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Microscopy is essential for examining cellular structures that are often too small to see with the naked eye.
Instruments developed to extend human sensory capabilities have advanced the study of cells.
Robert Hooke first observed cell walls in 1665, while Antoni van Leeuwenhoek used advanced lenses to visualize living cells, which he called "animalcules."
Light microscopes (LM) and electron microscopes (EM) are the two main types of microscopes used in cell biology.

Cells are classified into two types: prokaryotic and eukaryotic.
Prokaryotic cells are found in organisms from the domains Bacteria and Archaea.
Eukaryotic cells are present in organisms such as protists, fungi, animals, and plants.
The internal structures of these cells are organized by membranes that separate the various cellular functions.

Eukaryotic cells have a defined nucleus, which contains most of the cell's DNA.
Ribosomes, found in all cells, synthesize proteins based on genetic instructions.
In prokaryotic cells, DNA is located in a nucleoid region, which is not membrane-bound.

The endomembrane system is a variety of membranes, including the nuclear envelope, endoplasmic reticulum (ER), and Golgi apparatus, which coordinate the synthesis, modification, and transport of proteins and lipids.

Mitochondria are the powerhouses of the cell, converting chemical energy from food into ATP through cellular respiration.
Chloroplasts, found in plant cells, conduct photosynthesis, converting light energy into chemical energy stored in glucose.

The cytoskeleton consists of microtubules, microfilaments, and intermediate filaments that provide structural support, maintain shape, and facilitate motility and intracellular transport.

Extracellular structures, such as the cell wall in plants and the extracellular matrix in animals, provide support, protection, and communication between cells.

Cells are fundamental units of life, analogous to atoms in chemistry.
All living organisms are composed of cells.
The cell is the simplest collection of matter that can be alive.
Single-celled organisms, like paramecia, demonstrate that life can exist as individual cells.
Multicellular organisms, including plants and animals, consist of specialized cells forming tissues and organs.
Cells share common features but can vary widely in structure and function due to evolutionary adaptations.

Used to study the internal structure of cells by directing an electron beam through thin slices of specimens.
Employs staining with heavy metals to enhance contrast.
Utilizes electromagnetic lenses rather than glass lenses to focus images on a monitor.

Provides detailed surface images by scanning the outer layer of a specimen with an electron beam.
Secondary electrons ejected from the surface create a three-dimensional effect in the images.

A technique to separate cellular components based on size and density using a centrifuge.
It enables the study of specific cell fractions, enhancing understanding of structural and functional relationships in cells.
Example: Testing fractions for enzymes involved in cellular respiration and correlating this with the presence of mitochondria.

Utilizes electron beams for imaging, capable of achieving much higher resolutions, typically around 2 nm.
Significant improvement over light microscopy due to shorter wavelengths of electrons.

Prokaryotic cells range from 1-10 μm while eukaryotic cells range from 10-100 μm in diameter.
The relationship between surface area and volume is critical for cell function:
- Surface area grows at a squared rate; volume grows at a cubed rate.
- A smaller cell has a higher surface area to volume ratio, which is essential for efficient nutrient and waste exchange.
- Example: Smallest known bacteria, mycoplasmas, range between 0.1 and 1.0 μm in diameter.