Download Similarities and Differences Among Living Organisms

KEY IDEA #1
SIMILARITIES AND DIFFERENCES AMONG LIVING ORGANISMS
LIVING VERSUS NONLIVING
Living things carry out almost all the life processes or activities. These life processes include
digestion, respiration, circulation, excretion, locomotion, immunity, coordination, and synthesis.
Non-living things are incapable of carrying out at least one or more of the life processes. The
sum of the energy used in all the life processes represents the metabolism of the organism.
Homeostasis
The ability to carry on the life processes allow a living thing to maintain dynamic equilibrium or
homeostasis with their surroundings. Homeostasis is a state of balance or steady state
between a living thing and its environment. Homeostasis in an organism is constantly
threatened. Failure to respond effectively to a failure of homeostasis can result in disease or
death.
ORGANIZATION LEVELS
Levels of Organization
Living things have different levels of organization. The simplest level of organization is that of
the cell. A group of cells with a similar function is called a tissue. Groups of tissues working
together to perform a common function are called organs. An example of this would include the
nervous, muscle, and other tissues which make up the heart. Groups of organs working together
to perform a common function are referred to as a system or organ system. The blood vessels,
blood, and the heart are organs which work together to form the circulatory system. Many
different systems function together to allow a complex organism to function.
Homeostasis
All the components of the living things, from the cells and the organelles within them to the
organ systems of complex organisms must interact to maintain a balanced internal environment
within the organism. Organisms possess many control mechanisms to detect internal and
external changes and make changes to correct any deviations. This maintenance of a stable
internal environment by an organism is called homeostasis. Homeostasis in an organism is
constantly threatened. Failure to respond effectively can result in disease or death.
CELL STRUCTURE
Cell Theory
All organisms contain one or more
cells which are capable of
carrying on the life activities
needed by the organism. This
idea is often referred to as the
cell theory.
Parts of the Cell Theory
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The cell is the unit of structure in all living things.
The cell is the unit of function in all living things.
All cells come from preexisting cells.
A few exceptions to this theory exist. Viruses lack typical cellular structure. There also is
some question as to how the first cell arose. In general, the cell theory holds true for most
living things, however.
Cell Organelles
Cells have particular structures that perform specific jobs.
These cell structures are called organelles and perform the
actual work of the cell. These organelles are formed from
many different molecules. Some functions carried out by
organelles include the transport of materials, energy capture
and release, protein building, waste disposal, and information
storage. Single celled organisms also have organelles similar
to those in more advanced organisms to complete their life
processes. Many enzymes are needed for the chemical
reactions involved in cellular life processes to occur.
A Typical Animal Cell
Some Cell Organelles
Cell Organelle
Function
nucleus
control center of the cell
contains DNA which directs the synthesis of proteins by the cell
mitochondrion
carries on the process of cell respiration converting glucose to ATP
energy the cell can use
endoplasmic
reticulum
transport channels within the cell
ribosome
found on the endoplasmic reticulum and free within the cell
responsible for the synthesis of proteins for the cell
cell membrane
selectively regulates the materials moving to and from the cell
food vacuole
stores and digests food
contractile
vacuole
pumps out wastes and excess water from the cell
chloroplast
found in plant cells and algae
carries on the process of photosynthesis
cell wall
surrounds and supports plant cells
Cell Membrane
The cell membrane or plasma membrane performs
a number of important functions for the cell.
These functions include the separation of the cell
from its outside environment, controlling which
molecules enter and leave the cell, and recognition
of chemical signals. The cell membrane consists
of two layers of phospholipids with proteins
embedded within these layers. The surface of
the cell contains molecules which recognize
(receptors) other molecules which may attach to
the outside of the cell.
Cell Membrane Structure
Membrane Processes
The processes of diffusion and active transport are important in the movement of materials in
and out of cells.
Diffusion
Diffusion or passive transport is
the movement of materials from a
region of higher to a region of
lower substance concentration. The
diagram at the right shows the
movement of molecules from higher
concentration on side A to a lower
concentration on side B.
Active Transport
In active transport, molecules move from a region of
lower concentration to a region of higher
concentration. As this process does not naturally
occur, the cell has to use energy in the form of ATP
to make active transport occur.
Cell Chemistry
Many organic and inorganic substances dissolved in cells allow necessary chemical reactions to
take place in order to maintain life. Large organic food molecules such as proteins and starches
must initially be broken down through the life process of digestion in order to enter cells.
Organic Molecules and Digestive End Products
Organic Molecule
Digestive End Product(s)
carbohydrates
simple sugars (glucose)
proteins
amino acids
lipids (fats)
fatty acids and glycerol
LIFE PROCESSES
Humans and other complex organisms require many different organ systems to carry on the
activities required for life. These life activities or processes include digestion, respiration,
reproduction, circulation, excretion, movement, coordination, and immunity. It is important to
realize that cell organelles are involved in many of these life processes, as well as the organ
systems of complex organisms.
Life Processes
Digestion
breakdown of food to simpler molecules which can enter the cells
Circulation
the movement of materials within an organism or its cells
Movement
(locomotion)
change in position by a living thing
Excretion
removal of waste products by an organism (wastes may include carbon dioxide,
water, and urea in urine and sweat)
Respiration
process which converts the energy in food to ATP (the form of energy which
can be used by the cells)
Reproduction
the making of more organisms of one's own kind -- not needed by an individual
living thing but is needed by its species
Immunity
the ability of an organism to resist disease causing organisms and foreign
invaders
Coordination
the control of the various activities of an organism (mostly involves the
nervous system and endocrine glands in complex animals)
Synthesis
the production of more complex substances by combining two or more simpler
substances
CELLULAR COMMUNICATION
Cell Membrane Receptors
Cell Membrane Receptors
Many cell membranes have
receptor molecules on their
surface. These receptor sites
play an important role in
allowing cells and organs to
communicate with one another.
Hormonal Regulation
Hormones provide a primary way for cells to communicate with each other. A hormone is a
chemical messenger with a specific shape that travels through the bloodstream influencing
another target cell or target organ. Upon reaching the cell the hormone is targeted for, the
hormone often activates a gene within a cell to make another necessary compound. One example
of this is provided by the pituitary gland. This gland at the base of the brain makes a hormone
called LH (luteinizing hormone). This hormone travels through the bloodstream and stimulates
the ovary to produce yellow tissue that produces the hormone progesterone, which maintains
the thickness of the uterus lining. The graphic below illustrates how this kind of hormonal
regulation can work in a plant cell. Animal cell hormonal regulation involves a similar mechanism.
A Hormonal Feedback Mechanism
The animation at the right
illustrates how a hormone
can bind to receptors on a
cell membrane and trigger
that cell to produce a
needed compound.
Nervous Regulation
Nerve cells or neurons also allow cells to communicate with each other. Neuron communications
are one way organism can detect and respond to stimuli at both the cellular and organism level.
This detection and response to stimuli helps to maintain homeostasis in the cell or organism.
Neurons may stimulate other nerve cells or muscle cells, thus causing the later to contract and
produce movement.
Structure and Function of a Nerve Cell
Structures and their Functions
1. dendrite -- neuron branch which detects stimuli (changes in the environment)
2. cyton -- body of the neuron where normal metabolic activities occur
3. axon -- longest dendrite covered by a myelin sheath which provides electrical
insulation -- carries nerve message or impulse to the end brushes
4. end brushes -- release nerve chemicals called neurotransmitters which
stimulate adjacent dendrites on the next neuron or a muscle cell
Any change in nerve or hormone signals will change the communication between cells and organs
in an organism and thus may cause problems for organism’s stability and ability to maintain
homeostasis.
KEY IDEA #2
HOMEOSTASIS IN ORGANISMS
PHOTOSYNTHESIS
The energy for life comes primarily from the Sun. Photosynthesis is the major way the energy
of the Sun is converted to sugars which provide for the energy needs of living systems.
