Biol 1000 – Light and Life September 7 , 2012
Astrobiology refers to the study of life in the universe
We must know how life sustaining environments exist. Through experimentation and
hypothesis, we can figure out what is needed for life to exist.
Food, water, oxygen, proper atmosphere, LIGHT AND ENERGY
Science is a dynamic discipline, through research we can figure out how events occur
Light refers to the region of the electromagnetic spectrum that humans can detect with their
eyes. (The spectrum of visible light)
It consists of shorter wavelengths and longer wavelengths.
The photoreceptors that humans have can only detect wavelengths from 380 nm – 750 nm.
The shorter the wavelength, the higher the amount of energy that is present. The longer the
wavelength, the lower the amount of energy that is present.
These waves are made up of small energy packets called photons.
These photons are present throughout the EM spectrum; a photon within the visible light
spectrum is called a visible light particle.
Photons have a precise amount of energy, but they have no mass.
How can we tell that photons from other areas in the spectrum are present?
For example UV rays cause sunburn, therefore these particle exist because they show a
physical manifestation on you. We can’t see these waves, but we know they exist through
How can photons interact with matter?
For example with a chloroplast, light can be reflected and bounced away, transmitted through
and interacts with nothing, or it can be absorbed by the object.
Absorption is the most useful interaction because you can only use something if it absorbed.
How does this absorption occur? It occurs through pigments.
Pigments have a molecular structure that allows them to absorb light energy.
The colour we see on a pigment is the wavelength that is being REFLECTED! That wavelength
was not absorbed. If it is reflected, that is the colour you will see.
These pigments consist of alternating double-single bonds. This is called the conjugated system.
These pigments differ depending on the wavelengths they can absorb.
For example, chlorophyll a is heavily involved in vision, retinal is involved in vision, carmine can
be found in sea animals, beta carotene can be found in fruits and vegetables, any phyto-
pigment is related to plants, for example the phyto pigment in the PowerPoint slide is related to
Indigo is extracted from plants and is used primarily for dyeing.
These chemical structures are important because they allow us to determine what wavelengths
they will absorb.
How are light and life linked?
Light has many different functions, but the first thing to remember is that light is a source of
energy, including us. One of the main processes that it is involved in is photosynthesis.
Photosysnthesis occurs when energy is obtained from the sun, and this energy undergoes this
process with carbon dioxide to create sugar and other food molecules (carbohydrates). Plants
will also release oxygen into the environment.
This energy is then converted to glucose, living animals then consume this glucose and utilise it
for cellular respiration. Oxygen for this process is obtained from the plants.
All life depends upon capturing energy from the sun and converting it into a form that living
organisms can use. (Plants need us, we need plants)
Photosynthesizing organisms (plants) can be any colour in the visible light spectrum. The
difference in colour reflects the wavelength that reflects off the plant, as mentioned above.
Organisms also use light as a source of information!
This occurs through photoreceptors. Photoreceptors are light sensitive proteins that are
involved in the sensing and response to light in multiple organisms.
(Refer to photoreceptor slide) The orange and yellow mesh is the cell membrane; the
photoreceptor is referred to as a trans-membrane protein. Within the protein, there is an
associated pigment molecule. In the case of the example shown on the slide, the pigment is
retinal. Light will hit that photoreceptor, and the photoreceptor will undergo a confirmational
change, the pigment will change shape. Because the pigment changes shape, this results in the
protein changing shape. This process (which is much more complex, it is grossly simplified in this
example) is referred to as a sig