Exam 2 Example Questions: Dietary Fiber, Crime Scene DNA, and Invasive Plant Competition

These notes cover example questions from an exam focusing on scientific method application in diverse scenarios. Topics include fermentation of dietary fiber, DNA profiling in forensic science, and ecological interactions between invasive and native plant species.

Dietary Fiber and Gases in the Breath: When dietary fiber enters the gut, it's broken down by primary degraders, leading to intermediate products, hydrogen (H2), and carbon dioxide (CO2). These intermediates are further processed into butyrate by butyrate producers, releasing more H2 and CO2. H2 and CO2 can combine to form methane (CH4) in some individuals. These gases (H2, CO2, and CH4) then enter the bloodstream, travel to the lungs, and are exhaled.

Experimental Design for Fiber Fermentation: In experiments studying dietary fiber fermentation, appropriate controls are crucial. A negative control would be tap water or a fiber-free substance to show no increase in fermentation. A positive control would be a known fermentable fiber or a substance known to increase breath gases. Confounding variables in such studies may include inconsistent fiber amounts in different soft drinks, age range of subjects, or different gut microbiomes among participants due to randomly assigned drinks.

Crime Scene Investigation and DNA Profiling: DNA profiling uses PCR and gel electrophoresis to analyze differences in DNA, focusing on Short Tandem Repeats (STRs). STRs are regions of DNA with variable repeat sequences unique to individuals. This unique combination of variable regions makes up the DNA profile. PCR is used to amplify these STR sequences from DNA samples.

PCR Principles and Troubleshooting: During PCR, different temperatures are used for specific purposes. 95°C denatures the DNA, 52°C allows primers to anneal, and 72°C enables strand elongation. Primer design is critical; melting temperatures should be close (within 5°C) and above the annealing temperature. Contamination in negative controls indicates a failed PCR reaction, requiring a restart of the process.

Post-PCR Processing: After PCR, purification is necessary to remove excess primers, dNTPs, longer DNA fragments, the original template strand, buffer, salt, and Taq polymerase. The purified PCR products are then analyzed via gel electrophoresis to determine the size and number of STR sequences.

Invasive Species and Competition: Invasive species are organisms introduced to regions outside their native range, where they compete with native wildlife. This competition can be either exploitative (competing for the same resources like space, water, nutrients, and light) or interference-based. Invasive plants may alter herbivory patterns, potentially serving as refuges for herbivores and impacting native plants.

Experimental Design in Ecology: Common garden experiments are used to evaluate competitive interactions, manipulating the presence or absence of invasive species. The impact of competition can be assessed by measuring herbivory levels on native plants. Stronger competitive effects are often observed in regions where a species is invasive because native species lack a shared evolutionary history and are less adapted to competition with the invader. Over time, native species may adapt through natural selection.

De Wit Replacement Series Experiments: These experiments assess the impact of species abundance on fitness. Fitness is defined as an individual's ability to survive and reproduce. Competition reduces fitness by limiting access to necessary resources. The experimental setup involves planting different proportions of two species in garden beds while maintaining a constant total plant density. Analyzing survival, productivity, and reproduction can reveal competitive effects.

Interpreting De Wit Series Graphs: A de Wit series graph displays the relationship between species abundance and productivity. A data line below the 1:1 line indicates interspecific competition. Statistical analyses, such as p-values from hypothesis testing, help determine if experimental results support predictions. A significant decrease in seed production (reproduction) indicates a negative effect on fitness, even if survival is not significantly affected.

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