Plants and many microorganisms use solar energy to combine the inorganic molecules carbon
dioxide and water into energy-rich organic compounds such as glucose sugar and release oxygen
to the environment.
A Representation of Photosynthesis
The overall process of photosynthesis in a plant or algal cell is shown in the graphic
below. Plants use water and the energy provided by sunlight to combine carbon
dioxide into glucose sugar with oxygen being released as a waste product.
chloroplasts: organelles that carry on photosynthesis in green plant cells
chlorophylls: the variety of green pigments within the chloroplasts
RESPIRATION
In all organisms, organic compounds such as glucose can be used to make other molecules. These
molecules include proteins, DNA, starch, and fats. The chemical energy stored in bonds can be
used as a source of energy for life processes.
Stored energy is released when chemical bonds are broken during cellular respiration and new
compounds with lower energy bonds are formed. Cells usually transfer this energy temporarily in
phosphate bonds of a high-energy compound called ATP. (adenosine triphosphate)
Equations for Cell Respiration
glucose + oxygen → carbon dioxide + water + 36 ATP
The energy from ATP is then used by the organism to obtain,
transform, and transport materials, and to eliminate wastes.
water + ATP → ADP + P + Energy
(ATP-ase)
Note: ADP is adenosine diphosphate.
This reaction is reversible and ADP can be converted back to ATP in cellular respiration.
Types of Reactions
Hydrolysis: reaction in which large molecules are broken down into smaller molecules. Chemical
digestion is an example of a hydrolysis reaction
Synthesis: the combining of simpler molecules to form a more complex molecule
Biochemical processes, both breakdown (hydrolysis) and synthesis, are made possible
by enzymes. Enzymes and other molecules, such as hormones and antibodies, have specific
shapes that influence both how they function and how they interact with other molecules.
ENZYME STRUCTURE AND FUNCTION
catalyst: inorganic or organic substance which speeds up the rate of a chemical reaction without
entering the reaction itself.
enzymes: organic catalysts made of protein.
 most enzyme names end in -ase
 enzymes lower the energy needed to start a chemical rx. (activation energy), thus
speeding the reaction
How do enzymes work?
substrate: molecules upon which an enzyme acts. The enzyme is shaped so that it can only lock
up with a specific substrate molecule.
enzyme
substrate -------------> product
Lock and Key Theory
Each enzyme is specific for one and ONLY one substrate (one lock - one key)
active site: part of the enzyme that fits with the substrate
Note that the active site has a specific fit for this particular substrate and no other.
Since the enzyme may unhook from the substrate, it may be reused many times.
Factors Influencing Enzyme Activity
pH: the optimum (best) in most living things is close to 7 (neutral). High or low pH levels usually
slow enzyme activity
Temperature: strongly influences enzyme activity
 optimum (best) temperature for maximum enzyme function is usually about 35-40 C.
 reactions proceed slowly below optimal temperatures
 above 45 C. most enzymes are denatured (change in their shape so the enzyme active site
no longer fits with the substrate and the enzyme can't function)
Concentrations of Enzyme and Substrate
When there is a fixed amount of enzyme and an excess of substrate molecules the rate of
reaction will increase to a point and then level off.
This leveling off occurs because all of the enzyme is used up and the excess substrate has
nothing to combine with.
If more enzyme is available than substrate, a similar reaction rate increase and leveling off will
occur. The excess enzyme will eventually run out of substrate molecules to react with.
FAIRLURE OF HOMEOSTASIS: DISEASE
Some Causes of Disease
Living organisms which cause disease are known as pathogens. Some viruses, bacteria, fungi, and
parasites are examples of living things which are pathogens causing disease. Other factors may
be involved which contribute to or cause the body to develop disease. Some of these factors
include heredity, exposure to poisonous (toxic) substances, poor nutrition, organ failure or
malfunction, and poor personal behavior and choices. Smoking, obesity, and over consumption of
alcoholic beverages would be a few examples of poor personal choices which may have immediate
or long term consequences for our health.
Immunity and Disease
Immunity describes the ability of an organism to resist foreign organisms or invaders
which enter its body. The immune system is designed to protect against microscopic
organisms (bacteria, viruses) and foreign substances which enter an organism from
outside its body. The immune system also protects from many cancer cells which arise
within our bodies. An antigen is any foreign substance which invades the body of an
organism, while a pathogen is a living antigen (such as viruses or bacteria) which invade
an organism.
Many different kinds of white blood cells exist which are able to help the body fight foreign
invaders in various ways. These various ways include:
 engulfing (eating) invaders (phagocytes are white blood cells doing this)
 producing antibodies (chemicals which destroy or neutralize antigens) (lymphocytes are
the kind of white blood cells which produce antibodies)
 marking antigens for attack and killing by other white blood cells
Below are graphics of two different categories of white blood cells in action:
Lymphocyte White Blood Cell Function
Phagocytic White Blood Cells in Action
It is important to note that an antibody has a specific shape to destroy a specific antigen.
Immune System Memory and Vaccinations
When organisms are exposed to disease, they make specific antibodies which destroy that
antigen during their first exposure to it. This first exposure to a disease and our making of
antibodies in reaction to this to defend ourselves is sometimes called the primary immune
response. Our immune system has a memory. This means that if we ever are exposed to that
same particular disease antigen again, our immune system has a memory and will make antibodies
so rapidly in response to another exposure that we will not get the disease. Our immune memory
is sometimes called the secondary immune response.
Immune System Memory
Vaccinations use dead or weakened microbes or parts of them to stimulate the primary immune
response or first production of antibodies. Using dead or weakened microbes has the advantage
of not making the organism sick as they would become if they caught and recovered from a
disease. Because the vaccine has stimulated the immune system, the organism will now have a
memory to subsequent exposures to that disease causing antigen.
Allergies and Auto-immune Diseases
In allergies, the body's immune system produces chemicals in response to normally harmless
substances which do not trouble other individuals. These chemicals make people with allergies
feel sick. In auto-immune diseases, the body's immune system for usually unknown reasons
may attack and destroy some its own cells. Some kinds of arthritis and degenerative diseases
result from auto-immune diseases.
AIDS, Cancer, and Disease Research
Some viral diseases damage the immune system which leaves it unable to cope with many
antigens and other infectious agents. AIDS is a viral disease which destroys the ability of the
immune system to produce antibodies, so the afflicted individual is unable to cope with
infections and cancer cells which arise within the body.
Cancer is a group of diseases resulting from gene mutations which cause cells to divide
uncontrollably. Exposure of cells to certain chemicals and radiation appears to increase the
chance of mutations and thus cancer.
Biological research is constantly ongoing to find knowledge about diagnosing, preventing,
treating, controlling and curing diseases in plants and animals. The human genome project has
provided a great deal of information of the genetic basis of many diseases.
FEEDBACK MECHANISMS
Homeostasis is the maintenance of a
stable internal state within an
organism. Homeostasis is also known
as steady state. Organisms must
respond and maintain homeostasis in
relation to many factors.
Stimulus and Response
Organisms detect changes in their environment and respond to these changes in a variety of
ways. These changes may occur at the cellular or organism level. The graphic above shows the
response of a human to being struck on the knee with a hammer. Change in the environment is
called a stimulus. In this situation, the stimulus is the being struck with the hammer. A
response is the manner in which the organism reacts to the stimulus. The knee jerk reflex
which is pictured at the right is the response of this individual to being hit with this hammer.
Feedback Mechanism Examples
Feedback mechanisms have evolved in living things as a mechanism by which they maintain
homeostasis or dynamic equilibrium.
A feedback mechanism occurs when the level of one substance influences the level of another
substance or activity of another organ. An example of a feedback mechanism in humans would
be the increase in heart rate and respiratory rate which occurs in response to increased
exercise or other increased muscle cell activity. Some other examples of feedback mechanisms
in living things appear below.
