Foundations of Biology: Shared Characteristics of Life

Unit 1: Foundations of Biology

Shared Characteristics of Life

This unit introduces the fundamental properties that define living organisms, providing a basis for understanding biological systems. The following topics outline the essential features shared by all life forms.

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

• Replication: Life forms reproduce to pass genetic information to the next generation.

• Information Processing: Organisms store, transmit, and respond to genetic information.

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

• Energy Utilization: Life requires energy to maintain structure and function.

Life is Cellular

Cell Theory

The cell theory is a foundational concept in biology, stating two main principles:

• All living things are composed of cells.

• All cells arise from pre-existing cells.

Types of Cells: Eukaryotic vs. Prokaryotic

Cells are classified into two major types based on structural differences:

• Prokaryotic Cells: Lack a membrane-bound nucleus; examples include Bacteria and Archaea.

• Eukaryotic Cells: Possess a membrane-bound nucleus and organelles; examples include Plants, Animals, Fungi, and Protists.

Comparison Table:

Feature	Prokaryotic	Eukaryotic
Nucleus	No	Yes
Organelles	No	Yes
Size	Small	Larger
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Life Replicates

Cell Division Mechanisms

Organisms reproduce through various mechanisms of cell division:

• Binary Fission: Simple division in prokaryotes, producing two identical cells.

• Mitosis (with cytokinesis): Division in eukaryotic cells for growth and repair, resulting in two genetically identical daughter cells.

• Meiosis (with cytokinesis): Specialized division in eukaryotes for sexual reproduction, producing four genetically unique gametes.

Asexual vs. Sexual Reproduction

• Asexual Reproduction: Offspring arise from a single parent; genetically identical to the parent.

• Sexual Reproduction: Offspring arise from the fusion of gametes from two parents; genetically diverse.

Life Processes Information

Heredity

Heredity is the transmission of genetic traits from parents to offspring.

Chromosome Theory of Inheritance

This theory states that genes are located on chromosomes, which are passed from parents to offspring during reproduction.

Central Dogma of Biology

The central dogma describes the flow of genetic information:

• DNA stores genetic information.

• RNA transmits information from DNA to protein synthesis machinery.

• Proteins carry out cellular functions and determine organismal traits.

Central Dogma Equation:

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

Life Evolves

Evolution

Evolution is the change in the genetic composition of populations over time.

Mutation and Natural Selection

• Mutation: A change in DNA sequence; source of genetic variation.

• Natural Selection: The process by which advantageous traits increase in frequency within a population.

Life Requires Energy

Metabolism

Metabolism refers to all chemical reactions that occur within an organism to maintain life.

• Autotrophic Metabolism: Organisms produce their own food (e.g., photosynthesis in plants).

• Heterotrophic Metabolism: Organisms obtain energy by consuming other organisms.

Homeostasis

Homeostasis is the maintenance of stable internal conditions despite external changes.

• Conformative Homeostasis: Internal conditions change with the environment.

• Regulatory Homeostasis: Internal conditions are actively maintained within a narrow range.

Example:

Humans regulate body temperature (regulatory homeostasis), while some fish allow their body temperature to fluctuate with water temperature (conformative homeostasis).

Additional info: These foundational concepts are essential for understanding subsequent topics in biology, including genetics, evolution, and physiology.