Chapter 1: Life & Light 10/21/2010 1:24:00 PM
1.1 The Physical Nature of Light
Light is a portion of the electromagnetic spectrum (Figure 1.4). It is made of particles of energy
(photons). One photon is 3.01x10 -19J/photons. Light is used for these two reasons: (1) It’s a source of
energy for life, and (2) it gives information about the environment. When light photons hit an object it
can be (1) reflected off, (2) transmitted through, or (3) absorbed by the object. In the process in which a
molecule absorbs photons of light called pigment. Pigments all have one thing in common in terms of
light absorption, and that is that the carbon atoms are all covalently bonded with alternating single and
double bonds (conjunctive systems). Thus, for this reason with no particular closely related atom, they
are able to interact with photons of light.
Photon (light) Electron (pigment)
EXAMPLE we can use it chlorophyll. It is important to keep in mind that only one excited
photon can pair with only one chlorophyll molecule. Also, the energy of the photon must
match/equal the frequency (characteristics) and the wavelength (required) so that the
photon is absorbed. If it does not match then the photon will be reflected off or transmitted
through. When the photon is absorbed it allows the electrons in the chlorophyll to move up
an orbital (shell) which in turn excites the photon (^^). In this case the chlorophyll absorbed
only blue and red, whereas, the green light is being reflected off/transmitted through
because its energy (wavelength) level does not match (Refer Figure 1.4). Thus giving
chlorophyll (plant) its green color.
An action spectrum will allow us to see the effectiveness of different wavelengths of light (Figure 1.8
graph of wavelengths & how it affects photosynthesis through chlorophyll a)
1.2 Light as a Source of Energy
The source of energy found in light is also used to energize (work) the breaking down of
EXAMPLE of this could be used in the photosynthesis electron transport where they you
energy filled compounds like NADPH and ATP to convert CO2 into carbohydrates. The
biological molecules could also be lipids (fats), proteins, and nucleic acids found in the
EXAMPLE Prokaryote Group = Halobacterium are extremophiles. In such harsh conditions,
they contain protein complexes called bacteriorhodopsin. This proteins role is to be a light-
driven proton pump, which means it is the proton used to synthesize ATP.
1.3 Light as a Source of Information
Organisms use light as a sensor.
The most universal light-sensing system is the photoreceptor, such as rhodopsin. EXAMPLE Rhodopsin consists of a protein (opsin) that binds a pigment molecule (retinal).
When it absorbs the light photon the retinal changes its shape which triggers the change to
the protein/opsin molecule. This is what allows the organism response to light.
For organisms that lack eyes,
EXAMPLE Prokaryotes use the process of phototaxis to sense light.
EXAMPLE Plants use the process of photmorphogensis to sense light.
EXAMPLE Complex organisms have “Image-forming eyes” (camera eyes(
o Compound eyes are commonly found in insects.
Darwin theory gives us insight that even though an eye of a human is so complex you also need the
brain of the human to be as complex, which allows the information process to become more advanced.
1.4 Light can Damage Biological Molecules
As we know light is essential to life on Earth, although it is only a small wavelength from 400-700nm
which is used for photosynthesis, vision, phototaxis, navigation, and many other light-driven processes.
Living things are made up of molecules that are strongly held together by chemical bonds, in spite of
that, wavelengths that are shorter (ionizing radiation) than light, can destroy all these bonds. Short
wavelengths are absorbed by the ozone layer, whereas longer wavelengths are absorbed by the water
vapor and CO i2 the atmosphere. Absorption of longer wavelengths would increase the orbital of the
pigment through oxidizing the molecule creating ions. They also