G9 Summary 11 (10.1+10.2+10.3) PDF - Cambridge Biology

Academic Year 2024-2025/ First Semester Student’s Name: Subject: Biology Summary sheet no. 11 Chapter 10 Cellular Respiration Grade: 9 (A, B) Lessons (1, 2, & 3) Date: /11/2024 Teacher: Marah Ham...

Academic Year 2024-2025/ First Semester Student’s Name: Subject: Biology Summary sheet no. 11 Chapter 10 Cellular Respiration Grade: 9 (A, B) Lessons (1, 2, & 3) Date: /11/2024 Teacher: Marah Hammouda Lesson 10.1 Cellular Respiration: An Overview A calorie: is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. The Calorie (capital C) that is used on food labels is actually a kilocalorie, or 1000 calories. In general, carbohydrates and proteins contain approximately 4000 calories (4 Calories) of energy per gram, whereas fats contain approximately 9000 calories (9 Calories) per gram. If oxygen is available, organisms can obtain energy from food by cellular respiration. Cellular respiration: is a process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. Stages of cellular respiration: Cellular respiration captures the energy from food in three main stages: 1. Glycolysis 2. The Krebs cycle 3. Electron transport chain 1 Pathways of cellular respiration that require oxygen are aerobic ("in air"). The Krebs cycle and the electron transport chain are both aerobic processes. Glycolysis, however, does not directly require oxygen, nor does it rely on an oxygen-requiring process to run. Glycolysis is therefore anaerobic ("without air"). Glycolysis occurs in the cytoplasm. In contrast, the Krebs cycle and electron transport chain, which generate the majority of ATP during cellular respiration, take place inside the mitochondria. If oxygen is not present, another anaerobic pathway, known as fermentation, makes it possible for the cell to keep glycolysis running, generating ATP to power cellular activity. Comparing photosynthesis and cellular respiration: If nearly all organisms break down food by the process of cellular respiration, why doesn't Earth run out of oxygen? As it happens, cellular respiration is balanced by another process: photosynthesis. Photosynthesis removes carbon dioxide from the atmosphere, and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses that oxygen to release energy from food. 2  Lesson 10.2 The Process of Cellular Respiration 1) Glycolysis: The first set of reactions in cellular respiration is known as glycolysis, which literally means "sugar-breaking." During glycolysis, 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of the 3-carbon compound pyruvic acid. Like NADP+ in photosynthesis, each NAD+ molecule accepts a pair of high-energy electrons and a hydrogen ion. The advantages of glycolysis: Although the energy yield from glycolysis is small, the process is so fast that cells can produce thousands of ATP molecules in just a few milliseconds. Besides speed, another advantage of glycolysis is that the process itself does not require oxygen. This means that glycolysis can quickly supply chemical energy to cells when oxygen is not available. 3  2) The Krebs Cycle: In the presence of oxygen, the pyruvic acid produced in glycolysis passes to the second stage of cellular respiration, the Krebs cycle. During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions. Because citric acid is the first compound formed in this series of reactions, the Krebs cycle is also known as the citric acid cycle. The Krebs cycle begins when pyruvic acid produced by glycolysis passes through the two membranes of the mitochondrion and into the matrix. The matrix is the innermost compartment of the mitochondrion and the site of the Krebs cycle reactions. Once inside the matrix, 1 carbon atom from pyruvic acid is split off to produce carbon dioxide, which is eventually released into the air. The other 2 carbon atoms from pyruvic acid rearrange to form acetic acid, which is joined to a compound called coenzyme A. The resulting molecule is called acetyl-CoA. As the Krebs cycle begins, acetyl-CoA hands off that 2-carbon acetyl group to a 4-carbon molecule already present in the cycle, producing a 6-carbon molecule called citric acid. For each turn of the cycle, a molecule of ADP is converted to a molecule of ATP. Each starting molecule of glucose results in two complete turns of the Krebs cycle and, therefore, 2 ATP molecules. What happens to these Krebs cycle products: carbon dioxide, ATP, and electron carriers? Carbon dioxide diffuses out of the mitochondria, out of the cell, and into the bloodstream, and then is exhaled. The ATP molecules are very useful, becoming immediately available to power cellular activities. Regarding the carrier molecules like NADH, in the presence