Chapter 10 Test: Cellular Respiration

Glycolysis is an energy-releasing process, but the cell needs to invest a little energy to get started. To keep glycolysis functioning during cellular respiration, two molecules of ATP from the 4 molecules produced are continually being cycled back to the beginning of glycolysis, and as a result glycolysis only yields 2 molecules of ATP.

Alcoholic fermentation, as opposed to lactic acid fermentation, causes bread to rise. The products are ethyl alcohol and carbon dioxide. The carbon dioxide gas gets trapped inside the dough, forming bubbles that cause the bread to rise. The small amount of ethyl alcohol produced dissipates during baking. In the case of sourdough bread, lactic acid fermentation also takes place in the initial stages of feeding the 'starter dough,' and this gives sourdough its sour taste.

There is energy stored in chemical bonds such as the bonds in glucose, and when they are broken, energy is released and made available. Cells break down food molecules gradually, capturing a little bit of chemical energy every step along the way. Cellular respiration, a process of energy conversion that requires the presence of oxygen, releases energy from food.

Cellular respiration is an aerobic process of energy conversion that releases energy from food in the presence of oxygen, so if there is oxygen available, the three stages of cellular respiration - glycolysis, the Krebs cycle, and the electron transport chain - will take place. Lactic acid fermentation only takes place if there is not enough oxygen, since it is anaerobic.

Cells must release the chemical energy in food molecules a little bit at a time, trapping the energy in the form of ATP, or it would mostly be lost to heat and light. Cells break down food molecules gradually, capturing a little bit of chemical energy every step along the way. Also, the inner mitochondrial membrane contains enzymes known as ATP synthases, and these enzymes act as catalysts to make the reaction occur at body temperature.

Cellular respiration is balanced by photosynthesis. The energy flows in photosynthesis and cellular respiration run in opposite directions, and therefore the equations for photosynthesis and cellular respiration are the reverse of each other. The product of cellular respiration (carbon dioxide) is the reactant of photosynthesis. The global balance between photosynthesis and cellular respiration is essential to keep Earth alive and functioning.

Explain how cellular respiration works.

Cellular respiration takes oxygen and glucose and converts it into carbon dioxide, water, and energy.

Identify what happens during glycolysis.

During glycolysis, 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of the 3-carbon compound pyruvic acid.

identify what happens during the Krebs cycle.

During the Krebs cycle, pyruvic acid is broken down into carbon dioxide and citric acid. Citric acid is then broken down into a 4-carbon compound that can then start the cycle over again by combining with acetyl CoA.

For ATP to be made from ADP, an input of energy is required. This energy comes from high-energy electrons. In the mitochondria, hydrogen ions build up in the inter-membrane space, making it positively charged compared to the matrix. At the same time, the other side becomes negatively charged, and this charge difference results in potential energy being stored and available to do work.

Electron transport results in the build-up of a charge difference across the mitochondrial membrane, which is a source of potential energy. The charge difference across the membrane allows hydrogen ions to diffuse through channels in enzymes, causing ATP synthase to spin. With each rotation, the enzyme attaches a phosphate group to an ADP molecule, producing ATP.

Explain how organisms get energy in the absence of oxygen.

In the absence of oxygen, glycolysis is maintained 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.

Lactic acid fermentation takes place in the muscles when the demand for oxygen is too high for the body to meet. The process involves glycolysis only, and produces much less ATP per molecule of glucose. The process also produces lactic acid as an end product.

Lactic acid fermentation takes place in the cytoplasm rather than the mitochondria. Fermentation, which occurs without oxygen, yields much less ATP than the electron transport chain.

Glycolysis nets merely 2 ATP molecules per glucose molecule, whereas the electron transport chain releases 32 ATP molecules. Together, glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose.

Long-distance runners need steady energy over an extended period of time, and the best source for this energy is cellular respiration, not lactic acid fermentation. In trained marathon runners, leg muscle cells have developed more mitochondria - where most of cellular respiration occurs - to allow for greater long-term ATP production.

Identify how organisms get energy.

Organisms get energy from the food they eat.

Explain the relationship between photosynthesis and cellular respiration.

Photosynthesis removes carbon dioxide from the atmosphere, while cellular respiration adds it to the atmosphere. Photosynthesis releases oxygen, while cellular respiration uses it. The global balance between the two processes is essential to maintain Earth as a living planet.

Cellular respiration, an aerobic process, liberates energy from food by converting glucose to ATP. Glucose molecules from food are broken down in the presence of oxygen to form water and carbon dioxide, and the released energy from food is captured in ATP.

Plants use both cellular respiration and photosynthesis. They make food with photosynthesis, then use cellular respiration to transfer the energy in food to ATP.

Glycolysis is an energy-releasing process, but the cell needs to invest some energy to get started. To keep glycolysis functioning during cellular respiration, two molecules of ATP from the 4 ATP molecules produced are continually being cycled back to the beginning of glycolysis.

The Krebs cycle takes place in the matrix, the innermost part of the mitochondria. At the beginning of the Krebs cycle, pyruvic acid produced by glycolysis passes through the two membranes of the mitochondria and into the matrix.

Explain how the electron transport chain uses high-energy electrons from glycolysis and the Krebs cycle.

The electron transport chain uses the high-energy electrons from glycolysis and the Krebs cycle to synthesize ATP from ADP.

A calorie is the amount of energy that it takes to raise the temperature of 1 gram of water by 1 degree Celsius. The number on food labels that tells how much energy is in a serving of food has the unit of Calories, which is a kilocalorie, or 1000 calories.

The energy in food comes from the sun. Photosynthetic organisms obtain energy from the sun and perform photosynthesis. The flow of energy can be traced to consumers, which are organisms that take in food that other organisms make.

In prokaryotes, the electron transport chain is located in the cell membrane. In eukaryotes, the electron transport chain is composed of a series of electron carriers located in the inner membrane of the mitochondria. Prokaryotic cells do not have nuclei.

There are many steps to the Krebs cycle, but because citric acid is the first compound formed in the series of reactions, the Krebs cycle is also known as the citric acid cycle. The Calvin cycle is the light-independent reaction in photosynthesis and does not occur in cellular respiration.

Identify the pathways the body uses to release energy during exercise.

To release energy during exercise, the body uses cellular respiration and lactic acid fermentation.

Calculate how much ATP cellular respiration generates.

When the phases of cellular respiration are complete, the end result is 36 ATP molecules created with each molecule of glucose.