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Chapter 6 : Obtaining from – make their own organic matter from inorganic and Society: . Marathoners versus Sprinters • Heterotrophs (other-feeders) • Sprinters do not usually compete at short and long distances. – include and other animals that cannot • Natural differences in the muscles of these athletes favor make organic from inorganic ones. sprinting or long-distance running. Producers and Consumers Figure 6.0

• Autotrophs are producers because ecosystems depend upon them for food. • The muscles that move our legs contain two main types of muscle fibers: • Heterotrophs are consumers because they eat plants or other animals. • slow-twitch and Figure 6.1 • Chemical Cycling between and Cellular Respiration fast-twitch. • The ingredients for photosynthesis are carbon dioxide (CO 2) and (H 2O).

• Slow-twitch fibers ’ – CO 2 is obtained from the air by a plant s leaves. last longer, – ’ – H2O is obtained from the damp soil by a plant s roots. – do not generate a lot of quick power, and

– generate ATP using (aerobically). • Chloroplasts in the cells of leaves use light energy to rearrange the of CO and H O, which produces • 2 2 Fast-twitch fibers – (such as ),

– contract more quickly and powerfully, – other organic molecules, and

– fatigue more quickly, and – oxygen gas.

– can generate ATP without using oxygen (anaerobically). • Plant and animal cells perform cellular respiration , a chemical process that • All muscles contain both types of fibers but in different ratios. – primarily occurs in mitochondria, ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE – harvests energy stored in organic molecules, • Animals depend on plants to convert the energy of sunlight to – uses oxygen, and – chemical energy of sugars and – generates ATP. – other organic molecules we consume as food.

• Photosynthesis uses light energy from the sun to • The waste products of cellular respiration are – power a chemical process and – CO 2 and H 2O, – make organic molecules. Producers and Consumers – used in photosynthesis.

• Plants and other autotrophs (self-feeders) • Animals perform only cellular respiration. • Plants perform – oxidation-reduction reactions or

– photosynthesis and – redox reactions for short. Redox Reactions – cellular respiration. • The loss of electrons during a redox reaction is oxidation .

• Plants usually make more organic molecules than they need for • The acceptance of electrons during a redox reaction is fuel. This surplus provides material that can be reduction .

– used for the plant to grow or • During cellular respiration

– stored as starch in potatoes. – glucose is oxidized and Figure 6.2 CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY – oxygen is reduced. Figure 6.UN02

• Cellular respiration is • Why does electron transfer to oxygen release energy? – the main way that chemical energy is harvested from food and converted to ATP and – When electrons move from glucose to oxygen, it is as though the electrons were falling. – an aerobic process —it requires oxygen.

– This “fall ” of electrons releases energy during cellular respiration. • Cellular respiration and breathing are closely related. Figure 6.4

– Cellular respiration requires a cell to exchange gases with its surroundings. • Cellular respiration is

– Cells take in oxygen gas. – a controlled fall of electrons and – Cells release waste carbon dioxide gas. – a stepwise cascade much like going down a staircase.

– Breathing exchanges these same gases between the blood and outside air. • Figure 6.3 The path that electrons take on their way down from glucose to Figure 6.3a oxygen involves many steps. Figure 6.3b The Simplified Equation for Cellular Respiration • The first step is an electron acceptor called NAD +. • A common fuel for cellular respiration is glucose. – NAD is made by cells from niacin, a B . • Cellular respiration can produce up to 32 ATP molecules for + – The transfer of electrons from organic fuel to NAD each glucose molecule consumed. reduces it to NADH .

• The overall equation for what happens to glucose during cellular respiration is • The rest of the path consists of an , which

– glucose & oxygen  CO 2, H 2O, & a release of energy. involves a series of redox reactions and Figure 6.UN01 –

Redox Reactions – ultimately leads to the production of large amounts of ATP. • Figure 6.5 Chemical reactions that transfer electrons from one substance Figure 6.5a to another are called An Overview of Cellular Respiration • Cellular respiration is an example of a , – uses some of this energy to make ATP, and which is a series of chemical reactions in cells.

