Questions/ Main Ideas 8 1 Energy and Life Autotrophs and Heterotrophs Chemical Energy and ATP Energy is the ability to do work. Nearly every activity in modern society depends on one kind of energy or another. Energy is needed to play, work and study. However, there are times when that need is less obvious. For example, when you are sleeping, your cells are busy using energy to build new proteins and amino acids. Plants and some other types of organisms are able to use light energy from the sun to produce food. Organisms such as plants, which make their own food, are called autotrophs. Other organisms, such as animals, cannot use the sun's energy directly. These organisms, known as heterotrophs obtain energy from the foods they consume. For example, impalas eat grass. Grass is an autotroph, where as impalas are heterotrophs. Living things also use chemical fuels. The chemical compound that cells use to store and release energy is adenosine triphosphate (ATP). ATP consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups. The three phosphate groups are the key to ATP's ability to store and release energy. ATP is like a fully charged battery, ready to power the machinery of the cell. Storing Energy Releasing Energy Adenosine diphosphate (ADP) is a compound that looks almost like ATP, except that it has two phosphate groups instead of three. How is the energy that is stored in ATP released? By breaking the chemical bond between the second and third phosphates, ENERGY is released. Because a cell can subtract that third phosphate group, it can release energy as needed. ATP has enough energy to power a variety of cellular activities, including active transport across cell membranes, protein synthesis, and muscle contraction.
8-2 Photosynthesis The key cellular process identified with energy production is photosynthesis. In the process of photosynthesis, plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates sugars and starches and oxygen, a waste product. Van Helmont's Experiment 1643 Wanted to find out if plants grew by taking material out of soil. After careful measurements of plant s water intake and mass increase, van Helmont concludes that trees gain most of their mass from water. Priestley's Experiment 1771 Joseph Priestley Using a bell jar, a candle, and a plant, Priestley finds that plants release a substance that keeps a candle burning. Oxygen Jan Ingenhousz 1779 Finds that aquatic plants produce oxygen bubbles in the light but not in the dark. Plants need sunlight to produce oxygen. The Photosynthesis Equation Because photosynthesis usually produces 6-carbon sugars (C 6 H 12 O 6 ) as the final product, the overall equation for photosynthesis can be shown as follows: Light and Pigments You can see from the equation that water and carbon dioxide are required for photosynthesis. In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts. Energy from the sun travels to Earth in the form of light. Sunlight, which your eyes perceive as white light, is actually a mixture of different wavelengths of light. Many of these wavelengths are visible to your eyes and make up what is
8-3 The Reaction of Photosynthesis known as the visible spectrum. Your eyes see the different wavelengths of the visible spectrum as different colors. Plants gather the sun's energy with light-absorbing molecules called pigments. The plants' principal pigment is chlorophyll. Photosynthesis takes place inside the chloroplast. Chloroplast contain saclike photosynthetic membranes called thylakoids. Thylakoids are arranged in stacks called a granum (grana; plural). Stroma: the space outside the thylakoids TWO REACTIONS The reactions of photosynthesis occur in two parts: Light Dependent Reaction 2) Light Independent Reaction also known as the Calvin Cycle THE LIGHT DEPENDENT REACTION This reaction takes place within the thylakoid membranes. This reaction requires light. The reaction uses light to produce oxygen gas and convert ADP and NAHDP+ into ATP and NAHDPH. NAHDP+ = PARTIALLY CHARGED BATTERY NAHDPH = FULLY CHARGED BATTERY. It carries charged electrons. CALVIN CYCLE Light - independent reaction takes place in the stroma of chloroplast. No light required. ATP & NADPH are used to produce high energy sugars. The Calvin Cycle works to remove carbon from the atmosphere and turning out energy rich sugars.
Overview of Photosynthesis STAGE 1 - THE LIGHT DEPENDENT REACTIONS. Energy is captured from Sunlight. Water is Split into Hydrogen Ions, Electrons, and Oxygen (O 2 ). The O 2 Diffuses out of the Chloroplasts (Byproduct). STAGE 2 The Light Energy is Converted to Chemical Energy, which is Temporarily Stored in ATP and NADPH. STAGE 3 - THE CALVIN CYCLE. The Chemical Energy Stored in ATP and NADPH powers the formation of Organic Compounds (Sugars), Using Carbon Dioxide, CO 2. Factors Affecting Photosynthesis Many factors affect the rate at which photosynthesis occurs. Because water is one of the raw materials of photosynthesis, a shortage of water can slow or even stop photosynthesis. Temperature is also a factor. o Photosynthesis depends on enzymes that function best between 0 C and 35 C. o At very low temperatures, photosynthesis may stop entirely. CELLULAR RESPIRATION Chemical Energy and Food Cells gradually release the energy from glucose and other food compounds. How much energy is actually present in food? One gram of the sugar glucose (C 6 H 12 O 6 ), when burned in the presence of oxygen, releases 3811 calories of heat energy. A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. Overview of Cellular Respiration Glycolysis, the Krebs cycle, and the electron transport chain make up a process called cellular respiration. Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
Glycolysis Glycolysis is the process in which one molecule of glucose is broken in half. This gives the cell a net gain of 2 ATP molecules. Glycolysis occurs in the cell s cytoplasm. 9-2 Krebs Cycle and Electron Transport At the end of glycolysis, about 90 percent of the chemical energy that was available in glucose is still unused. Oxygen is required for the final steps of cellular respiration. Because the pathways of cellular respiration require oxygen, they are said to be aerobic. The Krebs Cycle In the presence of oxygen, the second stage of cellular respiration, the Krebs cycle. The Krebs cycle is named after Hans Krebs, the British biochemist who demonstrated its existence in 1937. In eukaryotes, the Krebs cycle takes place in the mitochondrion The Electron Transport Chain is the third stage of cellular respiration. The electron transport chain uses the high energy electrons from the Krebs cycle to convert ADP to ATP. ATP Synthase is the enzyme responsible for the conversion of ADP to ATP. Fermentation When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called fermentation. Fermentation releases energy from food molecules by producing ATP in the absence of oxygen. Because fermentation does not require oxygen, it is said to be anaerobic. The term anaerobic means without oxygen. The two main types of fermentation are alcoholic fermentation and lactic acid fermentation. Alcoholic Fermentation Yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes. Alcoholic fermentation causes bread dough to rise. When yeast in the dough runs out of oxygen, it begins to ferment, giving off bubbles of carbon dioxide that form the air spaces you see in a slice of
bread. The small amount of alcohol produced in the dough evaporates when the bread is baked. Lactic Acid Fermentation Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues. Without enough oxygen, the body is not able to produce all of the ATP that is required. When you exercise vigorously by running, swimming, or riding a bicycle as fast as you can, the large muscles of your arms and legs quickly run out of oxygen. Your muscle cells rapidly begin to produce ATP by lactic acid fermentation. The buildup of lactic acid causes a painful, burning sensation. The Totals Recall that glycolysis produces just 2 ATP molecules per glucose. Krebs cycle and electron transport enable the cell to produce 34 more ATP molecules. Total is 36 ATP molecules Comparing Photosynthesis and Cellular Respiration