Methods of Studying Cells
- There are 3 main types of microscopes used to observe cells:
Light Microscope | Scanning Electron Microscope | Transmission Electron Microscope | |
Medium | Light Beam | Electron Beam | Electron Beam |
Dimensions | 2D | 3D | 2D |
Max Magnification | X1,500 | X200,000 | X2,000,000 |
Max Resolution | 200 nm | 20nm | 0.1nm |
- Magnification is how much bigger the image is compared to the original object viewed with the naked eye
- Magnification = (size of image)/(size of object)
- Resolution is how well a microscope distinguishes between two points that are close together.
- To prepare slides for light microscopy, the specimen must be:
- Dehydrated
- Embedded in wax and sectioned
- Stained
- Mounted
- Staining is used to increase contrast in a specimen, in order to observe transparent and colourless structures. Stains work by binding to different types of molecules or cell structures. This allows different components of cells to be identified, and is known as differential staining
Eukaryotic Cells
- Eukaryotes include animal, plant & fungal cells.
- The following organelles are presents in eukaryotic cells:
- There are additional organelles in plants, algae & fungi:
- The cytoskeleton is a complex network of proteins in the cytoplasm.
- Microfilaments are composed of repeating actin subunits. Important to maintain cell shape and give mechanical strength
- Microtubules are composed of repeating tubulin subunits. Involved in organelle and substance movement
- Intermediate fibres are made of interlocking protein fibres. Helps anchor the nucleus in the cytoplasm and stabilising tissues
- In complex multicellular organisms, eukaryotic cells become specialised for specific functions.
- Specialised cells are organised into tissues, tissues into organs and organs into systems.
Prokaryotic Cells
- Prokaryotes are smaller and simpler than eukaryotes.
Feature | Eukaryotic | Prokaryotic Cell |
Nucleus | Present | Absent |
DNA | Linear and packaged into chromosomes in nucleus | Circular and freely floating in cytoplasm |
Cell Membrane | Present | Present |
Membrane-bound organelles | Present | Absent |
Ribosomes | Present (80S | Present (70S) |
Cell Wall | Sometimes (cellulose or chitin) | Present (peptidoglycan) |
Chloroplasts | Sometimes | Absent |
Flagellum | Absent | Sometimes |
Capsule | Absent | Sometimes |
Plasmid | Absent | Sometimes |