Light and Life
Why it Matters?
Because of light we are able to see colors. Reason being that the color is reflected off the object.
The rest of the colors are absorbed by the object. For example green light is reflected off the leaf.
The rest of the colors are absorbed by the leaf.
1.1 The Physical Nature of Light
Two important functions of light:
A source of energy that sustains all organisms
Provides information about the physical world that surrounds organisms
o Example: Chlamydomanas Reinhardtii
Single celled – Eukaryote
Ponds and lakes
One chloroplast that absorbs energy to do photosynthesis.
Light sensor in the eye allows the gathering of information
(location and intensity of light)
1.1a What is Light?
Due to the exact distance between the earth and the sun, the sun is able to make energy
off of matter in a matter of seconds. This helps life to sustain on earth.
Light is the most common part of the electromagnetic spectrum that humans are able to
detect with their eyes.
Light has no mass
Light is composed of photons which is a stream of energy particles.
The longer the wavelength the lower the energy of photons it contains.
1.1b Light Interacts with Matter
Light is able to interact with matter and cause change which allows living things to use
Light can do three actions
o Reflect off the object
o Transmit through the object
o Absorbed the by the object
To be used as a source of energy light needs to be absorbed
If the energy of the photon matches the difference of the electrons ground state and
excited state, only then the photon is able to give energy to the electron. Once the energy is given to the electron it moves the electron moves from the ground
state into the excited state.
Pigments also absorb photons very efficiently which. This is what allows us to see color.
The reason why pigments are able to absorb photons so efficiently is because they
contain a conjugate system. Conjugated system is a system in which the carbon atoms are
covalently bonded to one another with alternating single double bonds.
1.2Light as a Source of Energy
Light is a source of energy due to the process of photosynthesis. During photosynthesis a
photon is absorbed by leaves which are then used to produce glucose.
This glucose is then used in cellular respiration to produce ATP. Because of ATP we are
able to do action and bring about our day to day lives.
An archea halobacterium absorbs a photon of light which causes the archea to pump
protons out of the cell creating a proton gradient. This proton gradient causes potential
energy. This creates the energy to create ATP.
1.3Light as a Source of Information
Light is used to provide organisms with the knowledge of what is around them.
1.3a Rhodopsin, the Universal Photoreceptor
The basic light seeing system is known as a photo receptor. The most common is
Rhodopsin consists of a protein called opsin. Opsin forms a complex with retinal in the
center of the retinal.
Once the rhodopsin absorbs light it the opsin changes shape.
1.3b Sensing light without eyes
There are many plants and living organisms that can sense light without the organ of the
In reinhardtiis the eyespot is in the chloroplasts. It is composed of carotenoid rich lipid
globules that help to direct the light toward the photoreceptors.
Eyespot does not play a role in photosynthesis.
Photoreceptors allow the cell to sense light direction and its intensity.
According to that, flagella either cause the light o move away from the cell or towards the
cell. This allows the cell to stay in the maximum amount of light it needs.
Light absorption- swimming away or towards light- rapid changes in concentration ions
which creates energy for the flagella to move. In pants the photoreceptor phytochrome senses the light and sends signal to the nucleus
for the development of a new leaf or to code for protein needed in the process of
1.3c The eye
The eye is an organ in animal used to sense light.
To be able to see with the eye, the brain and the eye need to work together.
o is the simplest eye.
o It consists of 100 photoreceptor cells.
o Photoreceptor cells contain individual photoreceptor molecules.
o The light hits the cerebral ganglion and orient them work away from the light
towards darker areas.
o Organ can sense light and direction to a light
o Objects and shapes can be seen as well
Common in an arthropods such as insects and crustaceans
In these insects there hundreds of eyes that are fitted closely to
each other. The singular form is ommatidium
The photoreceptor cells detect light which helps the brain create a
mosaic image of the world
Compound eyes cause it to easily detect motion.
Single Lens Eye
Light enters through the cornea. The lens concentrate the light and
focus it on a layer of photoreceptor cells at the back of the eye, the
retina. The retina sends the information to the brain through an
1.3d Darwin and the Evolution of the Eye
The eye has evolved into a single lens eye has guessed by Darwin. See page 11!
1.4 The Uniqueness of Light
Light is the narrowest band of the electromagnetic wavelength, yet it is used the most by
Wald reasoned that visible light is used mostly by organisms because it’s the most
dominant form of electromagnetic radiation that reaches the earth.
The energy light contains is the right amount of energy for bonds to get bursts of energy
and for life to be sustained on earth. Other wavelengths such