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Lecture 1

BIOL 1000 Lecture 1: BIOL 1000

Course Code
BIOL 1000
Nicole Nivillac

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Chapter 1 Light and Life
1.1 The Physical Nature of Light
2 Major Functions of Light:
1) Energy
2) Information
Electromagnetic Radiation
— Variable wavelengths (distance
between 2 peaks) and energy
Typically measured in
nanometers (10-9 m)
Wavelength & energy is
inversely related
— Visible region of the electromagnetic spectrum that humans can detect with their eyes
— Includes visible light, ultraviolet light, & infrared light
— Shorter wavelength = higher energy
— Longer wavelength = lower energy
— Particle - wave duality: light has both properties of a wave & a stream of photons
Photons — Energy particles that contains a precise energy but no mass
Light Interacting with Matter
1) Reflected off the object
2) Transmitted through the object
3) Absorbed through the object
How is Light Absorbed?
— When energy of a photon is transferred to an electron within a
molecule it excites the electron which moves it from its ground
state to a higher energy shell in an excited state, this can only
happen when energy of photon exactly matches the amount of
energy needed to excite an electron
— Molecules that are highly efficient at absorbing photons
(ex. vision, photosynthesis, dye colours)
— Have a common feature needed for light absorption — covalently linked carbons by
alternating single and double bonds which is a conjugated system of delocalized
electrons so the electron is not attracted to a specific atom/bond and is able to interact
with light
— Colour of pigment is the photon of light that is reflected off the photon

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1.2 Light as a Source of Energy
1) Photosynthesis
2) Cellular Respiration
3) Light Driven Proton Pump
(ex. Halo bacteria)
1.3 Light as a Source of Information
Photoreceptor: light sensor (vision)
— Made of 2 parts: Pigments & Protein
— Most common is Rhodopsin
Rhodopsin has a protein called opsin that binds to a single pigment molecule called retina
Absorption of a photon causes retinal pigment to change shape [cis to trans
(conformational shape)] which then causes changes to opsin protein which then leads to
a downstream of events
— Example: Chlamydomonas — contain rhodopsin & can detect light (advantage:
optimal photosynthesis)
1.3 The Eye
— Organ used to sense light
— Process of vision requires eyes & brain (detailed vision happens in the brain)
Simplest Eye — Ocellus
— Consists of a cup lined with 100 photoreceptor cells
— Example: Flatworms — Information from cerebral ganglion enabling themselves to
swim to/away from light thus dark area = less predation
Compound Eyes
— Built of hundreds of different units called ommatidia which are close together
— Detects movement well, with incoming light focused on a bundle of photoreceptor
cells & signals the brain to receive a mosaic image
— Common in arthropods such as insects & crustaceans
Single-Lens Eyes
— Light enters through transparent cornea, a lens concentrates the light & focuses it on
a layer of photoreceptors at the back of the eye, the retina which sends information
through the optic nerve to the brain

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Chapter 45 Control of Animal Processes: Neural Integration
45.4 Photoreceptors and Vision
— Photoreceptors detect light at certain wavelengths & centres in a brain or central ganglion
integrate signals from receptors — perception of light
— Use retinal to absorb light energy
Invertebrate Eyes
— Coloured component
— Contains muscles that contract, surrounds the pupil (opening where light enters eye) when
light is bright circular muscles contract shrinking pupil reducing light, when light is dim radial
muscles contract enlarging pupil increasing light
— Muscles move lens forward & back in respect to retina to focus on image
Vertebrate Eyes (Humans)
— Contains cornea, iris, retina, pupil & lens just like invertebrates
— Light enters eye through cornea passes iris & then lens, lens focuses image on retina &
axons of afferent neurons originate in retina converge to form optic nerve leading from eye to
Aqueous Humour — Clear fluid fills space between cornea & lens carrying nutrients
Vitreous Humour — Jelly like between lens and retina
Sclera — Outer wall (tough connective tissue)
Choroid — Dark pigmented layer inside that prevents light enter through (except pupil)
Types of Photoreceptors:
1) Rods — Specialized for detection of light at low intensities
2) Cones — Specialized for detection of different wavelengths (colours)
— Lens change shape to focus
— Held in place by fine ligaments, surrounding layer of connective tissue & muscle
(ciliary body)
— Keeps lens under tension when ciliary muscle relaxed, tension flattens lens for
distant objects & when muscles contract, relieves tension lens into sphere for
nearby objects
45.5 Retina of Mammals & Birds Contains Rods, Cones, and a Complex Network of
— Human eyes have more rods than cones all in single layer
— Neural networks of retina on top of photoreceptor cells so light rays focused by lens
pass neurons before photoreceptors in addition to passing blood vessels over retina
— In mammals & birds, cones concentrated in small regions of retina, the fovea
— Image focused on lens is centred on fovea & rods are operated throughout
— Surrounding image that is not on the fovea is our peripheral vision
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