Photosynthesis and Cellular Respiration Chapter 9

Trapping the Sun’s Energy The process by which plants capture energy from the sun to build carbohydrates is called photosynthesis –Solar energy converts water and carbon dioxide into chemical energy stored in simple sugars The simple sugar that photosynthesis produces is glucose which the plant uses to store energy. The equation that represents photosynthesis is: 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Solar energy

Phases of Photosynthesis Photosynthesis requires energy from the sun, but the sun is not available 24 hours a day. Photosynthesis must occur in two phases –Light-dependent Reactions (light reactions) Convert light energy into chemical energy (ATP and NADPH) –Light-independent Reactions (dark reactions) Uses the ATP and NADPH from the light-dependent reactions to build glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Solar energy

The Role of Chloroplasts and Pigments Photosynthesis takes place in the chloroplasts Light-dependent reactions take place in the membranes of the thylakoid disks Light-independent reactions take place in the stroma

The Role of Chloroplasts and Pigments The thylakoid membranes contain the pigments that can absorb certain wavelengths of sunlight. The most common pigment in the chloroplasts is chlorophyll. Chlorophyll a and b absorb most wavelengths of light except for green. Green is reflected making the plants appear green. In the fall, plants reabsorb chlorophyll leaving other pigments that reflect other wavelengths of light – making the leaves appear red, yellow, or orange.

Light-dependent Reactions Sunlight strikes the chlorophyll molecules in the thylakoid membrane. Light energy is transferred to electrons The electrons become highly energized and are passed down an Electron Transport Chain

Light-dependent Reactions The Electron Transport Chain is a series of proteins in the thylakoid membrane As the electrons are transferred from one protein to another, some energy is released which –helps join ADP and Phosphate to form ATP –Pump hydrogen ions into the center of the thylakoid disk to join H+ and NADP+ forming NADPH –ATP and NADPH will be used during the light-independent reactions

Light-dependent Reactions The electrons excited by the light energy that passed down the electron transport chain and left with NADPH need to be replaced so the reaction can happen again. To replace those electrons, a water molecule is split (photolysis), sending electrons back to the chlorophyll and releasing Oxygen and Hydrogen ions into the atmosphere – this supplies the oxygen that we breath Photolysis 

Light-dependent Reactions Solar Energy absorbed by chloroplasts NADPH released Oxygen released ATP Released Products of Light Reactions (ATP and NADPH) fuel the dark reactions

Light-independent Reactions The second phase of photosynthesis does not require light and is called the Calvin Cycle. The Calvin Cycle occurs in the stroma of the chloroplast. The Calvin Cycle uses the ATP and NADPH that was built during the light-dependent reactions

The Calvin Cycle Uses Carbon Dioxide from the air Uses ATP and NADPH from light reactions Builds a glucose molecule Uses another ATP to replenish RuBP

Photosynthesis Equation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Carbon Dioxide from the air – Used in the Calvin Cycle during the Dark Reactions Water Split during Photolysis in the Light Reactions Glucose Made in the Calvin Cycle during the Dark Reactions Oxygen Released during Photolysis in the Light Reactions Light Energy chlorophyll Plants can use this glucose molecule for energy during Cellular Respiration. Plants can also convert this glucose molecule into other organic compounds such as proteins and fats/lipids or other carbohydrates like starch and cellulose

3 Factors that Affect Photosynthesis Carbon Dioxide (CO 2 ) –Without CO 2, the plant would not have one of the raw materials needed in the photosynthesis equation –CO 2 is used in the first step of the Calvin Cycle Temperature –The temperature must be in the appropriate range for the plant in order for photosynthesis to properly occur

3 Factors that Affect Photosynthesis Intensity of Light –If the intensity of light is lower, the available energy for photosynthesis is lower. In a greenhouse, if the light source is further away, intensity is lower and less photosynthesis can occur If light is not available at all, the light-dependent reactions cannot occur (nor can they provide the materials used in the light-independent reactions)

Cellular Respiration Cellular Respiration: Process by which mitochondria break down food molecules to produce ATP in plants and animals Nutrients + oxygen  water + ATP + CO 2 Changes organic chemical energy (glucose) into inorganic chemical energy (ATP) There are three stages of Cellular Respiration –Glycolysis Anaerobic – does not require oxygen –Citric Acid Cycle Aerobic – does require oxygen –Electron Transport Chain Aerobic – does require oxygen

Glycolysis Glycolysis: Breaks down glucose into two molecules of pyruvic acid This reaction uses enzymes and takes place in the cytoplasm of the cell Produces –2 pyruvic acid molecules (used in the next step of Cellular Respiration) –2 ATP molecules (energy the cell can use) –2 NADH (electron carrier)

Into the Mitochondria… Before the next step of Cellular Respiration can occur, the pyruvic acid molecules must go into the mitochondria The two aerobic reactions are the Citric Acid Cycle (or Krebs Cycle) and the electron transport chain Pyruvic acid  CO 2 + water + ATP

Citric Acid/Krebs Cycle (see page 210 in your book) CO 2 is released Pyruvate from Glycolysis fuels the cycle CO 2 is released ATP is released NADH and FADH 2 is released

Electron Transport Chain Electron Transport Chain uses the electron carriers (NADH and FADH 2 ) to pass electrons down the protein chain and slowly release energy that is used to form ATP and water molecules

Cellular Respiration Glycolysis Citric Acid Cycle Electron Transport Chain Glucose Pyruvic Acid ATP Pyruvic Acid CO 2 ATP NADH and FADH Oxygen Water

Cellular Respiration Equation C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy Water – released from Electron Transport Chain Oxygen from the atmosphere Used in Electron Transport Chain Carbon Dioxide – waste product of the Citric Acid Cycle ATP released from Glycolysis, Citric Acid Cycle, and Electron Transport Chain Between ATP can be made with this process. This ATP can be used by the cells for cellular metabolism. Glucose made in photosynthesis by plants or consumed by animals Used in Glycolysis

Fermentation When oxygen is not available anaerobic respiration, fermentation, can follow glycolysis in order to continue to produce energy. This is not as efficient as aerobic respiration and produces far fewer ATPs Two types of fermentation: –Lactic acid Fermentation –Alcoholic Fermentation

Lactic acid Fermentation Lactic acid fermentation occurs in muscle cells during strenuous exercise when a lot of energy is required and oxygen is scarce (oxygen debt). Glucose  pyruvic acid  lactic acid + ATP The lactic acid is transferred from the muscle cells to the liver where it will be converted back into pyruvic acid The build up of lactic acid in the muscles is what causes them to be fatigued and sore.

Alcoholic Fermentation Yeast and some bacteria cells are capable of alcoholic fermentation during which glucose is broken down to release CO 2 and ethyl alcohol Glucose  pyruvic acid  alcohol + CO 2 + ATP The bubbles formed by the CO 2 make bread rise The alcohol released turns grape juice into wine

Photosynthesis vs. Cellular Respiration PhotosynthesisCellular Respiration Stores Energy as glucose Releases Energy in glucose Occurs in Living Cells Uses an Electron Transport Chain Occurs in Plant Cells Occurs in Animal Cells Releases Oxygen Releases Carbon Dioxide Creates Energy Neither!