Ocr Biology F211

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Cells, Exchange and Transport
Cells (a) state the resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope; Resolution Magnification Light microscope 200nm x1,500 Transmission Electron Microscope 0.1nm x500,000 Scanning Electron Microscope 0.1nm X100,000 (b) explain the difference between magnification and resolution; Magnification is the degree to which the size of an image is larger than the image itself. Resolution is the degree to which it is possible to distinguish between two objects that are very close together. (c) explain the need for staining samples for use in light microscopy and electron microscopy; A lot of biological material inside a cell isn’t coloured, so it might be difficult to distinguish between different features. Coloured stains are used to stain specimens for use with the light microscope. Chemicals which bind to other chemicals on, or in, the specimen, which allows the specimen be to seen. Some chemicals bind to specific structures, such as Acetic orcein staining DNA red. Electron micrographs start off black and white, with the colour being added by a specialised computer program afterwards. (d) calculate the linear magnification of an image; Image size =Actual size x Magnification I



(e) describe and interpret drawings and photographs of eukaryotic cells as seen under an electron microscope and be able to recognise the following structures: Nucleus, Larges organelle. Nucleolus, Dense, spherical structure inside nucleus Nuclear envelope, Surrounds the nucleus Rough and smooth endoplasmic reticulum (ER), Continuous with the nuclear envelope. RER is studded with ribosomes, SER is not. Golgi apparatus, Stack of membrane-bound flattened sacs Ribosomes, Tiny. Some are in the cytoplasm and some are bound to the RER Mitochondria, Spherical or sausage shaped. Double membrane. Lysosomes, Spherical sacs. Single membrane. Chloroplasts, Only in plant cells. Two membranes. Contain Thylakoids. Plasma (cell surface) membrane, Phospholipid bilayer Centrioles, Small tubes of protein fibres. Pair of them next to Nucleus in Animal cells. Flagella and cilia; Hair-like extensions projecting from the surface of a cell.


June 10

Cells, Exchange and Transport
(f) outline the functions of the structures listed in (e); Nucleus, Houses all of the cell’s genetic material in the form of DNA, which contains the instructions for protein synthesis. Nucleolus, Makes ribosomes and RNA which pass into the cytoplasm and are used in protein synthesis Nuclear envelope, A double membrane with nuclear pores. Rough endoplasmic reticulum, Transports proteins made by the attached ribosomes. Smooth endoplasmic reticulum (ER), Involved in the making of lipids. Golgi apparatus, Modifies proteins received from the Rough ER and then packages them into vesicles so they can be transported. Ribosomes, Site of protein synthesis. Mitochondria, Where ATP is made. Lysosomes, Contain digestive enzymes that are used to break down material Chloroplasts, Site of photosynthesis in plant cells. Plasma (cell surface) membrane, Controls the entry and exit of substances into and out of the cell. Centrioles, Form the spindle which moves chromosomes during cell division. Flagella and cilia; Move by ATP. E.g. wave mucus along trachea or make sperm swim. (f) outline the interrelationship between the organelles involved in the production and secretion of proteins (no detail of protein synthesis is required); 1. The gene containing the instructions for the production of the hormones is copied onto a piece of mRNA 2. mRNA leaves the nucleus through the nuclear pore. 3. mRNA attaches to a ribosome 4. Ribosome reads the instruction to assemble the protein 5. Molecules are ‘pinched off’ in vesicles and travel towards the Golgi Apparatus 6. Vesicle fuses with Golgi Apparatus 7. Golgi apparatus processes and packages the molecules, ready for release 8. The...
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