AS biology new spec cells

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Cells

·         microscopes are used to produce a magnified image of an object. A convex lens with light makes a light microscope but the long wavelength of light makes resolution low, 0.2µm.

·         the material put under the microscope is the object and the view under the microscope is the image.

·         magnification is how many times bigger the image is compared to the object. Size of image/ size of real object.

·         To work out magnification, you need both to be in the same unit. Nm= 10-9 m, µm= 10-6 m, mm= 10-3 m

·         Resolution is the minimum distance apart 2 objects can be to be seen separate.

·         Cell fractionation is the process of breaking up cells so the organelles can be separated out.

·         First you need to break up the tissue in cold (to reduce enzyme action breaking down organelles), isotonic (to prevent bursting or shrinking), buffer (so the pH doesn’t fluctuate altering enzymes or organelles) solution. Then homogenisation is needed to release the organelles from the cell. This done in a homogeniser and the homogenate produced is filtered to remove large debris and unbroken cells.

·         Ultracentrifugation spins the homogenate at high speeds, creating centrifugal force. It is first spun at 1000 gs for 10 minutes, producing a nuclei pellet and then the supernatant is spun at 3500gs to get a mitochondria pellet and then the supernatant is spun at 16500 gs to get lysosomes.

·          Electron microscopes are better than light microscopes as electron beams have short wavelengths so they have a higher resolving power and as electrons are negatively charged, the beam can be focused using electromagnets.

·         Transmission electron microscope is an electron gun that produces a beam of electrons focused by a condenser electromagnet. The beam passes through a thin specimen and parts absorb them making them appear darker and the image is produced on a screen giving photomicrograph.

·         Limitations are that the difficulties preparing the specimen limits the resolving power, the high-energy electron beam can destroy the specimen, it must be in vacuum so no live specimens, there is a complex staining process and the image is not in colour, the specimen must be thin and artefacts from the preparing if the specimen may be seen on the photomicrograph. Also, images are only in 2D. however the resolving power is 0.1nm.

·         With scanning electron microscopes, a beam of electrons passes back and forth over a section of the specimen causing them to be scattered and this pattern depends on the contours of the specimen. This means that 3D images can be created. However, SEM has a resolving power of 20nm.

·         To measure the size of objects, you can use an eyepiece graticulate ion light microscopes. It must be calibrates using a stage micrometre.

·         Eukaryotic cells have a nucleus and membrane bound organelles. They have ultrastructure’s that depend

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