Unit 1: Science and the Living Environment Study Guide

Laboratory Safety and Improper Practices

• Identification of Unsafe Laboratory Procedures: In a standard biological laboratory setting, safety protocols are paramount. Identifying unsafe practices is a critical skill for students. Examples of hazards depicted in experimental diagrams include:

  • Improper Test Tube Handling: Pointing the opening of a test tube toward oneself or others while heating or performing a reaction is extremely dangerous as substances can splash or boil over.

  • Lack of Personal Protective Equipment (PPE): Failing to wear safety goggles during an experiment exposes the eyes to chemical splashes or glass shards.

  • Stopper Protocol: Leaving a test tube unstoppered when it should be sealed, or conversely, heating a stoppered tube which could cause a pressure-induced explosion.

  • Fire Safety: Ensuring the flame is at an appropriate height and that equipment like beakers and tripods are positioned correctly to prevent accidental spills or fire hazards.

Foundations of Scientific Theory and Inquiry

• The Scientific Theory: In biology, a theory (such as the Cell Theory) represents a well-accepted body of knowledge. It is the culmination of investigations and observations performed by many scientists over long periods. A theory is more robust than a single hypothesis because it is supported by a large volume of evidence.

• Basic Scientific Assumptions:

  • Evidence and Prior Knowledge: Scientific explanations are constructed by synthesizing observable evidence with existing knowledge.

  • Inquiry and Reliability: Inquiry requires the ability to judge the reliability of information sources and the relevance of the data provided.

  • Values and Ethics: While science provides empirical information and data, human values are essential for making ethical decisions regarding scientific applications.

• Validity and Reproducibility: A fundamental rule of science is that if a conclusion is valid, the same investigation conducted by other scientists using the same methods should yield the same results. Reproducibility is the standard by which new discoveries are verified.

Design and Components of a Controlled Experiment

• The Hypothesis:

  • Definition: A hypothesis is a tentative explanation or prediction that serves as a basis for determining what data to collect and how to design an experiment.

  • Value of a Hypothesis: It is valuable even if it is disproved by experimental results, as it provides a structured path for further investigation.

  • Example Case: A student might hypothesize that lettuce seeds require soil coverage to germinate. If data shows high germination both under and on top of the soil, the student must revise the hypothesis rather than ignore the data.

• Experimental Variables:

  • Independent Variable: The single factor that the scientist changes or manipulates (e.g., the pH of water, the amount of a supplement, or the type of music played).

  • Dependent Variable: The factor that is measured or observed as a result of the change (e.g., the height of a plant, the rate of bacterial growth, or a person\'s pulse rate).

• Controlled Parameters: To ensure a fair test, all other factors must be kept identical for all groups. For example, in a plant growth study, both groups should receive the same intensity of light, volume of water, and type of soil.

• The Control Group: This group serves as a baseline for comparison. It does not receive the experimental treatment (e.g., a group given a glucose pill instead of an actual asthma drug). Without a control group, it is impossible to determine if the results were caused by the variable being tested.

• Improving Reliability and Validity:

  • Sample Size: Increasing the number of subjects (using a larger sample size) reduces the impact of chance and outliers, making the results more reliable.

  • Repeated Trials: Performing the experiment multiple times provides more data and confirms original findings.

  • Specific Supplement Case Study: In a study testing a mineral supplement at dosages of $100\,mg$ and $200\,mg$, the study would be more valid if a third group was included that received $0\,mg$ (no supplement).

Data Organization and Visual Analysis

• Purpose of Scientific Tools: Scientists use diagrams, tables, and graphs primarily to organize data and identify general trends or patterns that might not be visible in raw numbers.

• Interpreting Graphs:

  • Human Fetal Growth: Between weeks 26 and 32 of development, specific quantitative changes can be tracked. For example, fetal mass may increase by $750\,g$ while length increases by approximately $100\,mm$.

  • Bacterial Reproduction Rates: Graphs can show that different species (e.g., Species A, B, C, D) have specific temperature ranges for optimal reproduction. Some species thrive at high temperatures while others cannot survive beyond a specific threshold.

  • Genetic Relationships: DNA similarity graphs can indicate the evolutionary proximity of species. If Species A shares the highest percentage of DNA with Species E, it can be concluded they are closely related or share a recent common ancestor.

• Laboratory Measurements (Potato Osmosis Example): In experiments measuring the length of potato pieces in different sugar concentrations ($0\%$, $5\%$, $10\%$, $15\%$), data tables show how the physical dimensions change over a $24\text{-hour}$ period. This data is best represented by a line graph to show the relationship between concentration and physical change.

Specific Experimental Scenarios

• Mouthwash Effectiveness Study:

  • Method: Bacteria are inoculated onto nutrient agar in petri dishes. Paper disks ($1\,cm$ in diameter) are soaked in different mouthwashes and placed on the agar.

  • Incubation: The dishes are kept at $37^\circ C$ for $24\,hours$.

  • Analysis: The most effective mouthwash is indicated by the largest region of inhibited bacterial growth (the largest clear/non-shaded area around the disk).

• Radish Plant pH Study:

  • Question: Does the pH of water affect the growth of radish plants?

  • Setup: One group is watered with pH $3.0$ and the other with pH $7.0$.

  • DV: The height of the plants (measured every $2\,days$ for $2\,weeks$).

  • IV: The pH of the water.

• Music and Pulse Rate Study:

  • Observation: A student tested pulse rates after listening to seven different music selections for $30\text{-seconds}$ each.

  • Critical Flaw: The experiment lacked a control group (e.g., measuring the resting pulse rate in silence) to compare the changes accurately.

• Water Plant Gas Release:

  • Setup: A green water plant is placed under an inverted funnel and test tube in a beaker of water.

  • Hypothesis: Green water plants release a gas (oxygen) in the presence of light, which can be observed as bubbles displacing water in the test tube.