Biology Chapter 9: Energy and Life
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Questions and Answers

What is the primary function of Crassulacean acid metabolism (CAM) in plants?

  • To release carbon dioxide during the daytime
  • To increase water loss during the daytime
  • To trap carbon dioxide within leaves during the night (correct)
  • To produce carbohydrates during the nighttime
  • Why do CAM plants open their stomata at night?

  • To reduce water loss during the night
  • To increase photosynthesis during the night
  • To allow CO2 to enter the leaf during the night (correct)
  • To release oxygen during the night
  • What is the unit of energy used to measure the energy stored in food?

  • Calorie (correct)
  • Watt
  • Joule
  • Kilocalorie
  • Why do organisms need to obtain energy from food?

    <p>To perform cellular activities</p> Signup and view all the answers

    What is the difference between a calorie and a Calorie?

    <p>A calorie is a unit of energy, while a Calorie is a unit of energy multiplied by 1000</p> Signup and view all the answers

    What is the primary purpose of cellular respiration?

    <p>To generate ATP from glucose</p> Signup and view all the answers

    What type of plants are most likely to have Crassulacean acid metabolism (CAM)?

    <p>Desert plants</p> Signup and view all the answers

    During the daytime, what happens to the organic acids produced in CAM plants?

    <p>They are broken down to release CO2</p> Signup and view all the answers

    What is the primary function of ATP in cells?

    <p>To transfer energy from one molecule to another</p> Signup and view all the answers

    What is the role of electron carriers in photosynthesis?

    <p>To transport high energy electrons from chlorophyll to other molecules</p> Signup and view all the answers

    What is the by-product of light dependent reactions in photosynthesis?

    <p>Oxygen</p> Signup and view all the answers

    What is the name of the enzyme that combines CO2 molecules with 5-carbon compounds in the Calvin cycle?

    <p>Rubisco</p> Signup and view all the answers

    What is the term for the process of using energy from sunlight to synthesize high energy sugars from carbon dioxide and water?

    <p>Photosynthesis</p> Signup and view all the answers

    What is the name of the pigment that absorbs light energy in photosynthesis?

    <p>Chlorophyll a</p> Signup and view all the answers

    What is the name of the organelle where photosynthesis takes place?

    <p>Chloroplast</p> Signup and view all the answers

    What is the term for the process of generating ATP and NADPH from light energy in photosynthesis?

    <p>Light dependent reactions</p> Signup and view all the answers

    What is the factor that can limit the rate of photosynthesis in plants?

    <p>All of the above</p> Signup and view all the answers

    What is the term for the adaptation of plants to conserve water in hot conditions?

    <p>CAM photosynthesis</p> Signup and view all the answers

    What is the primary function of cellular respiration?

    <p>To release energy from food molecules in the presence of oxygen</p> Signup and view all the answers

    Which stage of cellular respiration does not require oxygen?

    <p>Glycolysis</p> Signup and view all the answers

    What is the net gain of ATP molecules during glycolysis?

    <p>2 ATP molecules</p> Signup and view all the answers

    What is the byproduct of the Krebs cycle?

    <p>Carbon dioxide and ATP</p> Signup and view all the answers

    What is the role of NADPH in cellular respiration?

    <p>To accept high-energy electrons and hydrogen ions</p> Signup and view all the answers

    What is the difference between photosynthesis and cellular respiration?

    <p>Photosynthesis releases oxygen, while cellular respiration consumes oxygen</p> Signup and view all the answers

    What is the energy yield of glycolysis?

    <p>2 ATP molecules per glucose molecule</p> Signup and view all the answers

    Where do the Krebs cycle and electron transport chain take place?

    <p>In the mitochondria</p> Signup and view all the answers

    What is the purpose of fermentation?

    <p>To produce ATP molecules in the absence of oxygen</p> Signup and view all the answers

    What is the energy source for cellular respiration?

    <p>Chemical energy from food molecules</p> Signup and view all the answers

    What is the primary function of the electron transport chain in cellular respiration?

    <p>To generate ATP from ADP and Pi</p> Signup and view all the answers

    What is the net gain of ATP molecules during glycolysis?

    <p>2 ATP</p> Signup and view all the answers

    In which part of the mitochondrion is the electron transport chain located?

    <p>Inner membrane</p> Signup and view all the answers

    What is the purpose of chemiosmosis in cellular respiration?

    <p>To generate ATP from ADP and Pi</p> Signup and view all the answers

    What is the byproduct of lactic acid fermentation in muscle cells?

    <p>Lactic acid and ATP</p> Signup and view all the answers

    What is the primary source of energy for short, quick bursts of activity?

    <p>Lactic acid fermentation</p> Signup and view all the answers

    What is the purpose of the ATP synthase enzyme in chemiosmosis?

    <p>To generate ATP from ADP and Pi</p> Signup and view all the answers

    What is the result of the electron transport chain in the presence of oxygen?

