2Obtaining EnergyThe sun is the direct or indirect source of energy for most living things.Autotrophs —organisms that can make their own foodHeterotrophs —organisms that can not make food. They obtain energy from eating food.
3PhotosynthesisPhotosynthesis is the process used by autotrophs to convert light energy from sunlight into chemical energy in the form of organic compounds.Involves a complex series of chemical reactions known as a biochemical pathway.Product of one reaction is consumed in the next reaction
4Overview Photosynthesis is often summarized in the following equation: 6CO H2O C6H12O O2The Reactants are carbon dioxide and waterThe Products are glucose and oxygenLight energy
5The Stages of Photosynthesis There are two stages to the processLight Reactions —light energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPHDark Reactions (Calvin Cycle)—organic compounds are formed using CO2 and the chemical energy stored in ATP and NADPH
6The Light Reactions Require light to happen Take place in the chloroplastsChloroplasts contain pigments that absorb sunlight.Pigment —a compound that absorbs light
7The Structure of a Chloroplast Surrounded by an outer and inner membraneThylakoids —membrane system arranged as flattened sacs. (from the Greek meaning “pocket”)Grana (pl.) Granum (singular)—stacks of thylakoid membrane sacsStroma —solution that surrounds the grana
8Thylakoids contain the pigments known as Chlorophylls . Chlorophylls —absorb colors other than green. Therefore, green is reflected and is visible.Two types:Chlorophyll a and Chlorophyll bChlorophyll a —directly involved in the light reactionsChlorophyll b —accessory pigment that assists in photosynthesisCarotenoids —accessory pigments responsible for fall colors and also assist in photosynthesis
9Converting Light Energy to Chemical Energy Chlorophylls and carotenoids are grouped in clusters embedded in proteins in the thylakoid membrane.These clusters are called photosystemsTwo photosystems exist, each with its own job to do:Photosystem I and Photosystem IIPlants have both photosystems. Prokaryotic autotrophs only have photosystem II. It is only numbered as II because it was the second one discovered. However, it probably evolved 1st.
11The Calvin Cycle Named for Melvin Calvin Most common pathway for carbon fixationCarbon fixation —changing CO2 into organic compounds (carbohydrates)It is the second set of reactions in photosynthesis and does not require light.It uses the energy that was stored in ATP and NADPH during the light reactions to produce organic compounds in the form of sugars.The Calvin Cycle occurs in the stroma of the chloroplasts and requires CO2
12The Calvin Cycle 3 ADP 3 CO2 3 ATP 3 RuBP 6 PGA 6 ATP 6 ADP 5 G3P glucose6 G3P1 G3P6 NADPHstarch6NADP+6 P
13Plant species that fix carbon using the Calvin Cycle only are known as C3 plants because of the three-carbon compound that is initially formed in the process. They include most plants.
14Alternative PathwaysPlants living in hot, dry climates have trouble using the Calvin Cycle to fix carbon.This is because they must partially close their stomata to conserve water.This allows less CO₂ to enter and an excess of O₂ to build up, both of which inhibit the Calvin CycleTwo alternate pathways have evolved for these plants—both allow the plants to conserve water.They are the C4 pathway and the CAM pathway
15The C4 Pathway C4 plants include: corn, sugar cane and crab grass Cells called mesophyll cells in C4 plants use an enzyme to fix CO2 into a four carbon compoundThis compound travels to other cells where CO2 can be released and enter the Calvin CycleThese plants lose about ½ as much water as C3 plants when producing the same amount of carbohydrates.
16The CAM PathwayCAM plants include: cactuses, pineapples, and jade plants.These plants open their stomata at night and close them during the day (opposite of most plants).CO2 absorbed at night can enter the Calvin Cycle during the day, allowing the stomata to stay closed and conserve water.These plants lose less water than any other plants
18Cellular RespirationCellular Respiration —the process by which cells get energy from carbohydrates; oxygen combines with glucose to form water and carbon dioxideC6H12O O CO H2O energy (ATP)
19The equation is a simple summary of a very complex process. The overall purpose is to convert food into energy by breaking down organic fuel molecules.When oxygen is present during this process it is called aerobic respiration ( which is the most efficient).If no oxygen is present it is called anaerobic respiration (which is much less efficient).Both types (aerobic and anaerobic) start with a process called glycolysis.
20Glycolysis Glycolysis —first stage of cellular respiration. Glycolysis means “glucose splitting”Occurs in the cytosolNo oxygen is neededGlucose molecules are broken down into two carbon molecules of pyruvic acidPyruvic acid is then used in the Krebs Cycle (which is the second stage of aerobic respiration)Specific enzymes are needed2 molecules of ATP are produced2 molecules of NADH (an electron carrier molecule) are produced
22Summary of Glycolysis Basically: One glucose (6C) is broken into two molecules of pyruvic acid (3C)If oxygen is available, the pyruvic acid will move into the mitochondria and aerobic respiration will begin.4 ATP molecules are produced. Two are used to break apart the next glucose molecule and keep glycolysis going.This leaves a net yield of 2 ATP molecules for use by the cell.Two NAD+ are converted into 2 NADH and 2H+. These go to Electron Transport.
