Cell Theory and Microscopy History

Study Notes

History of Microscopy and Cell Discovery

Zacharis Janssen invented the first microscope in 1590.
Robert Hooke discovered cells in 1665 by observing cork under a microscope, noting a honeycomb-like structure, which he called "Cella" (Latin for compartments).
Anton van Leeuwenhoek observed free-living cells in 1675, contributing to cell science.

Cell Theory

Cells are the structural and functional units of life.
Structural hierarchy: Cell → Tissues → Organs → Organ Systems → Whole Body.
Functional units include processes such as excretion, reproduction, respiration, and digestion in unicellular organisms, with division of labor in multicellular organisms.
Schleiden and Schwann proposed cell theory in the 19th century, including key tenets:
- All organisms are made of cells.
- Cells consist of protoplasm containing a nucleus and plasma membrane, with or without a cell wall.
- New cells arise from pre-existing cells (Rudolph Virchow's modern cell theory).
- All cells share chemical composition and metabolic functions.
- Organism functions result from the sum of cell activities.
- Every cell is totipotent, capable of developing into a complete organism.

Exceptions to Cell Theory

Viruses lack true cellular structures (no cytoplasm or organelles).
Bacteria and cyanobacteria do not possess a true nucleus.
Coenocytic organisms (e.g., Mucor, Rhizopus) have multinucleated bodies without partitions.
Mature mammalian red blood cells and sieve tube cells lack nuclei.
Paramecium contains two nuclei.

Cell Characteristics and Functions

Cells are independently functional and contain complete genetic information.
Cells convert micro to macro molecules and produce/store energy as ATP.
They regulate the flow of energy and information, with each cell having a specific life span (RBC - 4 months, skin cells - 2 to 4 weeks, pancreatic cells - 1 year, bone cells - 25 to 30 years).
Cells perform respiration and facilitate gas exchange.

Energy and Information Flow in Cells

Energy flow: Sunlight → Green parts (photosynthesis) → Non-green parts (respiration) → Energy release → Transfers to higher trophic levels.
Intrinsic information flow: DNA → mRNA (Transcription) → Protein (Translation).
Extrinsic information flow: Stimuli, metal ions, or hormones influence cellular response.

Differences Between Unicellular and Multicellular Organisms

Unicellular: single-cell organisms (e.g., Amoeba, Chlamydomonas); no division of labor; susceptible to injury.
Multicellular: composed of multiple cells; division of labor; more resilience to injury and can reproduce multiple times.

Cellular Totipotency

Defined as the ability of a living, vegetative cell to regenerate into a complete organism.
Concept introduced by Haberlandt in 1902.
White cultured tomato roots from a single cell in 1932.
Steward's experiments demonstrated totipotency using carrot tissue:
- Phloem cells cultured in a nutrient-rich medium produced clusters.
- These clusters developed into rooted clumps and eventually full plants when transferred to a natural environment.

Types of Cells

Prokaryotic Cells: Lack a true nucleus and membrane-bound organelles; possess a nucleoid without a nuclear membrane (e.g., Bacteria, Cyanobacteria).
Eukaryotic Cells: Have a defined nucleus and membrane-bound organelles, surrounded by a plasma membrane.

Description

Explore the fascinating history of microscopy and the development of cell theory. Learn about the pioneering scientists such as Zacharias Janssen, Robert Hooke, and Anton van Leeuwenhoek who contributed to our understanding of cells. This quiz covers key concepts, discoveries, and the structural hierarchy of life.