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24 Cards in this Set
- Front
- Back
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What is the purpose of cell fractionation? |
To break open cells and obtain isolated organelles |
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Why is a tissue placed in a cold, isotonic, buffer solution? |
Cold - reduce enzyme activity that breaks down cells Isotonic - prevent bursting/ shrinking Buffered - maintain constant pH |
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What is a homogenation? |
Cells broken up in homogeniser to release organelles from cell, Homegenate filtered to remove cells/debris - filtrate |
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What occurs in an ultracentrifuge? |
Filtrate separated - spun at high speeds Low speed - most dense - nuclei - form pellet - removed when decanted |
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What is removed during ultracentrifuge at medium and high speeds? |
Medium - mitochondria and chloroplasts High - ER, golgi Extra high - ribosomes |
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What remains in the supernatant? |
Organelle-free cytoplasm |
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What is full proccess of cell fractionation? |
Tissue in cold, isotonic buffer Homogenation Filtered Separated in ultracentrifuge Forms varying pellets |
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Actual size = |
Image size / magnification |
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How do you calculate cell size? |
Measure image in millimetres Convert measurement to unit used in question Divide image by magnification |
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What is magnification? |
How much bigger an image is than the actual object |
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What is resolution? |
Smallest distance at which two seperate objects can be seen |
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What are the features of a light microscope? |
Uses light to observe live/dead cells w/o detailed structures Poor resolution/ magnification Light micrographs - colour |
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Why does a light microscope have poor resolution? |
Light has a long wavelength |
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What are the features of an electron microscope? |
Use electrons to view dead cells + very detailed structures w/ high resolution + magnification Electron micrographs - b/w |
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Why does an electron microscope have high resolution? |
Electron beams have a very short wavelength |
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What are the limitations of electron microscopy? |
Electron beams scattered by air particles so vacuum - dead cells Thin embedded specimens Damaging electron beam Heavy metal stains interfere with structure Artefacts - created structures |
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What is transmission electron microscopy? |
Electron beam passed through thin section of specimen which absorb electrons to appear dark |
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What are the limitations of transmission and scanning electron microscopy? |
Whole system must be in vacuum - only dead specimens Complex staining process Extremely thin - 2D images May contain artefacts |
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What is scanning electron microscopy? |
Electron beam directed onto surface of specimen then passed back/forth in regular pattern, scatters depending on surface contours 3D images - lower Res - not thin |
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What are the independent and dependent variables when investigating water potential of a piece of tissue? |
I.V : conc. of sucrose solution D.V: change in mass (%) |
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What are some control variables when investigating water potential of a piece of carrot? |
Type of tissue Surface area Bung on test tube Length of time left in solution Blotting tissue with paper Temperature (thermostatically controlled water bath) Solution volume/ touching sides |
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Why is mass change processed into % mass change? |
Allows comparison with a range of starting masses |
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How would you use data to estimate the water potential of the tissue? |
Plot graph Draw line of best fit At point where there is no mass change = conc of sucrose Use resources to find w.p of sucrose conc |
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What benefits does recording closer results have? |
Reliable means Reduced number of anomalous results Increased accuracy |
