Biologist ___________________________ Date ______________
Prokaryotes 20-2 – PowerPoint
• Classifying Prokaryotes
The smallest and most abundant microorganisms on Earth are ____________—unicellular organisms that lack a _____________.
Prokaryotes have DNA, like all other cells, but their DNA is not found in a membrane-bound
_____________envelope as it is in eukaryotes. Prokaryote DNA is located in the _____________.
Recently, biologists have divided prokaryotes into two very distinct groups: Bacteria and
_____________.
These groups are very different from each other; therefore, biologists now consider each group of prokaryotes as a separate _____________. Eukaryotes are the third domain.
• Bacteria
The larger of the two domains of prokaryotes is the _____________.
Bacteria include a wide range of organisms with lifestyles so _____________that biologists do not agree exactly how many phyla are needed to classify this group.
Bacteria live almost _____________—in fresh water, in salt water, on land, and on and within the bodies of humans and other eukaryotes.
Bacteria are usually surrounded by a cell wall made from _____________that protects the cell from injury and determines its shape.
In addition, some prokaryotes have _____________that they use for movement, or pili, which in
serve mainly to anchor the bacterium to a surface or to other bacteria.
• Archaea
Under a microscope, archaea look very _____________to bacteria. Both are equally small, lack nuclei, and have cell walls, but there are important differences.
The walls of archaea _____________ peptidoglycan, and their membranes contain different lipids.
The DNA sequences of key archaea genes are more like those of _____________ than those of bacteria.
Based on these observations, scientists have concluded that archaea and eukaryotes are
_____________more closely to each other than to bacteria.
Many archaea live in extremely _____________environments.
• Structure and Function
How do prokaryotes vary in their structure and function?
Prokaryotes vary in their size and shape, in the way they move, and in the way they obtain and release _____________.
• Size, Shape, and Movement
Rod-shaped prokaryotes are called _____________.
Spherical prokaryotes are called _____________.
Spiral and corkscrew-shaped prokaryotes are called _____________.
Prokaryotes can also be distinguished by whether they move and how they move.
Some prokaryotes do not move at all. Others are propelled by flagella. Some glide slowly along a layer of _____________material they secrete.
• Nutrition and Metabolism
Energy is released from these fuel molecules during cellular _____________, fermentation, or both.
• Growth, Reproduction, and Recombination
When a prokaryote has grown so that it has nearly doubled in size, it replicates its DNA and divides in half, producing two identical cells. This type of reproduction is known as binary
_____________.

Because binary fission does not involve the exchange or recombination of genetic information, it is an asexual form of _____________.
When conditions are favorable, prokaryotes can grow and divide at astonishing rates—some as often as once every ___ minutes!
When growth conditions become unfavorable, many prokaryotic cells form an _____________—a thick internal wall that encloses the DNA and a portion of the cytoplasm.
Endospores can remain dormant for months or even _____________.
• Mutation
Mutations are one of the main ways prokaryotes _____________.
Mutations are random changes in ______ that occur in all organisms.
In prokaryotes, mutations are inherited by daughter cells produced by binary fission.
• Conjugation
Many prokaryotes exchange genetic information by a process called conjugation.
During _____________, a hollow bridge forms between two bacterial cells, and genetic material, usually in the form of a plasmid, moves from one cell to the other.
This transfer of genetic information increases _____________diversity in populations of prokaryotes.
• Decomposers
By decomposing dead organisms, prokaryotes, supply raw materials and thus help to maintain
_____________in the environment.
Bacterial decomposers are also essential to industrial sewage treatment, helping to produce purified water and chemicals that can be used as _____________.
• Producers
Photosynthetic prokaryotes are among the most important _____________on the planet.
Food chains everywhere are dependent upon prokaryotes as producers of food and biomass.
• Nitrogen Fixers
All organisms need _____________to make proteins and other molecules.
Nitrogen gas (N organisms.
The
2
) makes up 80 percent of Earth’s atmosphere, but only a few kinds of organisms—all of them prokaryotes—can convert N
2
into useful forms.
The process of nitrogen fixation converts nitrogen gas into _____________ (NH then be converted to nitrates that plants use, or attached to amino acids that all organisms use.
Nitrogen-fixing bacteria and archaea provide _____ percent of the nitrogen used by other
3
). Ammonia can bacteria often live _____________within nodules attached to roots of legumes, such as clover, where they convert atmospheric nitrogen into a form that is useable by plants.
• Human Uses of Prokaryotes
Prokaryotes, especially bacteria, are used in the production of a wide variety of foods and other commercial products.
_____________is produced by the bacterium
Some bacteria can digest _____________and remove human-made waste products and poisons from water.
Other bacteria are used to synthesize ______ and chemicals through the techniques of genetic engineering.
Bacteria and archaea _____________to extreme environments may be a rich source of heat-stable enzymes that can be used in medicine, food production, and industrial chemistry.