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Chapter 4
Patterns of Life
SECTION 4.1 Characteristics of Life
All living things must:
1.
be highly organized and made up of one or more cells. The chemical compounds and reactions found in
non-living things are quite simple as compared to those in organisms. The cell is the basic unit of life. The
cells of multicellular organisms can be organized into tissues, organs, and systems.
2.
3.
4.
5.
6.
metabolize matter and use energy. Many of the chemical reactions in living things are endothermic and require
energy. The material used to carry out these reactions comes in the form of food from the organisms
environment.
interact with their environment and maintain homeostasis. Organisms constantly exchange material with their
environment in order to survive. They do this to keep a constant internal environment (homeostasis) which is
different from their surroundings.
grow and develop. Living things increase in mass over time. As they grow, they go through various stages to
become an adult.
reproduce. If the individual does not reproduce, there is no problem. However, if a species as a whole does not
reproduce, that species will become extinct. Through reproduction, genetic information is passed to the
offspring regarding growth, metabolism, organization, and reproduction.
adapt to their surroundings. In the short term, they will respond to changes such as light intensity, temperature,
and the amount of food/prey. In the long term, they must adapt to suit their changing environment (evolve).
Classification
There are currently 1.5 million different species on Earth. A conservative estimate is that there are 20 million
species yet to be discovered. Some estimate 100 million speceis!
taxonomy - the branch of biology which deals with the naming and classifying of living things
Early Taxonomy
1) 4th century B.C. -> Aristotle
- 2 kingdom system used: Kingdom Animalia and Kingdom Plantae
- grouped animals based on their movement and according to where they lived -> air dwellers, land dwellers, and water
dwellers
2) 4th century B.C. -> Theophrastus
- student of Aristotle
- studied plants and grouped them according to reproductive and external tissue structures
Problems
- system was used for Europe and area of the Mediterranean (where Aristotle and Theophrastus lived)
- by the 1400's and 1500's, explorers discovered many new species
- development of the microscope in the 1600's lead to discovery of a whole new world of microorganisms
-> need for a more effective method of classification
3) 1866 -> German biologist Ernst Haeckel
- classified all micro-organisms in a third kingdom Protista
Later, biologists realized that even though some organisms like mushrooms and molds resemble some plants, they
do not obtain food by photosynthesis. They absorb nutrients from their surroundings. This lead to the creation of a 4 th
kingdom, Fungi. When it was discovered that bacteria were much simpler than eukaryotic cells, they were put into a
separate kingdom, Monera. Finally, in the 1990's, a group of bacteria which grow in extreme conditions (archaebacteria)
were found to have mechanisms of survival which were different from other bacteria. Thus, a 6 th kingdom was created,
Archaea.
Fossil evidence has shown that the earliest life forms on Earth were bacteria whose remains were found in rocks
dating back 3.5 billion years. Eukaryotic cells did not arrive until 1.5 billion years ago. In fact, multicellular organisms
did not evolve until 700 million years ago! However, bacteria and archaebacteria are as much different from one another
as they are from eukaryotes. Thus, a new level of classification has been made: Domains. There are 3 domains to
classify
the 6 kingdoms based on cellular structure. They are grouped as follows:
Domain Bacteria
Domain Archaea
Domain Eukarya
Kingdom Monera
Kingdom Archaea
Kingdom Protista, Kingdom Fungi, Kingdom Plantae, Kingdom Animalia
SECTION 4.2 Naming and Classifying Organisms
Carolus Linnaeus (the Founder of Modern Taxonomy)
- a Swedish botanist who used structural similarities to classify plants
- improved upon past systems and his system is still used today
- since then, more categories have been added to include the following listing
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
Binomial Nomenclature
-> a two name, naming system which is the "scientific name" of the organism
Rules for binomial nomenclature:
1) the name is made using the Latin language because it is no longer used in society and it no longer evolves
2) the "species" name is made up of the genus and species names from taxonomy which are often indicative of some
aspect of the organism
e.g. Homo sapiens - man, wise
3) the genus name is capitalized and the species name is not
4) the name is italicized if typed or underlined if hand written
5) the genus name is often shortened to one letter if the name is repeated over and over in a paper or article
e.g. Escherichia coli -> E. coli
Reasons for the need of scientific names:
1) common names can be inexact
e.g.
a starfish is not a fish
a cat fish is not a cat with gills
2) one species may have many common names which vary from place to place or which may be for a different organism
elsewhere
e.g.
a blue jay a.k.a. corn thief, nest robber, blue coat
dozens of species known as raspberries
Information used to Classify Organisms
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
Evolution/Taxonomy
- the theory that organisms slowly change over time and that new species arise and older species go extinct
- if two organisms are similar in a number of ways there is probably a very good chance that at some point in
evolution they shared a common ancestor
e.g. wolves and dogs
- phylogeny is the evolutionary history of a group of organisms which looks like a tree
- cladistics is a classification scheme based on phylogeny
SECTION 4.3 Viruses
People are generally familiar with viruses because they cause a number of disorders in living things. Because of
this, people tend to think of viruses as alive. However, they are not. They are not composed of cells. They do not
carry
out the activities of life. They are simply a protein shell called a capsid containing some genetic information. Scientists
have grouped viruses into about 160 categories based on their structure and how they reproduce.
Viral Reproduction
Viral genomes consist of DNA or RNA and tend to be very small due to the small physical size of viruses. Some
have less than 10 genes and have just the information needed to reproduce. Because of their simplicity and the methods
they use to reproduce, errors are made easily. Viruses tend to evolve and change much more quickly than cells.
Viruses can not reproduce on their own. They must infect cells and use the cell’s machinery to produce more
viruses. Some think of viruses as a simple, cellular parasite. They have proteins on its capsid which allow it to attach
to
proteins on the cell membrane or cell wall. These viral proteins are very specific to the cells they infect. For example,
a
virus which has evolved to attach to cells in the mucus membrane of a human, will not affect skin cells or the cells of a
plant. Some viruses, such as bacteriophages, attach to the bacterial cell wall and inject the cell with viral DNA. This
causes the host bacterium to produce more viruses (200 new viruses in 30 minutes). Eventually the bacterium ruptures
and releases the viruses to attack more bacteria. This is called the lytic cycle of viral reproduction.
Some viruses attach to specific receptors on the cell membrane and trigger receptor assisted endocytosis. The
virus enters the cell inside a vacuole which it will later break out of and then takes over the cell to make new viruses.
HIV is an example of a retrovirus. It injects the host cell with RNA and an enzyme called reverse transcriptase.
This enzyme will make a copy of DNA based on the viral RNA. The DNA can then enter the host cell’s chromosome
and
produce new viral RNA and protein from there.
Sometimes, when viral DNA becomes a part of the host cells chromosome, it remains dormant. Every time the
cell undergoes cell division, the viral DNA (provirus) is replicated along with the host’s chromosomes. In the end,
many
cells within the organism are silently infected until the virus is triggered to enter the lytic cycle.
Viral Infection http://www.hhmi.org/biointeractive/disease/animations.html