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Properties of Life
Life defies a simple, one-sentence definition
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Distinguishing a living thing from a non-living thing is much easier task
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This is because even though we do not
know exactly what life is, we know the properties that separate a living thing from a non-living thing
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At the chemical level, atoms are organized into
biomolecules which in turn comprise cellular organelles
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In complex multicellular organisms, cells are organized into tissues,
tissues form different organs and organs are components of organ systems which comprise an
organism
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Organisms of the same
species make up a population, a collection of population of different species form a community,
biological communities together with the abiotic components of the environment forms an
ecosystem and the collection of all ecosystem forms our planet’s biosphere
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The cell membrane is a
part of a cell like a neuron (C)
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Different tissues that function together forms an
organ like the brain(E)
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The nervous system is one of the many organ systems
that form an organism such as a man (G)

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These adaptations are a result of natural
selection
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This ensures that over time, the population becomes more and more adapted to its
environment
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Its gills effectively absorb dissolved
oxygen in seawater
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Sharks also have
electroreceptors called ampullae of Lorenzini
which it uses to detect bioelectric fields of prey
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Biological processes occur only at a small range of set conditions which must
be maintained
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In response to low external temperatures,
human muscles contract automatically to generate
heat
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Reproduction
Living organisms reproduce their own kind
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Only characteristics encoded in genetic materials are
passed on from parent to offspring through reproduction
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A

B

A
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The fruit serve the purpose of attracting animals that will eat
and thereby disperse the seeds
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This newly hatched reticulated python is only several
centimeters but, like its parents, it will grow to over 20ft in
length
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Organisms
react to various forms of stimuli including visual, tactile, olfactory and auditory
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Internal signals are also perceived by
organism
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(touch)

its

ribs

forming

a

menacing hood to look larger in
response to visual and vibration
stimuli
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For a multicellular organism, growth means
addition of more cells through mitosis
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The elephant moth larva on the left will develop into
the mature elephant moth on the right through the
process of metamorphosis
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Metabolic processes can be categorized into anabolic and catabolic processes
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Catabolic processes, on the other hand, are breaking-down processes
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These raw materials are used for photosynthesis:
the process by which plants synthesize energy rich carbohydrates
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Animals like the monkey on the left, actively obtain organic matter from their
environment as energy source and material source for growth and development
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Organisms are composed of cells
All modern organisms are composed of either a single cell (unicellular organisms) or many cells
(multicellular) which work in relation to each other to function as a single complex living thing
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This euglena is unicellular but it shows all properties of
life
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It reproduces through
binary and multiple fission
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This means that it can perceive and orient
itself towards light
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Origin of Life
Spontaneous Generation
In ancient times, people have a notion of spontaneous generation – the development of living
organisms from non-living things
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Insects come from dew
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There is even a recipe for creating mice! According to John Baptiste van Helmont, you can create a
mouse by placing a piece of soiled cloth with some wheat or corn in a jar
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He put meat inside
three jars
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The
third jar is tightly sealed with cork
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After several days maggots
developed in the uncovered jar and in the jar with a cloth mesh cover but not in the jar sealed with
cork
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In his experiment, he put fermentable broth inside jars with S-shaped necks that was
open on its end
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The
broths were then left undisturbed
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This is means
that due to the shape of the neck, the microbes in the air were not able to reach the broth suggesting
that microbes in the air were responsible for the fermentation process and the broth itself cannot
produce the microbes
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Fossils and
isotopic “finger print” of early life forms provide a glimpse of the past although at best, an incomplete
picture
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We know that the Earth is approximately 4
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2
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3
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Abiotic synthesis of organic molecules

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polymerization
c
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Packaging of organic molecules into protobionts or protocells
4
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5 to 3
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5
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Abiotic Synthesis of organic molecules
The first step in the development of life on earth is the abiotic synthesis of organic matter
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The concept that simple organic molecules like sugar and amino acids formed spontaneously from
inorganic precursors was first put forth by Alexander Ivanovich Oparin and John Burdon Sanderson
Haldane
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This is based on the fact that water is a very
stable environment for biochemical reactions
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If the early atmosphere was oxidizing, organic molecules would have broken
down as fast as it was formed
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The energy required for the chemical reactions may have come from the
electrical energy discharge during a thunderstorm, UV rays from the sun or the thermal energy of the
young Earth
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They exposed a mixture
of water vapor, methane, ammonia and hydrogen (their proposed composition of the Earth’s early
atmosphere) to an electric discharge (simulating thunderstorms)
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Another possibility is that the first organic molecules may have been extra-terrestrial
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Recent analysis of meteorites that reached the Earth’s surface, especially
carbonaceous chondrites, revealed that many contain organic matter like amino acids, sugars, lipids
and nucleotide bases
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Chemical analysis of this
meteorite revealed that it is composed of 3% organic matter by mass
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The conditions around hydrothermal vents are similar to the conditions proposed to be present in

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It is rich in hydrogen, methane and ammonia
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Another important characteristic of
alkaline hydrothermal vents is the fact that it supports a diverse community of organisms
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This means that the internal
environment of the early cell-like structures or protocells may have been sufficiently different from
that of the external environment
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The properties of the protocells described above are supported by experiments conducted in
abiotically produced vesicles
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It is possible
that the protocells are very similar to vesicles produced from abiotic precursors
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RNA (Ribonucleic
acid) is unique in its ability to act like an enzyme in biological processes (these RNA enzymes are
called ribozymes)
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This idea is supported by the results of the experiment of Dr
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First True Cells
The first true cells were most likely unicellular prokaryotes
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Fossil evidence called
stromatolites (stromatolites are basically preserved imprints of biofilms) suggest that prokaryotes
existed some 3
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The earliest forms of true cells were also most likely heterotrophic
anaerobes
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The earliest fossils of eukaryotes suggest that eukaryotes may have been present 1
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The evolution of the eukaryote cell is believed to be the result of endosymbiosis
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Eventually, the endosymbiont evolved
into an organelle of its larger host
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mitochondrion, possesses its own genetic materials
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