activation energy

Examples of activation energy in the following topics:

• Activation Energy

  • This small amount of energy input necessary for all chemical reactions to occur is called the activation energy (or free energy of activation) and is abbreviated EA.
  • However, the measure of the activation energy is independent of the reaction's ΔG.
  • The source of the activation energy needed to push reactions forward is typically heat energy from the surroundings.
  • The higher the activation energy, the slower the chemical reaction will be.
  • This figure implies that the activation energy is in the form of heat energy.

• ATP: Adenosine Triphosphate

  • ATP provides the energy for both energy-consuming endergonic reactions and energy-releasing exergonic reactions, which require a small input of activation energy.
  • Since ATP hydrolysis releases energy, ATP synthesis must require an input of free energy.
  • Exactly how much free energy (∆G) is released with the hydrolysis of ATP, and how is that free energy used to do cellular work?
  • To harness the energy within the bonds of ATP, cells use a strategy called energy coupling.
  • ATP is the primary energy currency of the cell.

• Animal Bioenergetics

  • An animal's body size, activity level, and environment impacts the ways it uses and obtains energy.
  • No energy system is one hundred percent efficient as an animal's metabolism produces waste energy in the form of heat.
  • The more active an animal is, the more energy is needed to maintain that activity and the higher its BMR or SMR.
  • Torpor is a process that leads to a decrease in activity and metabolism, which allows animals to survive adverse conditions.
  • Differentiate among the ways in which an animal's energy requirements are affected by their environment and level of activity

• The Role of Energy and Metabolism

  • All organisms require energy to complete tasks; metabolism is the set of the chemical reactions that release energy for cellular processes.
  • Plants convert light energy from the sun into chemical energy stored in molecules during the process of photosynthesis.
  • Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed.
  • Energy is needed to perform heavy labor and exercise, but humans also use a great deal of energy while thinking and even while sleeping.
  • Just as energy is required to both build and demolish a building, energy is required for both the synthesis and breakdown of molecules.

• ATP and Muscle Contraction

  • ATP first binds to myosin, moving it to a high-energy state.
  • ADP and Pi remain attached; myosin is in its high energy configuration .
  • The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
  • ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.
  • The cross-bridge muscle contraction cycle, which is triggered by Ca2+ binding to the actin active site, is shown.

• Secondary Active Transport

  • Unlike in primary active transport, in secondary active transport, ATP is not directly coupled to the molecule of interest.
  • While this process still consumes ATP to generate that gradient, the energy is not directly used to move the molecule across the membrane, hence it is known as secondary active transport.
  • Both antiporters and symporters are used in secondary active transport.
  • This secondary process is also used to store high-energy hydrogen ions in the mitochondria of plant and animal cells for the production of ATP.
  • The potential energy that accumulates in the stored hydrogen ions is translated into kinetic energy as the ions surge through the channel protein ATP synthase, and that energy is used to convert ADP into ATP.

• ATP in Metabolism

  • A living cell cannot store significant amounts of free energy.
  • Rather, a cell must be able to handle that energy in a way that enables the cell to store energy safely and release it for use as needed.
  • ATP is often called the "energy currency" of the cell and can be used to fill any energy need of the cell.
  • Often the released phosphate is directly transferred to another molecule, such as a protein, activating it.
  • Recall the active transport work of the sodium-potassium pump in cell membranes.

• Life History Patterns and Energy Budgets

  • Plants, for example, acquire energy from the sun via photosynthesis, but must expend this energy to grow, maintain health, and produce energy-rich seeds to produce the next generation.
  • Thus, all species have an energy budget in which they must balance energy intake with their use of energy for metabolism, reproduction, parental care, and energy storage, as when bears build up body fat for winter hibernation.
  • Most of their energy budget is used to produce many tiny offspring.
  • Animal species that have few offspring during a reproductive event usually give extensive parental care, devoting much of their energy budget to these activities, sometimes at the expense of their own health.
  • It is a matter of where the energy is used: for large numbers of seeds or for fewer seeds with more energy.

• The Two Parts of Photosynthesis

  • In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll and converted into stored chemical energy, in the form of the electron carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate) and the energy currency molecule ATP (adenosine triphosphate).
  • The process that converts light energy into chemical energy takes place in a multi-protein complex called a photosystem.
  • Each photosystem plays a key role in capturing the energy from sunlight by exciting electrons.
  • After the energy is transferred, the energy carrier molecules return to the light-dependent reactions to obtain more energized electrons.
  • In addition, several enzymes of the light-independent reactions are activated by light.

• Transferring of Energy between Trophic Levels

  • Energy is lost as it is transferred between trophic levels; the efficiency of this energy transfer is measured by NPE and TLTE.
  • The fact is, after four to six energy transfers, there is not enough energy left to support another trophic level.
  • Assimilation is the biomass (energy content generated per unit area) of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste.
  • The extra heat generated in endotherms, although an advantage in terms of the activity of these organisms in colder environments, is a major disadvantage in terms of NPE.
  • Because the NPE is low, much of the energy from animal feed is lost.