CK-12 Life Science
Page 20
Helpful Bacteria
Bacteria are crucial in nature since they are common decomposers, organisms that break down dead materials and waste products. This decomposition of dead organisms is necessary so that the nutrients in their bodies can be recycled back into the environment. This recycling of nutrients, such as nitrogen, is essential for living organisms; organisms cannot produce nutrients, so they must come from other sources. We get them from the food we eat; plants get them from the soil. How do these nutrients get into the soil? One way is from the actions of decomposers. Without decomposers, we would eventually run out of materials essential for our survival. We also depend on bacteria to decompose our wastes in sewage treatment plants.
Bacteria also help you digest your food. Several species of bacteria, such as E. coli, are found in large amounts in your digestive tract. In fact, bacteria cells outnumber your own cells in your gut!
Bacteria are involved in producing some foods. Yogurt is made by using bacteria to ferment milk, and cheese can also be made from milk with the help of bacteria (Figure below). Furthermore, fermenting cabbage with bacteria produces sauerkraut.
Figure 8.9
Yogurt is made from milk fermented with bacteria. The bacteria ingest natural milk sugars and release lactic acid as a waste product, which causes proteins in the milk to form into a solid mass, which becomes the yogurt.
In the laboratory, bacteria can be altered to provide us with a variety of useful materials. Bacteria can be used as tiny factories to produce desired chemicals and medicines. For example, insulin, which is necessary to treat people with diabetes, can be produced from bacteria. Through the process of transformation, the human gene for insulin is placed into bacteria. The bacteria then turn that gene into a protein. The protein can be isolated and used to treat patients. The mass production of insulin by bacteria made this medicine more affordable for patients.
Harmful Bacteria
There are also ways that bacteria can be harmful to humans and other animals. Various species of bacteria are responsible for many types of human illness, including strep throat, tuberculosis, pneumonia, leprosy, and Lyme disease. The Black Death (also known as Plague), which killed at least one third of Europe’s population in the 1300’s, is believed to have been caused by the bacterium Yersinia pestis.
Bacterial contamination can also lead to outbreaks of food poisoning. Raw eggs and undercooked meats can contain bacteria that can cause digestive tract problems. Foodborne infection can be prevented by cooking meat thoroughly and washing surfaces that have been in contact with raw meat. Washing of hands before and after handling food is also important.
Some bacteria also have the potential to be used as biological weapons by terrorists. An example is anthrax, a disease caused by the bacterium Bacillus anthracis. Since inhaling the spores of this bacterium can lead to a fatal infection, it is a dangerous weapon. In 2001, an act of terrorism in the United States involved B. anthracis spores sent in letters through the mail.
Lesson Summary
Bacteria contain a cell wall containing peptidoglycan and a single chromosome contained in the nucleoid.
Bacteria can obtain energy through several means including photosynthesis, decomposition, and parasitism, symbiosis, and chemosynthesis.
Bacteria reproduce through binary fission.
Bacteria are important decomposers in the environment and aid in digestion.
Some bacteria can be harmful when they contribute to disease, food poisoning, or biological warfare.
Review Questions
What are prokaryotes?
What are the possible shapes that bacteria can have?
What is the purpose of the flagella?
Describe the DNA of bacteria.
How do bacteria reproduce?
How do bacteria assure genetic recombination?
What is a chemoautotroph?
How do cyanobacteria obtain energy?
How are bacteria important in nature?
How can you avoid becoming sick from the bacteria that cause food poisoning?
Further Reading / Supplemental Links
http://www.bt.cdc.gov/agent/anthrax
http://www.cdc.gov/ncidod/dvbid/plague/index.htm
http://www.cdc.gov/nczved/dfbmd/disease_listing/salmonellosis_gi.html
http://www.ucmp.berkeley.edu/bacteria/bacteria.html
http://commtechlab.msu.edu/sites/dlc-me/zoo
http://www.cellsalive.com/cells/bactcell.htm
Vocabulary
bacilli
Rod-shaped bacteria or archaea.
binary fission
Type of asexual reproduction where a parent cell divides into two identical daughter cells.
cocci
Sphere-shaped bacteria or archaea.
chemotrophs
Organisms that obtain energy by oxidizing compounds in their environment.
conjugation
The transfer of genetic material between two bacteria.
cyanobacteria
Photosynthetic bacteria.
decomposers
Organisms that break down wastes and dead organisms and recycle their nutrients back into the environment.
flagella
Long, tail-like appendages that allow movement.
nucleoid
The prokaryotic DNA consisting of a condensed single chromosome.
peptidoglycan
Complex molecule consisting of sugars and amino acids that makes up the bacterial cell wall.
plasmid
Ring of accessory DNA in bacteria.
prokaryotes
Organisms that lack a nucleus and membrane-bound organelles; bacteria and archaea.
transduction
Transfer of DNA between two bacteria with the aid of a bacteriaphage.
transformation
Changing phenotypes due to the incorporation ("taking up") of foreign DNA from the environment.
spirilli
Spiral-shaped bacteria or archaea.