Temperature Homeostasis
Humans maintain a relatively constant body temperature of
about 37° C.
 when we "heat up" we sweat if possible
 the evaporation of this perspiration returns the body
to its original temperature
Blood Sugar Regulation
The pancreas is an endocrine gland which
produces hormones which regulate blood
glucose (sugar) levels
An increase in blood sugar level triggers
the release of the hormone insulin by the
pancreas
the hormone insulin lowers blood sugar level
restoring the body to its original blood
glucose level in two major ways:
 it increases the ability of body cells
to take in glucose from the blood
 it converts blood glucose to the
compound glycogen -- this
compound is also called animal starch
and is stored in our liver and muscles
Homeostasis by Plants
Maintenance of Water
 plants need to regulate water loss and carbon
dioxide intake for photosynthesis and other
life activities
 when plants do not keep enough water in their
cells, they wilt and die
stomate: a microscopic hole in a plant leaf which
allows gases to enter and leave and water vapor to
leave as well. Stomata is the plural of stomate.
guard cells: open and close the stomate.
 the ability of the guard cell to close during
periods of limited water availability for the
plant allows the plant to maintain water
homeostasis
KEY IDEA #3
GENETIC CONTINUITY
DNA STRUCTURE AND FUNCTION
DNA provides the set of coded instructions required by every organism for specifying its traits.
The DNA molecule also provides for a reliable way for parents to pass their genetic code from
one generation to the next. Heredity refers to this passage of these instructions from one
generation to another.
DNA is a double stranded molecule, which has the shape of a twisted ladder. This shape is
called an alpha helix. The sides of this twisted ladder are composed of alternating phosphate
and deoxyribose sugar units, while the rungs of the ladder are composed of pairs of nitrogenous
bases. These bases are called adenine (A), thymine (T), guanine (G), and cytosine (C). These
bases exist in pairs on the rungs of the ladder with A always pairing with T and G pairing with
C. This principle is sometimes called complementary base pairing. (The saying G CAT provides
a means of remembering this idea.)
Structure of the DNA molecule
Location of DNA
GENE-CHROMOSOME MODEL
Hereditary information is contained
The Gene Chromosome Model
in genes, which are composed of
DNA, located in the chromosomes of
each cell. Chromosomes are found in
the nucleus of each cell.
Each gene carries a separate piece of
information. An inherited trait of an
individual can be determined by one
genes, but is usually determined by
the interaction of many different genes.
A single gene can influence more than one trait. A human cell contains many thousands of
different genes coding for many different traits. Changes in the sequence of the DNA molecule
and therefore the gene are called mutations. A mutation may change the manner in which a
trait is expressed by an organism.
ASEXUAL VERSUS SEXUAL HEREDITY
Asexual Heredity
Every organism requires a set of coded instructions for specifying its traits. For offspring to
resemble their parents, there must be a reliable way to transfer information from one
generation to the next. Heredity is the passage of these instructions from one generation to
another. The DNA molecule provides the mechanism for transferring these instructions.
In asexually reproducing organisms, all the genes come from a single parent. As asexually
produced offspring are produced by the cell division process of mitosis, all offspring are
normally genetically identical to the parent.
Sexual Heredity
In sexually reproducing organisms, the new individual receives half of the genetic information
from its mother through the egg and half from its father from his sperm. Sexually produced
offspring resemble, but are not identical to, either of their parents. Some reasons for these
variations between sexually reproduced offspring and their parents include crossing over when
gametes are formed in each parent and genetic recombination, which is the combining of the
genetic instructions of both parents into a new combination in the offspring when fertilization
occurs.
Genetic Recombination
Note that two of the four offspring in the punnett square at the right
have a completely different genetic makeup than that of either parent
The processes of crossing over and genetic recombination will result in offspring exhibiting
variation from the original parents. The variations shown between different sexually produced
offspring provide the driving force for the process of natural selection.
Heredity and Environment
The characteristics of an organism can be described in terms of combinations of traits. Traits
are inherited, but their expression can be modified by interactions with the environment.
Examples of this include the lack of color in completely shaded grass, even though it still
possesses the genetic makeup to appear green and the change in fur color of returning fur in a
shaven Himalayan hare at cold temperatures.
Effect of Cold on Himalayan Hare Fur Color
The application of an ice pack to a region of shaved hair results in black
hair growing back instead of the original white color.
The many body cells in an individual can be very different from one another, even though they
are all descended from a single cell and thus have identical genetic instructions. This is because
different parts of these instructions are used in different types of cells, influenced by the
cell’s environment and past history. Poor health habits can have an adverse effect on the
development and expression of many genes in human cells, resulting in sickness or even death.
Mutation
A mutation is a change in the genetic material of an organism. Mutations which occur in non sex
cells of sexually reproducing organisms will
Mutations
not be passed on to the offspring,
although they may result in disease or
death for the organism involved. One
possible consequence of a mutation in a non
sex cell is uncontrolled mitotic cell division
or cancer.
Mutations which occur in sex cells or gametes may be passed to the offspring. Along with
crossing over and genetic recombination, mutation provides for a source of variation in sexually
reproducing individuals.
PROTEIN SYNTHEIS
DNA
In all organisms, the coded instructions for specifying the characteristics of the organism
are carried in DNA. The genetic code is contained in the four nitrogenous bases of DNA;
adenine, guanine, cytosine, and thymine. These bases are often indicated only by using their
beginning letters A, G, C, and T. Each individual DNA strand serves as a template or model for
the formation of other DNA molecules by replication.
RNA
DNA codes for the formation of RNA in the nucleus of the cell. RNA is short for another kind
of nucleic acid called ribonucleic acid. RNA is very similar in structure to DNA except for
three small differences. These differences include the fact that RNA is a single stranded
molecule, lacks the base thymine (T) as it is replaced by the base uracil (U), and its five carbon
sugar ribose has one more oxygen atom than the sugar in DNA. Three different types of RNA
exist, mRNA or messenger RNA, tRNA or transfer RNA, and rRNA or ribosomal RNA.
Protein Synthesis
Cells store and use coded information. The genetic information stored in DNA is used to direct
the synthesis of the thousands of proteins that each cell requires. The chemical and structural
properties of DNA are the basis for how the genetic information that underlies heredity. DNA
is encoded in the sequence of nitrogenous bases which directs the formation of proteins in the
cell. How does this process work? First, the DNA code is copied on to the mRNA (messenger
RNA) codon. A codon is a sequence of three nitrogenous bases. This process is called
transcription. This mRNA codon is then carried from the nucleus out to the ribosome.
Messenger RNA attaches to another kind of RNA called tRNA (transfer RNA). Transfer RNA
attaches to amino acids and carries them to the ribosome. This assembly of amino acids due to
the code provided to RNA by the original DNA molecule is what produces proteins for the cell.
Remember a protein is a long molecule formed from amino acid subunits.
In summary, the code of DNA directs the synthesis of RNA, which in turn directs the making of
proteins on the ribosomes. This is sometimes referred to as being the central dogma or idea of
biology. There are 64 possible combinations of triplets (sequences of 3 nitrogenous bases)
which code for the 20 different possible amino acids. As the DNA of different organisms and
most individuals (except for identical twins) is different, this means the proteins produced by
different humans and other organisms exhibit differences. It is these differences which make
us unique individuals.
The work of the cell is carried out by the many different types of molecules it assembles,
mostly proteins. Protein molecules are long, usually folded chains made from 20 different kinds
of amino acids in a specific sequence. This sequence influences the shape of the protein. The
shape of the protein, in turn, determines its function.
Offspring resemble their parents because they inherit similar genes (DNA sequences) that code
for the production of proteins that form similar structures and perform similar functions.
Protein Synthesis
Cell Regulation
Cell functions are regulated. Regulation occurs both through changes in the activity of proteins
and through the selective expression of individual genes, as humans and other organisms have
genes which direct the expression of other genes. This regulation allows cells to respond to
their environment and to control and coordinate cell growth and division.
