| Scientific Method All Materials © CmassengaleHow can we determine if something is a fact or an opinion? How can we determine an answer to a problem? The answer is use the scientific method.What is the Scientific Method? It is a series of steps used to help solve a problem.
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Doolittle, W. Ford. Uprooting the Tree of Life. Scientific American, February 2000, pp.90-95.
About 10 years ago, scientists finally worked out the basic outline of how modern life forms evolved. Now, parts of their tidy scheme are unraveling. Charles Darwin contended more than a century ago that all modern species diverged from a more limited set of ancestral groups, which themselves evolved from still fewer progenitors and so on back to the beginning of life. In principle, the relationships among all living and extinct organisms could be represented as a single genealogical tree. Discoveries made in the past few years have begun to cast serious doubt on some aspects of the tree, especially on the depiction of the relationships near the root.
Scientists could not even begin to contemplate constructing a universal tree until about 35 years ago. From the time of Aristotle to the 1960’s, research deduced the relatedness of organisms by comparing their anatomy or physiology or both. For complex organisms, scientists were frequently able to draw reasonable genealogical inferences in this manner. Microscopic single-celled organisms, however, often provided too little information for defining relationships. In the mid-1960’s, Emile Zuckerland and Linus Pauling of the California Institute of Technology came up with a different strategy other than just comparing anatomy and physiology. They proposed basing family trees on differences in the building block sequences for genes and proteins. Their approach is known as molecular phylogeny, and it states that individual genes are composed of unique sequences of nucleotides that typically serve as the blueprint for making specific proteins. These proteins are in turn composed of particular strings of amino acids. Consensus holds, that in the universal tree of life, the early descendant’s last common universal ancestor was a small cell without a nucleus. This ancestor was a prokaryote.
At this same time, Carl R. Woeses of the University of Illinois was turning his attention to a powerful new yardstick for evolutionary distances — a small molecular subunit known as ribosomal RNA. Higher sections of the universal tree of life have based many of their branching patterns on sequence analysis of rRNA genes. By the 1960’s, microscopists had determined that the world of living things could be divided into two separate groups —eukaryotes and prokaryotes, depending on the structure of the cells that composed them. The endosymbiont hypothesis proposes that mitochondria formed after a prokaryote that had evolved into an early eukaryote engulfed and then kept one or more alpha-proteobacteria cell. Eventually the bacterium gave up its ability to live on its own and transferred some of its genes to the nucleus of the host becoming a mitochondrion. Later, some mitochondrion bearing eukaryote ingested a cyanobacterium that became a chloroplast. Eventually most scientists accepted this hypothesis because the overall structures of certain molecules in archaeal species of bacteria. Similarly, the archaeal proteins responsible for several crucial cellular processes have a distinct structure from the proteins that do the same tasks in more modern bacteria.
Once scientists accepted the idea of 3 domains of life instead of two, they naturally wanted to know which of the 2 structurally primitive groups — true bacteria or archaic— gave rise to the first eukaryotic cell. In 1989, research groups led by J. Peter Gogarten of the University of Connecticut and Takashi Miyata of the Kyushu University in Japan used sequence information from genes for other cellular components to establish the “root” for the universal tree of life. Comparisons of rRNA can indicate which organisms are closely related, but for technical reasons, cannot be themselves indicate which groups are the oldest and therefore closest to the root of the tree. DNA sequences encoding 2 essential cellular proteins agreed that the last common ancestor spawned both the true bacteria and archaic bacteria and then the eukaryotes (with a nucleus) branched from the archaic.
