All About . . . . BACTERIA
Read the information on the following slides, then use it to create an outline on pages 7 and 8 in your student packet of facts … All About Bacteria.
What Is Food Poisoning? • Food poisoning comes from eating foods that contain harmful bacteria or their toxins, which are poisonous substances. Bacteria are all around us, so mild cases of food poisoning are common. You may have had mild food poisoning — with diarrhea and an upset stomach — but your mom or dad just called it a stomach bug or stomach virus. • You might think the solution is to get rid of all the bacteria. But it isn't possible and you wouldn't want to do it, even if you could. Bacteria are all around us, including in food, and sometimes they can be good for you. It's confusing, but one thing is for sure — the bacteria in the leftovers weren't good for you, but you can learn how to prevent those bacteria from living in and spoiling your food and making you sick.
Classification • All bacteria are called Prokaryotes(pro-carry-oats), which means that the single cells do not have a nucleus. Instead, the one strand of genetic material, called DNA, floats freely in the cytoplasm. Bacteria are the only prokaryotes. • All other cells, like those in fungus, plants, animals, and in your body, are Eukaryotes (you-carry-oats), which means they do have a nucleus that holds the DNA.
There are two bacteria kingdoms, Archaebacteria and Eubacteria. The two kingdoms are genetically different from each other, and those differences have only recently been discovered. • Archaebacteria is the smaller group, and they thrive in extreme environments, where no other things have been found, such as in the hot springs at Yellowstone National Park, or under 430 meters of ice in Antarctica. One type produces methane in swamps, a second type thrives on the heat of ocean floor vents where temperatures reach 360 degrees C, and a third group lives in highly salty places, such as the dead sea. Archaebacteria are interesting, but they are not the organisms that compete with us for food.
Most bacteria are in the second bacteria kingdom, called eubacteria. Some of the eubacteria compete with humans for food, so we will focus on them. The eubacteria kingdom is larger, with more individual organisms, than any of the other five kingdoms. Eubacteria have existed for 3.5 billion years • Some eubacteria are producers, which means they use chlorophyll to make their own food from the sun’s energy, like plants do. Most, however, are consumers, which means they get their nutrients from other organisms. Some consumers are decomposers, which means they consume dead organic matter, and others are parasitic, which means they invade the body of another organism to consume food. These are the organisms that make us sick.
Early Origins • Bacteria are among the earliest forms of life that appeared on Earth over 3.5 billions of years ago, and they were the only form of life for 2 billion years. • Scientists think that they helped shape and change Earth’s environment, eventually, by creating oxygen in the atmosphere that enabled other, more complex life forms to develop. • More complex cells may have developed when once free-living bacteria took up residence inside other cells, eventually becoming the organelles in modern complex cells.The mitochondria (mite-oh-con-dree-uh) that make energy for your body cells is one example of such an organelle that may have developed that way.
What They Look Like There are thousands of species of bacteria, but all of them are basically one of three different shapes. Each shape has a specific name and specific advantages. Some bacterial cells exist as individuals while others cluster together to form pairs, chains, squares or other groupings. cocci spirilli bacilli
Bacilli • Some are rod- or stick-shaped and called bacilli (buh-sill-eye). • Rod shaped bacteria have a large surface area, which helps them absorb nutrients through the cell membrane. • A large suface area, however, also means bacilli can dry out easily.
Cocci • Others are shaped like little balls and called cocci (cox-eye). • Round shaped bacteria are much more resistant to drying out than rod shaped bacilli cells are.
Spirilli • Others still are helical or spiral in shape, called spirilli (spuh-ril-eye). • Spirilli are the least common shape • Spirilla cells move easily in a corkscrew motion using a “whip”, called flagella, at each end.
Where They're Found Bacteria live on or in just about every material and environment on Earth from soil to water to air, and from your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about 100,000 bacteria. A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria.
How They Move Bacterium with flagella Some bacteria move about their environment by means of long, whip-like structures called flagella. They rotate their flagella like tiny outboard motors to propel themselves through liquid environments. They may also reverse the direction in which their flagella rotate so that they tumble about in one place. Other bacteria secrete a slime layer and ooze over surfaces like slugs. Others are fairly stationary, which means they stay in one place. .
What They Eat Some bacteria are producers, called photosynthetic (foe-toe sin-theh-tick). They can make their own food from sunlight, just like plants. Also like plants, they give off oxygen. They do not compete with us for food. Other bacteria are consumers. They absorb food from the material they live on or in. Some of these bacteria can live off unusual "foods" such as iron or sulfur. The microbes that live in your intestine absorb nutrients from the digested food you've eaten. We will pay particular attention to the bacteria that compete with humans by living in and on the food we intend to eat.
How They Reproduce • Binary fission is the form of asexual reproduction used by most prokaryotes (bacteria) to reproduce. The result is the reproduction of a living cell by division into two equal or near-equal parts. • It begins when the DNA replication occurs. Each DNA strand then attaches to the cell membrane. The cell elongates, causing the two strands to separate. The cell membrane then grows inwards and splits the cell into two daughter cells through a process called cytokinesis. • Organisms that reproduce by binary fission grow exponentially. • This type of asexual reproduction normally results in two identical cells. However, bacterial DNA has a relatively high mutation rate. This rapid rate of genetic change is what makes bacteria capable of developing resistance to antibiotics and helps them exploit invasion into a wide range of environments.