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Macroevolution Biological Kingdoms Updated: |
Topics for February 25
Macroevolution.
Vocabulary of classification.
Origin of life.
The 3 kingdoms.
Life of the Paleozoic, Mesozoic, Cenozoic.
Quiz #4.
Macroevolution: The major kingdoms.
Modern biological classification recognizes 5 major kingdoms.
The major kingdoms represent the major branches of the history of macroevolution.
The 5 kingdoms are:
(1) Monerans (bacteria)
(2) Protistans (single celled eukaryotes)
(3) Plants - (4) Animals - (5) Fungi
The Kingdom Monera
The monerans , mostly bacteria, came first: more than 3 billion years ago.
Monerans are single-celled, with little internal structural complexity.
In spite of their structural simplicity, they represent great biochemical diversity.
Monerans include: producers (photosynthetic or chemosynthetic) and decomposers.
The Kingdom Protista.
Protistans are single-celled eukaryotes. They have considerable structural complexity.
Protista are very diverse: photosynthetic algae, molds, amoebas, protozoans, etc.
Most are free-living, but some are parasitic. Example: Plasmodium, the organism that causes malaria.
The Kingdom Plantae
Plants are multicellular, photosynthetic eukaryotes.
Plants possess distinctive cell organelles that provide photosynthesis: the chloroplasts.
Plants are responsible for nearly all the primary productivity on land.
The Kingdom Fungi
Fungi are multicellular eukaryotes that are heterotrophic: the obtain energy by decomposing other organisms.
A characteristic feature of fungi is that they use "extra-cellular" digestion and absorption to obtain their food.
Most fungi are decomposers. A few are parasites or pathogens.
The Kingdom Animalia
Animals are multicellular eukaryotes that obtain their energy by consuming other organisms.
Animals are very diverse: more than 1 million species on earth.
Many animals are herbivores, but there are also many species of parasites and predators.
Levels of classification.
Biologists have adopted a hierarchical system of classification that reflects the history of diversification. The categories:
Kingdom
Phylum
Class
Order
Family
Genus
Species
How real are these categories?
The categories are artifacts of human scholarship.
Exception: species are real.
The hierarchy is natural: a consequence of diversifying evolution.
The binomial system.
Linneaus introduced the "Binomial system" for naming species.
The standard technique is to list species by Genus name and Specific name.
Some examples:
Cyclotella compta
Homo sapiens
The Geologic Time Scale
An elaborate version of the time scale is given in figure 17.8, p269
We will focus on:
Paleozoic (600mya-250mya)
Mesozoic (250mya-65mya)
Cenozoic (65mya-present)
What marks the boundaries between these major eras?
Mass extinctions have been used to identify the horizons between the successive eras.
At the end of the paleozoic, or the Permian Period, there was a massive extinction. More than 90% of all living species disappeared.
At the end of the mesozoic, or the Cretaceous Period, the dinosaurs and many other species disappeared.
Origin of life (p264ff)
The precise sequence of events is not known. However, some broad details are well known.
Atmosphere: Prior to the origin of photosynthetic cyanobacteria, the atmosphere lacked molecular oxygen, O2. The atmosphere was much more reducing, with CO and H2 present along with N2 and CO2.
Simulation experiments of the origin of life.
The general knowledge about the composition of the early atmosphere was used to construct simulation experiments.
Stanley Miller was the first to try (see p265) He prepared a mixture of reducing gases similar to those of the early earth. Energy was provided by electric spark ("lightning"). Results: A wide variety of organic molecules, including some essential to life.
The first cells.
The first cells were prokaryotes (with some living relatives still present).
Fossils from 3.8 bya indicate that prokaryotes had developed by that time.
Two major lineages of prokaryotes are still present on earth:
eubacteria and archaebacteria (see p 271)
Characteristics of prokaryotes.
Living prokaryotes are chemically and ecologically complex.
Cell structure is uncomplicated. Prokaryotes lack distinctive cell organelles.
DNA is organized as a single loop of DNA attached to the cell wall.
Prokaryotes are still an important part of the biota of the earth.
Two major groups of prokaryotes
Eubacteria, include:
Most of the common bacteria, including decomposers and pathogens.
The cyanobacteria, photosynthetic bacteria.
Archaebacteria include:
Halophiles, Methangens, Thermophiles
The eukaryotes.
Eukaryotes are identified by their cell structure.
Eukaryotic cells have distinctive organelles: nucleus (with the chromosomes), mitochondria (for the manufacture of ATP), chloroplasts (in the case of plants), and other cell organelles.
Eukaryotic cells originated from pre-existing prokaryotic cells.
Evidence for the endosymbiotic theory:
Organelles possess characteristics which identify them as "symbiotic eubacteria".
Example: Mitochondria have an inner membrane that resembles bacterial cell membranes.
Example: Mitochondria divide independently of nuclear events, and have some of their own unique DNA.
Life in the Paleozoic.
The paleozoic lasted a very long time: 350 million years.
Most of the animal and plant phyla had appeared by the start of the paleozoic.
The paleozoic ended with the largest of all mass extinctions at the end of the Permian.
Life in the Mesozoic.
The mesozoic is famous for the rise of the dinosaurs, but were not the dominant until later in the mesozoic.
Many other groups of plants and animals also proliferated. An important example: flowering plants originated about 130 mya, and began to displace conifers.
Life in the Cenozoic
The mesozoic came to an end with the massive extinction of the dinosaurs and many other species at the end of the Cretaceous.
Mammals and flowering plants proliferated during the Cenozoic, and are the dominant large animals today.
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