Chapter 1: Themes in the Study of Life – Foundations of Biology

Chapter 1 – Themes in the Study of Life

Introduction to Biology

Biology is the scientific study of life. Defining life is complex, but biologists characterize living things by a set of shared properties and processes. Understanding these properties helps distinguish living organisms from non-living matter.

• Reproduction: The ability of organisms to produce new individuals, ensuring the continuation of their species.

• Evolutionary adaptation: Populations of organisms change over generations through adaptations that enhance survival and reproduction in specific environments.

• Order: Living things exhibit highly ordered structures, from cells to complex organs.

• Energy processing: Organisms obtain and use energy to power their activities and maintain organization.

Additional info: Other key properties of life include regulation (homeostasis), response to the environment, and growth and development.

Properties of Life

Living organisms share several fundamental properties that define life. These properties are observable across diverse forms of life, from single-celled bacteria to complex multicellular animals and plants.

• Order: Life is organized at multiple levels, from molecules to cells, tissues, organs, and organisms.

• Evolutionary adaptation: Populations evolve over time, adapting to their environments through natural selection.

• Response to the environment: Organisms detect and respond to stimuli in their surroundings.

• Regulation: Living things regulate their internal environment to maintain stable conditions (homeostasis).

• Energy processing: Organisms acquire energy and transform it to carry out life processes.

• Reproduction: Life comes from pre-existing life; organisms reproduce their own kind.

• Growth and development: Organisms grow and develop according to instructions encoded in their DNA.

Example: A sunflower exhibits order in its spiral arrangement of seeds, a hummingbird processes energy from nectar, and giraffes grow and develop from birth to adulthood.

Evolution as a Unifying Theory

The Role of Evolution in Biology

Evolution is the central, unifying theory of biology. It explains both the similarities and differences among living organisms. The concept of a common ancestor helps us understand why species share certain traits and why they differ.

• Similarities between species: Shared traits often result from descent from a common ancestor.

• Differences between species: Over millions of years, populations accumulate variations that are selected for in different environments.

Example: The last common ancestor of humans and bats lived about 65 million years ago and had limb structures that evolved into both human hands and bat wings.

Charles Darwin and Natural Selection

Charles Darwin developed the theory of natural selection based on key observations about populations and their traits.

• Variation: Individuals in a population vary in their traits.

• Overproduction: Populations produce more offspring than can survive, leading to competition.

• Adaptation: Each species is suited to its environment.

From these observations, Darwin proposed that individuals with advantageous traits are more likely to survive and reproduce, passing those traits to future generations.

• Key points for natural selection:

  • Variation must exist in a population.

  • Advantageous variation must be heritable.

  • Many generations are required for traits to become common.

Selective Pressure: Any factor that alters the fitness of organisms in an environment, such as predation, climate, or competition for resources.

Example: Birds eating lighter-colored beetles create selective pressure favoring darker beetles.

Classification and Domains of Life

The Three Domains of Life

All living organisms are classified into three domains based on cellular structure and genetic relationships.

• Bacteria: Prokaryotic cells without membrane-enclosed nuclei or organelles.

• Archaea: Prokaryotic cells, distinct from bacteria, often found in extreme environments.

• Eukarya: Eukaryotic cells with membrane-enclosed nuclei and organelles; includes protists, plants, fungi, and animals.

Additional info: Although both Bacteria and Archaea are prokaryotes, Archaea are genetically more similar to Eukarya than to Bacteria.

Domain	Cell Type	Examples
Bacteria	Prokaryotic	Escherichia coli, Cyanobacteria
Archaea	Prokaryotic	Halophiles, Thermophiles
Eukarya	Eukaryotic	Plants, Animals, Fungi, Protists

Genetic Information and Unity of Life

DNA and Genetic Code

All organisms use DNA to store and transmit genetic information. The genetic code is universal, providing strong evidence for a common origin of life on Earth.

• DNA: Deoxyribonucleic acid, the molecule that carries genetic instructions.

• Genetic code: The set of rules by which information encoded in DNA is translated into proteins.

Example: The same codons specify the same amino acids in bacteria, plants, and animals.

The Scientific Method

Steps of the Scientific Method

The scientific method is a systematic approach to investigating natural phenomena. It ensures that scientific knowledge is based on evidence and logical reasoning.

1. Observation: Gathering information about phenomena.

2. Formulate a hypothesis: Proposing a testable explanation for observations.

3. Design an experiment: Creating a procedure to test the hypothesis.

4. Refine hypothesis: Modifying or generating new hypotheses based on results.

5. Repeat: Repeating experiments to confirm findings.

Testing Hypotheses

• Testable: Hypotheses must be able to be tested by experiment or observation.

• Falsifiable: There must be a possible outcome that could prove the hypothesis false.

Example: "Plants grow faster in sunlight than in shade" is a testable and falsifiable hypothesis.