In 1873, James Clerk Maxwell proposed that light consists of electromagnetic waves. According to his theory, an electromagnetic wave has an electric field and magnetic field components. These two components vibrate in two mutually perpendicular planes (Figure 1.6). EMR is the emission and transmission of energy in the form of electromagnetic waves. Figure 1.6: The electric field and magnetic field components of an electromagnetic waves Electromagnetic waves have three primary characteristics: wavelength, frequency and speed. Wavelength (λ, Greek lambda), is the distance the wave travels during one cycle (Figure 1.7). It is expressed in meters (m) and often, for very short wavelengths, in nanometers (nm), picometers (pm), or angstrom (Å). Frequency (ν, Greek letter nu) is the number of cycles the wave undergoes per second and is expressed in units of l/second (1/s; also called hertz, Hz).

Photosynthesis

The process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll.

Cellular Respiration

The metabolic processes that convert biochemical energy from nutrients into ATP, and then release waste products.

Ecosystem

A biological community of interacting organisms and their physical environment.

Biodiversity

The variety of life in the world or in a particular habitat or ecosystem.

Natural Selection

The process whereby organisms better adapted to their environment tend to survive and produce more offspring.

Genotype

The genetic constitution of an individual organism.

Phenotype

The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Trophic Levels

The hierarchy of levels in an ecosystem, consisting of producers, primary consumers, secondary consumers, and so on.

Detritivore

An organism that feeds on dead organic material, especially plant detritus.

Homeostasis

The ability of an organism to maintain a stable internal environment despite external changes.