Chapter 19: History of Life Chapter 20: Viruses and Prokaryotes

1. Chapter 19: History of LifeChapter 20: Viruses and Prokaryotes Wilmaris Padilla Reyes #16 Yamaris Rodríguez Adames #20

2. Lesson 19.1: The Fossil Record

3. The remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock. What is a fossil? What is record? Document that memorializes and provides objective evidence of activities performed, events occurred, results achieved, or statements made.

4. What is fossil record? Refers to the placement of fossils throughout the surface layers of the Earth. Older fossils are buried more deeply than younger ones. Scientists use the placement of fossils as a guide for determining when life forms existed, and how they evolved.

5. Did you know? • Most fossils are preserved in sedimentary rock. • Sediments accumulate over time, and buries the remains and traces of dead organisms. • Scientists who study fossils are called paleontologists. • Relative dating and radiometric dating are used to determine the age of fossils. • Relative dating establishes the relative age of the fossils. • Fossils of the deeper layers of rock are supposed to be older than the fossils in the rock layers closer to the surface. • Index fossils represent species that lived for a short period of time, but within a wide geographical range. • Fossil guide can help determine the relative age of rock layers and fossils.

6. Geologic Time Scale • The geologic time scale is a time line of Earth’s history based on relative and absolute dating. • The scale begins with the Precambrian. • Geologic time is divided into four eons: • the Hadean • Archean • Proterozoic • Phanerozoic • The Phanerozoic eon is divided into three eras: • the Paleozoic • Mesozoic • Cenozoic • Each era is further divided into smaller lengths of time, called periods.

7. Life on a Changing Planet • Climactic, geological, astronomical, and biological processes have affected the history of life on Earth. • Earth’s climate has changed often in the course of its history. Small temperature shifts can bring about heat waves and ice ages which have great effects on living things. Plate tectonics is a theory that Earth’s outermost layer is divided into plates that move. • The movement, called continental drift, has transformed life on Earth through the formation of mountain ranges, supercontinents, and other geologic features. • The impact of objects from space has affected the global climate

8. Video

9. Lesson 19.2: Patterns and Processes of evolution

10. Patterns and Processes of Evolution Speciation and Extinction • Macro evolutionary patterns are grand transformations in anatomy, phylogeny, ecology, and behavior that usually take place in clades larger than a single species. • If the rate of speciation in a clade is equal to or greater than the rate of extinction, the clade will continue to exist. • If the rate of extinction in a clade is greater than the rate of speciation, the entire clade will eventually become extinct. • Background extinction is extinction caused by the slow process of natural selection. • Mass extinctions affect huge numbers of species over a relatively short time. Rate of Evolution • Evidence shows that evolution has occurred at different rates for different organisms at different times. • The idea that evolution occurs slowly and gradually is called gradualism. • In punctuated equilibrium, long periods of little or no change are interrupted by short periods of rapid change.

11. Adaptive Radiation and Convergent Evolution • Adaptive radiation is the process in which a single species evolves into diverse species that live in different ways. • Convergent evolution is the process in which unrelated species come to look alike because they have evolved similar adaptations in response to similar environments. Adaptive radiation Convergent evolution

12. Coevolution • Coevolution is the process by which two species evolve in response to changes in each other over time. • Example: plants evolved poisons that protected them from insects. In response, insects evolved ways of protecting themselves from the poisons.

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14. Lesson 19.3: Earth's Early History

15. The Mysteries of Life’s Origins • Earth’s early atmosphere contained toxic gases. The atmosphere also contained little or no oxygen. • In the 1950s, Stanley Miller and Harold Urey set out to determine if organic molecules could assemble under earthy Earth conditions. They filled a container with water and gases that they thought represented the composition of Earth’s early atmosphere. They passed electric sparks through the mixture to simulate lightning. Soon, organic compounds formed. The experiment showed that molecules needed for life could have arisen from simpler compounds.

16. Under some conditions, large organic molecules form tiny bubbles called proteinoid microspheres. Structures similar to proteinoid microspheres might have become the first living cells. RNA and DNA also could have evolved from simple organic molecules. • The first known life forms evolved about 3.5 billion years ago. They were single celled and looked like modern bacteria. Eventually, photosynthetic bacteria became common. During photosynthesis, the bacteria produced oxygen. The oxygen accumulated in the atmosphere. The rise of oxygen drove some life forms to extinction. At the same time, other life forms evolved that depended on oxygen. Miller-Urey Experiment

17. Origin of Eukaryotic Cells • The first eukaryotes evolved from prokaryotes that began to develop internal cell membranes. One explanation for how eukaryotes evolved is the endosymbiotic theory. This theory proposes that smaller prokaryotes began living inside larger cells and evolved a symbiotic relationship with the larger cells.

18. Sexual Reproduction and Multicellularity • Sexual reproduction evolved after eukaryotic cells. Sexual reproduction increased genetic variation, so evolution could occur more quickly. Several hundred million years after sexual reproduction evolved, multicellular life evolved.

