Chapter 1 – Light and Life
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Major Themes Covered in Chapter 1:
The physical nature of light
Light as a source of energy
Light as a source of information
Light can damage biological molecules
Role of light in ecology and behavior
Life in the dark
Organisms making their own light: bioluminescence
1.1 The physical nature of light
Chlamydomonas reinhardtii is a very common
form of single-celled green alga. It is an
excellent example of an organism that uses light
as a form of energy and information. Each cell
has a huge chloroplast to process light and signal
to the flagella to move to an optimal position for
light absorption.
The Sun:
Earth has the optimal distance from the sun allowing proper light absorption. Light then
converts matter into energy. Produces electromagnetic radiation off all different wavelengths.
Electromagnetic radiation: Moves in the
form of two
waves, one
electrical and
on magnetic,
which are
oriented at 90
degrees to each
other.
Many of the
wavelengths
are reflected,
some do not
reach the earth.
Shorter wave
length is higher
energy (ex.
Purple and blue) and longer wave length is less energy (ex. Red).
What is light?
Light is the electromagnetic radiation that humans can detect with their eyes. It is a wave of
discrete particles called photons. Light behaves as waves and photons.
To be used, light energy must be absorbed by molecules called pigments.
The light being absorbed is interacting with the matter. Ex light interacts with pigments in
chloroplasts driving the photosynthetic process. This interaction is important.
When light is absorbed by a pigment it causes molecular changes in said pigment.
Light can be used in three ways: transmitted, absorbed, and reflected. The most important to
our study is the absorbed light.
Pigment Structure:
The pigment has a conjugated structure that has a commonality in every pigment; they have
alternating single and double bonds in the carbon chain.
At the molecular level, there is a delocalized electrons that are free to interact with the
photons from light. Absorption of light by Chlorophyll:
One or more electrons are being excited to
a higher energy state.
There is not a higher energy state that green
light can be promoted to. The amount of
energy in the photon absorbed must match
the difference in energy between the
ground state and the higher energy state.
It is the absorbance of one photon can
change the excitation state of one electron. Chapter 1 – Light and Life
Action Spectrum:
The effectiveness of
different wavelengths of
light and photosynthesis.
These shorter wave
lengths of light are more
efficient at driving
photosynthesis
Green wavelengths of
light drive photosynthesis
because there are more
pigments then just
chlorophyll
1.2 Light as a Source of Energy:
Absorption of light by a pigment results in electrons becoming excited
Represents a source of potential energy.
The pigment is converting light energy into potential energy that is then used to dive
the photosynthetic process.
It is potential energy because the electron is now in a higher state of energy of which
it does not wish to remain; wanting to give off energy
Halobacteria:
Halobacteria can also capture light energy via a pigment molecule called retinal
The halobacteria are pick as a result of the molecule it uses to capture light energy
The defining characteristic of this bacteria is a protein call bacteriorhodopsin which
holds the pigment molecule retinal
The protein absorbs photons of light and changes its structure once this absorption
occurs and the electrons are promoted to a higher energy state. When the protein
becomes activated by the change in structure it pumps on hydrogen ion out (causing
ATP synthase) and the protein reverts back to its original structure.
1.3 Light as a Source of Information
Photoreceptors: A photoreceptor is a basic light-sensing system, found almost universally in all
organisms (the most basic type at the
molecular level).
Rhodopsin: Most common
photoreceptor in nature
o Basis of vision in animals
o Also used by many other
organisms
o Consists of a pigment
molecule (retinal) bound to a
protein (opsin)
o It is a membrane protein that
has seven trans membrane
domains
o When it absorbs a photon of
light it changes its state. The
structural change is big
enough that it activates the protein.
o It is a G-protein coupled receptor
An eyespot
o Sensing light without eyes
o Allows sensing of light direction and
intensity
o Organism responds by phototaxis
o The yellow globules are full of
rhodopsin, serves as the photoreceptor
o Senses the direction and the intensity of
light
o As the direction and the intensity of the
light changes so do the conditions within the cell. Optimizes the amount of
energy that it is receiving as an indicator of where to move
Photomorphogensis
Phytoc
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