23Efficiency of Glycolysis Measured in kilocalories (kcal)One kilocalorie equals 1,000 calories (cal)Complete oxidation of glucose releases 686 kcalProduction of ATP absorbs 7 kcal2ATP are produced from every glucose molecule broken down by glycolysisThe efficiency is therefore calculated by the following formula:Efficiency of Energy required to make ATPglycolysis = Energy released by oxidation of glucose= x 7 kcal x % = 2%686 kcal
24Aerobic RespirationIn most cells, the pyruvic acid produced in glycolysis enters the pathway of aerobic respiration.This pathway produces nearly 20 times as much ATP as is produced by glycolysis alone and is therefore the most efficient.Oxygen must be available for this to happen.There are two major stages: The Krebs Cycle and the Electron Transport Chain
25Intermediate StepAerobic Respiration takes place in the mitochondria of the cell.Before the Krebs Cycle can begin, each of the two pyruvic acid molecules must be converted.The pyruvic acid enters the mitochondrial matrix (space inside the inner membrane of the mitochondria)It reacts with a molecule called coenzyme A to form Acetyl Coenzyme A (acetyl CoA)
26The Krebs CycleThe Krebs Cycle (named for Hans Krebs) is a biochemical pathway that breaks down acetyl CoA.Two turns of the Krebs Cycle produce:2 ATP molecules4 CO2 molecules6 NADH molecule2 FADH2 molecules
28Review of the Gylcolysis and the Krebs Cycle In Glycolysis, one glucose molecule produces two pyruvic acid molecules, which can then form two molecules of Acetyl CoA.Both of the Acetyl CoA molecules enter the Krebs Cycle creating two turns of the cycle.This produces 6 NADH, 2 FADH2, 2 ATP and 4 CO2 molecules (waste product that diffuses out of the cell).The 6 NADH and 2 FADH2 molecules drive the next stage of aerobic respiration—the Electron Transport Chain.
29Electron Transport Chain The Electron Transport Chain, linked with chemiosmosis makes up the second stage of aerobic respiration.Electrons are transferred from one molecule to another by several electron carrying molecules located in the membrane of the mitochondria.All steps occur in the cristae (inner membrane)
31Efficiency of Cellular Respiration Through Aerobic Cellular Respiration, a maximum of 38 ATP molecules can be produced from one glucose molecule.2 from Glycolysis2 from Krebs cyclefrom the Electron Transport Chain
32To see how we get 38, follow along…. 2 ATPs directly from glycolysis 2ATPs directly from Krebs cycleEach NADH can generate 3ATPs from electron transport (30 total)Each FADH2 can generate 2ATPs from electron transport (4 total)
33The actual number of ATP molecules generated through Aerobic Respiration varies from cell to cell. (36-38)Most eukaryotic cells produce only 36 molecules per glucose molecule because the active transport of NADH through a cell membrane uses up some ATP.When 38 ATP molecules are generated the efficiency is calculated as follows:Efficiency of Energy required to make ATPCellular Respiration = Energy released by oxidation of glucose= x kcal x 100% = 39%686 kcalThis is 20 times more efficient than glycolysis alone !!
34Anaerobic Respiration If no oxygen is present, the Krebs Cycle and Electron Transport Chain are not utilized.The cell must have a way to keep glycolysis going.Glycolysis would stop without a cellular process that recycles NAD+ and NADH.Without such a process, glycolysis would quickly use up all the NAD+ in the cell.Glycolysis and ATP production would stop and the cell would die.Fermentation to the rescue
35FermentationFermentation is the chemical pathway that recycles NAD+ in the absence of oxygen. It keeps glycolysis going. No additional ATP is made. Therefore, you still have the 2% efficiency rate for energy release.Two types of fermentation:Lactic Acid FermentationAlcoholic Fermentation
36Lactic Acid Fermentation Pyruvic acid is converted by a specific enzyme into lactic acid.Two hydrogen atoms from NADH and H+ are transferred to pyruvic acid to form the lactic acid molecule.NADH is oxidized to NAD+ and reused to keep glycolysis going.
37Occurs mostly in muscle cells during hard exercise. Lactic acid fermentation occurs in foods such as yogurt and cheese as well as certain animal cells.Occurs mostly in muscle cells during hard exercise.Muscle cells use up oxygen too fast and switch from aerobic to anaerobic respiration.Lactic acid builds up reducing the cells ability to contract. This causes fatigue, pain and cramps.Slow down!!! Allow the lacticacid time to diffuse back into theblood stream and to the liverwhere it is converted back intopyruvic acid.
38Alcoholic Fermentation Converts pyruvic acid to carbon dioxide and ethyl alcohol.NAD+ is recycled in the same manner as before.
39Bakers use the alcoholic fermentation of yeast to make bread. CO2 is produced and trapped in the dough, causing it to rise.When the dough is baked, yeast cells die and the alcohol evaporates.You can’t get drunk from eatingbread !!!
40COMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATION Click to revealCOMPARING PHOTOSYNTHESIS AND CELLULAR RESPIRATIONPHOTOSYNTHESISRESPIRATIONFUNCTION Production of Glucose Oxidation of GlucoseLOCATION chloroplasts mitochondriaREACTANTS 6CO2 + 6H2O C6H12O O2PRODUCTS C6H12O O2 6CO H2OEQUATION light6CO2 + 6H2O C6H12O O2 C6H12O O CO2 + 6H2O +ATP