Overview
This lecture covers types of microscopy, the basic components of all cells, and explains why cells are small, emphasizing diffusion and the surface area to volume ratio.
Types of Microscopy
- Light microscopy uses visible light to view cells and is also called bright field microscopy.
- Light microscopes allow observation of live and dead cells, but only a few organelles are visible.
- Staining cells helps visualize cellular structures but usually kills the cells.
- Electron microscopy uses electrons for imaging and provides much greater magnification and detail than light microscopy.
- Transmission electron microscopy (TEM) produces detailed 2D images of internal structures by passing electrons through the specimen.
- Scanning electron microscopy (SEM) produces 3D images of cell surfaces by scanning electrons across the surface.
- Electron micrographs are originally black and white; colors can be added by computer ("false color").
- Fluorescence microscopy uses fluorescent proteins or stains to visualize structures, mainly in dead cells unless GFP is used.
Magnification vs. Resolution
- Magnification is how much larger an image appears compared to the object.
- Resolution is the ability to distinguish two close objects as separate and is key to image clarity.
Common Components of All Cells
- All cells have a cell (plasma) membrane which forms the cell’s boundary.
- Cytoplasm, the fluid inside cells, is present in all cells.
- DNA serves as the genetic material in every cell.
- Ribosomes are present in all cells and are responsible for protein synthesis.
Why Cells Are Small
- Cells must be small to facilitate diffusion, which is the passive movement of molecules from high to low concentration.
- Smaller cells have a higher surface area to volume ratio, allowing efficient transport of nutrients and waste.
- Larger organisms have more cells, not larger individual cells.
- Eukaryotic cells can be larger due to internal organelles that make molecule transport and cell function more efficient.
Key Terms & Definitions
- Light Microscopy — Uses light to view cells; allows observation of live samples.
- Electron Microscopy — Uses electrons for much higher magnification and resolution; samples are dead.
- Transmission Electron Microscopy (TEM) — Electron microscopy method for detailed 2D internal images.
- Scanning Electron Microscopy (SEM) — Electron microscopy for 3D images of cell surfaces.
- Staining — Adding dyes to color cellular structures, usually kills cells.
- Resolution — The clarity and detail of a microscopic image.
- Surface Area to Volume Ratio — Comparison of the cell’s surface to its volume; higher ratios aid diffusion.
- Diffusion — Passive movement of molecules from areas of high to low concentration.
- Cytoplasm — The fluid inside all cells.
- Ribosome — Organelle responsible for protein synthesis.
Action Items / Next Steps
- Review and complete the provided cell component worksheet in the next few days.
- Prepare to study the organelles of eukaryotic cells for the next lecture.