Biology 1011: Chapter 1 – The Study of Life and the Scientific Method

Biology: The Study of Life

Defining Characteristics of Life

Biology is the scientific study of living organisms and their interactions with the environment. To determine if something is alive, biologists look for several fundamental characteristics shared by all living things.

• Cellular Organization: All living organisms are composed of one or more cells, which are the basic units of life.

• Replication: Living things reproduce, passing genetic information to offspring.

• Information Processing: Organisms process hereditary information encoded in genes and respond to environmental signals.

• Energy Utilization: Life requires energy to carry out cellular processes and maintain organization.

• Evolution: Populations of living organisms evolve over time through changes in genetic makeup.

Example: Humans, plants, and bacteria all exhibit these characteristics, though in different ways.

The Scientific Method in Biology

Overview of the Scientific Method

The scientific method is a systematic approach used by scientists to investigate natural phenomena, develop hypotheses, and test predictions.

• Observation: Gathering information about a phenomenon.

• Question: Formulating a question based on observations.

• Hypothesis: Proposing a testable explanation for the observed phenomenon.

• Prediction: Stating a measurable or observable result that should occur if the hypothesis is correct.

• Experiment: Designing and conducting tests to evaluate the prediction.

• Analysis: Interpreting results to support or refute the hypothesis.

Example: Testing whether giraffes have long necks due to food competition or sexual selection.

Key Terminology

• Theory: An explanation for a broad pattern in nature, supported by a large body of evidence.

• Hypothesis: A testable statement that explains something observed.

• Experiment: A procedure to test the effect of a factor on a particular phenomenon.

• Prediction: A measurable or observable result that must be correct if the hypothesis is valid.

Hypothesis Testing in Biology

Steps in Hypothesis Testing

After formulating a hypothesis, scientists follow a two-step process to test it:

1. State the hypothesis as precisely as possible and list the predictions it makes.

2. Design an observational or experimental study capable of testing those predictions.

Case Study: Why Do Giraffes Have Long Necks?

Food Competition Hypothesis

This hypothesis suggests that giraffes evolved long necks to reach food unavailable to other mammals.

• Predictions:

  • Neck length is variable among giraffes.

  • Neck length is heritable.

  • Giraffes feed high in trees.

Experimental Test: Simmons and Scheepers tested these predictions and found that giraffes do not usually feed at heights requiring long necks, refuting the food competition hypothesis.

Sexual Competition Hypothesis

This alternative hypothesis proposes that long necks evolved because longer-necked males win more fights and father more offspring.

• Predictions:

  • Longer-necked males have greater reproductive success.

  • Neck length is variable and heritable.

Example: Male giraffes use their necks in combat to establish dominance and mating rights.

Experimental Design: Ants and Internal Pedometer Hypothesis

Testing the Pedometer Hypothesis

Researchers investigated how ants find their way back to the nest after foraging for food, proposing that ants use an internal pedometer to measure distance.

• Pedometer Hypothesis: Ants know how far they are from the nest by counting steps.

• Null Hypothesis: There are no differences among ants with altered leg lengths.

Experimental Setup

• Three groups of ants:

  • Stumps: Legs shortened

  • Normal: Legs unaltered

  • Stilts: Legs lengthened with pig bristles

• Ants walked from nest to feeder, then returned "home" after leg manipulation.

Predictions and Results

• Pedometer Hypothesis Prediction: Ants with stilts will go too far; ants with stumps will stop short.

• Null Hypothesis Prediction: No differences among the three groups.

Group	Expected Result	Actual Result
Stumps	Stop short of nest	Stopped short
Normal	Return to nest	Returned to nest
Stilts	Go too far past nest	Went too far

Conclusion: Desert ants use information on stride length and number to calculate how far they are from the nest, supporting the pedometer hypothesis.

Important Characteristics of Good Experimental Design

• Replication: Repeating tests to ensure reliability.

• Sample Size: Using enough subjects to ensure results are statistically significant.

• Control: Including control groups to compare against experimental groups.

Summary Table: Key Concepts in the Scientific Method

Term	Definition	Example
Theory	Broad explanation supported by evidence	Cell theory, theory of evolution
Hypothesis	Testable statement explaining an observation	"Giraffes have long necks to reach food"
Experiment	Test to evaluate a hypothesis	Manipulating ant leg length
Prediction	Measurable result expected if hypothesis is correct	Ants with stilts go too far

Central Dogma and Chromosome Theory (Additional info)

Central Dogma: Describes the flow of genetic information from DNA to RNA to protein.

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Chromosome Theory of Inheritance: States that genetic information is carried on chromosomes, which are passed from parent to offspring during cell division.

Example: Mendelian inheritance patterns are explained by the behavior of chromosomes during meiosis.

Additional info: The notes reference the central dogma and chromosome theory, which are foundational concepts in biology and relevant for understanding how life processes information and passes traits to offspring.