Praxis Biology

A student sets up an experiment testing whether light intensity affects algae growth rate. She uses three tanks: one in bright light, one in dim light, and one covered in foil. Which tank is the control group?

• AThe bright-light tank, because it represents the ideal growth condition
• BThe dim-light tank, because it is in the middle of the range tested
• CThe foil-covered tank with no light, because it establishes baseline growth without the t…
• DAll three tanks equally serve as controls for each other

A researcher measures blood pressure in 500 patients over one year and finds that those who exercise more have lower blood pressure. She concludes that exercise lowers blood pressure. What is the main limitation of this conclusion?

• AThe sample size of 500 is too small to draw any conclusion
• BCorrelation between exercise and blood pressure does not establish that exercise causes l…
• CBlood pressure cannot be measured accurately outside of a clinical trial
• DThe study lasted only one year, making all findings invalid

A biology textbook states that 'cells arise only from pre-existing cells.' This statement is best classified as which type of scientific knowledge?

• AA hypothesis, because it has not been tested experimentally
• BA theory, because it is a well-tested, broad explanation of a natural phenomenon
• CA law, because it describes an observed phenomenon without explaining why
• DAn inference, because it was derived from indirect observations

Scientists conduct the same experiment multiple times and get similar results. Another research group then performs the same experiment independently and gets the same result. Which scientific principle does this best demonstrate?

• AParsimony — choosing the simplest explanation
• BFalsifiability — the experiment can be disproven
• CReproducibility — independent replication confirms reliability of findings
• DPeer review — experts evaluate research before publication

A student measures enzyme activity (in units per minute) at five temperatures and creates a graph. The curve rises steeply, peaks at 37°C, then drops sharply at higher temperatures. The drop above 37°C is most likely due to:

• ASubstrate depletion as the reaction proceeds too quickly
• BEnzyme denaturation causing the active site shape to change permanently
• CThe reaction reaching chemical equilibrium at high temperatures
• DCO₂ production inhibiting the enzyme's active site

A study reports that eating dark chocolate is associated with reduced cardiovascular disease risk (p = 0.03). What does p = 0.03 mean in the context of this study?

• AThere is a 3% chance that dark chocolate prevents cardiovascular disease
• BThere is a 3% probability that the observed association occurred by chance if there were…
• CThe study has 97% statistical power to detect a true effect
• DDark chocolate reduces cardiovascular disease risk by 3%

A researcher graphs photosynthesis rate (y-axis) vs. CO₂ concentration (x-axis). The line rises steeply at first, then levels off into a plateau. A second line, measured at higher light intensity, reaches the same plateau but more slowly. What does this graph demonstrate?

• ACO₂ concentration alone determines photosynthesis rate regardless of light
• BAt the plateau, CO₂ is no longer needed for photosynthesis
• CAt the plateau, light intensity has become the limiting factor
• DHigher CO₂ always produces a higher photosynthesis rate

A double-blind randomized controlled trial (RCT) is considered the gold standard for evaluating the effectiveness of a new drug because it:

• AUses the largest possible sample size
• BEliminates both placebo effects and observer bias through blinding and random assignment
• CEnsures that all participants receive the experimental treatment
• DGuarantees that no side effects will occur during the trial

What is the primary purpose of peer review in the scientific publication process?

• ATo guarantee that published findings are always correct and free of error
• BTo have qualified experts evaluate methods, analysis, and conclusions for soundness befor…
• CTo replace the need for independent replication of experimental results
• DTo ensure that only revolutionary findings are published in major journals

A student measures the heights of 30 bean seedlings grown under identical conditions. The mean height is 12 cm with a standard deviation of 2 cm. According to the empirical rule for a normal distribution, approximately what percentage of seedlings would be expected to fall between 10 cm and 14 cm?

• A50%
• B68%
• C95%
• D99.7%

A student accidentally gets a corrosive base on their skin during a titration experiment. What is the immediate first action?

• AApply an acid solution to neutralize the base before it causes further damage
• BFlush the affected area with large amounts of water for at least 15 minutes
• CCover with a bandage and inform the teacher at the end of class
• DCheck the SDS for antidote information before taking any action

Which symbol identifies a substance as a biological hazard on laboratory containers and safety signs?

• AA skull and crossbones
• BA flame over a circle
• CA three-lobed interlocking arc trefoil on a circular background
• DAn exclamation point in a diamond outline

A Safety Data Sheet (SDS) has 16 standardized sections. Which section specifically lists first-aid measures for inhalation, skin contact, eye contact, and ingestion?

• ASection 2: Hazard Identification
• BSection 4: First-Aid Measures
• CSection 8: Exposure Controls and Personal Protection
• DSection 11: Toxicological Information

A student receives a minor cut while dissecting a preserved specimen. What is the correct sequence of actions?

• AContinue working and inform the teacher after the lab is complete
• BApply direct pressure, wash with soap and water, report to the teacher immediately, and s…
• CPour 70% ethanol directly into the wound and continue the dissection wearing a glove
• DApply antibiotic ointment from a personal bag and resume work after 5 minutes

Which personal protective equipment (PPE) is most important when working with volatile organic solvents that emit harmful vapors?

• AChemical-resistant gloves only, since solvents primarily harm through skin contact
• BSafety goggles and a properly functioning fume hood
• CA lab coat and disposable plastic face shield
• DHeat-resistant gloves and a fire extinguisher nearby

A teacher notices that a Bunsen burner is lit on the bench next to containers of flammable ethanol. What should the teacher do first?

• AContinue the demonstration — the ethanol containers are closed
• BMove the ethanol containers to the opposite end of the bench
• CExtinguish the Bunsen burner or remove the flammable containers before proceeding
• DAsk students to keep the containers closed at all times during the demonstration

Blood-stained glass slides from a blood-typing lab should be disposed of in which way?

• AWrapped in paper towels and placed in the regular classroom trash
• BRinsed with tap water and placed in the glass recycling bin
• CIn a puncture-resistant sharps container designated for biohazardous waste
• DLeft in the slide tray so the teacher can handle disposal later