1) Living organisms need energy, which is supplied through photosynthesis or the breakdown of chemical compounds. Autotrophs use photosynthesis or inorganic compounds, while heterotrophs rely on organic compounds from autotrophs. 2) Energy is stored and transported within cells as ATP and is used for anabolic reactions, transport, movement, bioluminescence, and maintaining homeostasis. 3) ATP is synthesized during glycolysis, the Krebs cycle, and chemiosmosis, where electrons are used to create a proton gradient across membranes that is then used by ATP synthase to add a phosphate to ADP.

1. ENERGY AND RESPIRATION
The need for energy in living organisms
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2. • Supply of energy: either from the absorption of
light energy or from chemical potential energy
• Photosynthesis supplies: energy supply and
usable carbon compounds
• Autotrophs – organisms which can use an
inorganic carbon source in the form of carbon
dioxide
• Heterotrophs – organisms needing a ready-
made organic supply of carbon
• Organic molecules can be used in 2 ways:
– Serve as ‘building bricks’ for making other organic
molecules
– Represent chemical potential energy released by
breaking down molecules in respiration (energy used
for work)
• Heterotrophs depend on autotrophs for material
and energy
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3. • Energy is used for:
– The synthesis of complex substances from
simpler ones (anabolic reactions) –
polypeptides from amino acids
– The active transport of substances against a
diffusion gradient – sodium-potassium pump
– Mechanical work such as muscle contraction
and other cellular movements – cilia and
flagella, amoeboid movement and vesicles
through cytoplasm
– Bioluminescence and electrical discharge
– Maintaining a constant body temperature
(mammals and birds)
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5. ATP
• Structure:
– Consists of adenine (organic base) and ribose
(pentose sugar) – adenosine (nucleoside)
– Combined with 3 phosphate groups
(phosphorylated)
– Small, water soluble (transported easily)
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6. Adenosine
14.2 kJmol-1
30.5 kJmol-1
30.5 kJmol-1
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7. • Energy currency – ATP is the universal
intermediary molecule between energy-yielding
and energy-requiring reactions used in a cell
– Interconversion of ATP and ADP is all-important in
providing energy fro the cell
• ATP + H2O ↔ ADP + H3PO4 30.5 kJ
– The cell’s energy-yielding reactions are linked to ATP
synthesis and ATP is used in all forms of work
– Excess energy is converted to thermal energy
– Energy currency molecule: acts as the immediate
donor of energy to the cell’s energy-requiring
reactions
– Energy storage molecule: is a short-term (glucose or
sucrose) or long-term (glycogen, starch or
triglyceride) store of chemical potential energy
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9. • ATP Synthesis:
– Energy for ATP synthesis can become available in 2
ways:
• Chemical potential energy – glycolysis and Krebs cycle
• Electrical potential energy
– transfer of electrons by electron carriers in mitochondria and
chloroplasts
– stored as a difference in H+ concentration across some
phospholipid membranes in mitochondria and chloroplasts
– H+ are then allowed to flow down concentration gradient
through a protein (ATP synthase)
– Transfer of 3 H+ allows the production of 1 ATP molecule (ADP
and an inorganic phosphate group, Pi, are available inside the
organelle) - chemiosmosis
– ATP synthase has 3 binding sites and a part of the
molecule (γ) that rotates as H+ pass
– Produces structural changes in binding sites and
allows H+ to pass sequentially through 3 phases:
• Binding ADP and Pi
• Forming tightly bound ATP
• Releasing ATP
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