Energy Transformation Reactions ١٣/١٢/١٤٣٥ Palestine Polytechnic University

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Energy
Transformation Reactions
Palestine Polytechnic University
Department of Environmental Engineering
Technology
Course: Environment & Biological
Diversity
• By controlling energy-releasing reactions,
organisms are able to use the energy to power
activities (reproduction, movement, growth...)
• These reactions form biochemical pathways when
they are linked to one another.
• The products of one reaction are used as the
reactants for the next.
• All of the chemical reactions in a cell are referred
to as the cell’s metabolism.
Instructor
Dr. Ayman Salah
Chapter 7
Energy
Transformation Reactions
• All living organisms require energy to sustain life.
• The source of this energy comes from the
chemical bonds of molecules.
• Burning organic molecules release energy by
breaking chemical bonds.
 What are the products of burning?
• Living organisms are capable of doing so but in a
controlled manner.
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Energy
Transformation Reactions
• Living organisms are two types according to the
way by which they obtain energy:
1- Autotrophs : "self-feeders (auto means "self," and
trophs means "feed"); organisms that make their
own food;
• Chemoautotrophs: use inorganic substances
such as hydrogen sulfide as a source of energy.
• Photoautotrophs: convert light energy from the
Sun into chemical energy, such as the plants.
2- Heterotrophs: organisms that need to ingest food
to obtain energy.
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Energy
Transformation Reactions
Metabolism
• All of the chemical reactions in a cell
• Metabolic pathways include two broad types:
1. Catabolic pathways: release energy by breaking
down larger molecules into smaller molecules.
2. Anabolic pathways: use the energy released by
catabolic pathways to build larger molecules from
smaller molecules.
• The relationship of anabolic and catabolic
pathways results in the continual flow of energy
within an organism.
Energy
Transformation Reactions
Metabolism
• Two important
metabolic pathways:
1- Photosynthesis is
the anabolic pathway
in which light energy
from the Sun is
converted to
chemical energy for
use by the cell
• In this reaction, autotrophs use light energy, carbon
dioxide, and water to form glucose and oxygen.
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Energy
Transformation Reactions
Metabolism
2- Cellular respiration is
the catabolic pathway
in which organic
molecules are broken
down to release
energy for use by the
cell.
• In these reactions, oxygen is used to break down
organic molecules, resulting in the production of
carbon dioxide and water
Energy
Transformation Reactions
Photosynthesis
• Photosynthesis is a process in which light energy
is converted into chemical energy.
• The overall chemical equation for photosynthesis
is:
light
6CO2 + 6H2O
C6H12O6 + 6O2
• This process occur in the chloroplast of plants
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Energy
Transformation
Reactions
Energy
Transformation Reactions
The location of
photosynthesis
• Leaves are the major
organs of
photosynthesis in
plants.
• Photosynthetic pigments
such as chlorophyll are
clustered together on
the thylakoid
The end products of
photosynthesis also
can be used to make
other organic
molecules, such as
proteins, lipids, and
nucleic acids
membranes
Energy
Transformation Reactions
Photosynthesis
Photosynthesis occurs in two phases:
1- The light-dependent reactions (Light reactions):
light energy is absorbed and then converted into
chemical energy in the form of ATP and NADPH.
2- The light-independent reactions (Dark reactions
or Calvin cycle): the ATP and NADPH that were
formed in phase one are used to make glucose.
• Once glucose is produced, it can be joined to
other simple sugars to form larger molecules such
as starch or used to make other organic molecules.
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Energy
Transformation Reactions
Cellular Respiration
• Organic compounds possess potential energy as
a result of their arrangement of atoms.
• All organisms use glucose (C6H12O6) as a source
of energy, except the chemoautotrophs.
• Covalent bonds in the sugar glucose contain
potential energy
• Through a series of enzyme-controlled redox
reactions, organisms break the covalent bonds in
C6H12O6 and rearrange them into new and more
stable configurations (CO2 , water ).
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Energy
Transformation Reactions
Cellular Respiration
• The overall reaction is as follows:
• The redox reactions result in the
transfer of electrons from glucose
to O2.
• Glucose is oxidized to 6CO2 and
oxygen is reduced to water
• From where does energy release?
Energy
Transformation Reactions
Cellular Respiration
• When the hydrogen atoms form covalent bonds
with oxygen, the shared electron pairs occupy
positions closer to the oxygen nuclei than they did
when they were part of the glucose molecule.
• As electrons (in hydrogen atoms) move from less
electronegative carbon atoms in glucose to highly
electronegative oxygen atoms, they lose potential
energy .
• Their energy could be used to phosphorylate ADP
molecules, producing higher energy ATP
molecules
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Energy
Transformation Reactions
Cellular Respiration
• Cellular respiration occurs in two main parts:
1- Glycolysis; anaerobic process
• the 6-carbon sugar (glucose) is broken into two
smaller 3-carbon molecules of pyruvic acid
• 2 ATP are produced.
• Hydrogens and their electrons are sent to the
electron-transport system (ETS) for processing.
2- Aerobic respiration; includes the Krebs cycle and
electron transport
Energy
Transformation
Reactions
Cellular Respiration
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Energy
Transformation Reactions
Cellular Respiration
• This is known as aerobic cellular respiration. why?
• O2 is not the only possible electron acceptor in the
oxidation of glucose in a cell.
• Some microorganisms use NO2, SO4, and even
Fe+3 as final electron acceptors.
• These microorganisms are known as obligate
anaerobes -live in environments that contain no O2
Energy
Transformation Reactions
Cellular Respiration
• Living organisms are three types according to
their requirements of O2 :
1. Obligate aerobes: require oxygen as the final
electron acceptor and cannot survive without it
2. Obligate anaerobes: use something other than O2
as its final hydrogen acceptor. must live in
environments that contain no oxygen.
3. Facultative anaerobes: can tolerate aerobic and
anaerobic conditions (mostly pathogenic bacteria)
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Energy
Transformation Reactions
Cellular Respiration
Anaerobic Cellular Respiration - Fermentation
• Organisms use something other than O2 as a final
hydrogen acceptor.
• The acceptor molecule could be
 inorganic; NO2, SO4, CO2, Or
 organic molecule such as pyruvic acid.
• When organic molecule is the electron accepter
the process is called fermentation.
• Anaerobic respiration is the incomplete oxidation
of glucose
Anaerobic Cellular Respiration - Fermentation
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Energy
Transformation Reactions
Linking Photosynthesis and Cellular Respiration
• Photosynthesis and cellular respiration are closely
related to one another.
• In plants and other autotrophs, both processes
may occur within individual cells.
• Animals and other heterotrophs undergo cellular
respiration, but not photosynthesis.
• Heterotrophs require the products of
photosynthesis to carry out cellular respiration.
• Photosynthesis uses the products of cellular
respiration, and cellular respiration uses the
products of photosynthesis
Linking Photosynthesis and Cellular Respiration
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Questions
• Are photosynthesis and respiration exact
opposites? Explain?
• What would happen to humans and most other
living organisms on Earth if photosynthesis
stopped?
• Which contains more free energy: three molecules
of CO2 or one molecule of pyrovic acid? Explain.
• List two differences between aerobic respiration
and fermentation.
• Name an organism in which alcoholic fermentation
takes place.