Bio1100 Chapter 4 Energy
  1. Energy exists in two states: potential   energy and kinetic   energy.
    • Objects that have the capacity to move but are not moving have potential energy.
      Water sitting on top of a dam has potential energy.
      A concentration gradient also has potential energy.
      Objects in motion have kinetic energy.
      Water falling from the top of a dam has converted potential energy into kinetic energy.
      Note the conversion of energy is one-way: from potential energy to kinetic energy. Quiz

  2. Living systems transfer energy in chemical   reactions that involve energy change.
    • Energy transformations
      Kinetic energy from the sun (in the form of light) is converted to potential energy of carbohydrates by photosynthesis. Potential energy in carbohydrates is converted to kinetic energy by cellular respiration for organisms to use.

  3. An important molecule in the transformation of energy in organisms is ATP   (adenosine triphosphate).

    • The nucleotide ATP (adenosine triphosphate) is the main energy currency of the cell.

      It contains the nitrogen-containing base adenine, a ribose sugar, and 3 phosphates linked by high-energy bonds.

      The high-energy bonds in the phosphates can be broken to release energy and drive cellular processes, forming ADP (adenosine diphosphate). Quiz

    • Chemical energy is required to form ATP from ADP and inorganic phosphate (Pi).

      When energy is needed for cellular work, the ATP is broken down to ADP and Pi.

      Note that this is not a closed cycle: a continuous supply of energy is needed to regenerate ATP.

  4. Energy flows   from the sun to living organisms.
    • Energy flow

      Plants and other photosynthetic organisms undergo photosynthesis to capture energy from sunlight and store them in covalent bonds of sugars.

      Living organisms undergo cellular respiration to convert the potential energy in covalent bonds of sugars into kinetic energy for their use.


  5. Plant leaf cells contain chloroplasts   with pigments   for photosynthesis.
    • Cells near the surface of a leaf are packed with chloroplasts which carry out the reactions of photosynthesis.

    • Photosynthesis takes place within chloroplasts in two stages.

      • The "photo" reactions occur within the thylakoid membranes, where chlorophyll pigments absorb energy from light.

      • The "synthesis" reactions occur in the semifluid stroma.

    • Photosynthetic pigments

      Chloroplasts contain pigment molecules such as chlorophyll a, chlorophyll b, and carotenoids that absorb light at different wavelengths.

      Chlorophyll pigments absorb mainly violet-blue and red light, and reflect green.

      Carotenoids absorb mostly blue and green light, and reflect orange and yellow.

      • What colors are absorbed by a substance that looks white?
        • None. A white substance absorbs no colors,and reflects all colors of the visible spectrum.


    • Light is type of kinetic energy that is carried in particles called photons, which are organized into waves.

      The energy carried by a particular photon is measured by the length of its wave, or wavelength.

      Visible light represents only a small part of the electromagnetic spectrum, between wavelengths of about 400 and 740 nanometers.

      The shorter the wavelength, the greater its energy.

    • Why are leaves green?

      During spring, chlorophyll in leaves mask the presence of other pigments called carotenoids.

      The chlorophyll absorb most of the visible wavelengths except those around 500 to 600 nm, and reflect these green wavelengths, so leaves appear green.

      Cool temperatures in the fall cause many trees to cease producing chlorophyll, and the carotenoids reflect orange/yellow light, giving bright colors to autumn leaves.



    • Photosynthesis can be divided into two stages:

      1. "photo" reactions

      2. "synthesis" reactions (Calvin Cycle)

      The inputs (reactants) are carbon dioxide and water, plus energy from the light.

      The outputs (products) are sugar and oxygen.

      Note the intermediate molecules ATP and NADPH serve to store energy harvested in "photo" reactions to be used by "synthesis" reactions.


    • In the thylakoid membranes, green chlorophyll pigments capture sunlight energy in "photo" reactions, where water is split to release oxygen.

      The energy is stored in ATP and NADPH molecules that are later used by the "synthesis" reactions.


    • The ATP and NADPH molecules that are generated in the "photo" reactions are used to synthesize sugar such as glucose from carbon dioxide.

      These "synthesis" reactions take place in the semifluid stroma of chloroplasts in a cycle of chemical reactions called the Calvin Cycle.


  6. Cellular respiration requires oxygen   to produce ATP   from glucose  .
    • Cellular (aerobic) respiration is the harvesting of energy from sugars such as glucose.

      The inputs are oxygen and glucose, and outputs are carbon dioxide, water, and ATP.


    • Cellular respiration steps

      1. Glycolysis:
        The 6-carbon glucose is split into 2 molecules of the 3-carbon pyruvate, yielding 2 ATP.

      2. acetyl-coA production:
        In the presence of oxygen, the pyruvate is broken down in the mitochondrion to form the 2-carbon acetyl-coA, releasing carbon dioxide (CO2).

      3. Krebs cycle:
        The acetyl-coA is broken down to release CO2 and yield more ATP.

      4. Electron Transport Chain (ETC):
        NADH and FADH2 are electron carriers from previous steps. Their high-energy electrons are used by proton pumps to produce ATP.

      A total of 36 ATP molecules are produced from 1 glucose.


  7. In anaerobic   conditions, glycolysis   is followed by fermentation  .
    • Fermentation

      In the presence of oxygen, pyruvate enters the Krebs cycle and ETC.

      In anaerobic conditions (absence of oxygen), the high-energy electrons cannot enter ETC, but are removed by fermentation, yielding either of two possible products:

      • Animals (and some bacteria) produce lactic acid as an end product.

      • Yeasts produce ethanol as an end product.


  8. Other macromolecules such as proteins   and fats   can also enter cellular respiration via different pathways.
    • Respiration pathways

      Many different kinds of macromolecules can be broken down to enter the Krebs cycle at various points.