Study Notes for Scientific Investigation and Biological Taxonomy
Scientific Investigation
Objectives
At the end of the lab activity, students should be able to:
Identify questions or problems that can be answered through scientific investigation;
Discuss and explain the characteristics of a good hypothesis and distinguish between null and alternative hypotheses;
Describe the essential components of a scientific experiment;
Present and discuss results of an experiment and critique its merits;
Convey the experimental results in a concise but clear manner for the whole class to understand and appreciate.
Introduction
Scientific inquiry is a critical skill for biology students, developed through self-motivation or guided learning.
The course introduces basic concepts of the scientific method, a structured process used in scientific investigations.
Biology aims to elucidate the workings of the natural world through evidence-based explanations, distinguishing itself from non-scientific beliefs.
Key characteristics of scientific explanations:
Objectivity: Uninfluenced by personal faith or opinions.
Testability: Can be verified through experiments or observations.
Consistency: Results are reproducible.
Steps of the Scientific Method
Observations & Questions
Begin by observing biological phenomena and formulating questions based on these observations. E.g.,
"The life cycle of a snail is about 30 days (at 29 degrees Celsius). How do changes in temperature affect the life cycle of a snail?"
Hypothesis
Formulate a hypothesis—a testable statement to address the question.
Null Hypothesis (H₀): A statement asserting no effect or relationship.
Alternative Hypothesis (Hₐ): A statement asserting an effect or relationship.
Example:
H₀: "Decreasing the temperature of a snail's environment will not increase the time it takes the snail to complete its life cycle."
Hₐ: "Decreasing the temperature of a snail's environment will increase the time it takes the snail to complete its life cycle."
The Experiment
Design and conduct an experiment that tests the hypothesis.
The experiment should allow for clear support or refutation of the hypothesis.
Use “If-Then” predictions based on the hypothesis.
Example:
"Place 33 snails at 18 and 29 degrees Celsius for one generation. If the hypothesis is correct, then the snails at 18 degrees Celsius will complete their life cycle slower than those at 29 degrees Celsius."
Analyze Results and State Conclusions
Accept or reject the null hypothesis based on the results:
If results align with the alternative hypothesis, suggest it may be true; if not, modify the hypothesis.
Example: Snails at lower temperatures did develop slower, possibly due to inadequate diet, suggesting alternative explanations.
Experimental Design
A well-designed experiment incorporates several elements:
Independent Variable: The altered factor in the experiment.
Example: Temperature, shown on the x-axis.
Dependent Variable: The variable measured as an outcome.
Example: Length of the snail's life cycle, shown on the y-axis.
Experimental Group: Subjects receiving the change in the independent variable.
Example: Snails raised at 18 degrees Celsius.
Control Group: Subjects receiving no experimental treatment or a standard treatment.
Example: Snails raised at 29 degrees Celsius, the optimal temperature.
Sample Size: Utilize a large group to reduce errors due to chance; each group contained 33 snails.
Well-defined Procedure: Document all of the materials, conditions, and steps involved clearly for reproducibility.
Standardized Variables: Factors kept constant in the experiment.
Additional Aspects of Experimental Design
Positive Control: An experimental component intended to give a positive result that validates the experimental setup.
Indicates that the experiment correctly works under expected conditions.
Negative Control: Shows that the experimental setup can produce a negative result, confirming the test's validity.
Results: Data should be quantitative, allowing for statistical analysis.
Example protocols include using the same species (Biomphalaria glabrata), identical environmental conditions (e.g., light, dietary provisions, etc.) to maintain consistency throughout experiments.
Scientific Theory
Distinctions:
Commonly misunderstood; "theory" in regular language implies mere guesses. In science, a scientific theory is a well-substantiated explanation based on a group of extensively tested hypotheses.
Supports large bodies of evidence; much broader than hypotheses, but can be modified or replaced with better explanations.
Systematics and Taxonomy
Objectives
At the end of the lab activity, students should be able to:
Recognize the significance and applications of systematics and taxonomy in evolutionary biology;
Understand binomial nomenclature and the hierarchical system of taxonomy;
Discuss organismal identification and classification using dichotomous keys;
Design a functional dichotomous key and present it for critique;
Conduct research on newly discovered species and report on them.
Introduction
Systematics: The science of classifying organisms, establishing identities and evolutionary relationships.
Taxonomy: Related to naming and classifying but currently understood as a part of systematics focused on naming protocols.
Biodiversity is organized hierarchically through taxa from Domain to Species: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
Mnemonic: "Dear King Philip Came Over For Good Soup"
Capitalization rules: Genus is capitalized; species epithet is not; both are italicized.
Example:
Gallus domesticus (commercial chicken) descends from Gallus bankiva (red jungle fowl).
Modern Taxonomy
Phylogenetic systematics (cladistics): Classification based on evolutionary history using shared derived characters (synapomorphies).
Dichotomous Key
A series of paired statements for classification;
Structure to provide two choices guiding identification until the organism is classified.
Cladistics
Objectives
Understand basic cladistics terms and concepts;
Analyze examples of cladograms to discern clades and interpret phylogenetic relationships;
Construct phylogenetic trees;
Grasp evolutionary relationships.
Introduction to Cladistics
Developed by Willi Hennig; focuses on homology (shared traits).
Cladogram: Represents taxonomic relationships as a tree structure.
Identifies sister taxa (closely related groups).
Synapomorphy: Shared derived traits among taxa.
Plesiomorphy: Ancestral traits shared with other taxa.
Natural Selection and Population Genetics
Objectives
Design experiments to demonstrate natural selection;
Recognize selective pressures impacting populations and evolutionary changes;
Explore genetic basis for evolutionary changes using Hardy-Weinberg principles;
Analyze experimental data using key population genetics concepts.
Introduction
Natural Selection: Differential survival based on advantageous traits within a population. Factors include:
Physical (e.g., climate);
Biological (e.g., competition);
Chemical (e.g., toxins);
Hardy-Weinberg Model
Conditions: Large population, no mutation, random mating, no migration, no selection.
Use of simulations (Candy and Bead models) to illustrate genetic equilibrium and the effects of natural selection.
Prokaryotes & Protists
Objectives
Distinguish between Bacteria and Archaea domains;
Recognize characteristics of bacterial species including cyanobacteria;
Identify protist morphological characteristics and their ecological significance.
Introduction
Overview of prokaryotes and taxonomy; examination of microscopic organisms in laboratory settings through slides and wet mount methods.