Directions: Answer questions 1-10 on the front side of your reading guide. Be prepared to show your work for credit and discuss your answers with your classmates.
Reading – Cellular Respiration
CP Biology
Cellular Respiration
We all need energy to function and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a process that produces adenosine triphosphate (ATP). ATP is a high energy molecule used by working cells. Cellular respiration occurs in both eukaryotic and prokaryotic cells. It has three main stages: glycolysis, the citric acid cycle, and electron transport. The overall chemical equation for cellular respiration (below) shows what molecules are needed for the process to work as well as what molecules are produced as a result. As you read through the following sections, keep track of these different molecules.
Glucose + Oxygen → Carbon Dioxide + Water + ATP
Glycolysis:
Glycolysis literally means "splitting sugars" and occurs in the cytoplasm of cells. During this stage, glucose, a six carbon sugar, is split into two molecules of a three carbon sugar called pyruvate. In the process, two molecules of ATP and two "high energy" electron carrying molecules of NADH are produced. Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called fermentation.
The Citric Acid Cycle:
The Citric Acid Cycle or Krebs Cycle begins after the two molecules of pyruvate produced in glycolysis enter the mitochondria of the cell. Through a series of intermediate steps, several molecules capable of storing "high energy" electrons are produced. These molecules, known as nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH), capture and carry the "high energy" electrons to the next stage of cellular respiration. Harvesting these electrons is the main purpose of The Citric Acid Cycle. In the end, two ATP molecules are produced and carbon dioxide molecules given off as waste.
Electron Transport:
Electron Transport also requires oxygen to perform its major function of manufacturing large amounts of ATP. The electron transport "chain" is a series of electron carriers located in the membrane of the mitochondria in eukaryotic cells. During several steps, the "high energy" electrons are passed to oxygen, eventually forming water. In the process, 32 ATP molecules are produced using the energy from the “high energy” electrons to add phosphate groups to molecules of ADP.
Maximum ATP Yields:
Cells can yield a maximum of 36-38 ATP molecules for every molecule of glucose they consume. Only small amounts of ATP are produced by the first two steps of cellular respiration. It is not until the last stage when multiple molecules of energy-rich ATP are formed.