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PSYC 388 Midterm Questions and Verified
Answers
Q: Proximate causality
ANS: - the 'how' questions
- biological mechanism
Ex: how do biological clocks work at the biological level
* most of the course
Q:
Ultimate causailty
ANS: 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
Q:
Natural selection
ANS: differential reproductive fitness that results from differential adaptation to
features of the environment
Q:
Local features
, Page | 2
ANS: more or less unique to that place
- temperature
- precipitation
- topography
drive speciation by favoring animals that have adaptations to these specific
features
Q:
Global features
ANS: shared with other places; they are
- enduring
- stable
- nontrivial
- obvious: features associated with daily cycles of light (solar day)
Q:
When did circadian clocks evolve?
ANS: approximately 3.5 billion years ago
Q:
Multicellular organisms that exhibit circadian rhythms
ANS: - fungi: Neurospora
- plants: Arabidopsis
- animals: nematodes, fruit flies, zebrafish, reptiles, birds, mice, humans
Q:
Unicellular eukaryotic oranisms (protisa) that exhibit circadian rhythms
ANS: - green algae (chlamydomonas, acetabularia)
- gonyaulax, paramecium, euglena
- have true (bona fide) circadian rhythms
Q:
, Page | 3
Prokaryotic organisms: How old are they and what are some characteristics about them?
ANS: - about 3.5 billion years old
- no cell nuclei
- no membrane-bound organelles
Q:
What prokaryotic organisms have circadian rhythms? (3)
ANS: - cyanobacteria (blue-green algae)
- human gut bacteria
- some extremophile archaea (grow in high salinity or temp)
Q:
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)
ANS: - 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
Q:
What is hypothesis 1A: escape from light?
ANS: - 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
Q:
What was the solution to not having protection against UV light? (2)
ANS: - restrict replication/transcription to the night
- mobilize light-avoidance behaviour in *anticipation* of sunrise
, Page | 4
Q:
What is the evidence for "escape from light"?
ANS: - 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)
Q:
External coordination
ANS: - 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)
Q:
Internal coordination
ANS: - 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
Q:
Hypothesis 1b: escape from oxygen (radicals) (5)
ANS: - 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)
Q:
PSYC 388 Midterm Questions and Verified
Answers
Q: Proximate causality
ANS: - the 'how' questions
- biological mechanism
Ex: how do biological clocks work at the biological level
* most of the course
Q:
Ultimate causailty
ANS: 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
Q:
Natural selection
ANS: differential reproductive fitness that results from differential adaptation to
features of the environment
Q:
Local features
, Page | 2
ANS: more or less unique to that place
- temperature
- precipitation
- topography
drive speciation by favoring animals that have adaptations to these specific
features
Q:
Global features
ANS: shared with other places; they are
- enduring
- stable
- nontrivial
- obvious: features associated with daily cycles of light (solar day)
Q:
When did circadian clocks evolve?
ANS: approximately 3.5 billion years ago
Q:
Multicellular organisms that exhibit circadian rhythms
ANS: - fungi: Neurospora
- plants: Arabidopsis
- animals: nematodes, fruit flies, zebrafish, reptiles, birds, mice, humans
Q:
Unicellular eukaryotic oranisms (protisa) that exhibit circadian rhythms
ANS: - green algae (chlamydomonas, acetabularia)
- gonyaulax, paramecium, euglena
- have true (bona fide) circadian rhythms
Q:
, Page | 3
Prokaryotic organisms: How old are they and what are some characteristics about them?
ANS: - about 3.5 billion years old
- no cell nuclei
- no membrane-bound organelles
Q:
What prokaryotic organisms have circadian rhythms? (3)
ANS: - cyanobacteria (blue-green algae)
- human gut bacteria
- some extremophile archaea (grow in high salinity or temp)
Q:
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)
ANS: - 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
Q:
What is hypothesis 1A: escape from light?
ANS: - 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
Q:
What was the solution to not having protection against UV light? (2)
ANS: - restrict replication/transcription to the night
- mobilize light-avoidance behaviour in *anticipation* of sunrise
, Page | 4
Q:
What is the evidence for "escape from light"?
ANS: - 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)
Q:
External coordination
ANS: - 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)
Q:
Internal coordination
ANS: - 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
Q:
Hypothesis 1b: escape from oxygen (radicals) (5)
ANS: - 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)
Q:
