Chapter 4
Patterns of Life
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Review the characteristics of Life (from previous chapters)
Reminder:
There are two basic cell types based on structure: prokaryotes and eukaryotes. All bacteria and archaea are
included in the classification of prokaryotes, which are considered to be the most primitive of the two cell
types (3.5 billion years old). Eukaryotic cells (1.5 billion years old) are present in all other organisms.
Prokaryote and eukaryotic cells may be either autotrophs or heterotrophs. In some cases, they may be both.
Review the differences (notes chap. 1) between eukaryotic and prokaryotic cells. See figure 4.4 pg. 106.
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Taxonomy is the branch of biology that deals with classification of living things.
Early classification:
Aristotle classified all organisms into two large groups: the Kingdom Animalia and the Kingdom Plantae. He then
divided the animals as land dwellers, air dwellers, or water dwellers.
Theophrastus, a student of Aristotle, classified the plants according to their stem structure. There were herbs(soft
stems), shrubs (several woody stems) and trees (a single woody stem).
In the mid-1600's an English Naturalist John Ray classified many plants and animals. He was the first to use the term
species for each different kind of organism.
Species - a group of organisms that were structurally similar and that passed these similarities down to their offspring.
Until recently, scientists have recognized five different kingdoms to which all organisms on Earth have been
classified. These kingdoms were Animalia, Plantae, Fungi, Protista, and Monera. These kingdoms were originally
determined by Robert Whittaker.
Currently, six-kingdom scheme is currently used by many biologists:
Archaea, Bacteria, Protista, Fungi, Plantae, and Animalia.
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The archaea were originally grouped with bacteria in the Kingdom Monera, which itself was originally part of
Kingdom Protista. However, it is believed that Archaea evolved first using the various atomospheric gases to
metabolize and develop. Bacteria also show different development of the DNA molecule, leading to separate
placement in the evolutionary tree.
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The Kingdoms are also grouped into three domains based on the type of cells the organisms in each have. See figure
4.5 p.107
Characteristics of the Kingdoms
Characteristic
Bacteria
Archaea
Protista
Fungi
Cell type
Body form
Cell wall
Composition
Mode of
nutrition
nervous
system
Locomotion
Examples
* Be able to briefly describe each Kingdom. (Written and chart form)
Plantae
Animalia
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Why did scientists change their method and criteria for classification (so that there were more than that just
Kingdom Animalia and Kingdom Plantae)?
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The Swedish botanist Carolus Linnaeus, considered the founder of modern taxonomy, improved upon the work
of early taxonomists. He used structural similarities as a basis of his classification system. He classified every
organism according to a binomial name (two-word system) consisting of genus and species.
The two-word system of identifying each kind of organism is called binomial nomenclature.
Since the time of Linnaeus, taxonomists have added several categories to the classification scheme. The broadest
and largest taxa are the Kingdoms while the Species are the smallest and most specific taxa.
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taxon
Domain
Kingdom
Phlyum
Class
Order
Family
Genus
Species
definition
- a group of related kingdoms
- a group of related phyla
- a group of related classes
- a group of related orders
- a group of related families
- a group of related genera
- a group of related species
- a group of similar organisms which interbreed in nature to create productive offspring like themselves
Classification of Some Familiar Organisms
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Category
Human
Chimpanzee
Housefly
Dandelion
Kingdom
Animalia
Animalia
Animalia
Plantae
Phylum
Chordata
Chordata
Arthropoda
Tracheophyta
Class
Mammalia
Mammalia
Insecta
Angiospermae
Order
Primates
Primates
Diptera
Asterales
Family
Hominidae
Pongidae
Muscidae
Asteraceae
Genus
Homo
Pan
Musca
Taraxacum
Species
Homo sapiens
Pan troglodytes
Musca
domestica
Taraxacum
officinale
Most plants and animals have common names. However, common names are often confusing and inexact. A
starfish, for example, is not a fish. Also, common names may vary from language to language.
Ex: an English “dog” is a Spanish ‘perro’ and a Japanese “inu”. However, the scientific name for dog, Canis
familiaris is understood by biologists everywhere.
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Another important aspect of taxonomy is to determine the evolutionary history of groups of organisms.
Phylogeny is the evolutionary history of a species or group of organisms. Phylogenetic trees show the
relationships between different organisms that are thought to have a common ancestry.
To classify organisms and study evolutionary relationships, scientists can use several different types of evidence:
structural, biochemical, cytological, embryological, behavioural, and fossil information.
* Be able to describe each type of evidence (pages 113-116)
1) structural information - anatomy -> physical structure of organisms
2) biochemical information - DNA, RNA, protein sequence information
3) cytological information - cellular structure
4) embryological information - examining embryos
5) behavioral information - organism behavior
6) fossil information - similarity in fossil structure
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Cladistics is a type of systematics that is a more concise method of classifying organisms. It is based on the
assumption that each group of related species has one common ancestor and that organisms retain ancestral traits.
Cladograms are used to test various hypothesized relationships. Specific characteristics are used to unite
particular groups of organisms that share the characteristic. For example, birds, reptiles and mammals all have an
amniotic egg of sorts. This amniotic egg is a characteristic that is used to unite the above three groups of
organisms.
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The study of phylogeny provides information about relationships between species that can be applied to other
areas of scientific research. For example, medical doctors are looking for ways to use organs from species closely
related to humans as possible replacements for human organs that have failed. In one example, doctors have
suggested using a pig heart to replace the defective heart of a human infant. This could not be possible without
the results of phylogeny that show the connection between human and pig characteristics.
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Viruses
Viruses are not considered to be living unless they are in a host organism. They cannot reproduce in the manner
that other organisms can, and they do not metabolize. They have no cytoplasm, organelles, or cell membranes.
They do not carry out respiration or many other life processes. Thus, many scientists consider viruses to be in a
unique category, distinct from living organisms.
The shape of a virus is determined by the type and arrangement of proteins in the capsid. See figure 4.20, pg
122.
Viruses are infectious agents responsible for a variety of diseases that exist in all organisms. They attach to the
host cell receptor proteins (found in the membrane of the host cell) and inject their nucleic acid core into the cell.
Once inside, the virus can follow one of two pathways: lytic cycle or lysogenic cycle.
Viruses that contain DNA generally follow the lytic cycle in which they deactivate the host mRNA (a special
nucleic acid that transmits messages from the nucleus to the ribosomes to make proteins) and direct the host to
make viral mRNA, which is used by the host ribosomes to make more viruses. Once the cell is full of virus
particles, an enzyme is produced by the virus (again using host machinery) to lyse the cell. Then the virus
particles spread to infect other cells. See figure 4.21 pg. 123.
The lysogenic cycle is a little more complicated. Viruses that contain RNA as their nucleic acid follow this cycle.
Once inside the host cell, an RNA virus will activate a special enzyme (reverse transcriptase) to change its RNA
into viral DNA. This DNA becomes spliced into the host DNA and the virus becomes dormant. Some trigger
eventually activates the virus once more, and it then follow the lytic cycle, eventually spreading to other cells.
HIV is an example of a type of RNA virus called a retrovirus.
Summary (also an answer to question #3 on page 126)
A virus can reproduce using three different mechanisms, which are usually dependent on the type of virus particle.
DNA viruses can reproduce in one of two ways.
I.
Some DNA viruses gain access to the host cell, deactivate the host mRNA, and use the host to make new viruses.
II.
Other DNA viruses can splice their DNA into the host DNA and remain dormant for periods of time until they
become reactivated.
These types of DNA viruses are called proviruses, and once they become reactivated, they will proceed along the same
path as the other DNA viruses until they go dormant again.
RNA viruses...
RNA viruses have an enzyme (reverse transcriptase) that they use to alter their RNA into viral DNA, which is then spliced
into the host DNA. RNA viruses then go dormant usually for very long periods of time. Once reactivated, they proceed
along the same pathway as DNA viruses.
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Viruses are host-specific and cell-specific. Certain viruses attack only particular types of organisms and cells.
However, some mutations have allowed some viruses to change their hosts. (i.e. AIDS virus)
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Although viruses can be very dangerous, how can they be helpful for genetic engineers?