GENETIC ENGINEERING
Selective Breeding
For thousands of years new varieties of cultivated plants and domestic animals have resulted
from selective breeding for particular traits. Some selective breeding techniques include
artificial selection, where individuals with desirable traits are mated to produce offspring with
those traits. A variation of this process traditionally used in agriculture is inbreeding, where
the offspring produced by artificial selection are mated with one another to reinforce those
desirable traits. Hybridization is a special case of selective breeding. This involves crossing
two individuals with different desirable traits to produce offspring with a combination of both
desirable traits. An example of this are Santa Gertrudis cattle, which were developed by
breeding English shorthorn cattle, which provided for good beef, but lacked heat resistance,
with Brahman cattle from India which were highly resistant to heat and humidity. The Santa
Gertrudis breed of cattle has excellent beef, and thrives in hot, humid environments.
Genetic Engineering
In recent years new varieties of farm plants and animals have been engineered by manipulating
their genetic instructions to produce new characteristics. This technology is known as genetic
engineering or recombinant DNA technology. Different enzymes can be used to cut, copy
(clone), and move segments of DNA. An important category of enzyme used to cut a section of a
gene and its DNA from an organism is known as a restriction enzyme. When this piece of DNA,
which has been cut out of one organism, is placed in another organism, that section of gene will
express the characteristics that were expressed by this gene in the organism it was taken from.
An Example of Genetic Engineering
Knowledge of genetics, including genetic engineering, is making possible new fields of health
care. Genetic engineering is being used to engineer many new types of more efficient plants and
animals, as well as provide chemicals needed for human health care. It may be possible to use
aspect of genetic engineering to correct some human health defects. Some examples of
chemicals being mass produced by human genes in bacteria include insulin, human growth
hormone, and interferon. Substances from genetically engineered organisms have reduced the
cost and side effects of replacing missing human body chemicals. While genetic engineering
technology has many practical benefits, its use has also raised many legitimate ethical concerns.
Other Genetic Technologies
Cloning involves producing a group of genetically identical offspring from the cells of an
organism. This technique may greatly increase agricultural productivity. Plants and animals with
desirable qualities can be rapidly produced from the cells of a single organism.
Genetic mapping, which is the location of specific genes inside the chromosomes of cells makes
it possible to detect, and perhaps in the future correct defective genes that may lead to poor
health. The human genome project has involved the mapping of the major genes influencing
human traits, thus allowing humans to know the basic framework of their genetic code
Knowledge of genetics is making possible new fields of health care. Genetic mapping in
combination with genetic engineering and other genetic technologies may make it possible to
correct defective genes that may lead to poor health.
There are many ethical concerns to these advanced genetic technologies, including possible
problems associated with the cloning of humans. Another down side to genetic mapping
technologies it is possible that some organizations may use this genetic information against
individuals.
KEY IDEA #4
REPRODUCTION AND DEVELOPMENT
ASEXUAL REPRODUCTION
Reproduction and development are necessary for the continuation of any species. Asexual
reproduction is a method of reproduction with all the genetic information coming from one
parent.
Some Methods of Asexual Reproduction
1. binary fission -- involves an equal division of
both the organism cytoplasm and nucleus to
form two identical organisms
-- the diagram of the protist at the right is
example of this
2. budding -- involves one parent dividing its
nucleus (genetic material) equally, but
cytoplasm unequally
-- the diagram of a yeast at the right is an
example of this
3. sporulation (spore formation) -- is
reproduction involving specialized single cells
coming from one parent
-- the diagram of mold spores being formed at
the right is an example of this
Asexual reproduction is sometimes called cloning. Cloning is the production of identical genetic
copies. All forms of asexual reproduction are variations of the cell division process of mitosis.
Mitosis is associated with asexual reproduction, as well as growth and repair in sexually
reproducing organisms.
MITOSIS
Mitosis is the method used for
cell division and reproduction in
cells not involved in sexual
reproduction. This process
starts with one replication
(copying of the chromosome
material) and one division of the
chromosome material. This
results in the chromosome
numbers in the two cells produced
being the same as in the parent
cell. This process is represented
in the graphic which follows.
An Overview of the Process of Mitosis
Key Results of Mitosis
1. The same chromosome
number is retained from
generation to generation.
2. 2. Each daughter cell
receives an exact copy of
the chromosomes of the
parent cell. (clones)
SEXUAL REPRODUCTION
The process of sexual reproduction involves two parents. Both
parents normally contribute one gamete or sex cell to the process.
This process assures that the genetic information given to the
offspring will be obtained equally from each parent. The female
gamete is called the egg or the ovum and the male gamete is called a
sperm. These gametes are formed in specialized reproductive
structures called gonads. The sperm is much smaller than the egg, but
is capable of moving on its own power using a whip-like tail called a
flagellum.
Sperm and Egg
(fertilization)
The sperm and egg unite in a process called fertilization. This process forms a single celled
structure called a zygote which contains the complete genetic information to develop into a
complete new organism having characteristics
Process of Fertilization
This zygote will then divide by mitosis and form the specialized cells, tissues, and organs of the
organism. This development of specialized structures from the zygote is called differentiation.
Meiosis
The process of meiosis produces
gametes or sex cells. While some
parts of this cell division process are
similar to the asexual cell division
process of mitosis, there are several
key differences. Meiosis produces
gametes, while mitosis produces
other cell types. The process of
meiosis halves the chromosome
number from the original parent cell
in the four cells it forms. It does
this by having two cell divisions
forming four cells, where mitosis has
only one cell division forming two
cells. Both processes start out with
one doubling or replication of the
chromosome material. The
graphic below will help to visually
illustrate some of the key events of meiosis.
Process of Meiosis
Another important way that meiosis differs from mitosis is the exchange of chromosome pieces,
which occurs in the first division of this process. This exchange of chromosome pieces is called
crossing over. Crossing over assures that the cells produced as a result of meiosis will be
different from and exhibit variations from the parent cell that produced them. This process is
chiefly responsible for the variations seen in members of the same species of sexually
reproducing organisms. These variations are the driving force for the process of natural
selection.
The process of crossing over and how it produces variation when these chromosomes are
recombined in the process of fertilization is illustrated in the graphic below.
Crossing Over and Genetic Recombination
Comparative Reproduction and Development
Different organisms possess different adaptations for reproduction and
development. Organisms which spend their lives or a large proportion of their lives in the water
tend to lay their eggs in great numbers (thousands) in the water and wait for the male of
the species to release sperm near them to fertilize them. The fertilization which occurs in the
water in this case outside the body of the organism is called external fertilization. These
young organisms then develop outside the mother in the water once this has occurred, which is
called external development. A disadvantage of this process is that the eggs and developing
young have little or no parental protection. Many fish and amphibians like frogs undergo
fertilization and development in this manner.
Reptiles and birds engage use the process of internal fertilization to fertilize their eggs. In
this situation, the male of the species inserts his sperm inside the female, who then lays her
fertilized eggs outside her body. The process of development is then external. Reptiles and
especially birds tend to lay fewer eggs and provide much more parental protection for their
developing young. Organisms (with some exceptions) which use the process of internal
fertilization tend to spend much of their lives on land. Mammals like humans have both their
fertilization and initial stages of development occur within the female organism. This is
referred to as internal fertilization and internal development. These organisms tend to
release very few eggs, but those eggs and the developing organism are very well protected by
one or both parents.
HUMAN REPRODUCTIVE SYSTEM
Male System
The structure and function of the human male reproductive system, is very similar to that of
many other mammals. The male system is designed to make sperm or male gametes and is
adapted to provide for the delivery of these gametes to the female to allow for fertilization.
Male Reproductive System
1. testes -- produces sperm and the hormone testosterone
2. scrotum -- pouch enclosing the testes keeping the sperm at an optimum
temperature for development
3. vas deferens -- tube carrying sperm away from the testes
4. prostate gland -- the largest of several glands which add lubricating and
other fluids to the sperm (this combination of sperm and fluids is called semen)
5. urethra -- tube through the penis carrying sperm to the outside of the body
6. penis -- adaptation for internal fertilization of the female
Female System
The structure and function of the human female reproductive system, is very similar to that of
many other mammals. It is designed to produce female gametes or eggs, allow for internal
fertilization, support the internal development of the embryo and fetus, and provide nutrition
through milk for the newborn.
