Unit 1:The Cell Development of the Cell Theory
Spontaneous Generation • From the time of the ancient Romans, through the Middle Ages, and until the late nineteenth century, it was generally accepted that some life forms arose spontaneously from non-living matter. • Such "spontaneous generation" appeared to occur primarily in decaying matter. • Why?
Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times. Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs.
The first serious attack on the idea of spontaneous generation was made in 1668 by Francesco Redi. • At that time, it was widely held that maggots arose spontaneously in rotting meat. • Redi believed that maggots developed from eggs laid by flies. • To test his hypothesis, he set out meat in a variety of flasks, some open to the air, some sealed completely, and others covered with gauze.
As he had expected, maggots appeared only in the open flasks in which the flies could reach the meat and lay their eggs.
Redi was one of the first scientists known to design a controlled experiment. • A hypothesis should be tested by an experiment in which only one variable is changed at a time. • All other variables should be kept unchanged, or controlled.
Read and Respond • Read pages 8-12 • Copy and define any bolded terms • What are the five steps in designing an experiment?
Warm-Up! • Describe Francisco Redi’s experiment on spontaneous generation. • What was his conclusion? • Why is his experiment considered a controlled experiment?
Three experiments: • Needham, • Spallanzani • Pasteur • Spontaneous generation is also referred as abiogenesis, meaning life arises from non-living matter.
Needham’s Experiment • Boiled loosely sealed flasks containing meat broth for a few minutes to kill the microbes. • Solutions appeared clear after boiling. • After a few days, the broth appeared cloudy, and was examined under the microscope. • Needham concluded that the microbes had come from nonliving things.
Spallanzani’s Experiment • About 25 years later, Spallanzani repeated Needham's experiment, but boiled the flasks longer, and sealed them completely. • Conclusion: No microorganisms were found; abiogenesis did not occur. • Objections: Once again, air (the "active ingredient") was missing.
Pasteur’s Experiment • 1864: Pasteur used a special swan-necked flask. • Broth was placed inside, and boiled for a long time to destroy the microbes. • Air was able to pass into the flask, but the microbes were trapped in the curve of the flask's neck. • Broth remained clear; microscopic examination confirmed his prediction.
Questions • How did the work of John Needham cause a resurgence of the theory of abiogenesis? • How did Spallanzani improve upon Needham's experiment? • Why were Needham's supporters cautious about accepting Spallanzani's results? • Explain how Pasteur refuted the theory of spontaneous generation.
Experiment #1 Stewie believes that a new vitamin pill he has developed will be able to make him super strong. He decides to test it on mice first. He feeds the pills to a group of 20 mice for 10 days, and gives another 20 mice a sugar pill for 10 days. As a test, he has the mice try to push a heavy block of wood. He found that 17 of the vitamin pill group could move the block, and 18 of the sugar pill group could do the same. Identify the: a) Control Group b) Manipulated (Independent) Variable c) Responding (Dependent) Variable d) Based on this initial evidence, what might Stewie conclude? e) How could this experiment be improved?
Experiment #2 Brian has designed a new flea powder that he wants to test on some other dogs. He uses three groups of 25 dogs each. Group A : new flea powder Group B: store brand flea powder Group C: no flea powder After one week, he checks each dog for fleas. Results: Group A : 4 dogs have fleas Group B : 12 dogs have fleas Group C: 15 dogs have fleas Identify the: a) Control Group b) Manipulated (Independent) Variable c) Responding (Dependent) Variable d) Based on this initial evidence, what might Brian conclude? e) How could this experiment be improved?
Experiment #3 Homer notices that his shower is covered in a green slime. His friends tell him that coconut juice will get rid of the slime, so Homer decides to spray half his shower with coconut juice. He sprays the other half with water. Results: After 3 days of treatment, there is no change in the appearance of the green slime on either side of the shower. Identify the: a) Control Group b) Manipulated Variable c) Responding Variable d) What should Homer's conclusion be?
Quiz Monday • The History of the Death of Spontaneous Generation • Scientific Method
The Discovery of the Cell • Mid-1600's: Scientists began to use early microscopes. • Robert Hooke (1665) examined slices of cork, which seemed to be made of thousands of tiny, empty chambers. • Hooke coined the term "cell" because what he observed reminded him of the small rooms in a monastery.
The Discovery of the Cell • Anton van Leeuwenhoek used a microscope to observe pond water and discovered a world of tiny, living things. • Schleiden: all plants are made of cells • Schwann: all animals are made of cells • Virchow: new cells are produced only by division of other cells
Modern Cell Theory • All living things are composed of cells. • Cells are the basic units of structure and function in living things. • New cells are produced from existing cells.
Prokaryotes and Eukaryotes • Cells fit into two broad categories depending on whether they contain a nucleus. • The nucleus is a the large, membrane enclosed structure that contains the cell's genetic material (DNA). • Eukaryotes: contain nuclei • Prokaryotes: do not contain nuclei • Prokaryotic cells are generally smaller and simpler than eukaryotic cells.
Prokaryotes and Eukaryotes • Prokaryotic cells have genetic material that is not contained in a nucleus. • Eukaryotic cells contain a nucleus in which their genetic material is separated from the rest of the cell.
Read and Respond • Read pages 169-173 • Answer questions #1,2,5 on page 173
Warm-Up • What is the difference between a eurkarotic cell and a prokaryotic cell? • What are the three parts of the cell theory? • Who was the scientist that coined the term “cell”
Complete the “Microscope Parts” worksheet with the textbook (Pg 1070)
Microscope: Safety and Usage • Carry the microscope with both hands - one on the base, and one on the arm. • Do not unravel the cord more than necessary, and be careful that the cord does not obstruct your work area. • Only use lens paper to clean the lens, and do not touch the lens with your fingers. • Clean slides and cover slips with paper towel and water. • To view an object, start at the lowest power and use the coarse focus to bring the object into view. Use the fine focus to adjust the image until it is clear.
Microscope: Safety and Usage • To show someone else an object, have that person move to your microscope. Do not push the microscope across the table. • Be sure all cover slips and slides are clean, dry and put away before you leave. • Wrap the power cord around the base and return the microscope to the storage cabinet.
Warm-Up! 2 1 4 3 5
Scientific Diagram Guidelines • Use unlined paper and a sharp pencil and a good quality eraser • Give yourself plenty of space. Your diagram should be at least 1/3 to 1/2 page in size. • Draw only what you see and keep your drawing simple. • Shading or colouring is not usually found on scientific drawings. If you want to indicate a darker area, you can use stippling (a series of dots). • Label the different structures carefully (straight line from the diagram) • Give your drawing a title. Use the proper scientific name, if you know it.
Electron Microscope Advantage: Can magnify up to 300 000 times! Disadvantage: Cannot be used on living things. Transmission Electron Microscope (TEM) Passes electrons through an object. Scanning Electron Microscope (SEM) Reflects electrons from the surface of the object and produces a 3D image.
Electron Microscope • Cannot be used on living matter as the matter being viewed has to be in a sealed vacuum.
Examples of SEM Intestinal Lining
Examples of SEM Cat Tongue
Examples of SEM Dog Tape Worm
Review! • Complete “Review for Test #1” • GrudgeBall
Question #2: Scientists • Which scientist supported abiogenesis? • Which scientist coined the term “the cell” • Which scientist stated all cell must come from pre-existing cells