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Chapter 112: The Three-Domain Classification System
The classification system used by scientists has changed many times.
Scientists use a system that accurately reflects evolutionary history and the relationships among organisms.
All organisms descend from a common ancestor according to our current system.
The three-domain system is what this system is called.
All life is divided into three parts:bacteria, Archaea and Eukarya.
The classification system reflects evolutionary relationships.
The archaea are more similar to prokaryotes than they are to eukaryotes.
All are single-celled prokaryotes with no internal structures.
Some of them are anaerobes.
Decomposers that recycle dead organic matter are a vital part of the system.
Many are causing disease.
Genetic engineering depends on the role thatbacteria play.
The human gut contains Escherichia coli, which is used to make humaninsulin.
A primitive form of sexual reproduction where individuals exchange genetic material is carried out by somebacteria.
They have a thick, rigid cell wall.
Some carry out photosynthesis while others don't.
There are no introns within the DNA.
Blue-green algae, E coli, Clostridium botulinum, and nitrogen-fixingbacteria are included in the corresponds.
We don't know where to put the Viruses are placed here because we don't know where else to put them.
Taxonomy is being replaced by the study of systematics, which considers biological diversity in an evolutionary context.
The ancestry of organisms is the focus of systematics.
Current advances in DNA techniques allow scientists to compare two species at the genetic level.
In the oceans, life was tiny, primitive and single-celled.
1.5 billion years ago, the first multicellular organisms evolved.
The evolution of a new and successful body plan can be seen in the appearance of each animal.
The important trends include: specialization of tissues, germ layers, body symmetry, and body cavity formation.
The sections that follow describe the specific trends.
Organisms are related to common ancestry.
We need to start with some definitions.
The basic unit of life is the cell.
A cell is a neuron.
A tissue is a group of cells.
The sciatic nerve is a part of the body.
An organ is a group of tissues that work together.
The brain is an organ.
The cells do not function as a unit, so they are not considered tissue.
They have cells that can sense the environment.
As larger and more complex animals evolved, specialized cells joined to form real tissues, organs, and organ systems.
Flatworms have no organs.
Annelids and arthropods have organ systems.
The main layers of the body are called germ layers.
Gastrulation formed them early in their development.
Complex animals are triploblastic.
There are threederms: the ectoderm, the endoderm, and the mesoderm.
The nerve cord and brain are included in the skin and nervous system.
The innermost layer of the body becomes the viscera.
The middle layer of the skin becomes blood and bones.
The Porifera and Cnidarians have only two cell layers and are called diploblastic.
Their bodies are made of glue which connects the two layers.
Most sophisticated animals exhibit bilateral symmetry, unlike primitive animals.
The echinoderms seem to be an exception because they only exhibit bilateral symmetry when they are young and then reverting to radial symmetry as adults.
The body is arranged along a longitudinal axis with right and left sides that mirror each other.
Along with bilateral symmetry comes a front and rear end.
The brain and sensory apparatus are located at the anterior part of the body.
Animals can move faster to flee or capture prey.
Bilateral animals are all triploblastic with three differentderms.
The principles of biology apply to all organisms because they evolved from a common ancestor almost 4 billion years ago.
The evolutionary history of these relationships is called phylogeny.
A cladogram is a diagrammatic reconstruction of the history.
Morphology and physical behaviors were used to determine phylogenetic trees.
Evolutionary relationships and DNA are now being used in the creation of trees.
Scientists have been able to reconstruct a history of human migration out of Africa.
The growing database of genes makes it easier for researchers to study more species, but it also makes it more difficult to build a phylogenetic tree.
The principle of maximum parsimony is used by scientists to narrow down the possibilities.
Evolutionary trees and cladograms are constantly being revised.
A trait is absent if a trait is present.
lamprey, bass, frog, turtle, and leopard are in groups and as a point of reference.
The outgroup is the group that changed before the lineage evolved.
The split is depicted as a nodes.
The development of a vertebral column, four walking legs, amnion, and the development of hair can be seen in this example.
The characteristics of all animals are similar to those of their ancestors.
The trait is known as a shared ancestral trait.
Each animal in one clade or lineage has a trait that is not shared with their ancestors.
A shared derived trait is a new trait.
Hair in the leopard is a derived trait.
It is possible to create a simple cladogram that correctly represents evolutionary history.
You can evaluate evidence presented in a tree or cladogram.
The chapter was an introduction to Big Idea: EVO.
The current system of classification is based on evolutionary history.
All organisms are linked by lines of descent from a common ancestor because they share many conserved processes.
Both genes are universal.
They have the same genetic code.
All organisms are placed into one of the three domains.
Organisms are grouped in a hierarchy of categories called taxa.
The most diverse grouping is the taxon.
Our system of classification requires that the scientific name of every organisms has two parts; the genus name and the species name.
A red maple tree is called acer rubrum.
A diagrammatic reconstruction is a model of evolutionary history.
They can be built in a variety of ways.
Out groups are not closely related to the in groups and are on a separate clade.
For comparison, out groups are included.
All organisms are descendants of their ancestors and have evolved new and different characteristics.
The shared ancestral traits and new derived traits are what the organisms share with their ancestors.
All organisms that share a trait are located on one branch.
You should be able to analyze and evaluate a tree.
The data used to construct the tree is presented in the study.
Our system of classification is presented in a pyramid.
The table below shows the presence or absence of five derived traits in four different species.
Assume that the ancestor had a long tail, ear flaps, external testes, and fixed claws.
Each taxon has fewer and fewer different species as you move down the pyramid.
Organisms are classified by their evolutionary history.
Every type of organisms is in the pyramid.
The organisms are named in the same way, with two names.
The prokaryotes are grouped into two categories:bacteria and Archaea.
Plants are not the only organisms that are photosynthetic.
There are organisms.
The cell walls of fungi are made of chitin.
The prokaryotes and archaea are thought to have differed in ancient times.
One of the ways in which the two differ is in their nucleic acids.
They digest food outside of the body.
This is a type of digestion.
When the food is broken down into building blocks, it is absorbed into the body of the organisms.
The fish do not descend from sharks.
They have a distant common ancestor.
Crocodiles and rodents are not related to one another.
The fact that the animals are near each other is not indicative of a relationship.
The primate and rodents and rabbits can change their position on this cladogram.
It needs to be separated from the others.
All the other species have the same trait.
The cladogram must show Trait 1 below all of them.
Only Species A and B have trait 2.
They need to be off on a line and above the 2nd line.
You'll see that only Species B has Trait 3, so it must be diverted off on a line above it.
No other species has the same trait as Species D. It is necessary for Species D to be above the other two, below the other one, and above the other one because it does have those traits.
There are short tail and abdominal testes.
Loss of ear flaps is a new trait that is not shared with the previous organisms.
The derived trait of retractable claws implies that all other organisms have fixed claws.
The earthworm doesn't have any of the traits listed in the table, so it must be placed in a clade separate from the other animals.
The three remaining animals have the same trait, "backbone," but the salmon has no other trait listed in the table.
The lizard and cat have legs, so their clades must be derived from that trait.
The cat has its own hair and is on its own.
They are the most closely related animals.
Frogs don't have an amnion.
They need to lay their eggs in a moist area so they don't dry out.
Bass, turtles, and leopards descended from an ancestors that had a hinged jaw.
Bass did not descend from an animal with four legs.
The animal that brought the lancelet down did not have a backbone.
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