Discussion:
1. You are a writer for "Consumer Reports" magazine and you are asked to design an experiment to evaluate the effectiveness of three brands of whitening strips for teeth. Describe how you would do this using the scientific method. Include all of the steps, control group, experimental groups, and variables.
2. Your biology class is performing an osmosis experiment. You are given three identical stalks of celery and three salt solutions of varying solute amounts. The data table below compares the solute amount of the celery stalks to the solutions.
Solute Amount of the Solution Water Amount of the Solution
Solution A less than the celery stalk more water than the celery stalk
Solution B same as the celery stalk same water as the celery stalk
Solution C more than the celery stalk less water than the celery stalk
a). Identify which solution is isotonic, hypertonic, or hypotonic to the celery stalk cells
b). Describe what happens when the celery stalk is placed into each of the respective solution.
3. Dihybrid cross. The kernels (seeds) on an ear of corn are all offspring of one set of parents. There are 2 pairs of alleles on separate homologous chromosomes (purple or yellow kernels on one pair, plump or shrunken kernels on another). Yellow (Y) is dominant to purple (y) and plump (P) is dominant to shrunken (p). If the genotype of parent plants are YyPp and yyPP, what are the expected probabilities of the genotypes and phenotypes of the offspring kernels? Explain your reasoning.
4. A population of grasshoppers in the Kansas prairie has two color phenotypes, with 90% of the grasshoppers green and 10% brown. Typically in the last century, the prairie receives adequate rain to maintain healthy green grass, but for the last decade the prairie suffers a severe drought and is also invaded by a bird that eats grasshoppers.
5. Briefly explain in terms of the four parts of natural selection listed below how the population of grasshoppers would be expected to change during the drought years.
overproduction -
variation -
competition & survival -
differential reproduction -
6. Describe an environmental problem that you feel is the most urgent worldwide. Which areas of the world are suffering the most from the problem? Propose a solution to the problem.
7. Describe three structures found in plant cells but not animal cells. Describe the function of each structure, and how each benefits plant cells but is not necessary for animal cells.
8. Apply your knowledge of the scientific method to design an experiment. We will use a real situation from my research project in Olympic National Park. There is no single correct answer to this exercise. Your proposed experimental design may well be better than the ones that I actually used. It is more difficult to design an experiment in the field than in a lab, because there are so many variables in nature.
9. Observation. When Olympic National Park was established over 60 years ago, it included scattered homesteads with small fields that were farmed for hay. The farms were abandoned, but many of the fields still remain today. Trees from the surrounding rain forest have been unable to invade the fields, in spite of fertile soils and abundant precipitation. This is unusual because abandoned fields that are surrounded by forest in most parts of the world are readily colonized by trees and become forest in a few decades. [The purpose of the experiment was both theoretical, to examine why these fields differed from the standard model of old-field succession in ecology, and practical, to provide knowledge to the Park Service who do not like non-native plants in our National Parks.]
10. The fields in Olympic National Park are mostly covered by non-native grasses that form a thick sod. Large amounts of wind-blown seeds of the surrounding Sitka spruce trees fall onto the fields each year, but the seeds are very small.
11. General Hypothesis. Sitka spruce trees fail to colonize the fields because competition from the thick grasses prevents the establishment of spruce seedlings.
Your assignment:
Using your knowledge of the scientific method, design an experiment to test this general hypothesis. Your experiment must include and identify a control group and an experimental group. You may modify the general hypothesis into a specific hypothesis, which is more limited and directly fits your experiment, if you wish. Explain how the data that you collect from your experiment will allow you to make a conclusion about your hypothesis (in your explanation, DO NOT make up imaginary results).
When considering your methods, you may assume that you have access to spruce seeds and any tools or materials that you might need to manipulate the environment for your experiment.
12. Using information from Ch. 18 of your textbook, choose three terrestrial biomes in North America that are adjacent to each other. Briefly describe how the difference in vegetation between the three biomes relates to a difference in climate.