How do an observation, a hypothesis, and a prediction differ?
- Observation - acquisition of information from a primary source
- Hypothesis - a testable statement to explain a phenomenon or a set of observations
- Prediction - a measurable or observable result that may be correct if a hypothesis is valid
What makes a hypothesis useful for scientific investigations that try to explain the natural world?
- A hypothesis is useful for investigations because you must have an original idea to test to see if that is correct. It also specifies the expected relationship between variables. It helps you identify controls and variables to test.
Give examples of hypotheses that are and are not scientifically useful. State the null hypothesis that corresponds to each of your examples.
- Scientifically Useful Hypothesis: Squirrels only eat nuts.
- Scientifically Useful Null Hypothesis: Squirrels do not only eat nuts.
- Scientifically Unuseful Hypothesis: Dinosaurs like cinnamon toast crunch.
- Scientifically Unuseful Null Hypothesis: Dinosaurs do not like cinnamon toast crunch.
What is the difference between a hypothesis and a scientific Theory?
A scientific theory is an explanation for a very general class of phenomena or observation that are supported by a wide variety of evidence.
A hypothesis is only a testable statement to explain a phenomenon or a set of observations.
Theory is also usually used to explain broad patterns while a hypothesis is used to explain more tightly focused questions. A theory replaces a hypothesis after testing confirms hypothesis. A theory also serves as the framework for the development of new hypothesis.
What are the two components of Cell Theory and of the Theory of Evolution by Natural Selection? What are the two conditions required by the process component of evolutionary theory?
Cell Theory:
- Pattern: All living things are made of cells
- Process: All cells come from preexisting cells - determined by Pasteur’s experiment
Natural Selection:
- Pattern: Species are related to one another and their characteristics change over time
- Process: Natural selection explains how evolution changes over time
Two conditions required by the process component of evolutionary theory: Characteristics have to be heritable, traits allow people to produce offspring and increased fitness
What is the hypothesis of Spontaneous Generation and how does Cell Theory challenge that hypothesis? In the Pasteur experiment two types of flasks were used. For each flask, what is the outcome predicted by Spontaneous Generation? By Cell Theory? Why did Pasteur use a swan-necked flask? Why did he boil the broth in both flasks?
- Spontaneous generation: cells arise spontaneously from nonliving materials and cell theory challenges that hypothesis by proposing that cells are produced only when preexisting cells grow and divide
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Straight neck flask
- Spontaneous generation prediction: Cells will appear in broth
- Cell theory prediction: Cells will appear in broth
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Swan-necked flask
- Spontaneous generation prediction: Cells will appear in broth
- Cell theory prediction: Cells will NOT appear in broth
- Pasteur used a swan-necked flask so it would prevent cells from the air from reaching the broth by trapping them in the swan neck
- He boiled the broth in both flasks to sterilize the broth and kill any living cells present in the flask
What are the similarities and differences between organisms in the three domains of life? What do the nodes and branches of a phylogenetic tree indicate? How can genetic information be used to generate a phylogenetic tree?
- Bacteria, Eukarya, Archaea
- A difference between prokaryotes and eukaryotes is that eukaryotes have a nucleus. The majority of Bacteria and Archaea are unicellular and many eukaryotes are multicellular.
- All contain genetic material, all contain plasma membrane
- The nodes of a phylogenetic tree indicate the species that the organisms are related to through evolution, including their most recent common ancestor.
- The nucleotides of a various species’ DNA may be compared in order to create a phylogenetic tree. Species that are more similar are drawn as sharing a common ancestor; ones that differ are shown to diverge on the tree.
- Species that are part of the same evolutionary lineage have the same changes in RNA
What are the key steps in hypothesis testing? What are the essential elements of a scientific experiment? Design an experiment to test the hypothesis that squirrels prefer nuts over chicken wings.
1. State the hypothesis as precisely as possible and the predictions it makes
2. Design an observational or experimental study that is capable of testing those predictions
Large sample size, include control groups, have constant/equivalent experimental conditions, repeatability
Describe the two hypotheses proposed to account for the observation that giraffes have long necks. What are the predictions of the first, “food competition” hypothesis? What evidence is cited in your textbook that supports one or more of these predictions? What are the observations that gave rise to the alternative, sexual competition hypothesis? What evidence is cited that is consistent with the second hypothesis? Do biologist agree that there is sufficient evidence to reject or confirm either hypothesis? Could both hypotheses be true?
- 1. Food competition - Giraffes compete for food with other species of mammals, can reach higher when there is less food on the ground
- 2. Sexual competition - Fighting with males over female reproduction, able to strike harder blows if neck is longer
- Food competition hypothesis predicts that neck length is variable among giraffes, neck length is heritable among giraffes, and giraffes feed in high trees (esp. during dry season when food is scarce)
- Evidence supporting predictions: neck length is variable and long necked males are more successful with fighting
- Observations that gave rise to the sexual competition hypothesis: based on observations of males fighting each other for reproduction with females
- Evidence cited for the second hypothesis is that males actually do perform better in fights if their necks are longer
- Biologists agree that there is not enough evidence to reject or confirm either hypothesis, however with more research/data they could be proven or unproven