Biology - Chatper 2 - microscopy and cell centrifugation

magnification definition

How much larger the image is compared to the object

resolution definition

the distance between the images in which they can be seen as seperate

compare optical(light) and electron microscope

1. light has low resolution (long wavelength) and electron has high resolution (short wavelength)

2. light can see images in colour and electron can see in black and white

3. light has low magnification and electron has high magnification

4. light can see living specimen and electron cant

describe transmission electron microscope and its strength & limitations

• creates 2D images using transmitted electrons - some parts of the specimen absorb electrons so it appears dark and some parts allow light to pass through so it appears light

• high resolution

• complex staining process

• cant see living specimen

• specimen has to be really thin

Explain why the scientist used very thin slices of alveolar tissue with the optical microscope (2)

• creates thin layer of tissue

• so light can pass through

describe scanning electron microscope and its limitations

• creates 3D images by detecting knocked off or reflected electrons

• lower resolution

• complex staining process

• cant see living specimen

how do you use a stage micrometer

• stage micrometer calibrates the eyepiece graticule

• line up stage micrometer and eyepiece graticule while looking down eyepiece

• count how many divisions on eyepiece graticule fit into 1 division on stage micrometer

describe and explain the solution used in cell centrifugation

• cold - prevents enzyme activity so organelles arent digested

• buffered - maintains pH so enzymes dont denature

• isotonic - prevents osmosis so organelles dont burst

describe the process of cell centrifugation

1. cell is homogenised in blender in cold, buffered, isotonic solution to break open cell

2. solution is filtered to remove complete cells

3. solution is centrifuged so organelles are separated based on density

(supernatant is removed from pellet and is centrifuged at higher speed)

order of density of organelles

1. nuclei

2. mitochondria and chloroplast

3. RER, SER, lysosome

4. ribosome