Everything that takes up space and has mass is matter. Matter is recycled over and over again. Matter consists of elements. Atoms are the smallest particles that exhibit the characteristics of an element. Forms of the same element that differ in atomic mass are called isotopes. Atoms often to join to form compounds. A pair or group of atoms that can exist as a single unit is known as a molecule. Charged atoms are called ions. Substances that readily give up hydrogen ions in water are known as acids. Substances that readily bond with H+ ions are called bases. We describe the strength of an acid and base by its pH. Acides have a pH below 7; bases have a pH greater than 7. There are four major categories of organic compounds in living things: lipids, carbohydrates, proteins, and nucleic acids. All living organisms are composed of cells. Enzymes are a special class of proteins. Altogether, the multitude of enzymatic reactions performed by an organism is called its metabolism.
Energy is the ability to do work. The energy contained in moving objects is called kinetic energy. Potential energy is stored energy that is latent but available for use. Chemical energy is potential energy stored in the chemical bonds of molecules. Heat is the energy that can be transferred between objects due to their difference in temperature. The study of thermodynamics deals with the rates of flow and the transformation of energy from one form or quality to another. The first law of thermodynamics states that energy is conserved; that is, it is neither created nor destroyed under normal conditions. The second law of thermodynamics states that, with each successive energy transfer or transformation in a system, less energy is available to do work; that is, energy is degraded to lower-quality forms, or it dissipates and is lost, as it is used. Nearly all energy for life comes from the sun. Green plants capture this energy through photosynthesis; plants and animals release this energy through cellular respiration.
Ecology is the scientific study of relationships between organisms and their environment. In biology, species generally refers to all organisms of the same kind that are genetically similar enough to breed in nature and produce live, fertile offspring. A population consists of all the members of a species living in a given area at the same time. All the populations living and interacting in a particular area make up a biological community. An ecosystem is composed of a biological community and its physical environment. The environment contains abiotic factors and biotic factors. Organisms that photosynthesize are known as producers. Other organisms in the ecosystem are consumers of the chemical energy harnessed by the producers. A food chain is a linked feeding series. Individual food chains become interconnected to form a food web. An organism’s feeding status can be expressed as its trophic level. Herbivores are plant eaters, carnivores are flesh eaters, and omnivores eat both plant and animal matter. One of the most important trophic levels is occupied by the many kinds of organisms that remove and recycle the dead bodies and wastes of others. Scavengers clean up dead carcasses; detritivores consume litter, debris, and dung; and decomposers complete the final breakdown and recycling of organic materials. As a broad generalization, only about one-tenth of the energy in one trophic level is represented in the next higher level. The amount of energy available is often expressed in biomass.
Water, carbon, nitrogen, and phosphorus are critically important to living organisms. The hydrologic cycle distributes water among atmosphere, biosphere, surface, and groundwater. The carbon cycle begins with the intake of carbon dioxide by photosynthetic organisms, which produce plant cells from the carbon, and carbon dioxide is eventually released during respiration, closing the cycle. Photosynthesis, accumulation of organic matter in soils and wetlands, and deposition of calcium carbonate (in the skeletons of some marine organisms) remove atmospheric carbon dioxide; therefore, expansive forested areas and the oceans are important carbon sinks. Bacteria in soil and water provide chemical reactions that drive many parts of the nitrogen cycle. On the scale of centuries, the phosphorus cycle is really a one-way path (to ocean sediments), because phosphorus has no atmospheric form in which it can quickly circulate.
—March 2021
Lance Jones 