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PSYC 388 Midterm Exam with complete solutions
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PSYC 388 Midterm Exam with completesolutions
Proximate causality - correct answer -- the 'how' questions
- biological mechanism
Ex: how do biological clocks work at the biological level
* most of the course
Ultimate causailty - correct answer -the 'why' question
Ex: why do we have clocks, what 'caused' them to evolve and why have they been conserved across
phylogeny
- questions of function (what is the function or purpose of the circadian clock?)
* lecture 2 topic
Natural selection - correct answer -differential reproductive fitness that results from differential
adaptation to features of the environment
Local features - correct answer -more or less unique to that place
- temperature
- precipitation
- topography
drive speciation by favoring animals that have adaptations to these specific features
Global features - correct answer -shared with other places; they are
- enduring
- stable
- nontrivial
- obvious: features associated with daily cycles of light (solar day)
,When did circadian clocks evolve? - correct answer -approximately 3.5 billion years ago
Multicellular organisms that exhibit circadian rhythms - correct answer -- fungi: Neurospora
- plants: Arabidopsis
- animals: nematodes, fruit flies, zebrafish, reptiles, birds, mice, humans
Unicellular eukaryotic oranisms (protisa) that exhibit circadian rhythms - correct answer -- green algae
(chlamydomonas, acetabularia)
- gonyaulax, paramecium, euglena
- have true (bona fide) circadian rhythms
Prokaryotic organisms: How old are they and what are some characteristics about them? - correct
answer -- about 3.5 billion years old
- no cell nuclei
- no membrane-bound organelles
What prokaryotic organisms have circadian rhythms? (3) - correct answer -- cyanobacteria (blue-green
algae)
- human gut bacteria
- some extremophile archaea (grow in high salinity or temp)
Prokaryotic organisms = the most ancient life forms on earth (evolved ~3.5 billion years ago) and have
biorhythms = what can we conclude about circadian rhythms based on this? (4) - correct answer -- they
are ancient and widely conserved
- they likely appeared early in evolution
- likely evolved several times (bacteria, plants, and animals don't have the same clock genes, which is
expected if they evolved from the same organism)
- must continue to make important contributions towards survival and reproductive fitness
What is hypothesis 1A: escape from light? - correct answer -- ionizing radiation (high energy ultraviolet
light can damage molecules and disrupt biochemical processes such as DNA repication and gene
transcription
,- earliest self-replicating organisms did not have barriers to block UV light
What was the solution to not having protection against UV light? (2) - correct answer -- restrict
replication/transcription to the night
- mobilize light-avoidance behaviour in *anticipation* of sunrise
What is the evidence for "escape from light"? - correct answer -- many genes exhibit a circadian rhythm
of transcription
- most clock-controlled genes are transcribed only at night (Ex: drosophila)
- cells are more easily damaged by UV light in the early night, when cell division and gene transcription
occur (Ex: in chlamydamonas)
External coordination - correct answer -- 1 biological challenge faced by early life that led to evolution of
circadian clocks
- challenge of coordinating biochemistry with daily cycles of solar radiation and temperature (external)
Internal coordination - correct answer -- 1 biological challenge faced by early life that led to evolution of
circadian clocks
- challenge of coordinating biochemical processes with each other so that they occur in the the correct
sequence and so that incompatible processes would occur at different times of day
Hypothesis 1b: escape from oxygen (radicals) (5) - correct answer -- earliest circadian clocks appear back
when atmospheric oxygen increased rapidly, killing of other anaerobic forms
- bacteria would synthesize antioxidants prior to sunrise to remove toxic metabolites (reactive O2 mlcs,
H2O2 and free radicals) that are created as byproducts of daytime photosynthesis and damage cells
- these metabolites must be removed for effective aerobic metabolism
- photosynthesis is dependent on light and restricted to the day, so clocks may have been used to
control production of antioxidants so organisms could use O2 processes
- may have been designed to 'escape from oxygen' (radicals)
Examples of hypothesis 2: Internal coordination of biochemical processes - correct answer -- separation
of incompatible processes
, - Ex: nitrogen fixation: inhibited by O2 and incompatible with photosynthesis (produces O2)
- separated spatially (different cell compartments) or temporally (different times of day)
- Ex: enzymes for storing and releasing glucose in the liver (glycogen synthase and glycogen
phosphorylase) must be produced at opposite times of day so as not to conflict
Why are circadian clocks still present in virtually all life forms? (3) - correct answer -- a core function of
circadian clocks in all 'circadian' species is to enable anticipation of predictable daily changes in the
environment
- Core principle: preparing in advance of daily environmental changes is superior to reacting in response
to daily changes
- environmental changes include geophysical and biological stimuli
Anticipation of daily changes in geophysical stimuli (2, 3 examples - correct answer -- changes in light,
temperature, humidity, etc.
- organisms anticipate the change from day to night and back
Ex: nematodes live in soil and migrate vertically to find optimal temperature and humidity --> they don't
move wuickly and must anticipate changes to be in optimal conditions
Ex: fruit fly eclosion (adult emerges from pupal case) occurs at dawn because the humidity is optimal for
drying wings (cool and humid to prevent wrinkling)
- senses light penetrating the pupal case, even when pupa completely reorganizing itself (has a circadian
rhythm)
Ex: plants produce enzymes required for photosynthesis before dawn so they have enough to ensure
metabolic efficiency
Periodic food sources
What is the FAA? - correct answer -- it is advantageous to know when food is going to arrive
Food aniticipatory activity (FAA): memory is inferred from the emergence of activity prior to mealtime
(behaviour rhythm)
- once FAA established, rats active 1-2 hrs before mealtime
- will stop being active about 1hr if food is not provided
- animal did not respond to internal hunger and instead is remembering the time of day
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