Points to Consider
In the next section we will discuss the Archae. “Archae” shares the same root word as “archives” and “archaic,” so what do you think it means?
What do you think the earliest life forms on Earth looked like?
How do you think these early life forms obtained energy?
Lesson 8.2: Archaea
Lesson Objectives
Identify the differences between archaea and bacteria.
Explain how the archaea can obtain energy.
Explain how the archaea reproduce.
Discuss the unique habitats of the archaea.
Check Your Understanding
What are the three shapes of bacteria?
Answer: The bacilli are rod-shaped, the cocci are sphere-shaped, and the spirilli are spiral-shaped.
How do bacteria reproduce?
Answer: Through binary fission, producing genetically identical organisms.
How can bacteria be harmful?
Answer: Bacteria can cause diseases such as strep throat. They can also be involved with food poisoning and biological warfare.
Introduction
For many years, archaea were classified as bacteria. However, when modern techniques allowed scientists to compare the DNA of the two prokaryotes, they found that there were two distinct types of prokaryotes, which they named archaea and bacteria. Even though the two groups might seem similar, archaea have many features that distinguish them from bacteria.
The cell walls of archaea are distinct from those of bacteria. In most archaea, the cell wall is assembled from surface-layer proteins, providing both chemical and physical protection. The cell wall acts as a barrier, preventing macromolecules from coming into contact with the cell membrane. In contrast to bacteria, most archaea lack peptidoglycan in their cell walls.
The plasma membranes of the archaea also are made up of lipids that are distinct from those in other organisms.
Furthermore, the ribosomal proteins of
the archaea resemble those of eukaryotic cells; the ribosomal proteins of archaea are different from those found in bacteria.
Although archaea and bacteria share some fundamental differences, they are still similar in many ways.
They both are unicellular, microscopic organisms that can come in a variety of shapes (Figure below).
Both archaea and bacteria have a single circular chromosome of DNA and lack membrane-bound organelles.
Like bacteria, the archaea can have flagella to assist with movement.
Figure 8.10
Archaea shapes can vary widely, but some are bacilli, or rod-shaped.
Obtaining Food and Energy
Most archaea are chemotrophs and derive their energy and nutrients from breaking down molecules from their environment. A few species of archaea are photosynthetic and capture the energy of sunlight; chemotrophs do not capture the energy from sunlight. Unlike bacteria, which can be parasites and are known to cause a variety of diseases, there are no known archaea that act as parasites. Some archaea do live within other organisms, however, but form mutualistic relationships with their host, where both the archaea and host benefit. In other words, they actually assist the host in some way, for example by helping to digest food.
Reproduction
Like bacteria, reproduction in archaea is asexual. Archaea can reproduce through binary fission, where a parent cell divides into two genetically identical daughter cells. Archaea can also reproduce asexually through budding and fragmentation, where pieces of the cell break off and form a new cell, also producing genetically identical organisms.
Types of Archaea
The first archaea described were unique in that they could survive in extremely harsh environments where no other organisms could survive. For example, the halophiles, which means "salt-loving," live in environments with high levels of salt (Figure below). They have been identified in the Great Salt Lake in Utah and in the Dead Sea between Israel and Jordan, which have salt concentrations several times that of the oceans.
Figure 8.11
Halophiles, like the Halobacterium shown here, require high salt concentrations.
The thermophiles live in extremely hot environments (Figure below). For example, they can grow in hot springs, geysers, and near volcanoes. Unlike other organisms, they can thrive in temperatures near 100ºC, the boiling point of water!
Figure 8.12
Thermophiles can thrive in hot springs and geysers, such as this one, the Excelsior Geyser in the Midway Geyser Basin of Yellowstone National Park, Wyoming.
Methanogens can also live in some strange places, such as swamps, and inside the guts of cows and termites. They help these animals break down cellulose, a tough carbohydrate made by plants (Figure below). This would be an example of a mutualistic relationship. Methanogens are named for their waste product, methane, which they make as they use hydrogen gas to reduce carbon dioxide and gain energy. Methane is a greenhouse gas and therefore contributes to global warming (see the Environmental Problems chapter). Therefore, the rate of methane released in swamps is of interest to scientists studying climate change.