19. Lesson 20.1 Viruses

20. The Discovery of Viruses • In 1935, the American biochemist Wendell Stanley isolated a virus for the first time. • A virus is a particle made of nucleic acid, protein, and, in some cases, lipids. • A typical virus is composed of a core of DNA or RNA surrounded by a protein coat called a capsid. • Viruses that infect bacteria are called bacteriophages. They enter living cells and, once inside, use the machinery of the infected cell to produce more viruses.

21. Viruses come in different sizes and shapes. There are three types of viruses shown in this picture.

22. Viral Infections Viruses have two methods of infection once inside a host cell: Lytic infection Lysogenic infection a virus integrates part of its DNA called a prophage into the DNA of the host cell. The viral genetic information replicates along with the host cell’s DNA. Eventually, the prophage will remove itself from the host cell DNA and make new virus particles. • a virus enters a cell, makes copies of itself, and causes the cell to burst, releasing new virus particles that can attack other cells. In the case of bacteriophage T4, viral DNA directs the synthesis of new viruses using materials in the cell.

23. In a retrovirus, the genetic information is copied backward—from RNA to DNA instead of from DNA to RNA. The virus that causes the disease AIDS is a retrovirus. Viruses must infect a living cell in order to reproduce. Although viruses are parasites, they are not made of cells and are not considered living things. Video

24. Lesson 20.2 Prokaryotes

25. Classifying Prokaryotes • The smallest and most common microorganisms are prokaryotes, which are unicellular organisms that lack a nucleus. Prokaryotes are classified either in domain Bacteria or domain Archaea. • They can be surrounded by a cell wall, which contains peptidoglycan. Inside the cell wall is a cell membrane surrounding the cytoplasm. • Archaea look similar to bacteria, but are genetically closer to eukaryotes. Archaea lack peptidoglycan and have different membrane lipids than bacteria. • Archaea- any of a group of microorganisms that resemble bacteria but are different from them in certain aspects of their chemical structure, such as the composition of their cell walls, they usually live in extreme, often very hot or salty environments

26. Structure and Function • Prokaryotes are identified by characteristics such as shape, the chemical nature of their cell walls, the way they move, and the way they obtain energy. • Bacilli are rod-shaped. Cocci are spherical. Spirilla are spiral or corkscrew-shaped. • Most prokaryotes are heterotrophs. Others are autotrophs. Autotrophs may be photoautotroph, or chemoautotrophs. • Prokaryotes that require a constant supply of oxygen to live are called obligate aerobes. Those that cannot survive in oxygen are called obligate anaerobes. Organisms that can survive without oxygen when necessary are called facultative anaerobes.

28. Prokaryotes reproduce asexually by binary fission (an organism replicates its DNA and divides it), which results in two identical “daughter” cells. • Many prokaryotes can form endospores ( thick internal wall that encloses the DNA and a portion of the cytoplasm) when conditions are unfavorable in order to protect their DNA. • They can also exchange genetic information by conjugation.

29. The Importance of Prokaryotes • Prokaryotes are vital to maintaining the ecological balance of the living world. • Some are decomposers that break down dead matter. • Others are producers that carry out photosynthesis. • Some soil bacteria convert natural nitrogen gas into a form plants can use through a process called nitrogen fixation. • Humans use bacteria in industry, food production, and other ways.

30. Lesson 20.3 Diseases Caused by Bacteria and Viruses

31. Bacterial Diseases • Microorganisms that cause diseases are known as pathogens. Bacterial pathogens can produce many diseases that affect humans and other animals. They do so in one of two general ways: ▶ They destroy living cells and tissues directly or by causing an immune response that destroys tissue. ▶ They damage the cells and tissues of the infected organism directly by breaking down the cells for food. ▶ They release toxins (poisons) that travel throughout the body, interfering with the normal activity of the host.

32. Many bacterial pathogens can be controlled by washing, using disinfectants, preparing and storing food safely, or sterilizing exposed items. Bacterial diseases can be prevented and treated through the following methods: ▶A vaccine is a preparation of weakened or killed pathogens or inactivated toxins. A vaccine can prompt the body to produce immunity to the disease. Immunity is the body’s natural way of killing pathogens. ▶When a bacterial infection does occur, antibiotics can be used to fight the disease. Antibiotics are compounds that block the growth and reproduction of bacteria.

33. Viral Diseases • Viruses produce disease by directly destroying living cells or by affecting cellular processes in ways that disrupt homeostasis. In many viral infections, viruses attack and destroy certain body cells, causing the symptoms of the disease. • Viral diseases in humans include the common cold, influenza, AIDS, chicken pox, and measles. • Viruses produce other serious diseases in other animals and in plants. • Protection against viruses, either by hygiene or vaccination, is the best way to avoid viral illness. A handful of antiviral drugs have been developed that help reduce the symptoms of specific viruses

34. Emerging Diseases • An unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control is called an emerging disease. • The increase of worldwide travel and food shipments is one reason new diseases are spreading. Another is virus and bacteria evolution. • Scientists are struggling to keep up with changes. • They recently discovered prions, which are disease-causing forms of proteins. Prions cause disease in animals, including humans.