![chapter 18 ap bio study guide answers chapter 18 ap bio study guide answers](https://s3.studylib.net/store/data/008035671_1-34b8a8a4b7c63fe54ff341435d5847de-768x994.png)
Beijerinck also determined that the pathogen could reproduce only within the host, could not be cultivated on nutrient media, and was not inactivated alcohol, generally lethal to bacteria. The sap from one generation of infected plants could be used to infect a second generation of plants that could infect subsequent generations. In 1897, Martinus Beijerinck ruled out the possibility that the disease was due to a filterable toxin produced a bacterium demonstrating that the infectious agent could reproduce. Ten years later, Dimitri Ivanovsky demonstrated that the sap was still infectious even after passing through a filter designed to remove bacteria. He concluded that the disease must be caused an extremely small bacterium. Lecture Outline for Biology, 7th Edition, Pearson Education, Inc. Mayer concluded that the disease was infectious when he found that he could transmit the disease rubbing sap from diseased leaves onto healthy plants. This disease stunts tobacco plant growth and mottles plant leaves. The story of how viruses were discovered begins in 1883 with research on the cause of tobacco mosaic disease Adolf Mayer. Concept 18 A virus has a genome but can reproduce only within a host cell Researchers discovered viruses studying a plant disease. Most viruses are little more than aggregates of nucleic acids and in a protein coat. Viruses are smaller and simpler still, lacking the structure and metabolic machinery of cells. Bacteria are prokaryotic organisms, with cells that are much smaller and more simply organized than those of eukaryotes, such as plants and animals. In addition, viruses and bacteria have unique genetic features with implications for understanding the diseases that they cause. Techniques enabling scientists to manipulate genes and transfer them from one organism to another were developed in microbes. Microbiologists provided most of the evidence that genes are made of DNA, and they worked out most of the major steps in DNA replication, transcription, and translation.
![chapter 18 ap bio study guide answers chapter 18 ap bio study guide answers](https://www.albert.io/blog/wp-content/uploads/2020/04/IMAGE-FRQ-2a.png)
coli and its viruses are called model systems because of their use in studies that reveal broad biological principles. Molecular biology was born in the laboratories of microbiologists studying viruses and bacteria. Preview text Chapter 18 The Genetics of Viruses and Bacteria Lecture Outline Overview: Microbial Model Systems Viruses and bacteria are the simplest biological microbial models in which scientists find fundamental molecular mechanisms in their most basic, accessible forms.