Light Flashcards
Cataracts
The lens in the eye becomes opaque because of protein denaturation that inhibits some wavelengths entering. Decreases the blue spectrum
Physical nature of light
Provides energy (direct or indirect) and provides information about the world around us
How the sun works
Converting hydrogen into helium, which converts matter into energy (EMR)
EMR
Energy that travels in waves at the speed of light.
Wavelength range of EMR
10^-12-10^6 (cosmic to radio waves)
Light
The portion of EMR that humans can detect with their eyes. 400-700 nm
Physics definition of light
Also includes ultraviolet and infared
Wave particle duality
Has no mass, is a wave and a photon particle. Creating a wave of photons.
Wavelength and energy relationship
Inverse
3 options for a photon hitting something
- Reflected
- Transmitted through
- Absorbed (the only way it can be used as energy)
Absorption process
A photon is transferred to an electron in a molecule. The electron is excited out of ground state, that state can be used for energy
Absorption only happens if
The energy of the photon exactly matches the amount needed to excite the electron
Pigment
Molecules that are good at absorbing light such as chlorophyll, retinal, and indigo
Why is pigment a good absorber
Because of the conjugated system.
Conjugated system
A region where carbon atoms covalent bonds alter single and double causing a delocalization of electrons. They are not busy so they can interact with photons
Colors of pigments
Every chemical structure has a unique energy and therefore absorbs a unique wavelength. The color is the not absorbed wavelengths
Ultimate energy source
The sun
Photosynthesis
Plants use photons to make CO2 into glucose. Light enters the biosphere through this process.
Not all that use light as energy are photosynthetic
There is not always a conversion of CO2 to glucose
Halobacterium
Archaea that contain a light driven proton pump called bacteriorhodopsin. The energy is used but not to make glucose
Rhodopsin
A common photoreceptor. Made of opsin protein that is bended with retinal pigment
Opsin
Spans the membrane many times. Retinal is in its middle
Photons enters the eye then…
Retinal pigment changes shape, alters the opsin protein, eventually leading to vison by altering intracellular concentration
Scale of photoreceptiors
125 million receptors per eye, millions of rhodopsin per receptor
Channel rhodopsin and bacteriorhodopsin
Structurally similar to rhodopsin, but evolutionarily different
Other photoreceptors
Less common, but are used to see different wavelengths of light
Opsin and the nose
Proteins very similar are used for smell. Therefore they are good at sensory perception
Sensing light without eyes
Used by plants, algae, invertebrates and some bacteria
C. reinhartii
An eyespot in the chloroplast that is 2 layers thick that focus and direct light to the photoreceptors. Doesn’t play a role in photosynthesis
Phototaxis
C. Reinhartti uses flagella to swim to or from light
Light absorption pathway
Triggers rapid response in ion concentration which triggers electrical events, which lets the cell move
Phytochrome
A photoreceptor critical for photomorphogenesis. Present in the cytosol and is red light activated. Tells the nucleus to make leaves
Photomorphogenesis
The developmental process when seedlings are exposed to sunlight
The eye
An organ animals use to sense lights. Distinguished from and eye spot via vision
Vision
Requires an eye and brain (or basic nervous system). Proves the eye and brain coevolved
Ocellus
The simplest eye. A photoreceptor lined pit
Photoreceptor
Modified nerve cell from photoreceptor molecules
Flatworms
Information about the ocellus-to the cerebral ganglion for orientation. How they avoid predication
Eye advancement
Produce an image of desirable objects and shapes
Compound eye
Common in insects and coruscations. 100’s of tightly packed ommatidia each gather a little bit of visual information. The brain gets a mosaic image.
What are compound eyes good at?
