BIO MID-TERM STUDY GUIDE
LIGHT AND LIFE
Define key terms: photon, pigment, photoreceptor, absorption spectrum, DNA, gene,
allele, enzyme, eyespot, eye, bioluminescence, melanin, vitamin D, camouflage, circadian
rhythms, light pollution. [Knowledge]
photon : discrete particles or packets of energy
pigment: a molecule that can absorb photons of light.
photoreceptor: basic light-sensing system
a photoreceptor (e.g rhodopsin) consists of a pigment molecule (retinal) bound to a protein (
absorption spectrum: curve representing the amount of light absorbed at each wavelength ( pg.
- A absorption spectrum is a plot of the amount of light a pigment absorbs in relation to the
wavelength of light
DNA- deoxyribonucleic acid - large, double-stranded, helical molecule that contains the genetic
material of all organisms.
gene- containing the code for a protein molecule or one of the parts, or functioning, or for
functioning RNA molecules such as tRNA and rRNA.
allele- one of two more versions of a gene
enzyme- protein that accelerates the rate of a cellular reaction.
eyespot- organisms use eyespot to sense light in their surroundings even though they lack eyes.
they are located within the chloroplast but does not play a function in photosynthesis-- the
photoreceptors of the eyespot allow the cell to SENSE LIGHT DIRECTION AND INTENSITY.
eye- the organ that animals use to sense light .
bioluminescence: A range of organisms can use chemical energy to make light. ( pg.21)
- Bioluminescent organisms use light to attract a mate, for camouflage, to attract prey, or to
melanin : a pigment that absorbs ultraviolet radiation to save the skin from damage especially
DNA. (PROTECTIVE MECHANISM) (pg 12-13)
- human populations vary in the amount of melanin they have according to where they are on
vitamin D: humans need some ultraviolet radiation to synthesize vitamin D which is very
important for normal bone development. ( pg.13) Camouflage: is used by animals to avoid detection as the blend into the background. ( pg. 14)
Circadian rhythms : known as using light to tell time.
- Many physiological and behavioral phenomena use internal organism- based biological clock
which is set by external light but can go on without input from external light to perform
functions such as sleep-wake cycles, cell-division , and etc. (pg 13)
ex. DNA is replicated at night in order to protect it from ultraviolet radiation.
light pollution: The widespread use of artificial lighting has been shown to disrupt many
biological phenomena and organism such as bird migration and orientation of nocturnal animals(
animals that see very well in dim light conditions) . ( pg 19/21)
Compare and contrast the three different ways that light can interact with matter.
- light has no mass but it is able to interact with and change matter - when photons of light hit an
object = 3 things can happen
1. reflected off the object
2. transmitted through the object
3. absorbed by the object
- light can be reflected or transmitted, or must be absorbed in order to used by organism. A
molecule that can absorb of light are called pigment and individual pigment absorb different
Absorption ( most important) - light absorption :l a region where carbon atoms are covalently
bonded with alternating single and double bonds ( bonding arrangement is called conjugated
system which results in delocalization of of electrons. (3,4)
Describe, in general terms, how the products of photosynthesis sustain most organisms
Photosynthesis use the energy in sunlight to build sugar molecules from CO2 and H2O releasing
O2 as a by-product. The products of photosynthesis not only sustain photosynthetic organisms
but through the process of cellular respiration are used by the vast majority of organism on Earth
as a usable form of energy. ( pg.5)
Describe how organisms can sense light without image-forming eyes. [Comprehension]
organisms that lack eyes can use eyespot to sense the direction of light and intensity. they are
located within the chloroplast but does not play a function in photosynthesis-- the photoreceptors
of the eyespot allow the cell to SENSE LIGHT DIRECTION AND INTENSITY. (pg. 7-8) Describe, in general terms, the evolution of image forming eyes from early simple
regions of photoreceptor cells. [Comprehension]
The eye evoked over time from being a simple region of photosensitive cells to a fully developed
eye ( refer to image fig.1.117 on pg. 10 )
a. region of photosensitive cells
b. depressed/folded area allows limited directional sensitivity
c. pinhole - eye allows finer directional sensitivity and limited imaging.
d, transparent humour develops in enclosed chamber.
e. distinct lens develops
f. iris and separate cornea (2nd) develops
Provide examples of how light can damage biological molecules, in particular,
information molecules (i.e., RNA and DNA), directly and indirectly. [Comprehension]
INDIRECTLY --DNA can easily be harmed by UV radiation because due it's high energy, it can
ionize molecules including pigments and proteins. The structure of the double helix can be
changed if affected by UV. the nucleotide bases can be changed to a dimer when 2 neighboring
bases become covalently linked which changes the shape of the DNA and can't replicate. (refer
to fig.1.20 on pg.12 )
DIRECTLY-- PHOTOSYNTHESIS - the photosynthetic apparatus which has photosystems that
trap energy of light and convert it into chemical energy can be damaged by too much sunlight.
There is an efficient repair system for damaged photosystems
Describe potential impact of DNA damage. [Comprehension]
The damage on DNA is that the shape of DNA is changed when the 2 bases right next to each
other create a covalent bond--- shape change (DIMERS) hinders DNA replication. Damaged
DNA causes cancer and rapid aging.
Compare and contrast the benefits and disadvantages of melanin production in human
- protection - absorbs UV radiation in order to protect the naked skin.
- less chances of skin cancer
-darker the skin is, the less likely it is to become wrinkled
disadvantages - skin becomes more reactive= means almost any stimulus -- a rash, scratch, pimple, or
inflammation -- may trigger the production of excess melanin, resulting in dark marks or
patches on the skin. These dark areas are the result of what is called postinflammatory
- vitamin D deficiency
Explain how light is involved in the synthesis of Vitamin D in humans. [Comprehension]
Humans need some ultraviolet radiation in order to synthesize vitamin D which is critical for the
normal development of bones in the body. People with high levels of melanin that live in areas
that don't receive enough sunlight. There is a lot of food products such as milk, yogurt and grain
Provide an example of how daylight (or length of day) can affect physiology or
behaviour of plants/animals. [Comprehension]
physiological and behavioural phenomenas such as sleep-wake cycles, body temperature,
locomotion, metabolic process, cell division; as well the behaviour associated with foraging food
- In humans, daily fluctuations in hormone levels are controlled by a circadian clock and will
occur even if a subject is placed in conditions of constant light or darkness.
In photosynthetic organisms, many proteins needed for photosynthesis are synthesized before
dawn which allows photosynthesis to occur at maximum efficiency during the daylight.
Replication of DNA only occurs at night in order to protect it from the damage of ultraviolet
Describe circadian rhythms and their uses, contrasting the systems in plants and
humans- the circadian rhythms are controlled melatonin is common in both humans and
by a central biological clock which is found in animals to control sleep-wake cycles
the superchiasmatic nucleus of the brain.
Changes in physiology and/ or behaviour are
linked to the central clock through changes in
the levels of the hormone melatonin ( refer to
figure 1.24 on pg. 14)
animals - the central biological clock
controlling many circadian rhythms is found
within the suprachaismatic nucleus ( region
within the hypothalamus). The suprachaismatic
nucleus receives light inputs directly from eye
via optic nerve, which it uses to set the
biological clock. The clock, in turn, regulates a