BIO 1000 Notes
Chapter 1.1 Notes:
• Light function #1: Source of energy that directly or indirectly sustains organisms.
• Light function #2: [Source of info] Provides organisms with info about physical world
that surrounds them.
• Ex: Green alga Chlamydomonas = uses light for both energy and information
• Sun releases electromagnetic radiation(differentiable by their wavelength-distance
between two successive peaks) Wavelength = measured in nanometers (10^-9 m)
Light: Portion of the electromagnetic spectrum that humans can detect with their eyes.
Photons: Stream of energy particles (light composed of this) LIGHT = wave of photons.
• Wavelength & Energy inversely related (SHOWN BELOW):
• The longer the wavelength = the lower the energy of the photons it contains.
• Shorter wavelength blue = consists of photons of higher energy than red light.
• 380(400) - 700(750) = visible light = wavelengths we can see.
• Light interacts with matter, when photon hits object, photon has 3 possible fates:
• 1. Reflected off object 2. Transmitted through object 3. Absorbed by
object(must take place if photons want to be used as a source of energy or info)
moved from ground state to excited state(higher-energy level)electron within molecule. Electron
• NOTE: proton only absorbed by electron if photon energy =’s energy difference
between electron’s ground state & excited state. If not = photon transmitted through molecule
• EXCITED STATE ELECTRON = source of energy required for photosynthesis & vision.
Eyespot: Allows individual cells to gather info about location & intensity of light source (light
sensor) DOES NOT GENERATE AN IMAGE---Eye does that.
Pigments: Major class of molecules that ar very efficient at absorbing photons (light absorbers)
• Ex: chlorophyll a(involved in photosynthesis), 11-Cis-retinal(involved in vision),
indigo(dye jeans blue), Carmine, Beta-Carotene
• Pigments absorb light at different wavelengths (cause they differ in # of excited states
available to excitable electrons) Ex: Pigment absorbs only blue photons cause they have only
one high-energy excited state.
• May look different but all have CONJUGATED SYSTEM. BIO 1000 Notes
Conjugated System: A bonding arrangement/region where carbon atoms are covalently
bonded to each other with alternating single & double bonds. RESULTS in delocalization of
electrons(electrons not attached to particular atom or bond in a molecule). CRITICAL TO LIGHT
• PIGMENTS COLOUR = result of photons of light it does NOT absorb(instead reflected
or transmitted through pigment to reach our eyes)
Chapter 1.2 Notes:
• 1. Light absorbed 2. Potential energy of excited electrons within pigment molecules
used in photosynthetic electron transport to synthesize NADPH & ATP 3. Molecules consumed
in Calvin cycle of photosynthesis to convert CO2into carbohydrates(sugar) & release O 2
• Photosynthetic apparatus of a C.reinhardtii cell absorbs millions protons/second.
• Cellular respiration breaks down carbohydrates, trapping released energy as ATP
PHOTOSYNTHESIS(rate of O relea2e) increases in blue/yellow/red light. Not green as
MOST(some is) is reflected not absorbed or transmitted(Why plants green).
• Not all organisms that use light as source of energy are photosynthetic(don’t use light
energy to convert CO 2nto carbohydrates). Ex: Halobacterium(hypersaline enviro) have
pigment-protein complex called bacteriorhodopsin(light-driven proton pump). Its pigment
component(retinal) = captures photons of light that provide energy supply to pump protons out
of cell(creates difference of H+ concentration across plasma membrane = source of potential
energy used by ATP synthase to convert ADP to ATP)
Chapter 1.3 Notes:
Photoreceptor: The basic light sensing system
• Most common in nature = Rhodopsin(basis of vision in animals, in C.reunhardtii serves
as light-sensing unit of the eyespot) -- structurally similar & evolutionarily related to
bacteriohodopsin found in Halobacterium
Rhodopsin Molecule: Consists of opsin(protein) that binds to retinal(single pigment molecule
& derivative of Vitamin A) RHODOPSIN = in bacteria & humans.
Opsin: Membrane proteins that span a membrane multi times and form complex with retinal
molecule at the centre.
• Absorption of photon of light = retinal pigment molecule change shape(straightens-
shape matters) = triggers alteration to opsin protein = alterations in intracellular ion
concentration & electrical signals. ULTIMATELY THEN trigger signaling events, which allows
organism to respond to the light.
• Some organisms can sense light without eyes (Plants,Algae,Invertebrates, some
Eyespot of C.Reinhardtii = found within chloroplast in region associated with cell membrane.
Composed of 2 layers of carotenoid-rich lipid globules(focus & direct incoming light toward
photoreceptors) BIO 1000 Notes
• Eyespot has no role in photosynthesis = instead photoreceptors allow cell to sense
light direction & intensity (ex: move away from predators)
• Using flagella, C. respond to light by swimming toward or away from light(called
• Phototaxis = allow cell to stay in optimum light environment to maximize light capture
• Light absorption(eyespot) = linked to swimming response by a signal transduction
pathway(light absorption triggers change in ion concentration(k,ca), which generate electrical
events THAT change beating pattern of flagella.
Phytochrome: Photoreceptor in plants that senses the light enviro & essential for
photomorphogenesis(normal developmental process activated when seedlings exposed to light
• present in cytosol of all plant cells. seedlings exposed to wavelengths of red light =
phytochrome becomes active & starts signal transduction pathway that reaches nucleus.
• In nucleus = signals activate genes which code for proteins involved in photo & leaf
- ABSORB RED LIGHT. CONTAIN chromophore which are linked to proteins
Differentiation between eye of invertebrate & eyespot of C.Reinhardtii:
• Vision. Vision needs eye to focus & absorb light but also brain(or simple nervous
system) to interpret signals from eye. WE SEE WITH OUR BRAIN NOT EYES.
Ocellus: Simplest eye, consists of a cup or pit lined with up to 100 photoreceptor cells.
• Photoreceptor cell = is a modified nerve cell that contains thousands of individual
• Flat worms of genus Planaria contain ocelli = allows them to orient themselves in
response to light
• Eye of planaria not much more advanced than eyespot of C.Reinhardtii = both sense
light intensity & direction to a light source.
2 types of image-forming eyes:
1. Compound eyes = Built of 100‘s of ommatidia(individual units) fitted together. Common in
arthropods(insects&crustaceans). Incoming light focused onto bundle of