bài giảng hóa học môi trường chương 5 sinh quyển

To accomplish this task, biodiversity describes the diversity of life at the following three biological levels:• Genetic Level or Genetic Diversity - Genetic diversity refers to the tota

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

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

complexity and function.

• (4) Living things have the ability to take energy

from their environment and change it from one form

to another This energy is usually used to facilitate their growth and reproduction We call the process that allows for this facilitation (sự thuận lợi) metabolism.

systems that replace parts of themselves that are subject to wear and tear This regeneration can be partial or it can involve the complete replacement of the organism Complete replacement is necessary because partial replacements cannot stop the unavoidable decline in the functioning state of the entire living system over time In other words, all organisms degrade into a final non-functioning state we call death.

• (6) Living creatures respond to environmental stimuli through feedback mechanisms Cues from the environment can cause organisms to react through behavior, metabolism, and physiological change Further, responses to stimuli generally act to increase a creature’s chance for day-to-day survival.

• (7) Organisms are able to maintain numerous metabolic reactions even in a single instance in time Living things also keep each of these reactions separated from each other.

nucleic acids into strands of replicating genetic code These moleculesthen organized and evolved to form the first simple forms of life At 3.8billion years ago, conditions became right for the fossilization of the Earth'searly 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 complexcells of animals and plants, known as eukaryotes, first showed up about

2.1 billion year ago Eukaryotes have a membrane-bound nucleus andmany specialized structures located within their cell boundary By 680million years ago, eukaryotic cells were beginning to organize themselvesinto multicellular organisms Starting at about 570 million years ago anenormous 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 andanimals

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

Table 9h-1: Major extinction events during the Phanerozoic

Date of the Extinction Event Percent

Species Lost Species Affected

65 Million Years Ago

213 Million Years Ago

(Triassic) 44% Marine vertebrates and invertebrates.

248 Million Years Ago

(Permian) 75-95% Marine vertebrates and invertebrates.

380 Million Years Ago

450-440 Million Years Ago

• Scientists developed the notion of biodiversity to overcome some of the difficulties of species concept To accomplish this task, biodiversity describes the diversity of life at the following three biological levels:

• Genetic Level or Genetic Diversity - Genetic diversity refers to the total 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 vàhữu 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 vegetationfound growing on top of a soil is closely linked to this component of anecosystem through nutrient cycling

• The atmosphere provides organisms found within ecosystems with

carbon dioxide for photosynthesis and oxygen for respiration The

processes of evaporation, transpiration, and precipitation cycle waterbetween the atmosphere and the Earth's surface

• Solar radiation is used in ecosystems to heat the atmosphere and to evaporate

and transpire water into the atmosphere Sunlight is also necessary for

photosynthesis Photosynthesis provides the energy for plant growth and metabolism, and the organic food for other forms of life.

• Most living tissue is composed of a very high percentage of water, up to and even

exceeding 90% The protoplasm of a very few cells can survive if their water content drops below 10%, and most are killed if it is less than 30-50% Water is the medium by which mineral nutrients enter and are translocated in plants It is also necessary for the maintenance of leaf turgidity and is required for photosynthetic chemical reactions Plants and animals receive their water from the Earth's surface and soil The original source of this water is precipitation from the atmosphere.

• Ecosystems are composed of a variety of living organisms that can be classified

as producers, consumers, or decomposers. Producers or autotrophs, are organisms that can manufacture the organic compounds they use as sources of energy and nutrients Most producers are green plants that can manufacture their food through the process of photosynthesis. Consumers or heterotrophs

get their energy and nutrients by feeding directly or indirectly on producers We can distinguish two main types of consumers. Herbivores are consumers that eat plants for their energy and nutrients Organisms that feed on herbivores are called

carnivores Carnivores can also consume other carnivores Plants and animals supply organic matter to the soil system through shed tissues and death Consumer organisms that feed on this organic matter, or detritus, are known as

detritivores or decomposers The organic matter that is consumed by the 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.

p) Biogeochemical Cycling: Inputs and Outputs of

atmosphere, and hydrosphere

• The biogeochemical cycles of all elements used by life have both an

organic and an inorganic phase For most of these nutrients, howefficiently these elements cycle from the organic component back to theinorganic reserviors determines how much is available to organismsover the short term This cycling involves the decomposition of organicmatter back into inorganic nutrients The major reservoirs for allmetabolically important elements are found either in the atmosphere, lithosphere (mainly rock, soil and other weathered sediments) or hydrosphere Flow from these reservoirs to the organic phase is

generally slower than the cycling of nutrients through organic matterdecomposition

Nutrient Inputs to Ecosystems

Important nutrients for life generally enter ecosystems by way of four processes:

(1) Weathering

(2) Atmospheric Input

ecosystems from the atmosphere This addition is done either through precipitation or by a number of biological

processes.

• Carbon - absorbed by way of photosynthesis

• Nitrogen - produced by lightning and precipitation

• Sulfur, chloride, calcium, and sodium - deposited by

way of precipitation

(3) Biological Nitrogen Fixation

(4) Immigration

• Nutrient Outputs to Ecosystems

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.

Figure 9r-1: Carbon cycle

Table 9r-1 : Estimated major stores of carbon on the Earth

Atmosphere 578 (as of 1700) - 766 (as of 1999) Soil Organic Matter 1500 to 1600

s) The Nitrogen Cycle

The nitrogen cycle represents one of the most important nutrient

cycles found in terrestrial ecosystems (Figure 9s-1) Nitrogen is used by

living organisms to produce a number of complex organic molecules like

amino acids, proteins, and nucleic acids The store of nitrogen found in

the atmosphere, where it exists as a gas (mainly N2), plays an importantrole for life This store is about one million times larger than the totalnitrogen contained in living organisms Other major stores of nitrogeninclude organic matter in soil and the oceans Despite its abundance in theatmosphere, nitrogen is often the most limiting nutrient for plant growth.This problem occurs because most plants can only take up nitrogen in twosolid forms: ammonium ion (NH4+ ) and the ion nitrate (NO3- ) Mostplants obtain the nitrogen they need as inorganic nitrate from the soil solution Ammonium is used less by plants for uptake because in large

concentrations it is extremely toxic Animals receive the required nitrogenthey need for metabolism, growth, and reproduction by the consumption

of living or dead organic matter containing molecules composed partially

of nitrogen

Figure 9s-1: Nitrogen cycle.