    <p>The production of ATP</p> Signup and view all the answers

    What is the purpose of the Krebs cycle in cellular respiration?

    <p>To synthesize NADH and FADH2</p> Signup and view all the answers

    What is the primary source of energy for long-distance events?

    <p>Oxidative phosphorylation</p> Signup and view all the answers

    Study Notes

    Energy and Life

    • Chemical energy and ATP:
      • ATP (Adenosine Triphosphate) consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups
      • The three phosphate groups are key to ATP's ability to store and release energy
      • ADP (Adenosine Diphosphate) is similar to ATP, but with only two phosphate groups
    • Storing energy:
      • All living things store energy in chemical bonds of certain compounds
      • When cells have excess energy, they can store small amounts of it by adding phosphate groups to ADP to produce ATP
    • Releasing energy:
      • Cells release energy stored in ATP by breaking the chemical bonds between the second and third phosphate groups
      • ATP functions like a rechargeable battery, with energy being used to add phosphate groups to ADP and released when a phosphate group is split off
    • How cells use ATP:
      • ATP is used for active transport, such as pumping sodium ions out of cells and potassium ions into them
      • ATP is used to power cellular processes, such as protein synthesis and responses to chemical signals
      • Most cells have a small amount of ATP, which is not suitable for long-term energy storage

    Heterotrophs and Autotrophs

    • Heterotrophs:
      • Obtain food by consuming other living things
      • May eat plants or other animals, or obtain food from decomposing organisms
    • Autotrophs:
      • Obtain energy from the sun
      • Convert light energy into chemical energy through photosynthesis
      • Produce high-energy carbohydrates, such as sugars and starches, that can be used as food

    Photosynthesis

    • Overview:
      • Photosynthesis uses energy from sunlight to convert water and carbon dioxide into high-energy sugars and oxygen
      • Plants use these sugars to produce complex carbohydrates, such as starches, and to provide energy for the synthesis of other compounds
    • Light-dependent reactions:
      • Take place in thylakoid membranes and use energy from sunlight to add a phosphate group to ADP to make ATP
      • Use energy from sunlight to raise low-energy electrons from water molecules to a higher energy level
      • Produce ATP and NADPH
    • Light-independent reactions:
      • Also known as the Calvin cycle
      • Take place outside the thylakoids in the stroma of the chloroplast
      • Use ATP and NADPH produced in the light-dependent reactions to build high-energy sugars from carbon dioxide
    • Process of photosynthesis:
      • Light-dependent reactions: generating ATP and NADPH
      • ATP and NADPH are used to synthesize high-energy sugars
      • Carbon dioxide enters the Calvin cycle, where it is converted into 3-carbon compounds
      • These compounds are used to produce glucose and other high-energy sugars

    Factors Affecting Photosynthesis

    • Temperature:
      • Photosynthesis is possible between 0°C and 35°C
    • Light:
      • High light intensity increases the rate of photosynthesis
      • Plants can reach a maximum rate of photosynthesis at high light intensities
    • Water:
      • Water shortage can slow or stop photosynthesis
      • Water loss can also damage plant tissues
    • Photosynthesis under extreme conditions:
      • C4 plants: have a specialized chemical pathway that allows them to capture low levels of CO2 and pass it to the Calvin cycle
      • CAM plants: have adaptations to conserve water and survive in hot conditions### CAM Plants
    • CAM plants (e.g. pineapple, desert cacti, fleshy "ice plant") have Crassulacean acid metabolism (CAM) photosynthesis
    • During photosynthesis, CO2 is incorporated into organic acids at night
    • At night, CO2 is combined with existing molecules to produce organic acids, "trapping" carbon within leaves
    • During the day, these compounds release carbon dioxide inside the leaf, enabling carbohydrate production

    Cellular Respiration: Overview

    • Chemical energy from food is expressed in units of calories (1 calorie = energy needed to raise 1 gram of water 1°C)
    • Cells use different molecules for food (e.g. fats, proteins, carbohydrates), with varying energy storage due to different chemical structures
    • Cellular respiration is the process of energy conversion that releases energy from food in the presence of oxygen
    • The overall equation for cellular respiration is: C6H12O6 + 6O2 → 6CO2 + 6H2O + Chemical Energy (in ATP)

    Stages of Cellular Respiration

    • Three main stages: glycolysis, Krebs cycle, and electron transport chain
    • Glycolysis:
      • 10% of glucose energy is captured to produce ATP
      • At the end of glycolysis, 90% of chemical energy is still unused
    • Krebs cycle:
      • More energy is captured
    • Electron transport chain:
      • Requires reactants from other two stages
      • Extracts energy using oxygen

    Oxygen and Energy

    • Oxygen is required at the end of the electron transport chain
    • When cell demand for energy increases, oxygen use also increases
    • Most energy-releasing pathways within cells require oxygen, which is why we need to breathe/respire

