CHƯƠNG V: SINH QUYỂN
1/ What is Life?
In a recent issue of the journal Science (March 22,
2002), molecular biologist Daniel E. Koshland Jr. was
asked to write a special essay where he would set out to
define life. In this article, he suggested that something
could be considered “alive” if it meets the following seven
conditions.
(1). Living things must have a program to make copies of
themselves from generation to generation. This program
would describe both the parts that make up the organisms
and the processes that occur between the various parts.
These processes are of course the metabolic reactions that
take place in a living thing allowing it to function over time.
In most living systems, the program of life is encoded in
DNA.
(2). Life adapts (thích nghi) and evolves (tiến hóa) in step
with external changes in the environment. This process
is directly connected to life’s program through mutation
(sự đột biến) and natural selection. This condition
allows life-forms to be optimized for gradual changes in
the environment.
(3). Organisms tend to be complex, highly organized, and
most importantly have compartmentalized (chia thành
ngăn) structures. Chemicals found within their bodies
are synthesized through metabolic processes into
structures that have specific purposes. Cells and their
various organelles (cơ quan tế bào) are examples of
such structures. Cells are also the basic functioning
unit of life. In multi-cellular organisms, cells are often
organized into organs to create higher levels of

2/ Origin of Life
• The Sun and its planets formed between 5 and 4.6 billion years ago as
matter in our solar system began to coalesce because of gravity. By
about 3.9 billion years ago, the Earth had an atmosphere that contained
the right mix of hydrogen, oxygen, carbon, and nitrogen to allow for the
creation of life. Scientists believe that the energy from heat, lightning, or
radioactive elements caused the formation of complex proteins and
nucleic acids into strands of replicating genetic code. These molecules
then organized and evolved to form the first simple forms of life. At 3.8
billion years ago, conditions became right for the fossilization of the Earth's
early cellular life forms. These fossilized cells resemble present day
cyanobacteria. Such cells are known as prokaryotes. Prokaryote cells
are very simple, containing few specialized cellular structures and their
DNA is not surrounded by a membranous envelope. The more complex
cells of animals and plants, known as eukaryotes, first showed up about
2.1 billion year ago. Eukaryotes have a membrane-bound nucleus and
many specialized structures located within their cell boundary. By 680
million years ago, eukaryotic cells were beginning to organize themselves
into multicellular organisms. Starting at about 570 million years ago an
enormous diversification of multicellular life occurred known as the
Cambrian explosion. During this period all but one modern phylum of
animal life made its first appearance on the Earth. Figure 9a-1 describes
the approximate time of origin of the Earth' s major groups of plants and
animals.
Figure 9a-1: Important events in the evolution of life. Dates for many of the events
shown are based on fossil evidence.
Figure 9a-2: This fish fossil from Wapiti Lake in British Columbia, Canada was alive during
the geologic period known as the Triassic (208-245 million yrs BP). Fish first appear on
our planet during the Ordovician Period about 500 million years ago.
h). Species Diversity and Biodiversity- các loại đdsh

number of genetic characteristics expressed and recessed in all of the
individuals that comprise a particular species
• Species Level or Species Diversity - Species diversity is the number of
different species of living things living in an area. As mentioned above, a species
is a group of plants or animals that are similar and able to breed and produce
viable offspring under natural conditions.
• Ecosystem Level or Ecosystem Diversity - Ecosystem diversity is the
variation of habitats, community types, and abiotic environments present in a
given area. An ecosystem consists of all living and non-living things in a given
area that interact with one another.
• The biodiversity found on Earth today is the product of 3.5 billion years of
evolution. In fact, the Earth supports more biodiversity today than in any other
period in history. However, much of this biodiversity is now facing the threat of
extinction because of the actions of humans
Figure 9i-1: Succession of plant species on abandoned fields in North Carolina.
Pioneer species consist of a variety of annual plants. This successional stage is then
followed by communities of perennials and grasses, shrubs, softwood trees and shrubs,
and finally hardwood trees and shrubs. This succession takes about 120 years to go
from the pioneer stage to the climax community.
Abandoned Field to Oak Forest
j). Introduction to the Ecosystem Concept (khái niệm)
- Major Components of Ecosystems
• Ecosystems are composed of a variety of abiotic and biotic (vô sinh và
hữu sinh) components that function in an interrelated fashion. Some of
the more important components are: soil, atmosphere, radiation from
the Sun, water, and living organisms.
• Soils are much more complex than simple sediments. They contain a
mixture of weathered rock fragments, highly altered soil mineral particles,
organic matter, and living organisms. Soils provide nutrients, water, a
home, and a structural growing medium for organisms. The vegetation

detritivores is eventually converted back into inorganic nutrients in the soil. These
nutrients can then be used by plants for the production of organic compounds.
• The following graphical model describes the major ecosystem components and
their interrelationships (Figure 9j-1).
Figure 9j-1: Relationships within an ecosystem
Động vật ăn cỏ
Động vật ăn thịt
Energy and Matter Flow in Ecosystems
Figure 9j-2: Inputs and outputs of energy and matter in a typical ecosystem
(l). Primary Productivity of Plants
Figure 9l-1: Inputs and outputs of the photosynthetic process.
6CO2 + 6H2O + light energy >>> C6H12O6 + 6O2
Table 9l-1: Average annual Net Primary
Productivity of the Earth's major biomes.
Ecosystem Type
Net Primary Productivity
(kilocalories/meter
-2
/year)
Tropical Rain Forest 9000
Estuary 9000
Swamps and Marshes 9000
Savanna 3000
Deciduous Temperate Forest 6000
Boreal Forest 3500
Temperate Grassland 2000
Polar Tundra 600
Desert < 200
p). Biogeochemical Cycling: Inputs and Outputs of
Nutrients to Ecosystems

(4). Immigration
• Nutrient Outputs to Ecosystems
• Important nutrients required for life leave ecosystems by
way of four processes:
(1). Erosion
(2). Leaching
(3). Gaseous Losses
(4). Emigration and Harvesting
• Just as material may be introduced to ecosystems by
migration, so too may it be lost. The emigration of animals,
and the removal of vegetation by humans are both
processes by which outputs can occur from an ecosystem.
(r). The Carbon Cycle
• All life is based on the element carbon. Carbon is the major
chemical constituent of most organic matter, from fossil fuels
to the complex molecules (DNA and RNA) that control genetic
reproduction in organisms. Yet by weight, carbon is not one of
the most abundant elements within the Earth's crust. In fact,
the lithosphere is only 0.032% carbon by weight. In
comparison, oxygen and silicon respectively make up 45.2%
and 29.4% of the Earth's surface rocks.
• Carbon is stored on our planet in the following major sinks
(Figure 9r-1 and Table 9r-1): (1) as organic molecules in
living and dead organisms found in the biosphere; (2) as the
gas carbon dioxide in the atmosphere; (3) as organic
matter in soils; (4) in the lithosphere as fossil fuels and
sedimentary rock deposits such as limestone, dolomite and
chalk; and (5) in the oceans as dissolved atmospheric carbon
dioxide and as calcium carbonate shells in marine
organisms.