Cell Biology and Discoveries

Early Cell Discoveries

• Robert Hooke first observed plant cells in cork using a microscope in 1665.
• Anton van Leeuwenhoek improved microscope design and discovered single-celled organisms.

Understanding Cells

• Cells serve as the fundamental units that constitute all living organisms.
• They are commonly referred to as the building blocks of life.

Cell Theory

• All living things are composed of cells.
• Cells are the basic structural and functional units of life.
• New cells are produced from existing cells, a principle established by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow in the 1800s.

Louis Pasteur's Experiment

• Pasteur aimed to disprove the theory of spontaneous generation, which claimed that microorganisms arise from non-living matter.
• Experiment utilized flasks with nutrient broth; straight necks allowed for direct air contact, while swan-neck flasks prevented dust contamination.
• Outcome: Straight-neck flasks became cloudy due to microorganisms, while swan-neck flasks remained clear unless contaminated.

Significance of Pasteur's Findings

• Demonstrated that microorganisms originate from other microorganisms rather than spontaneously from non-living materials.
• Contributed significantly to the understanding of germ theory and disease causation.

Investigation of Spontaneous Generation

• In 1861, scientists investigated the possibility of life emerging from inert materials.
• Pasteur's swan-neck flask design effectively filtered out dust while allowing air in, keeping the broth free of microorganisms.
• When the neck was broken, organisms from the air contaminated the broth, affirming that life comes from existing life.

Implications of Cell Theory

• In single-celled organisms, like bacteria, each cell is connected through a common ancestor, replicating with minor variations.
• Multicellular organisms, including humans and plants, derive all cells from a fertilized egg, illustrating cellular interconnection and evolution over time.

The Theory of Evolution by Natural Selection

• Darwin and Wallace proposed that all living beings share common ancestors if traced back far enough.
• Species undergo gradual changes and develop new traits over generations, facilitating adaptation to environments.

Key Concepts of Evolution

• Evolution entails gradual changes within species over time rather than sudden shifts.
• Natural selection favors organisms with advantageous traits that enhance their survival and reproductive success.
• Variation within populations is essential for providing the necessary traits for evolutionary change.
• Darwin elaborated on these theories in his seminal work "On the Origin of Species" published in 1859.

Key Terms

• Evolution: The process through which species change over time and share common ancestry.
• Natural Selection: The mechanism by which evolution occurs, favoring traits suited for the environment.
• Fitness: An individual's capability to produce offspring relative to others in the population.
• Adaptation: A trait that enhances an individual's fitness in a specific environment.