Female Reproductive System
1. ovary -- (females have two of these) -- produce female gametes or eggs
and the hormone estrogen
2. oviduct (fallopian tube) -- carries the egg away from the uterus
-- internal fertilization normally occurs here
3. uterus -- implantation and development of the embryo and fetus before
birth occurs here
4. vagina or birth canal -- entry point for sperm from the male and exit tube
for the baby when it is born
Endocrine Interactions
Human reproduction and development are influenced by factors such as gene expression,
hormones, and the environment. The reproductive cycle in both males and females is regulated
by several different hormones. Some of these hormones include:
testosterone --
produced by the testes in the male and stimulates the development of male
secondary sex characteristics (like facial hair and deeper voice).
estrogen --
produced by ovaries in the female and stimulates the development of female
secondary sex characteristics (wider hips and mammary glands) as well as starting
the thickening of the uterus lining in preparation for a possible pregnancy after
the egg is released by the female each month.
progesterone --
produced by yellow tissue called corpus luteum in the empty ovarian follicle (place
in ovary producing and releasing the egg) -- this hormone maintains the thickness
of the uterus lining in case fertilization occurs and development of a fetus occurs.
In human females of reproductive age, these hormones interact in a cyclic pattern called the
menstrual cycle. This pattern of events repeats itself on average every 28 days unless a
pregnancy or other disruption occurs. A graphic representation and written description of the
stages of the human menstrual cycle is provided below.
Human Menstrual Cycle
Note the influence of the hormone progesterone in beginning the thickening of the uterus
lining and the role of the hormone estrogen in maintaining the thickness of that lining.
Ovulation or release of the egg occurs at the midpoint of this cycle, while the uterine lining
thins and is shed (menstruation) when the level of estrogen begins to decline to a large extent.
Menstrual Cycle Stages
1. follicle stage (10-14 days average duration)

production of ova/eggs occurs in tiny cavities in the ovary called follicles
 enlarging follicle produces estrogen which causes the uterus to get ready for embryo
implantation (uterus thickens its lining)
2. ovulation (1 day)
 follicle enlarges and ruptures ovary wall
 egg is released to the oviduct (usually only 1 is released at a time)
3. corpus luteum stage (10 -14 days average duration)

yellow tissue fills the follicle after ovulation called the corpus luteum
 "yellow body" secretes progesterone which maintains the thickness of the uterus in case
a pregnancy occurs
4. menstruation (3-5 days average duration)
 periodic shedding of the thickened lining of the uterus which occurs if fertilization
does not occur
DEVELOPMENT
Initial Development and Differentiation
The processes of gamete production, fertilization, and development follow an orderly sequence
of events. Zygotes contain all the information necessary for growth, development, and eventual
reproduction of the organism.
The zygote, which is a fertilized egg consisting of one cell, will begin to divide rapidly by mitosis
forming the early developing human embryo. Fertilization and the initial stages of this mitotic
cell division occur in the oviduct. The early embryo is migrates down the fallopian tube and
completes most of its development in the wall of the uterus.
Fertilization and Initial Development of the Embryo
The embryo will eventually develop into a three cell layered structure. This structure is called
a gastrula and will eventually differentiate to form the specialized cells. Differentiation means
that the cells will develop specific jobs and develop into specific tissues in the maturing
organism. An example of this is that the outer cell layer of the developing gastrula will develop
into the skin and nervous system of a mature human organisms. Most multicellular animals
undergo a similar pattern of development and differentiation.
The placenta is a combination of maternal and fetal tissue which allows for the exchange of
materials with the fetus and mother. Needed materials such as food and oxygen diffuse
through the placenta to the fetus, while wastes from the fetus diffuse to the mother. The
umbilical cord is a fetal structure containing blood vessels which allows materials to be carried
between the fetus and placenta in both directions. The amniotic fluid surrounds the fetus and
helps to provide a shock absorber to protect the fetus against mechanical injury in the event
the mother is shaken or injured in some manner.
Fetal Development
Development is a highly regulated process After this small cluster of cells called the gastrula
forms in humans, tissues begin to form. In humans, the embryonic development of essential
organs occurs in early stages of pregnancy. During the first three months of human
development, organs begin to form. The human embryo is usually referred to as a fetus when
human like features become visible in its structure. All organs and body features are developed
by the end of the sixth month. During the last three months of pregnancy, organs and features
develop well enough to function after birth.
The embryo (or fetus) may encounter risks from faults in its genes and from its mother's
exposure to environmental factors such as inadequate diet, use of alcohol, tobacco, drugs, other
toxins, or infections. While the patterns of development discussed previously hold true for
humans, these developmental patterns vary between different plants and different animals.
Aging is a complex series of developmental changes which occur with the passage of time. This
process is influenced by both heredity and the environment. This process eventually leads to
the death of the organism.
Reproduction and development are subject to
environmental impact. Human development, birth, and
aging should be viewed as a predictable pattern of
events.
Fetal Development in the Uterus
REPRODUCTIVE TECHNOLOGIES
Reproductive technology has medical, agricultural, and ecological applications. In many
instances, these technologies have progressed at a faster rate than the ethical considerations
resulting from these technologies. Some of these techniques include birth control methods
used to block the process of fertilization. Many technologies now exist to enhance the process
of fertilization and development in humans and other organisms. Hormone therapy can cause
increased egg production. Surgery can open blocked fallopian tubes in females and the vas
deferens in males. In vitro fertilization (test-tube babies) is a widely used technique to aid
infertile couples, allowing them to have children where this otherwise would not be possible.
KEY IDEA #5
EVOLUTION
NATURAL SELECTION
Natural selection is the evolutionary process which selects the variation(s) of organisms best
suited for a particular environment. Natural selection and its evolutionary consequences provide
a scientific explanation for the fossil record of ancient life, as well as for the molecular and
structural similarities observed among the diverse species of living organisms.
The degree of kinship between organisms or species can be estimated from the similarity of
their DNA sequences; this similarity often closely matches organisms' or species' classification
based on anatomical similarities.
Theory of Natural Selection
1. Overproduction: Within a population more offspring are born than can possibly survive.
2. Competition: Since the number of individuals in a population tends to remain
constant from generation to generation due to limited resources, a struggle for survival
occurs.
3. Survival of the Fittest: The individuals who survive are the ones best adapted to exist
in their environment due to the possession of variations that best suit them to their
environment. This genetic variability within a species is chiefly due to mutation
and genetic recombination.The variation of organisms within a species increases the
likelihood that at least some members of the species will survive under
changed environmental conditions.
4. Reproduction: Variations assist or hinder individuals in their struggle for survival. The
best adapted individuals survive and reproduce, passing on the favorable variations to
their offspring.
5. Speciation: As time and generations continue, adaptations are passed on and new species
may evolve from a common ancestor.
Small differences between parents and offspring can accumulate in successive generations so
that descendants become very different from their ancestors. An adaptation is a variation
which assists an organism or species in its survival. Biological adaptations include include changes
in structures, behaviors, or physiology that enhance survival and reproductive success in a
particular environment. Some characteristics give individuals an advantage over others in
surviving and reproducing, and the advantaged offspring, in turn, are more likely than others
to survive and reproduce. The proportion of individuals that have advantageous characteristics
will increase.
Behaviors have evolved through natural selection. The broad
patterns of behavior exhibited by organisms have evolved to ensure
reproductive success.
Modern Examples of Natural Selection
1. Peppered moth:



two varieties of peppered moth existed, a light colored and a dark colored one
as industrialization and coal burning increased, the environment in England where these
moths lived became dirtier
the dark colored variety of the moth blended into the trees and increased in numbers,
while the light colored moth was less adapted and decreased in numbers
2. Insecticides kill insects not resistant to the insecticide, while insects resistant to the
insecticide live to reproduce. The insecticide acts as a selecting agent.
