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Chapter 8 Photosynthesis and Cellular Respiration Section 8.1 Energy and Life • Daily Question: What do you think of when you hear the word “energy”? • All living organisms must be able to obtain energy from the environment in which they live. • The law of conservation of energy states that energy can neither be created nor destroyed. Chemical Energy and ATP • The principal chemical compound that cells use to store and release energy is called ATP - adenosine triphosphate. • ATP is a quick energy source for any cell’s organelle that needs it. • ATP is made of an adenosine molecule, a ribose (sugar), and three phosphate groups. • Reminder- the three phosphate groups have the same charge and particles of the same charge repel each other (opposites attract). ATP Charged phosphate groups Adenine Ribose Storing Energy In ATP • ATP stores energy in the third phosphate group. • ATP is like a fully charged battery storing energy until needed. Third phosphate group Releasing Energy From ATP • The energy of ATP becomes available to a cell when the bonds between the 2nd and 3rd phosphate groups are broken. • Loss of the third phosphate group results in ADP (adenosine diphosphate) and the release of stored energy. ATP – ADP Cycle • ADP can form ATP again by bonding with another phosphate group. • This cycle allows the cell to make more ATP when phosphates are available, instead of having to store enough of ATP; which is very difficult. ATP – ADP Cycle Uses of Cell Energy • ATP fuels cellular activities which drives the organism and maintains homeostasis. • Ex. Active Transport, movement of organelles throughout the cell, synthesis of proteins and nucleic acids • All organisms will get their energy either directly or indirectly from the sun. (**remember food = energy) • Organisms that can make their own food are called autotrophs/producers (green plants). • Organisms that rely on other organisms for food are called heterotrophs/consumers (animals). Autotrophs • Make their own food Heterotrophs • Cannot make their own food Section 8.2 & 8.3 Photosynthesis • Daily Question: How does ATP differ from ADP? Photosynthesis • Using energy from sunlight, plants take light energy and convert it into chemical energy in the form of carbohydrates. Because light is a form of energy… • Anything that absorbs light also absorbs the energy from that light. • When chlorophyll in the plant absorbs light, much of the energy is transferred to electrons in the chlorophyll molecule, raising the energy level of these electrons. • These high-energy electrons make photosynthesis work. Photosynthesis Definition • The process in which plants use the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates and oxygen as a waste product. • In other words – the sun’s energy is converted into carbohydrates. Photosynthesis Photosynthesis • General equation for photosynthesis: 6CO2 + 6H2O -> C6H12O6 +6O2 Scientists describe the reactions of photosynthesis in two parts. 1. Light dependent reactions 2. Light Independent reactions Light Dependent Reactions • Converts light energy from the sun into chemical energy in the form of ATP and NADPH. • Occurs in the thylakoid discs of the chloroplast in the plant cells. Structure of the Chloroplast Structure of the Chloroplast • Remember – the chloroplasts in the plant cells are plastids that store the pigment Chlorophyll. • The chlorophyll in the grana of the thylakoid discs absorbs light energy in the blue-violet and red spectrum of visible light. (they reflect green that is why plants appear green) Absorption of Light by Chlorophyll a and Chlorophyll b Chlorophyll b Chlorophyll a V B GYO R Photolysis • Reaction taking place in the thylakoid membranes where two molecules of water are split to form oxygen, hydrogen ions, and electrons. – The oxygen is released into the air and supplies the oxygen we breathe. – The electrons are returned to the chlorophyll replenishing energy. – The hydrogens are pumped into the thylakoid where they accumulate, form a concentration gradient, and then diffuse out of the thylakoid where they are coupled with ATP in a process called chemiosmosis. The Light – Independent Reactions or Calvin Cycle • The ATP and NADPH formed by the lightdependent reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes. • The Calvin cycle uses CO2, and the ATP and NADPH from light – dependent reactions to produce high energy sugars. • This cycle does not require light. • Calvin Cycle takes place in the Stroma of chloroplast. Structure of the Chloroplast • The Calvin cycle occurs in a series of reactions or cyles. Basically: – Carbon fixation – CO2 carbon is “fixed” into a six – carbon sugar. – This sugar is broken down into two 3 Carbon sugars called phosphoglyceraldehyde or PGAL. – After three cycles the sixth PGAL is made available to make sugars, complex carbohydrates, or other organic compounds. Factors Affecting Photosynthesis Many factors influence the rate of photosynthesis. 1. Temperature – the enzymes that drive photosynthesis work best between 0 and 35 degrees Celsius. (32-95 Fahrenheit) Photosynthesis will not occur if it is too cold or too hot. 2. Light Intensity – high light intensity increases the rate of photosynthesis until saturation occurs. 