of oxygen, the electrons they hold are used to generate huge amounts of ATP. -Check figure 10-4 page 317 4  3) Electron transport chain The electron transport chain uses the high-energy electrons from glycolysis and the Krebs cycle to synthesize ATP from ADP. NADH and FADH2 pass their high-energy electrons to the electron transport chain. In eukaryotes, the electron transport chain is composed of a series of electron carriers located in the inner membrane of the mitochondrion. In prokaryotes, the same chain is in the cell membrane. High-energy electrons are passed from one carrier to the next. At the end of the electron transport chain is an enzyme that combines these electrons with hydrogen ions and oxygen to form water. Oxygen is the final electron acceptor of the chain, which is why electron transport is aerobic, or oxygen-requiring. Oxygen accepts low energy electrons at the end of the chain, and without it, the electron transport chain cannot function. Every time 2 high-energy electrons pass down the electron transport chain, their energy is used to transport hydrogen ions (H+) across the membrane. During electron transport, H+ ions build up in the intermembrane space, making it positively charged relative to the matrix. As in photosynthesis, the cell uses a process known as chemiosmosis to produce ATP. The inner mitochondrial membrane contains enzymes known as ATP synthases. The charge difference across the membrane forces H+ ions through channels in these enzymes, actually causing the ATP synthases to spin. With each rotation, the enzyme grabs an ADP molecule and attaches a phosphate group, producing ATP. Each pair of high-energy electrons that moves down the full length of the electron transport chain provides enough energy to produce 3 molecules of ATP that can be used to power cellular activities. -Check figure 10-5 page 319 The totals: Together, glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose. 5  Lesson 10.3 Fermentation What happens when you hold your breath and dive underwater like a dolphin, or use up oxygen so quickly that you cannot replace it fast enough? Do your cells simply stop working? When oxygen is not present, glycolysis is kept going by a pathway that makes it possible to continue to produce ATP without oxygen. The combined process of this pathway and glycolysis is called fermentation. In the absence of oxygen, fermentation releases energy from food molecules by producing ATP. During fermentation, cells convert NADH to NAD+ by passing high-energy electrons back to pyruvic acid, allowing glycolysis to keep going and to produce a steady supply of ATP. Fermentation is an anaerobic process that occurs in the cytoplasm of cells. Sometimes, glycolysis and fermentation are together referred to as anaerobic respiration. There are two different forms Alcoholic fermentation Lactic acid fermentation Alcoholic Fermentation: is carried out by yeast, producing ethyl alcohol and carbon dioxide. Alcoholic fermentation is used to produce beer, wine, and other alcoholic beverages. It is also the process that causes bread dough to rise. Lactic Acid Fermentation: Other organisms carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid. Unlike alcoholic fermentation, lactic acid fermentation does not give off carbon dioxide. However, like alcoholic fermentation, lactic acid fermentation also regenerates NAD+ so that glycolysis can continue. 6 Certain bacteria that produce lactic acid as a waste product during fermentation are important to the food industry. Fermentation by these bacteria help to produce cheese, yogurt, buttermilk, and sour cream. Humans are also lactic acid fermenters. How did swimmers (in figure 10-9 page 324) manage to swim such a fast race without breathing? The solution is lactic acid fermentation. The fermentation pathway doesn't involve the Krebs cycle, the electron transport chain, or oxygen. As a result, it works much more rapidly, supplying all the ATP a well-trained athlete needs to support maximum effort for 30 to 40 seconds. This process, of course, produces lactic acid as a byproduct, which quickly builds up in the muscles and bloodstream of the athletes. For exercise longer than about 90 seconds, cellular respiration is the only way to continue generating a supply of ATP. Your body stores energy in muscle cells and other tissues in the form of the carbohydrate glycogen. These stores of glycogen are usually enough to last for 15 or 20 minutes of activity. After that, your body begins to break down other stored molecules, including fats, for energy. This is one reason that aerobic forms of exercise, such as running, dancing, and swimming, are so beneficial for weight control. 7