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BIOL 1000 Study Guide - Midterm Guide: Osmoregulation, Ethanol Fermentation, Amphiphile

Course Code
BIOL 1000
Y I Sheng
Study Guide

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Light and Life Learning Outcomes
Define/Explain Key Terms:
Electromagnetic Radiation form of energy that is all around us and takes many forms, such as
radio waves, microwaves, X-rays and gamma rays. Sunlight is also a form of EM energy, but
visible light is only a small portion of the EM spectrum, which contains a broad range of
electromagnetic wavelengths.
Wavelength of Light Commonly defined as the part of the EM that is visible to us. Ranges
from 400-700nm and a color range from violet to red.
Photon Discrete bundle of electromagnetic (light) energy. Packets of energy.
Pigment Molecules that can absorb a photon of light.
Photoreceptor Sensory receptor that detects the energy of light.
Absorption Spectrum A curve representing the amount of light absorbed at each wavelength.
DNA Deoxyribonucleic Acid Carrier of genetic information.
Eye Organ used by animals to sense light.
Eyespot light sensitive pigmented spot on the bodies of invertebrates such as worms. Also
called stigma is a heavily pigmented region in certain one-celled organisms that apparently
functions in light reception.
Camera Eye - as light enters through the transparent cornea, a lens concentrates the light and
focuses it onto a layer of photoreceptor cells at the back of the eye, the retina and the
photoreceptors send information to the brain through optic nerves
Circadian Rhythms any biological activity that is repeated in cycles, each 24 hours long,
independent of any shifts in environments.
Explain two major functions of light in living systems; compare and contrast the different
ways that light can interact with matter. [Comprehension]
Two Major Functions of Light
1. Light as a Source of Energy The ultimate source of this energy is light from the sun,
which is made accessible to biological systems through the ability of plants and related
organisms to convert this light energy into a chemical form. This is known as
photosynthesis, plats absorb photons of light and use the potential energy to convert
Co2 into sugars (carbs). Also the energy from the sun enters the biosphere through
photosynthesis. Following the light absorption, the potential energy of the excited
electrons within chlorophyll (green pigment in all green plants and cyanobacteria) is
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used in photosynthetic electron transport to synthesize the energy-rich compounds
NADPH and ATP. These molecules then get consumed in the Calvin cycle of
photosynthesis to convert Co2 into carbs. While photosynthesis converts Co2 into carbs,
it is the process of cellular respiration that breaks down the carbs and other molecules,
trapping the released energy as ATP.
2. Light as a Source of Information many organisms use light to sense their environment
to provide them with crucial information about what is around them. Sense light
direction and intensity, which helps organisms because the mechanisms involved in
swimming will either swim towards or away from the light known as photo axis.
Compare and Contrast the different ways that light can interact with matter.
Although light has no mass it is still able to interact with matter and cause change.
When a photon of light comes in contact with an object it can either be reflected off the
object, transmitted through the object, or absorbed by the object. In order for a photon
of light to be used as a source of energy or information it must be absorbed by the
object. This happens when the energy from the photon of light put an electron into an
excited state (moving it to a higher a higher energy level rather than ground state). Also
the to eegys the eegy fo the photo ad the eegy euied to put the
electron into an excited state must be exactly identical otherwise the light will just be
transmitted through the molecule or reflected.
Describe the general physiology of the human eye (camera eye) and how light is sensed.
[Comprehension] UNFINISHED.
The eye is an organ used by animals to sense light. The process of vision does not only
require the eye to absorb the light but also a brain or a simple nervous system to
interpret the signals sent from the eye. Since the detailed visioning processing occurs in
the brain and not the eyes it is often said that we see with our brains and not our eyes.
Describe how organisms can sense light with and without image-forming eyes (including
structure and function of photoreceptors). [Comprehension]
Organisms such as plants, algae, invertebrates and even some bacteria can sense light
without eyes. As an example we can take a close look at the eyespot of C. Reinhardtii.
The eyespot is a light sensitive structure that is approximately 1m in diameter and is
found within the chloroplast of the cell in a region very closely associated with the cell
membrane. The eyespot is composed of two layers of carotenoid rich lipid globules that
play a role in focusing and directing incoming light toward the photoreceptor molecule
channelrhodpsin. The eyespot does not play a role in photosynthesis even though it is
found in the chloroplast. The eyespot allows the cell to sense light direction and
intensity. Using a pair of flagella, C. Reinhardtii cells respond by either swimming
towards or away from the light in a process called photo axis. This allows the cell to
optimize the light environment in order to maximize light capture for photosynthesis.
Light absorption by the eyespot is inked to the swimming response by a signal
transduction pathway; light absorption triggers a rapid change in the concentrations of
ions including potassium and calcium which generate electrical events which in turn
change the beating pattern of the flagella used for locomotion. In plants a
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photoreceptor cell called phytochrome senses the light environment and is crucial for
photomorphogenesis, the normal development process activated when seedlings are
exposed to light. Phytochrome is present in the cytosol of plants and when a seedling is
exposed to red wavelengths of light phytochrome becomes activated and initiates a
signal transduction pathway that reaches the nucleus. In the nucleus these signals
activate hundreds of genes many of which code for proteins involved in photosynthesis
and leaf development.
Describe the molecular basis of colour vision [Comprehension] and describe the outcome of
missing one or more opsins [Application]
Cone cells in the retina of the eye allow light of different wavelengths to be interpreted
as color in the brain. To produce the signal for color vision, retinal must stimulate the
opsin protein but this cannot occur while the retinal molecule is in its cis- conformation.
There are three types of proteins in cone cells for color sensing, S, M, L. S is for short
wavelength of blue light, M is medium for green light, and L is for long wavelength red
light. The L opsin differs from the M opsin in three significant places in the amino acid
sequence: Position 180: alanine to serine Position 277: phenylalanine to tyrosine
Position 285: alanine to threonine. The lack of L opsins will result in color blindness (S
opsin is in every eye). The outcome is that you will either have dichromatic vision which
is color blindness or trichromatic vision which is the norm. The gene coding for the s
opsin(SWS) is located on chromosome 7. The gene coding for the M(MWS) and L(LWS)
opsins are located on the X-chromosome. The L gene arose through gene duplication
and gene mutation of the M gene on the X-chromosome.
Describe the importance of circadian rhythms [Comprehension].
Circadian rhythms are not driven by an organism constantly detecting changes in day
light bur rather are governed by an internal biological clock (AKA circadian clock). A key
attribute of this clock is that it can run independent of external conditions a phenomena
known as free-running. The presence of biological clocks enhances an ogaiss ability
to survive under ever changing environments by giving them the ability to anticipate or
predict when a change will occur instead of responding after a change has occurred. It
also increases survivability because it enables organisms to restrict their activities to
specific most beneficial times of the day. Activities including: finding a mate, avoiding
predators. In many organisms, proteins required for DNA replication are controlled by a
biological clock and are synthesized at dusk. This allows for DNA replication to occur at
night, which protects replicating DNA from damaging ultraviolet radiation during the
Describe the different detrimental effects of light on organisms [Knowledge]
Absorption of of excessive light energy can result in damage that can potentially be
permanent; of particular concern are higher energy wavelengths of light like ultraviolet
radiation which reaches the earths surface. The photoreceptors cells that line the
human retina ca be damaged by exposure to bright light. The high energy environment
associated with pigment molecules and excited electrons can result in photo-oxidative
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