Detecting movement
Single lens eye (camera-like eye)
Humans, other vertebrates. Light enters one lens, hits the retina that sends the signal to the optic nerve
Darwin
Didn’t think the eye was from natural selection
Eyes today
Started with oight sensitive cells 500 million years ago. They have evolved from over 1000 species
Most eyes
Are fundamentally the same. Gene Pax6 is the master for eye formation. Rapid eye improvements are critical for survival
Why do we use visible light
It is the most plentiful on earth, and has the right amount of energy to break the bonds
Shorter wavelengths
Absorbed by the ozone layer
Longer wavelengths
Absorbed by carbon dioxide and water
What light is damaging
Ultra violet radiation that comes with visible light photons
Photo-oxidative damage
Too much light absorption by the retina. Excited electron react with oxygen causes water to become hydrogen peroxide
Plants and photo-oxidative damage
Often experience this damage. It can be repaired quickly
Ultraviolet light
200-400nm. Higher and therefore more damaging energy. Longer waves reach earth’s surface
Ozone layer
Protects the earth from short EMR wavelengths. O2 + ultraviolet photon— O3
Ionizing radiation
Photons are energetic enough to remove electrons and form ions. DNA is very susceptible to this
Dimer
When 2 neighboring bases covalently bons altering the DNA’s shape. Hinders replication and gene transcription.
Dimer outcomes
It can be fixed by enzymes or lead to skin cancer
Melanin
A pigment that absorbs ultraviolet light. Protects the human skin and is in squid ink
Spectrophotometer
A tool to detect the wavelengths of light that are not absorbed by something. Used to make a absorption spectrum
Absorption spectrum
A graph of absorbance vs wavelength
Melanocytes
Skin cells where melanin is produced
Why skin color
A balance of ultraviolet protection and vitamin D absorbtion
Circadian rhythms
Internal clock controlled by sleep/wake schedule, body temperature, metabolism, cell division, and mating.
Circadian rhythms set
Is set by the light pattern outside, but once done is good to go for a while
How were circadian rhythms discovered
In 1729 someone put plants is a dark room for a while and found they reacted the same as the did in the light
The clock gene
Transcription is controlled on a 24 hour cycle. Leads to circadian rhythms
All organisms studied
Have a circadian rhythm therefore it must have a purpose. Lets organisms predict and act preemptively on events
Photoperiod
Day length
Organisms clocks track…
Seasons by tracking the photoperiod. Tells them when to flower, fur, mate, migrate
Periperal clocks
Set by the suprachiasmatic nucleus (SCN). A small part in the brain.
SCN
Releases melatonin from the pineal gland for sleep
Jet lag
Day light and circadian rhythms are out of synch. Shows that biological clocks are not easily reset
Jet lag symptoms
Lack of appetite, fatigue, insomnia, or mild depression
Color as a signal
Use as a signal for mating and a sign of good health. Males are more colorful often to attract women.
Carotenoid in animals
Allows for pigment to be made, and shows a healthy diet. Breaks down harmful oxygens
Color in plants
Used to attract pollinators
Pollination
Movement of the pollen from anthers (male) to the female stigma
Animals and pollination
They are there for the food the pollen produces and pollination happens as a result
Flower-pollinator associations
Coevolution of plants and animals to have the right amount of food and pollination
Coevolution
A change in 1 leads to a change in the other. Shape, size, colour of a plant to attract the evolving animals
Bee pollination
Blue, yellow and ultraviolet plants are targeted as bees can’t see red
Camouflage
Hiding using similar appearances to the environment. Can be color, patters and behaviors.
Camouflage example
Peppered moths
Light pollution
Bad for nocturnal animals as their hunting advantage is gone. Turtles can’t find the ocean, and birds keep running into lights
Life in the dark
Our eyes loose color then shape because rods don’t see color and are active at night.
Nocturnal vision
Often have bigger eyes to get more light in. They have specially designed compound eyes
Eye evolution
Animals always in the dark (underwater or underground) have lost eye function. They still have functional receptors to set circadian rhythms
Bioluminescence
The process of animals making their own light.
How does bioluminescence work
The opposite of photosynthesis. ATP excites an electron into an excited state. When if falls back down a photon of light is released
Bioluminescence efficiency
95% compared to the 5% of a lightbulb
Why bioluminescence
Attract a mate or prey. Camouflage or communicate
Dinoflagellate
Bioluminescence buddies. When they are shook they release light which then makes the predators visible to their predators
Quorum sensing
Communication through light. Behind the phenomenon of milk seas. Mostly occurs in the deep sea where they is no natural light.