3. Bacteria not resistant to an antibiotic are killed by it, while resistant bacteria live to
reproduce. The antibiotic is a selecting agent for these bacteria.
EVOLUTION AND EXTINCTION
Evolution does not necessarily mean long
term progress is going to go in a certain
direction. Evolutionary changes often
appear to be like the growth of a bush.
Some branches survive from the beginning
with little or no change, many die out
altogether, and others branch out
repeatedly, sometimes giving rise to more
complex organisms.
Direction of Evolution
.
Note the divergence of the various groups from a
common ancestor and the fact that some branches
became extinct.
Extinction of a species occurs when the environment changes and the adaptive characteristics
of a species are insufficient to allow its survival. The fossil record indicates that many
organisms that lived long ago are extinct. Extinction of a species is common; most of the
species that have lived on earth no longer exist.
The Fossil Record
Fossils are direct or indirect remains of organisms preserved in media such as sedimentary
rock, amber, ice, or tar. Fossils have been found that indicate organisms existed well over 3
billion years ago. These organisms were simple, single-celled organisms. About a billion years
ago, increasingly complex multi-cellular organisms began to evolve.
The higher up you go in an undisturbed rock stratum (rock layer), the younger the rock layers
become and therefore it is believed the fossils within these layers, as compared to lower rock
layers.
Relative Dating of Undisturbed Sedimentary Rock and its Fossils
Upper strata generally contain fossils of younger, more complex
organisms, whereas, the lower strata contain fossils of simpler life
forms. This means there is a tendency toward increasing complexity
in life forms over time.
When comparing fossils in undisturbed strata, fossils can be found in upper strata which,
although different from fossils in lower strata, resemble those fossils. This suggests links
between modern forms and older forms, as well as divergent pathways from common ancestors.
Classification
Biological classification is based on how organisms are related. Organisms are classified into a
hierarchy of groups and subgroups based on structural similarities and evolutionary
relationships. The species is the most fundamental unit of classification. This is a group
of organisms which are close enough in their evolutionary relationship to be capable of
successful reproduction and having fertile offspring.
MUTATIONS
Mutations are any changes in genetic material. Mutations can be caused by such agents as
radiation and chemicals. When they occur in sex cells, the mutations can be passed on to
offspring. Mutations occurring in other cells can be passed on to other body cells only. The
experiences an organism has during its lifetime can affect its offspring only if the genes in its
own sex cells are changed by the experience.
Some Types of Chromosome Mutations




Inversion: chromosome pieces are attached upside down
Duplication: involves copying an extra section of chromosome
Translocation: chromosome pieces moved
Addition and deletion: chromosome is added or removed
Either changes in chromosomes or genes on chromosomes changes the genetic which contributes
to sources of variation.
Some Other Sources of Genetic Variability
In addition to mutation, other sources of the variation seen in sexually reproducing offspring
include crossing over and genetic recombination during fertilization (union of egg and sperm). In
crossing over, which occurs in the production of sex cells or gametes in meiosis, there is an
exchange of chromosome pieces between the chromosome pairs associated with each other in
this process.
Mutations, crossing over, and genetic recombination ensure that no two gametes formed as the
result of sexual reproduction will be exactly the same. As a consequence, the offspring formed
as a result of sexual reproduction will exhibit variations. Some of these variations will be
better suited for survival than others, thus driving the process of biological evolution.
Crossing Over and Genetic Variation
VARIATION
Sources of Variation
1. The exchanging and recombining of genes during meiosis and fertilization result in a
great variety of new possible gene combinations from that of the parents.
2. Mutations are random changes in the genes or DNA of sex cells may result in new gene
combinations creating variation in the offspring formed from these.
Only mutations that occur in sex cells can be passed on to the offspring. Mutations which occur
in other cells can be passed on to other body cells only. The experiences an organism has during
its lifetime can affect its offspring only if the genes in its own sex cells are changed by the
experience.
Variation and Evolution
Evolution is the consequence of the following factors:
1. the potential for a species to increase its numbers
2. the genetic variability of offspring due to mutation and recombination of genes
3. a finite supply of the resources required for life
4. the ensuing selection by the environment of those offspring better able to survive and
leave offspring.
Some characteristics give individuals an advantage over others in surviving and reproducing, and
the advantaged offspring, in turn, are more likely than others to survive and reproduce. The
proportion of individuals that have advantageous characteristics will increase.
An Example of Variation Driving Natural Selection
Natural selection favors longer necks better chance to get
higher leaves. Favored character passed on to next
generation.
Original group exhibits
variation in neck length.
After many generations,
the group is still variable,
but shows a general
increase in neck length.
The variation of organisms within a species increases the likelihood that at least some members
of the species will survive under changed environmental conditions.
The great diversity of organisms is the result of billions of years of selection for favorable
variations that has filled available niches of our planet with life forms.
KEY IDEA #6
ECOLOGY
ECOLOGICAL ORGANIZATION
Ecology is the study of the interactions of living things with each other and their physical
environment. The living things on earth may be organized into four different levels of ecological
organization. These levels of organization are indicated in the table below.
Levels of Ecological Organization
1. population
all the members of one
species in an area
2. community
all the members of the
different interacting
species in an area
3. ecosystem
all the members of a
community plus the abiotic
(physical) factors
influencing them
4. biosphere
entire region of the earth
where living things may be
found
A Representation of A Community
This is a community of many different
organisms which could exist on milkweed.
The community contains many organisms
of different species in one location.
ABIOTIC VERSUS BIOTIC FACTORS
Abiotic factors are those non-living physical and chemical factors which affect the ability of
organisms to survive and reproduce.
Abiotic factors vary in the environment and determining the types and numbers of organisms
that exist in that environment. Factors which determine the types and numbers of organisms
of a species in an ecosystem are called limiting factors. Many limiting factors restrict the
growth of populations in nature. An example of this would include low annual average
temperature average common to the Arctic restricts the growth of trees, as the subsoil is
permanently frozen.
Biotic factors are all the living things or their materials that directly or indirectly affect an
organism in its environment. This would include organisms, their presence, parts, interaction,
and wastes. Factors such as parasitism, disease, and predation (one animal eating another) would
also be classified as biotic factors.
Some Biotic Factors
Some Abiotic Factors







light intensity
temperature range
type of soil or rock
pH level (acidity or alkalinity)
water availability
dissolved gases
level of pollutant





animals
plants
parasitism
disease
predation
Carrying capacity is the maximum number of organisms the resources of an ecosystem can
support. The carrying capacity of the environment is limited by the available abiotic and biotic
resources (limiting factors), as well as the ability of ecosystems to recycle the residue of dead
organisms through the activities of bacteria and fungi.
NUTRITIONAL INTERACTIONS
Energy flows through ecosystems in one direction, typically from the Sun, through
photosynthetic organisms including green plants and algae, to herbivores to carnivores and
decomposers. Green plants and algae are called autotrophs or producer organisms, as they
capture solar energy to make sugars in the process of photosynthesis. Herbivores or primary
consumers use the producer organisms to provide them with their food. Carnivores are
secondary consumers as they eat the primary consumers as their source of food. Some
organisms are capable of functioning as primary consumers (eating plant material) and as
secondary consumers (eating animal material). These organisms are called omnivores. Humans
are examples of omnivores. All consumers are examples of heterotrophic organisms, as they
can not make their own food using the sun, but depend upon the ingestion of other organisms for
their nutrition.
A predator is a type of carnivore that kills its food. The organism the predator feeds upon is
called its prey. A wolf and rabbit would provide an example of a predator/prey relationship.
Scavengers feed upon organisms that other organisms have killed. A crow feeding off dead
carrion in the highway would be an example of scavenger in this instance.
Competition occurs when two different species or organism living in the same environment or
habitat use the same limited resources such as food, water, space, light, oxygen, or minerals. A
resource which restricts the growth of a population is sometimes called a limiting factor. The
more similar the requirements of the organisms involved, the more intense their competition will
become. If two different species compete for the same food source, reproductive site, water,
or other limiting factor, one species may be eliminated. This establishes one species per niche in
an ecosystem. A niche refers to an organism’s role, especially its feeding role, in a community.