3. Availability of Water – a shortage of water will stop or slow photosynthesis. Draw a diagram of photosynthesis CO2 Oxygen Glucose Sunlight Water A plant Arrows representing what is going in and out. Section 8.3 Cellular Respiration • Daily Question: What is the goal of photosynthesis? Has that been accomplished in the light reaction phase? Where will it be accomplished? Food • Food provides living things with the chemical building blocks they need to grow and reproduce. • Food serves as a source of raw materials used to synthesize new molecules. • Food serves as a source of energy. Cellular Respiration • The process in which mitochondria break down food molecules to produce ATP. • There are two stages of cellular respiration: Glycolysis and Krebs Cycle. • Glycolysis is anaerobic – no oxygen is required. • Krebs Cycle is aerobic – oxygen is required. The equation for cellular respiration is… O2 + C6H12O6 Oxygen Glucose CO2 + H2O + ATP Carbon dioxide Water Energy Glycolysis 2 Pyruvic acid Glucose • The process in which one molecule of glucose is broken in half producing two molecules of pyruvic acid. Energy yield from glycolysis is small. • Doesn’t require oxygen. • Occurs in the cytoplasm. • 2 molecules of ATP are used up to get glycolysis going. • 4 molecules of ATP are produced at the end of glycolysis. • Net gain of 2 ATP molecules. One of the reactions of glycolysis removes 4 high energy electrons and passes them to a carrier called NAD+ which then becomes NADH. NADH holds the electrons until they can be transferred to other molecules. Chemical Pathways Glucose Glycolysis Krebs cycle Fermentation (without oxygen) Electron transport Alcohol or lactic acid The Krebs Cycle • At the end of glycolysis, about 90% of the chemical energy that was available in glucose is still unused, locked in high energy electrons of pyruvic acid. • To export the rest of that energy, the cell turns to the worlds most powerful electron acceptor… Oxygen. Kreb’s Cycle (Citric Acid Cycle) • Occurs in the mitochondria. • Requires oxygen. • Pyruvic acid from Glycolysis enters the mitochondria and is converted to Acetyl CoA. The Kreb’s cycle breaks down this Acetyl CoA into CO2 and ATP. • Produces a net of 2 ATP. • The carbon dioxide produced diffuses out of the mitochondria, out of the cell and into the bloodstream where it is carried to the lungs and diffuses into the air that we exhale. Glucose Glycolysis Krebs cycle Fermentation (without oxygen) Electron transport Alcohol or lactic acid Fermentation • Releases energy from food in the absence of oxygen (anaerobic). • Occurs when a cell can’t get the oxygen that it needs to carry out aerobic respiration. • Less EFFECTIVE, doesn’t make as much ATP. • Waste products are left behind. • Occurs in the cytoplasm. • During fermentation, cells convert NADH to NAD+ by passing high energy electrons back to pyruvic acid. • Changes NADH back to NAD+. • Allows glycolysis to keep producing ATP. There are 2 main types of fermentation 1. Alcoholic Fermentation 2. Lactic Acid Fermentation Alcoholic Fermentation • Carried out by yeast Pyruvic Acid + NADH alcohol + CO2 NAD+ Fermentation Yeast Lactic Acid Fermentation • Regenerates NAD+ so that glycolysis can continue. Pyruvic Acid + NADH Glucose lactic acid + NAD+ Pyruvic acid Lactic Acid Fermentation • Lactic acid is produced during rapid exercise when the body is low on Oxygen (O2) • You quickly run out of Oxygen (O2) • The buildup of lactic acid causes painful burning sensation (This is why you feel sore). Lactic acid makes you sore • Your body creates an oxygen debt • You must repay that debt with heavy breathing after the exercise Good Lactic Acid • Unicellular organisms that produce lactic acid during fermentation are used to make • Cheese • Yogurt • Buttermilk • Sour cream • Pickles • Sauerkraut • Kimchi Energy and Exercise Quick Energy • For short, quick bursts of energy, the body uses ATP already in muscles as well as ATP made by lactic acid fermentation. Long – Term Energy • For exercise longer than 90 seconds, cellular respiration is the only way to continue generating a supply of energy. The whole process is divided into 2 parts: • Anaerobic – No Oxygen – Occurs in cytoplasm – Glycolysis is an anaerobic process – Glucose is broken into pyruvic acid and ATP • Aerobic – Oxygen – Occurs in mitochondria – Divided into 2 stages: • Kreb cycle (citric acid cycle) • Electron Transport Chain Comparing Photosynthesis and Cellular Respiration • They are almost the opposite processes. Photosynthesis Cellular Respiration Food synthesized Food broken down Energy from sun stored in glucose Energy of glucose released Carbon dioxide taken in Carbon dioxide given off Oxygen given off Oxygen taken in Produces sugars from PGAL Produces CO2 and H2O Requires light Does not require light Occurs only in presence of chlorophyll Occurs in all living cells • Photosynthesis • Cellular Respiration Function Energy capture Energy release Location Chloroplast Mitochondria Reactants CO2 and H2O C6H12O6 and O2 Products C6H12O6 and O2 CO2 and H2O Equation 6CO2 + 6H2O C6H12O6 + 6O2 6O2 + C6H12O6 6CO2 + 6 H2O