight to produce of to produce ATP NADPH O2 Chloroplasts High-energy sugars

Light Dependent Reactions  Part of photosynthesis that requires light Use light energy to produce ATP and NADPH, as well as oxygen

Light Dependent Reactions  Pigments of photosystem II absorb light Energy is absorbed by electrons High energy electrons are transferred to NADP+ (electron carrier molecule) These electrons are replaced by electrons produced by the breakdown of water Water is broken down into  2 electrons, 2 H+ ions, and 1 oxygen atom Oxygen is released Hydrogen is broken apart and released inside the thylakoid

Light Dependent Reactions The high energy electrons are passed through the  electron transport chain between photosystem II to photosystem I The energy from the electrons is used to transport H+ ions from  the stroma into the inner thylakoid space

Light Dependent Reactions  Light hits the electrons that are now in photosystem I to excite them again These high energy electrons are picked up by NADP+ The NADP+ also picks up the H+ ions to make NADPH

Light Dependent Reactions As the electrons move onto the NADP+,  more H+ ions are pumped across the membrane Eventually, the outside of the thylakoid becomes negatively charged and the inside becomes positively charged Difference in charge provides the energy to make  ATP

Light Dependent Reactions Thylakoid membrane contains an enzyme called ATP synthase  H+ ions pass through it to synthesize ATP This energy will be used to make energy-containing carbohydrates

Click the image to play the video segment. Light-Dependent Reactions, Part 1 Click the image to play the video segment. Video 3

Click the image to play the video segment. Light-Dependent Reactions, Part 2 Click the image to play the video segment. Video 4

Light Dependent Reactions Figure 8-10 Light-Dependent Reactions Light Dependent Reactions Section 8-3 Hydrogen Ion Movement Photosystem II Chloroplast ATP synthase Inner Thylakoid Space Thylakoid Membrane Stroma Electron Transport Chain Photosystem I ATP Formation

Light Dependent Reactions

Light Independent Reactions Also known as the  Calvin cycle Plants use the energy that  ATP and NADPH contain to build high-energy compounds that can be stored for a long time  Does not require light

Light Independent Reactions  Six carbon dioxide molecules enter the cycle from the atmosphere to produce 1 6-carbon sugar As the cycle continues,  12 3-carbon molecules are created These 3-carbon molecules obtain energy from ATP and NADPH to become high energy 3-carbon molecules.

Light Independent Reactions Two of the 12 3-carbon molecules are removed from the cycle Used to make  sugars, lipids, amino acids, and other materials needed for plant metabolism and growth Rest of the 3-carbon molecules combine to make  6 5-carbon molecules

Factors that Affect Photosynthesis Presence of water  Lack of water slows down photosynthesis Plants also have evolved ways to help prevent water loss (waxy covering on leaves) Temperature  Enzymes function best at 0-35 degrees Celsius Intensity of Light  Increasing light intensity increases the rate of photosynthesis There is a certain amount of light intensity where the amount of photosynthesis within a plant does not change

Click the image to play the video segment. Calvin Cycle Click the image to play the video segment. Video 5

Figure 8-11 Calvin Cycle Section 8-3 CO2 Enters the Cycle Energy Input ChloropIast 5-Carbon Molecules Regenerated 6-Carbon Sugar Produced Sugars and other compounds