This allows different species to coexist and helps to contribute to the overall stability of the
ecosystem.
Symbiotic Relationships
Close living associations are called symbiotic relationships. Parasitism is an example of such a
relationship. In this situation, the parasite feeds upon the tissues or fluids or another
organism, but usually does not kill the organism it feeds upon, as this would destroy its food
supply. The organism the parasite feeds upon is called the host organism. An example of this
sort of relationship would be fleas on a dog or athlete's foot fungus on a human.
Types of Symbiosis



parasitism: the parasite benefits at the expense of the host
mutualism: both organisms benefit from the association
commensalism: one organism is benefited and the other is
unharmed
Other Relationships
Some organisms such as certain pathogenic bacteria may cause disease in other organisms.
Decomposer organisms use the energy of dead organisms for food and break them down into
materials which can be recycled for use by other organisms. Bacteria of decay and many fungi
are examples of decomposer organisms.
Food Chains
If an ecosystem is to be self-sustaining it must contain a flow of energy. One way of
representing the flow of energy through the living components of an ecosystem is through the
use of a food chain. A food chain indicates the transfer of energy from producers through a
series of organisms which feed upon each other.
A Food Chain
The algae and floating plants are the
producers in this food chain. The aquatic
crustaceans are the primary consumers
which eat the producers.
Fish are secondary consumers eating the
primary consumers.
Note that the arrows in the food
chain point to the organisms which
are doing the eating. Thus the
arrows in the food chain represent
the flow of energy through the
ecosystem.
A food chain may also contain third level or
other consumers as indicated by the
raccoons in this food chain.
Food Webs
In a natural community, the flow of energy and materials is much more complicated than
illustrated by any one food chain. A food web is a series of interrelated food chains which
provides a more accurate picture of the feeding relationships in an ecosystem, as more than one
thing will usually eat a particular species.
A Food Web
Energy flow in a food web also
starts with the producer
organisms through the various
levels of consumer organisms as
in a food chain.
Energy Pyramids
An energy pyramid provides a means of describing the feeding and energy relationships within a
food chain or web. Each step of an energy pyramid shows that some energy is stored in newly
made structures of the organism which eats the preceding one. The pyramid also shows that
much of the energy is lost when one organism in a food chain eats another. Most of this energy
which is lost goes into the environment as heat energy. While a continuous input of energy from
sunlight keeps the process going, the height of energy pyramids (and therefore the length of
food chains) is limited by this loss of energy.
An Energy Pyramid
The picture at the left is an energy pyramid. Producer organisms
represent the greatest amount of living tissue or biomass at the bottom
of the pyramid. The organisms which occupy the rest of the pyramid
belong to the feeding levels indicated in each step. On average, each
feeding level only contains 10% of the energy as the one below it, with
the energy that is lost mostly being transformed to heat.
MATERIAL CYCLES
Water Cycle
The atoms and molecules on the Earth cycle among the living and nonliving components of the
biosphere. Some of the water molecules which are used in photosynthesis are returned to the
environment. The change of water from the liquid to the gas state is called evaporation, while
the water lost to the atmosphere by the activities of plants is referred to as transpiration
water loss. This water vapor eventually condenses to form clouds, and is returned to the earth
as precipitation. This process is called the water cycle. The processes of cell respiration and
excretion also releases some water to the environment as well.
The Water Cycle
Carbon-Oxygen Cycle
Carbon dioxide molecules are used in the
process of photosynthesis to form energyrich organic sugar compounds. These
carbon dioxide molecules are returned to
the environment by the process of cell
respiration, when the energy from these
compounds is eventually released by cells.
Some carbon is also returned to the
environment by the decomposition of dead
organisms.
The Carbon-Oxygen Cycle
Oxygen is required by many living things to
release the energy in their food in the
process of aerobic cellular respiration.
Oxygen is released to the environment as a
waste product of the process of photosynthesis.
Other compounds, such as nitrogen, are cycled in the environment when organisms synthesize
proteins from simpler compounds and then return these nitrogen compounds to the environment
when they die and decompose.
Role of Decomposers
The number of organisms any environment can support is the carrying capacity of the
environment. Carrying capacity is limited by the available energy, water, oxygen, and minerals,
and by the ability of ecosystems to recycle the remains of dead organisms through the
activities of decomposers such as bacteria and fungi.
BIODIVERSITY
The Need for Biodiversity
As a result of evolutionary processes, there is a diversity
of organisms and a diversity of roles in ecosystems.
Biodiversity refers to the differences in living things in
an ecosystem. Increased biodiversity increases the
stability of the ecosystem as it provides for more genetic
variation among species. A great diversity of species
increases the chance that at least some living things will
survive in the face of large changes in the environment.
Human Influences on Biodiversity
When humans alter ecosystems either by removing specific organisms, serious consequences may
result. Human beings are part of the Earth’s ecosystems. Human activities can, deliberately or
accidentally, change the equilibrium in ecosystems. Humans are destroying other species as a
result of population growth, consumption, and technology. Human destruction of habitats
through direct harvesting, pollution, atmospheric changes, and other factors is especially
threatening current global biodiversity.
An example of a human activity which has decreased biodiversity is the use of monoculture in
modern agricultural practices. Monoculture involves planting one variety of a species over a
huge area. This leaves this area more vulnerable to predation or disease and the loss of many
or all species.
Uses of Biodiversity
In addition to the aesthetic beauty added to the world by many different organisms,
biodiversity also ensures the availability of a rich variety of genetic material that may lead to
future agricultural or medical discoveries with significant value to humankind. As diversity is
lost, potential sources of these materials may be lost with it.
ECOLOGICAL SUCCESSION
Ecosystem Stability
The interrelationships and interdependencies of organisms affect the development of stable
ecosystems. The types of animal communities found in an ecosystem is dependent upon the
kinds of plants and other producer organisms in that ecosystem.
Succession
The environment may be altered in substantial ways through the activities of humans, other
living things, or when natural disasters occur, such as climate changes and volcanic eruptions.
Although these changes are sometimes occur very quickly, in most cases species replace others
gradually, resulting in long-term changes in ecosystems. These gradual long term changes in
altered ecosystems are called ecological successions. Ecosystems tend to change with time
until a stable system is formed. The type of succession which occurs in an ecosystem depends
upon climatic and other limitations of a given geographical area.
A Typical New York State Succession
Pioneer organisms are the first organisms to reoccupy an area which has been disturbed by a
disruption. Typical pioneers in a succession include grasses in a plowed field or lichens on rocks.
These pioneer organisms modify their environment, ultimately creating conditions which are less
favorable for themselves, but establishing conditions under which more advanced organisms can
live. Over time, the succession occurs in a series of plant stages which leads to a stable final
community which is very similar to the plant community which originally existed in the
ecosystem. This final stable plant community is called a climax community. This community may
reach a point of stability that can last for hundreds or thousands of years.
It has been observed that when natural disasters occur, such as a floods or fires, the damaged
ecosystem is likely to recover in a series of successional stages that eventually result in a stable
system similar to the original one that occupied the area.
A Typical New York State Succession
This chart represents a typical succession which is observed in New York State.
The annual grasses represent the pioneer or first organisms in this succession. The
beech-maple forest would represent a typical Northern New York climax
community. The climax community will last hundreds or thousands of years unless
again disrupted. A forest containing oak and/or hickory trees would be a more
typical Southern New York climax community.
KEY IDEA #7
HUMAN IMPACT ON ECOSYSTEMS
Interrelationships
The Earth has limited to resources to support populations of humans and other organisms. Our
ever increasing human numbers is depleting many of our planet's resources and placing severe
stress on the natural processes that renew many of our resources.
