The need for energy in living organisms

  • Anabolic reactions e.g growth.
  • Active transport of sustains against concentration gradient.
  • Phagocytosis, pinocytosis , exocytosis, endocytosis.
  • Electrical transmission of nerve impulse.
  • Mechanical, contraction of muscles.
  • Maintainace of temperature heat from respiration.
  • Bioluminescence.
  • Electrical discharge.


Energy is needed for several processes in the body, including:

  • Active transport
  • Exocytosis
  • Endocytosis
  • Anabolism
  • Cell division
  • Movement


The universal energy currency in all living organisms.

  • its the link between energy yielding and energy requiring reactions
  • this makes it easier for these processes to be controlled and coordinated
  • All organisms use ATP as their energy currency ie it is a universal energy currency
  • glucose and fatty acids are short-term energy stores, while glycogen, starch and triglycerides are long-term stores
  • When an ATP molecule is hydrolysed, losing one of its phosphate groups, energy is released and can be used by the cell, the ATP is converted to ADP.
  • ATP can be synthesised from ADP and an inorganic phosphate group using energy, and hydrolysed to ADP and phosphate to release energy
  • This interconversion is all important in providing energy for a cell
  • ATP + H20 ⇌ ADP + P1 30.5kjmol-1


The structure and synthesis of ATP

  • activated phosphorylated nucleotide.
  • ATP consists of the organic base ie adenine and the pentose sugar-ribose to make the nucleoside-adenosine.
  • The adenosine combines the three phosphate groups.
  • Hydrolysis of the terminal phosphate group of ATP releases 30.5 kJ mol–1 of energy for cellular work


Adenosine (a nucleoside) can be combined with one, two or three phosphate groups

    • One phosphate group = adenosine monophosphate (AMP)
    • Two phosphate groups = adenosine diphosphate (ADP)
    • Three phosphate groups = adenosine triphosphate (ATP)


All the biochemical reactions needed for an organism to stay alive is its metabolism. Metabolic pathway is a series of small enzyme-controlled reaction eg respiration and photosynthesis. Metabolism = anabolism + catabolism;

  1. i) Anabolism

is the building up of more complex molecules from simpler ones, eg carbohydrates. Enzymes are needed for these syntheses of the complex molecules needed for growth. Anabolic reactions are energy-consuming eg photosynthesis

  1. ii) Catabolism

is the enzymic breakdown of complex molecules to simpler ones. The catabolic reactions of respiration yield energy eg respiration.


ATP Synthesis


ATP is formed when ADP is combined with an inorganic phosphate (Pi) group by the enzyme ATP synthase

  • This is an energy-requiring reaction
  • Water is released as a waste product (therefore ATP synthesis is a condensation reaction)


Types of ATP synthesis

  • ATP is made during the reactions of respiration and photosynthesis
    • All of an animal’s ATP comes from respiration
  • ATP can be made in two different ways:
    • Substrate-linked phosphorylation (occurs in the glycolysis stage of respiration)
    • Chemiosmosis (occurs in the electron transport chain stage of respiration)



Synthesis of ATP by chemiosmosis

  • Movement of ions across a selectively permeable membrane.
  • Most ATP is generated in cells using electrical potential energy
  • This energy is from the transfer of electrons by electron carries in mitochondria and chloroplasts
  • As the electrons pass along an electron transport chain
  • Protons (hydrogen ions) are pumped across the membrane
  • Creating a proton concentration across the membrane
  • Creating a proton concentration across the membrane
  • The protons then flow down their concentration gradient (by facilitated diffusion) through a protein that spans the membrane
  • Part of this proteins acts as an enzyme that synthesizes ATP and is called ATP synthase


Practice Questions


Explain the role of ATP in active transport of ions and in named anabolic reactions.[6]

  • maintenance of, constant / stable, internal environment ;
  • irrespective of changes in external environment ;
  • negative feedback ;
  • receptor /appropriate named cell, detects change in, parameter / blood glucose concentration ;
  • (receptors are) beta / alpha , cells ;
  • in, Islets of Langerhans / pancreas ;
  • insulin / glucagon, released ;
  • action taken by effector / correct action described (liver / muscle, cell) ;


Describe the structure and synthesis of ATP and its universal role as the energy currency in all living organisms.

  • nucleotide ;
  • adenine + ribose / pentose + three phosphates ;
  • loss of phosphate leads to energy release / hydrolysis releases 30.5 kJ ;
  • ADP + Pi ↔ ATP (reversible reaction);
  • synthesised during, glycolysis / Krebs cycle / substrate level phosphorylation ;
  • synthesised, using electron carriers / oxidative phosphorylation /photophosphorylation
  • in, mitochondria / chloroplasts;
  • ATP synthase / ATP synthetase;
  • chemiosmosis / description;
  • used by cells as immediate energy donor;
  • link between energy yielding and energy requiring reactions;
  • active transport / muscle contraction / Calvin cycle / protein synthesis


Explain the different energy values of carbohydrate, lipid and protein as respiratory substrates.

  • idea of lipid > protein > carbohydrate ;
  • A lipid has more energy than either protein or carbohydrate
  • comparative figures ; e.g. 39.4, 17.0 and 15.8
  • kJ g-1 / per unit mass;
  • more hydrogen atoms in molecule, more energy;
  • lipid have more, hydrogen atoms / C-H bonds;
  • (most) energy comes from oxidation of hydrogen to water;
  • using reduced, NAD / FAD;
  • in ETC;
  • detail of ETC;
  • ATP production


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