    Pathways of Cellular Respiration

    • Aerobic pathways (require oxygen): Krebs cycle and electron transport chain
    • Anaerobic pathways (do not require oxygen): glycolysis and fermentation
    • Glycolysis occurs in the cytoplasm, while Krebs cycle and electron transport chain occur in mitochondria

    Comparing Photosynthesis and Cellular Respiration

    • Cellular respiration is balanced by photosynthesis
    • Their energy flows take place in opposite directions
    • Photosynthesis "deposits" energy, while cellular respiration "withdraws" energy
    • Photosynthesis uses water and CO2 to synthesize carbohydrates, while cellular respiration uses carbohydrates as a source of chemical energy and releases water and CO2

    Glycolysis

    • 1 molecule of glucose is transformed into 2 molecules of pyruvic acid
    • As bonds in glucose are broken and rearranged, small amounts of energy are released and captured in other molecules
    • ATP production: 2 ATP molecules are used to start glycolysis, and 4 ATP molecules are produced, resulting in a net gain of 2 ATP molecules
    • NADPH production: 4 electrons are removed from glycolysis and passed to NAD+, which becomes NADPH, holding the electrons until they can be transferred to other molecules

    Krebs Cycle

    • Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

    • Citric acid production: pyruvic acid is converted into acetyl-CoA, which is then joined to a 4-carbon molecule to form citric acid

    • Energy extraction: 2 carbon atoms are removed from citric acid, releasing 2 molecules of carbon dioxide and leaving a 4-carbon molecule

    • For each turn of the cycle, 1 molecule of ADP is converted to 1 molecule of ATP, and 2 ATP molecules are produced for each starting molecule of glucose### ATP Molecules and Cellular Activities

    • ATP molecules are useful and become immediately available to power cellular activities.

    • In the presence of oxygen, electrons from carrier molecules are used to generate huge amounts of ATP.

    Electron Transport and ATP Synthesis

    • The electron transport chain uses 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 carrier to carrier, and at the end of the chain, an enzyme 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.

    ATP Production

    • Cells use a process called chemiosmosis to produce ATP.
    • The inner mitochondrial membrane contains enzymes known as ATP synthases.
    • The charge difference across the membrane forces hydrogen ions through channels in these enzymes, causing the ATP synthases to spin.
    • With each rotation, the enzyme grabs an ADP molecule and attaches a phosphate group, producing ATP.
    • On average, each pair of high energy electrons that moves down the full length of the chain provides enough energy to produce 3 molecules of ATP.

    The Totals

    • Glycolysis nets just 2 ATP molecules per molecule of glucose.
    • Together, glycolysis, Krebs, and the chain release about 36 molecules of ATP per molecule of glucose.

    Fermentation

    • When oxygen isn't 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.
    • Cells convert NADH to NAD+ by passing high energy electrons back to pyruvic acid.
    • Fermentation is an anaerobic process that occurs in the cytoplasm.

    Alcoholic Fermentation

    • Carried out by yeast, producing ethyl alcohol and carbon dioxide.
    • Pyruvic acid + NADH → alcohol + CO2 + NAD+.

    Lactic Acid Fermentation

    • Chemical reaction that converts pyruvic acid to lactic acid.
    • Does not give off CO2.
    • Regenerates NAD+ so that glycolysis can continue.
    • Pyruvic acid + NADH → Lactic acid + NAD+.
    • Humans are also lactic acid fermenters.

    Energy and Exercise

    • During brief periods without enough oxygen, many of the cells in our bodies produce ATP by lactic acid fermentation.
    • Muscle cells are best adapted to doing that.
    • They need very large supplies of ATP for rapid bursts of activity.
    • As swimmers begin a race, they only have enough ATP in their muscle cells to power them for a few seconds.
    • To keep going, they must immediately generate new ATPs by cellular respiration or by lactic acid fermentation.
    • Quick energy is produced by lactic acid fermentation, which does not involve the Krebs cycle, electron transport chain, or oxygen, resulting in it working more rapidly.
    • This process produces lactic acid as a byproduct, which quickly builds up in muscles and the bloodstream of athletes.
    • When the race is over, the only way to get rid of lactic acid is by means of another chemical pathway that requires extra oxygen.
    • For that reason, you can think of a quick sprint as building up an “oxygen debt” that the swimmers have to repay with heavy breathing after the race.

    Long-term Energy

    • For exercise longer than 90 seconds, cellular respiration is the only way to continue generating a supply of ATP.
    • Cellular respiration releases energy more slowly than fermentation.
    • The body stores energy in muscle cells and other tissues in the form of carbohydrate glycogen.
    • These stores are usually enough to last for 15-20 minutes of activity.
    • After that, the body begins to break down other stored molecules, including fats, for energy.
    • One reason that aerobic forms of exercise are beneficial for weight control.
    • Athletes competing in long-distance events depend upon the efficiency of their respiratory and circulatory systems to supply oxygen to their muscles to support aerobic respiration.

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