– forms NADH and FADH 2. • All of the reactions involved in cellular respiration can be Figure 6.10 grouped into three main stages: Figure 6.10a 1. , Figure 6.10b 2. the cycle , and 3. electron transport . Figure 6.6 • Figure 6.6a Electron transport releases the energy your cells need to make the most of their ATP. The Three Stages of Cellular Respiration • • With the big-picture view of cellular respiration in mind, let ’s The molecules of the electron transport chain are built into examine the process in more detail. the inner membranes of mitochondria. Stage 1: Glycolysis • The chain • A six-carbon glucose molecule is split in half to form two molecules of . – functions as a chemical machine, which

• These two molecules then donate high energy electrons to uses energy released by the “fall ” of electrons to + – NAD , forming NADH. pump hydrogen ions across the inner Figure 6.7 mitochondrial membrane, and Figure 6.7a Figure 6.7b-1 Figure 6.7b-2 – uses these ions to store potential energy. Figure 6.7b-3

• When the hydrogen ions flow back through the membrane, they • Glycolysis release energy. Figure 6.8 Stage 2: The – The hydrogen ions flow through ATP synthase . • In the citric acid cycle, pyruvic acid from glycolysis is first “groomed. ” – ATP synthase

– takes the energy from this flow and – Each pyruvic acid loses a carbon as CO 2. – synthesizes ATP. – The remaining fuel molecule, with only two Figure 6.11 carbons left, is acetic acid. Figure 6.11a Figure 6.11b • Figure 6.11c Oxidation of the fuel generates NADH.

• is a deadly that • Finally, each acetic acid is attached to a molecule called to form acetyl CoA. – binds to one of the complexes in the electron transport chain, • The CoA escorts the acetic acid into the first reaction of the citric acid cycle. – prevents the passage of electrons to oxygen, and

• The CoA is then stripped and recycled. – stops the production of ATP. Figure 6.9 The Results of Cellular Respiration Figure 6.9a Figure 6.9b • Cellular respiration can generate up to 32 molecules of ATP per molecule of glucose. Figure 6.12 • The citric acid cycle Figure 6.12a

extracts the energy of by breaking the acetic – • “ ” acid molecules all the way down to CO 2, In addition to glucose, cellular respiration can burn – diverse types of , – could not diffuse away. Figure 6.15

– , and • Results : When could diffuse away, performance – . improved greatly. Figure 6.13 : ANAEROBIC HARVEST OF FOOD ENERGY • Conclusion : Lactic acid accumulation is the primary cause of failure in muscle tissue. • Some of your cells can actually work for short periods without oxygen. • However, recent evidence suggests that the role of lactic acid • in muscle function remains unclear. Fermentation is the anaerobic (without oxygen) harvest of Fermentation in food energy. Fermentation in Human Muscle Cells • Fermentation alone is able to sustain many types of microorganisms. • After functioning anaerobically for about 15 seconds, muscle cells begin to generate ATP by the process of fermentation. • The lactic acid produced by microbes using fermentation is used to produce • Fermentation relies on glycolysis to produce ATP. – cheese, sour cream, and , • Glycolysis – soy sauce, pickles, and , and – does not require oxygen and – sausage products. – produces two ATP molecules for each glucose broken down to pyruvic acid.

• Yeast is a microscopic fungus that • Pyruvic acid, produced by glycolysis, – uses a different type of fermentation and – is reduced by NADH, – produces CO 2 and ethyl instead of lactic acid. – producing NAD +, which • This type of fermentation, called alcoholic fermentation , is – keeps glycolysis going. used to produce • In human muscle cells, lactic acid is a by-product. – beer, Figure 6.14 Figure 6.14a Figure 6.14b – , and The Process of Science: What Causes Muscle Burn? – breads. Figure 6.16 • Observation : Muscles produce lactic acid under anaerobic Figure 6.16a conditions. Figure 6.16b Evolution Connection: Life before and after Oxygen • Question : Does the buildup of lactic acid cause muscle fatigue? • The Process of Science: Glycolysis could be used by ancient to make ATP What Causes Muscle Burn? – when little oxygen was available, and • Hypothesis : The buildup of lactic acid would cause muscle activity to stop. – before organelles evolved.

• Experiment : Tested frog muscles under conditions when lactic • Today, glycolysis acid

occurs in almost all organisms and – could and – – is a metabolic heirloom of the first stage in the breakdown of organic molecules. Figure 6.17 Figure 6.17a Figure 6.17b Figure 6.UN03 Figure 6.UN04 Figure 6.UN05 Figure 6.UN06 Figure 6.UN07 Figure 6.UN08 Figure 6.UN09