Figure 8.13
Cows are able to digest grass with the help of the methanogens in their gut.
Although archaea are known for living in unusual environments, like the Dead Sea, inside hot springs, and in the guts of cows, they also live in more common environments. For example, new research shows that archaea are abundant in the soil and among the plankton in the ocean. Therefore, scientists are just beginning to discover some of the important roles that archaea have in the environment.
Lesson Summary
Archaea are prokaryotes that differ from bacteria somewhat in their DNA and biochemistry.
Most archaea are chemotrophs but some are photosynthetic or form mutualistic relationships.
Archaea reproduce asexually through binary fission, fragmentation, or budding.
Archaea are known for living in extreme environments.
Review Questions
What domains include the prokaryotes?
How are the cell walls of archaea different from those of bacteria?
How do archaea obtain energy?
How do archaea reproduce?
Where do halophiles live?
Where do thermophiles live?
How did methanogens get their name?
Name an example of a mutualistic relationship with archaea.
Further Reading / Supplemental Links
[http://www.ucmp.berkeley.edu/archaea/archaea.html http://www.ucmp.berkeley.edu/archaea/archaea.
http://www.ncbi.nlm.nih.gov/pubmed/2112744?dopt=Abstract
http://www.popsci.com/environment/article/2008-07/they-came-underseas
http://www.sciencedaily.com/releases/2006/06/060605191500.htm
http://en.wikipedia.org/wiki/Archaea
Vocabulary
archaea
Single-celled, prokaryotic organisms that are distinct from bacteria.
halophiles
Organisms that live and thrive in very salty environments.
methanogens
Organisms that live in swamps or in the guts of cows and termites and release methane gas.
thermophiles
Organisms that live in very hot environments, such as near volcanoes and in geysers.
Points to Consider
In the next chapter we will move on to the protists and fungi. How do you think they are different from archaea and bacteria?
Can you think of some ways that fungi can be helpful?
Can you think of some ways that fungi can be harmful?
Chapter 9: Protists and Fungi
Lesson 9.1: Protists
Lesson Objectives
Explain why protists cannot be classified as plants, animals, or fungi.
List the similarities that exist between most protists.
Identify the three subdivisions of the organisms in the kingdom Protista.
Check Your Understanding
What are some basic differences between a eukaryotic cell and a prokaryotic cell?
List some characteristics that all cells have.
Introduction
So what’s a protist? Is it an animal or plant? Protists are organisms that belong to the kingdom Protista. These organisms, all eukaryotes and mostly unicellular, do not fit neatly into any of the other kingdoms. You can think about protists as all eukaryotic organisms that are neither animals, nor plants, nor fungi. Even among themselves, they have very little in common -- very simple structural organization and a lack of specialized structures are all that unify them as a group. Although the term protista was coined by Ernst Haeckel in 1866, the kingdom Protista was not an accepted classification in the scientific world until the 1960s.
What are Protists?
These unique and varied organisms demonstrate such unbelievable differences that they are sometimes called the “junk drawer kingdom”. This kingdom contains the eukaryotes that cannot be classified into any other kingdom. Most protists, such as the ones shown in (Figure below), are so tiny that they can be seen only with a microscope. Protists are mostly unicellular eukaryotes that exist as independent cells.However, a few protists are multicellular and surprisingly large.The protists that do form colonies (are multicellular) do not, however, show cellular specialization or differentiation into tissues. Cellular specialization is a major feature of multicellular organisms absent in these protists. For example, kelp is a multicellular protist and is over 100-meters long.
A few characteristics unify the protists:
they are eukaryotic which means they have a nucleus
most have mitochondria
many are parasites
they all prefer aquatic or at least moist environments.
For classification, the protists are divided into three groups: animal-like protists, plant-like protists, and fungi-like protists. But remember they are not animals or plants or fungi, they are protists ( (Figure below)). As there are many diffe
rent types of protists, the classification of protists can be difficult. Recently, molecular analysis has been used to confirm evolutionary relationships among protists. These molecular studies compare DNA sequences. Protists with higher amounts of common DNA sequences are evolutionarily closer related to each other. Protists are widely used in industry and in medicine.
Figure 9.1
Protists come in many different shapes.
Figure 9.2
This slime mold is a protist. Slime molds had previously been classified as fungi but are now placed in the kingdom Protista. Slime molds live on decaying plant life and in the soil.
Protists Obtain Food
Protists need to perform the necessary cellular functions to stay alive. These include the need to grow and reproduce, the need to maintain homeostasis, and the need for energy. So they need to obtain food to provide the energy to enable these functions.