The cell cannot derive any benefit from the heat energy it releases unless the heat-generating reactions inside the cell are directly linked to the processes that generate molecular order. It is the tight coupling of heat production to an increase sea of matter cell
Figure 2–15 an everyday illustration of the spontaneous drive toward disorder.
Reversing this tendency toward disorder requires an intentional effort and an input of energy: it is not spontaneous. in fact, from the second law of thermodynamics, we can be certain that the human intervention required will release enough heat to the environment to more than compensate for the reordering of the items in this room.
Figure 2–16 a simple thermodynamic analysis of a living cell. in the diagram on the left, the molecules of both the cell and the rest of the universe (the sea of matter) are depicted in a relatively disordered state. in the diagram on the right, the cell has taken in energy from food molecules and released heat through reactions that order the molecules the cell contains. The heat released increases the disorder in the environment around the cell (depicted by jagged arrows and distorted molecules, indicating increased molecular motions caused by heat). as a result, the second law of thermodynamics—which states that the amount of disorder in the universe must always increase—is satisfied as the cell grows and divides. for a detailed discussion, see panel 2–7 (pp. 102–103).
heat is released to pull of the foor 1 potential energy due to position kinetic energy heat energy two hydrogen oxygen gas rapid vibrations and heat dispersed to gas molecules molecule rotations of two newly surroundings formed water molecules in order that distinguishes the metabolism of a cell from the wasteful burning of fuel in a fire. Later, we illustrate how this coupling occurs. For now, it is sufficient to recognize that a direct linkage of the “controlled burning” of food molecules to the generation of biological order is required for cells to create and maintain an island of order in a universe tending toward chaos.
Cells obtain energy by the oxidation of organic molecules
All animal and plant cells are powered by energy stored in the chemical bonds of organic molecules, whether they are sugars that a plant has photosynthesized as food for itself or the mixture of large and small molecules that an animal has eaten. Organisms must extract this energy in usable form to live, grow, and reproduce. In both plants and animals, energy is extracted from food molecules by a process of gradual oxidation, or controlled burning.
The Earth’s atmosphere contains a great deal of oxygen, and in the presence of oxygen the most energetically stable form of carbon is CO2 and that of hydrogen
Figure 2–17 Some interconversions between different forms of energy.
all energy forms are, in principle, interconvertible. in all these processes the total amount of energy is conserved. Thus, for example, from the height and weight of the brick in (1), we can predict exactly how much heat will be released when it hits the floor. in (2), note that the large amount of chemical-bond energy released when water is formed is initially converted to very rapid thermal motions in the two new water molecules; but collisions with other molecules almost instantaneously spread this kinetic energy evenly throughout the surroundings (heat transfer), making the new molecules indistinguishable from all the rest.
is H2O. A cell is therefore able to obtain energy from sugars or other organic molecules by allowing their carbon and hydrogen atoms to combine with oxygen to produce CO2 and H2O, respectively—a process called aerobic respiration.