Ecosystem Processes
Natural ecosystems are involved in a wide variety of natural processes influencing humans and
other organisms. The activities of humans in the environment are changing many of these
natural processes in a harmful fashion. Some of these natural processes and a brief description
of a human influence on these processes is indicated in the table which follows.
Human Influence on Some Ecosystem Processes
Ecosystem Process
Human Influence
Generation of Soils
Agricultural practices have exposed soil to the weather resulting
in great loss of topsoil.
Control of the Water
Cycle
The cutting of forests and other human activities have allowed
increased uncontrolled runoff leading to increased erosion and
flooding.
Removal of Wastes
Untreated sewage wastes and runoff from farms and feedlots
have led to increased water pollution.
Energy Flow
Some industries and nuclear plants have added thermal pollution
to the environment. The release of some gases from the
burning of fossil fuels may be slowly increasing the Earth's
temperature.
(Greenhouse Effect).
Nutrient Recycling
The use of packaging material which does not break down,
burning of refuse, and the placing of materials in landfills
prevents the return of some useful materials to the environment.
Some Detrimental Human Activities
Humans are part of the Earth's ecosystem. Human activities can either deliberately or
inadvertently alter the balance of an ecosystem. This destruction of habitat, whether
accidental or intentional, is threatening the stability of the planet's ecosystems. If these
human influences are not addressed, the stability of many ecosystems may be irreversibly
affected. Some of the ways that humans damage and destroy ecosystems are indicated in the
table below.
Some Ways Humans Adversely Influence Ecosystems
Human Influence
Effect on Ecosystems
Population growth
Our increasing numbers are using excessive amounts of the Earth's
limited resources.
Overconsumption
Industrialized societies are using more resources per person from our
planet than people from poor nations.
Advancing
Technologies
Often we introduce technology without knowing how it will influence
the environment
Direct Harvesting
This has resulted in a large loss of rainforest and the many products
associated with its biodiversity.
Pollution
Atmospheric
Changes
Land, air, water, and nuclear pollution have had many adverse influences
on ecosystems.
These include the addition of Greenhouse gases mostly due to the
burning of fossil fuels and depletion of our stratospheric ozone layer.
Other pollutants also have negative effects on living things.
Technological Developments
Human technologies which degrade the environment result in a loss of diversity in the living and
nonliving environment. Biodiversity refers to the differences in living things in an ecosystem.
Many of our technologies and resource use practices have resulted in an irreversible loss of
biodiversity.
Some examples of human activities which have negatively influenced other organisms include our
land use practices and pollution. Excessive land use decreases the space and resources available
to other species on the planet. Air, soil, and water pollution changes the composition of these
environmental resources, making them harmful and unusable for other species and sometimes
ourselves.
Endangered Species
Endangered species are those species which are threatened with destruction due to habitat
destruction or other factors. Animals which were once endangered but are presently
successfully reproducing and increasing their numbers are the bisons, gray wolves and egrets.
Other endangered animals which are currently responding to conservation efforts and beginning
to make a comeback are the whooping crane, bald eagle, and peregrine falcon. Even with these
successes, the future of many endangered species remains in doubt.
Exotic Species
The importation of some organisms have caused problems for native organisms. Organisms
which are imported into an area from another region are called exotic species. Many examples
of this are found world-wide. Some common examples of exotic species having negative effects
would include the rabbits and deer which were imported into Australia. These exotic species
won the competition with many native herbivorous marsupials and became nuisance species.
The starling was brought into the United States from Europe. The starling has out competed
many of our native songbirds. We also have alien invasive species which have caused problems in
New York State. These include the plants such as the Water Chestnut, Eurasian Water milfoil,
and Purple Loosestrife and animals such as the Alewife and Zebra Mussel.
Use of Fossil Fuels
Fossil fuels are becoming rapidly depleted. The use of these fuels are adding to out air pollution
problems. The search and demand for additional fossil fuel resources also impact ecosystems in
a negative way. Industrialization has brought an increased demand for and use of energy. One
of the ways the increased burning of fossil fuels has had a harmful influence of the environment
is by causing an increased incidence of acid precipitation.
Relationship Between
Global Temperature and Carbon Dioxide Levels
Our
increased burning of fossil fuels and the release of excess carbon dioxide to the atmosphere
associated with their combustion is also contributing to the Greenhouse Effect or global
warming. It is believed the increase in level of carbon dioxide and some other gases is not
allowing much infrared or heat radiation to escape the planet into outer space. This is causing
our planet to slowly warm. The graphs in the table below show the link between increasing earth
carbon dioxide levels and the increase in global average temperatures.
Some Consequences of Global Warming
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Rising sea levels and coastal flooding
Changed precipitation patterns which may result in
droughts in some regions and increased levels of crop
failure
An increase in insect borne diseases in temperate
regions such as New York State as milder winters fail
to kill the disease carrying insects. (The increase in
the incidence of West Nile virus may be an example of
this.)
Ozone Depletion
CFC's (chloroflurocarbons) are very active chemicals associated with certain human
manufacturing processes and products. This CFC pollution from refrigerants and plastics are
destroying our thin ozone shield high up in our atmosphere or in the stratosphere. This layer of
ozone normally shields us from excessive incoming ultraviolet radiation. Some consequences of
this ever increasing ozone depletion appear to be an increased incidence of skin cancers and
cataracts in the human population.
Nuclear Energy
While nuclear energy avoids many of the pollution drawbacks associated with the increased
burning of fossil fuels, there are many risks associated with the use of nuclear fuels for
energy. Environmental dangers exist in reference to obtaining, using, and storing the wastes
from these fuels. Many of the waste products of used nuclear fuel stay in the environment for
thousands of years and release radiation which is harmful to humans or other living things.
Additionally, the water used to cool many nuclear reactors must be released eventually to the
environment. The thermal pollution associated with this released heat into the water is
potentially dangerous to the aquatic life in the area where this hot water is released.
Some Examples of Political or Cultural Views Influencing Environmental
Quality
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Wealthy people in the developed world tend to have fewer children.
Some countries like China have laws concerning the number of
children a couple may have without penalty.
In some countries such as many in Latin America, families tend to be
larger as birth control violates religious and societal norms.
In some poor cultures in third world countries, having many children
is seen as a means of having economic security in old age.
Other Factors Influencing Environmental Quality
Many different factors besides industry and resource use have influences on environmental
quality. Some factors include population growth and distribution, resource use, the capacity of
technology to solve environmental problems, as well as economic, cultural, political, and ethical
views.
Through a greater awareness of ecological principles and application of these principles to our
natural environment, humans can help assure there will be suitable environments for succeeding
generations of life on our planet.
Individuals in our societies will always have to make decisions on proposals involving the
introduction of new technologies. Individuals in these societies need to make decisions which
will assess the risks, benefits, trade-offs, and costs of these new technologies. The economic
rewards of these technologies must be properly balanced with any adverse consequences these
new technologies may have on the environment. It may be impossible to completely assess the
consequences of introducing a new technology, but critical questions in reference to its
introduction must be asked.
While the overall impact of humans on the planet's ecosystems have been negative, humans have
done many things to improve the overall quality for living things in ecosystems we have damaged
or destroyed. Activities having possible adverse effects on the environment in New York State
are subject to review by SEQR (State Environmental Quality Review Act). Some other ways in
which humans have attempted to minimize negative impacts or improve the ecosystems we are all
a part of are listed in the table which follows.
Some Positive Influences of Humans on the Ecosystem
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Sustaining endangered species by using habitat protection methods such as wildlife
refuges and national parks.
Passing wildlife management laws, such as game laws and catch restrictions.
Adding lime to Adirondack lakes in an effort to neutralize their
acid pollution so the original living things in these lakes can be reintroduced.
Design new products which meet basic needs without generating pollution.
Inspection of all materials before entering the country to prevent pest introduction.
Increased use of biodegradable packaging materials which will recycle themselves
quickly to the environment.
Use fuels which contain less pollutants, such as low sulfur coal and oil.
Remove pollutants by using such devices as afterburners or catalytic converters
before they enter the air.