AS Biology Unit 1 - Cells and movement in and out of them

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What is the material that is put under the microscope referred to as?
The object
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What is the appearance of the object when viewed under a microscope called?
The image
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What is magnification?
How many times bigger the image is when compared to the object
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How do you work out magnification?
Size of image DIVIDED by size of object
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Using manification, what is the equation to work out the size of the object?
Size of image DIVIDED by manification
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What is important to remember when completing calculations around manifications?
That all the units are the same
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What is resolution?
Minimum distance apart that two objects can be in order to appear seperate objects
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What does resolution depend on?
The wavelength or form of radiation used
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What will increasing the manification do?
Increase the size of the image but not always the resolution
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What is the process where cells are broken up and the different organelles they contain are seperate out
Cell fractionation
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What must happen to the tissue before cell fractionation?
It must be placed in a cold isotonic buffer solution
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What does the cold, isotonic buffer solution do?
Cold - reduce enzyme activity that might break down organelles, isotonic - prevent organelles bursting or shrinking due to osmotic gain or loss of water (isotonic solution has same water potential as tissue) buffered - maintain constant pH
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What is Homogenation?
Cells are broken up by a homogeniser (blender) which releases organelles from the cells
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What is Ultracentrifugation?
Process by which the fragments in the filtered homogenate are sperated in machine called a ultracentrifuge
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Explain the process of Ultracentrifugation
The tube of filtrate is placed in the untracentrifuge and spun at low speed, the heaviest organelles are forced to the bottom where they form a thin sediment, the supernatant (lightests) are transfered to another tube and that is spun again faster
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Name the order of the heaviest organelles to the lightest in an animal cell
Heaviest - Nuclei, Mitochondria, Lysosome and Ribsosomes
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Why do light microscopes have a poor resolution?
As they have long wavelengths of light
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Name the two advantages of an electron microscope
Electron beam has a very short wavelength so has high resolution, electrons are negatively charged so can be focused using electromagnets
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Name the two types of electron microscopes
TEM - Transmission electron microscope and SEM - Scanning electron microscope
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Describe how a TEM works
Trasmission electron microscope - Electron beam passes trhough object which absorbs electrons and appears dark, other parts allow them to pass through so appear light
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What are the limitations for a TEM?
Object cannot be living as has to be in a vacuum, image only in black and white due to staining, object must be thin to allow electrons through, images only in 2D
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Describe how a SEM works
It directs a beam of electrons onto surface of object from above, the beam is then passed back and forth scanning the object and creating a 3D image
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What is the difference between TEM and SEM in terms of resolution?
SEM has a lower resolution than TEM but still higher than a light microscope
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What is the appearance of the object when viewed under a microscope called?

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The image

Card 3

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What is magnification?

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Card 4

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How do you work out magnification?

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Card 5

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Using manification, what is the equation to work out the size of the object?

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