Still, as the DNA sequences of complete genomes have become increasingly available, research groups have noticed patterns that are disturbingly at odds with the prevailing beliefs. If the consensus tree were correct, transferred genes would be ones involved in cellular respiration or photosynthesis and not in other cellular processes. A good number of those bacterial genes though serve nonrespiratory and nonphotosynthetic processes critical to the cell’s survival. This classic tree also indicates that bacterial genes migrated only to a eukaryote, not to any archaic. However, archaic have been found to contain a substantial store of bacterial genes. Quite possibly, the pattern of evolution is not as linear and treelike as Darwin imagined it. Although genes are passed vertically from generation to generation, this vertical inheritance is not the only process that has affected the evolution of the cells. Lateral or horizontal gene transfer of genes has also profoundly affected evolution. Such lateral transfer involves the delivery of genes, not from a parent cell to its offspring, but across species barriers. Lateral gene transfer would explain how eukaryotes that supposedly evolved from an archaeal cell obtained to many bacterial genes important to metabolism. The eukaryotes picked up genes from bacteria and kept those that proved most useful.
The “revised” tree of life retains a treelike structure at the top of the eukaryotic domain and acknowledges that eukaryotes obtained mitochondria and chloroplasts from bacteria. But it also includes an extensive network of untreelike links between branches. These links have been inserted somewhat randomly to symbolize the lateral gene transfers that occur between unicellular organisms. This “tree” also lacks a single cell at the root; the three major domains of life probably arose from a population of primitive cells that differed in their genes.
Scientific Method Solution
Examples of AP Lab Reports  |
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| Lab 1 Osmosis & Diffusion Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 |
Lab 2 Enzyme Catalysis Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 |
| Lab 3 Mitosis & Meiosis Sample 1 Sample 2 Sample 3 Sample 4 |
Lab 4 Plant Pigments & Photosynthesis Sample 1 Sample 2 |
| Lab 5 Cell Respiration Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 |
Lab 6 Molecular Biology Sample 1 Sample 2 – 6B Sample 3 – 6A Sample 4 – 6A |
| Lab 7 Genetics of Organisms Sample 1 Sample 2 Sample 3 |
Lab 8 Population Genetics Sample 1 Sample 2 |
| Lab 9 Transpiration Sample 1 Sample 2 |
Lab 10 Physiology Of Circulatory System Sample 1 |
| Lab 11 Animal Behavior Sample 1 Sample 2 |
Lab 12 Dissolved Oxygen & Aquatic Primary Productivity Sample 1 |
| Lab – Bioremediation of Oil Spills Sample1 Sample 2 Sample 3 |
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| Scientific Method ppt Questions |
Steps in the Scientific Method
1. Name the steps in the scientific method.
2. Explain a scientist’s first step in the scientific method.
3. Give an example of an observation that a scientist might make.
4.Scientists use their __________ to make observations.
5. What is a hypothesis?
6. A hypothesis must be _____________ and it __________ an outcome.
7. Some hypotheses are written as __________ statements.
8. Write a hypothesis for the observation you wrote in question 3.
9. What is an experiment?
10. What part of an experiment is the variable?
11. How many variables should there be in a good experiment?
Controls and Variables
12.An experimenter changes ______ factor and then observes and _______ what happens.
13. Other factors in an experiment must be kept __________ so they won’t effect the ___________.
14. What are these constant factors called?
15. What is the purpose of having a control in an experiment?
16. Name the two types of variables in an experiment.
17. What is the independent variable?
18. What is the independent variable?
19. In the experiment to find the fastest route to school, what serves as:
a. the independent variable?
b. the dependent variable?
c. the control variable?
20. The best experiments make __________ trials with the independent variable.
Valid Experiments
21. Name the two group needed to have a valid experiment.
22. What is data?
23. What are the two types of data?
24. If the data is numbers, this is called ____________ data.
25. To be useful, collected data must be _____________.
26. Name 3 ways of organizing data.
27. What is the conclusion of an experiment?
28. What must be done to verify the results of an experiment?
Review
29.To solve a problem, you should _________ the problem and state _____________ you have made about it.
30. Next, you form a __________ or prediction and conduct an ____________ to test the prediction.
31. During an experiment, _________ must be collected and later ____________..
32. Finally, a scientist forms a ____________ based on your data.
33. To prove the experiment is correct, scientists ___________ their results.
