2.1.1 : CELL STRUCTURE Flashcards
Describe the principles and key features of light microscopes
Principles:
Use visible light to illuminate the specimen. Lenses focus light to produce a magnified image.
Key Features:
Maximum magnification: ×1500. Resolution: 200 nm (limited by wavelength of light). Can view live specimens.
State the advantages and disadvantages of light microscopes.
Advantages:
Relatively cheap and portable. Can observe living specimens. Simple preparation process.
Disadvantages:
Limited resolution (200 nm). Lower magnification (×1500). Cannot observe ultrastructure.
Describe the principles and key features of electron microscopes.
Principles:
Use beams of electrons instead of light. Electromagnets focus the beam to create an image.
Key Features:
Transmission Electron Microscope (TEM):
Magnification: up to ×500,000.
Resolution: 0.1 nm.
Produces 2D images of thin specimens.
.Scanning Electron Microscope (SEM):
Magnification: up to ×100,000. Resolution: 0.1–10 nm. Produces 3D images of surfaces
: State the advantages and disadvantages of electron microscopes.
Advantages:
Very high resolution (0.1–10 nm). High magnification (up to ×500,000). Detailed images of ultrastructure (organelles, membranes).
Disadvantages:
Expensive and large. Requires vacuum—cannot observe living specimens. Complex preparation process (risk of artefacts). Images in black and white.
Compare light microscopes and electron microscopes.
Light Microscope
Uses visible light and lenses to magnify images.
Maximum magnification: ~×1500.
Maximum resolution: ~200 nm.
Can view live specimens.
Produces color images.
Electron Microscope (EM)
Uses electron beams and magnetic fields to magnify.
Higher magnification: ~×500,000 or more.
Higher resolution: ~0.1 nm (transmission) or 20 nm (scanning).
Cannot view live specimens (requires vacuum).
Produces black-and-white images (color added artificially).
What are the differences between scanning electron microscopes (SEM) and transmission electron microscopes (TEM)?
Transmission Electron Microscope (TEM):
Electrons pass through the specimen.
Provides high-resolution, 2D images of internal structures.
Requires thin sections of specimens.
Scanning Electron Microscope (SEM):
Electrons reflected off the surface of the specimen.
Provides 3D images of surfaces.
Specimen does not need to be thinly sliced.
Explain the principle and application of laser scanning confocal microscopes.
Use laser light to scan fluorescently labeled specimens point by point.
Focused through a pinhole to eliminate out-of-focus light.
Produces high-resolution, 2D or 3D images.
Applications:
Studying living cells in real-time.
Observing biological processes (e.g., cell division).
What are the advantages and disadvantages of laser scanning confocal microscopes?
Advantages:
High resolution and contrast. 3D imaging. Can observe live specimens with fluorescent dyes.
Disadvantages:
Expensive. Requires fluorescent staining, which may affect cells.
Describe the process of preparing a temporary slide of a specimen for light microscopy.
- Place the specimen on a clean glass slide.
2.Add a drop of water or stain (e.g., iodine for plant cells).
3.Gently lower a coverslip using a mounted needle to avoid air bubbles.
4.Remove excess liquid using tissue paper.
What are the different types of slide preparation for Light Microscopes
1.Dry Mount: solid specimen cut with sharp blade with just a cover slip on top
2.Wet Mount: sample in liquid, cover slip at an angle
- Squash Slide: sample squashed W/ cover slip between 2 slides
- Smear Slide: Use edge of another slide to smear sample
Why is staining used in microscopy?
Enhances contrast between different components of the cell.
Allows specific structures to be visualized (e.g., nucleus, cell wall).
Enables differentiation between different cell types or tissues.
What is differential staining? Give an example.
Differential staining uses different stains to distinguish between types of cells or structures.
Example: Gram staining differentiates between Gram-positive and Gram-negative bacteria based on their cell wall structure.
Describe the steps of Gram staining.
Apply crystal violet (primary stain) to heat-fixed bacterial smear.
Add iodine (mordant) to fix the stain.
Wash with alcohol or acetone (decolorizer).
Gram-positive bacteria retain crystal violet (appear purple). Gram-negative bacteria lose crystal violet.
Counterstain with safranin.
Gram-negative bacteria take up safranin (appear red/pink).
Explain why Gram staining works.
Gram-positive bacteria have thick peptidoglycan layers, which retain crystal violet.
Gram-negative bacteria have thinner walls and an outer lipid membrane that dissolves in alcohol, losing the violet stain.
What is the definition of magnification & resolution
Magnification: How enlarged an image is compared to the original image
Resolution: How well microscope distinguishes between 2 points close together
