- Characteristics of Life
All life demonstrates the following 6 characteristics
each being: complex, interrelated, apparent at all levels of life (e.g.
organism level, cellular level, etc.).
- Structure and Organization
All living organisms are characterized by a recognizable
and repeatable organization (e.g. a moose is a moose; another: the structural
arrangement of leaves to minimize overshadowing). Structure and function
are correlated, if not inseparable, at every level (e.g. cell membrane,
mitochondrion, chromosomes, etc.).
- Metabolic activity: the acquisition
and processing of matter and energy
Photosynthesis: plants process CO2 and
water to produce glucose (energy). We are 100% dependent on photosynthesis
for energy (food). (Other examples: a lion eating a zebra, a fungus processing
dead organic matter, students in class sponging on free Starburst.)
- Reproduction
The perpetuation of a species.
- Asexual
Requires only one individual and results in genetically
identical offspring. (In asexual reproduction, mutation is the only means
of genetic variation.) Asexual reproduction is common in plants and involves
nuclear (cell) division in the form of mitosis (lecture
11). Example: the suculent plant Kalanchoe which forms embryonic
tissue on the edges of its leaves which eventually fall off as plantlets
and develop individually.
- Sexual
Usually requires two individuals and results in tremendous
genetic variation. Sexual reproduction involves gametes (sperm-is DNA with
a motor, and egg-is larger because it provides for development). Gametes
are the product of meiosis (lecture 12) and vary
genetically.
- Evolution: organisms change through
time
Occurs at the species, not the individual level.
- Genetic variation
Variants found in genes result in a diversity of
individuals (e.g. students: hair, eye colors, height, etc., there are an
estimated 8.7 million genetic variants in humans).
- Natural selection
Living and nonliving forces select for viable genetic
variations and against non-viable variations (e.g. a camoflauged variant
is more viable than 'a sitting duck:' one that is easily found by a predator.
Likewise, a variation of predator with keener senses is more likely to
survive and reproduce). "Survival of the fittest."
- Adaptation
An adaptation is a characteristic that promotes survivability
(genetic fitness); in other words, a genetic variation that counters selective
pressures. Examples are ubiquitous: (from class:) the archer fish has adapted
the ability to spit water, knocking insects from leaves to where they can
be devoured; the caterpillar with the back-underside resembling the head
of a snake, deceiving possible predators.
- Homeostasis: day to day (minute
to minute) survival
In response to external conditions, an individual's
internal conditions must be maintained within certain limits (e.g. temperature).
Comparing foxes of various environments shows the relationship between
homeostasis and adaptation: ears, for example: one way heat is dispersed
is through the ears, so a desert fox's ears are much larger than a local
fox, and an arctic fox has even smaller ears.
- Ecology: the study of interactions
Interactions occur at all levels (e.g. after nectar,
a butterfly pollenates a flower, which disguises an ambush bug, which eats
the butterfly).
- Biotic components
Living components: producers, predators, pollenators,
parasites, etc., (all living things). Interactions between living organisms.
(e.g. Drinking milk)
- Abiotic components
Non-living components: wind, temperature, fire, climate,
etc. (e.g. moths camouflauged in leaves is a biotic-abiotic interaction;
the north-facing slope of a particular mtn. provides for more foliage than
the south-facing slope, which holds less snow and water; trees changing
leaf color: when chlorophyll is taken out, we see the latent pigments,
as the change in temperature has signaled the tree to prepare for winter).
- The origin of life on earth
- Some theories
(What's in a theory?) Some of the following are testable,
others are not.
- Vitalism
The origing of life came from a supernatural force.
- Special creation
A subset of vitalism: the Biblical account (Genesis).
These first two are not scientifically testable, so we live by faith.
- Panspermia
Some propagule, a "seed," arrived on earth
from outer space: e.g. via meteorite; something from Mars.
- Spontaneous generation
Combining non-living components to form a living
system.
- Mechanism
Life originated through natural chemical, physical,
and biological laws.
- Theistic mechanism
Similar to mechanism, but directed by deity. The
'theistic' aspect of this isn't testable.
Class questions
were primarily directed toward differentiating between the theories, and
it was pointed out that one doesn't necessarily preclude any other. For
example: Spontaneous generation may or may not be mechanistic: one could
theorize that a supernatural force spontaneously generated life (special
creation via spontaneous generation); or one could theorize that spontaneous
generation could occur via natural forces (mechanism initiated by spontaneous
generation). In other words, these aren't presented as one-or-the-other
theories, but as an overview of approaches to the question.
- The primitive earth environment
Going back more than 3.5 billion years, the primitive
earth environment was a reducing environment: an electon-adding environment:
enables the synthesis (building) of larger molecules. A reducing environment
is characterized by a lack of oxygen, which is not favorable to the synthesis
of larger molecules. (In the presence of oxygen, molecules tend to break
down.) Eventually, primitive plant life changed the atmosphere by way of
photosynthesis, which puts oxygen into the atmosphere.
- Principal chemical components
Water, methane, ammonia, hydrogen. These contain
the building block elements or living (organic) materials.
- Energy interactions
Energy would be needed to synthesize organic materials:
high levels of UV radiation, lightning.
- Miller's early experiments
In the 1950's Miller and Uhrey simulated a primitive
earth environment and were able to demonstrate the formation of some organic
compounds.( figure
1.1)
- The first cells
What might have been the first cells on earth? Fossil
evidence indicates prokaryotic life as billions of years old, with eukaryotic
life coming later.
- Prokaryotes and eukaryotes
Prokaryotes: "before the nucleus") bacteria.
Eukaryotes: "with a nucleus" plants, animals, etc, are eukaryotic.
- Heterotrophs and autotrophs
These terms have to do with how an organism acquires
the energy it requires to survive. Heterotrophs are "other-feeders,"
dependent on other sources for energy. Autotrophs are "self-feeders,"
such as green plants, which are able to produce their own energy (photosynthesis)>.
The first cells are thought to be prokaryotic, but were they heterotrophs
or autotrophs? We think heterotrophs because autotrophs need oxygen which
was not readily available in the primitive earth environment. What did
they eat? Miller's experiment shows that the reducing environment could
have produced energy for life: carbohydrates, etc.. So it seems the first
cells were prokaryotic heterotrophs.
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