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AS OCR…read more

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Magnification and Resolution....
Magnification: Degree to which the image is larger than the object itself
Resolution: Degree to which it is possible to distinguish between two objects, the higher the
resolution the greater the detail.
Light Microscope Maximum magnification of x1500 Maximum resolution of 200nm
Transmission Electron Microscope Maximum magnification of x500 000 Maximum
resolution of 0.20nm
Scanning Electron Microscope Maximum magnification of x250 000 Maximum resolution
of 0.20nm
Staining and Sectioning
Staining: Chemicals that bind on or in the specimen, making it easier to be seen under the
Sectioning: Some tissue such as Brain is embedded in wax, making it easier to cut.
Linear Magnification
It is possible to work out the magnification of a image, or the actual size of a cell with this
formula A = I/M
Actual Size = Image Size over Magnification rearranging this formula can give the Image
size; I = A X M…read more

Slide 3

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Rough endoplasmic reticulum: Contains ribosomes which are the site of protein synthesis
Smooth endoplasmic reticulum
Carries out synthesis of lipids
Golgi apparatus: A stack of membrane bound vesicles. Packages macromolecules for transport
around the cell
Mitochondria: A double membrane bound organelle which is involved in aerobic respiration.
Inner membrane forms folds called cristae to increase surface area of membrane. An the
cristae, glucose is combined with oxygen to produce ATP.
Lysosomes: Contains hydrolytic enzymes which in a white blood cell, digest bacteria. Enzymes
are contained in the lysosomes to prevent necrosis (cell death)
Chloroplasts: Contain chlorophyll. Have a double outer membrane. Within the stoma there are
other membrane structures called grana where photosynthesis takes place
Plasma membrane: A phospholipids bilayer containing proteins. These proteins include
receptors, pores and enzymes. Responsible for controlled entry of water and minerals
Nuclear envelope: A double membrane around the nucleus containing nuclear pores which
allow exchange between the nucleus and the cytoplasm
Centriole: A hollow cylinder about 0.4µm long formed from a ring of microtubules which are
used to grow the spindle fibres used in nuclear division
Nucleus: Contains DNA responsible for the individual characteristics of each cell. DNA is
similar in all cells but depending on which type of cell it is, some genes maybe turned on or
off. Division of the nucleus proceeds cell division
Nucleolus: Inside the nucleus. Produces ribosomes which leave the nucleus to take positions on
the rough endoplasmic reticulum
Cilia: Move in a co-ordinated manner, each slightly out of phase with its neighbour so
substances around the cell are made to move.…read more

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Prokaryotic ...
Average diameter = 0.5-20µm
Circular DNA lies free in cytoplasm
Naked DNA
Slightly smaller ribosomes (18nm)
Very few organelles none of which are surrounded by
Cell wall present…read more

Slide 5

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Eukaryotic ...
Often up to 40µm and 1000-10000 x the volume of
DNA not circular and contained in nucleus
DNA associated with protein forming chromosomes
Slightly larger ribosomes (22nm)
Many organelles, many are bounded by a membrane
Cell wall only present in plant cells…read more

Slide 6

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Types of tissue...
1. Squamous epithelium: Individual cells are
smooth, flat and very thin. The cells fit together
to provide a smooth, low-friction surface. E.g.
alveoli ­ thinness allows rapid diffusion
2. Ciliated epithelium: A single layer of tall cells all
reaching to the basement membrane. Sometimes
also contains cilia. E.g. lining of bronchus…read more

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