2 Cells- Methods of studying cells Flashcards
What is magnification?
How many times bigger the image of a specimen observed is in compared to the actual (real-life) size of the specimen.
How is magnification calculated?
Size of image/ size of real object
What is resolution?
The ability of a microscope to distinguish two adjacent structures as separate. Higher resolution = better clarity and detail of image
What does cell fractionation do?
Separates organelles according to size, so they can be studied in an electron microscope
What are the steps of cell fractionation?
1.)Homogenisation
The tissue sample is homogenised in a blender to break the cells in ice cold, isotonic and buffered solution
2.)Filtration
The tissue sample is filtered into tubes through a gauze, separating larger components from smaller ones
3.) Ultracentrifugation
Samples are spun at a low speed in centrifuge , this separates the sample into fractions, heavier at the bottom, lighter on top.
4.)Cell debris forms a pellet at bottom, leaving a supernatant above with organelles. This is poured off and centrifuged at a higher speed to separate the next highest organelle. This is repeated at increasingly higher speeds
Why is the homogenised tissue sample kept in specific conditions?
Ice cold= reducing enzyme activity that could damage organelles
Isotonic solution= Prevents osmosis, could shrink or bust organelles
Buffered solution= Keeps pH constant, avoids damage to protein structure
What is the order of fractionation?
Heaviest to lightest:
-Nucleus
-Chloroplast
-Mitochondria
-Lysosomes
-Endoplasmic Reticulum
-Ribosomes
How do optical (light) microscopes work?
-Visible light passes, is bent through the lens so the user can see the specimen
-The specimen can be alive
-Individual cells are generally transparent and components aren’t distinguishable unless stained, which usually kills cells
What are the uses of light microscopes?
-Most student microscopes
- Max resolution is 0.2 micrometres
-Nucleus and mitochondria can be seen
-Max magnification is x1,500.
How do electron microscopes work?
-Beam of electrons passes through the lens, not beam of light
-Higher magnification and resolution (more detail seen)
What are the uses of electron microscopes?
-Max resolution 0.0002 micrometers (1000 times more than light)
-Max magnification is x1,500,000
What is a transmission electron microscope (TEM) ?
A type of electron microscope, where the electron beam penetrates the cell and provides details of a cell’s internal structures
-Use electromagnets to focus the electron beam
-High resolution
-Internal structures like chloroplasts can be seen in thin specimens
What is a scanning electron microscope (SEM)?
A type of electron microscope, where a beam of electrons moves back and forth across a cell’s surface , creating details of its characteristics
-Knock electrons off specimen which come together to form an image
-Can be 3D images
-Don’t have to be thin specimens like in TEM
-Lower resolution than in TEM
What is an artefact and how are they created?
Occur in various forms during specimen or slide preparation, from:
-Trapped air bubbles
-Folds in thin specimen slices
-Contamination from other cells/tissues
