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PLANT CELLS
Cellulose cell wall surrounds cell membrane
Chloroplasts present (not in roots)
Large central vacuole
Carbohydrates stored as STARCH
ANIMAL CELLS
No cell wall
No chloroplasts
No large central vacuole
Carbohydrates stored as GL
Algal cells
Contain flagella so they are motile
Contain a chloroplast for photosynthesis
Cell wall made of cellulose
Fungal cells
Multicellular or unicellular. They have a cell wall made up of chitin and contain nochloroplast. Fungi are made up of long thin strands called hyphae increasing their surface area for theabsorption of water and ions.
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Cell differentiation
Groups of specialised cells form tissues and groups of tissues form organs
Structure of prokaryotes
Prokaryotic means 'before nucleus'. Prokaryotes do not have nuclei or other membrane boundorganelles. The DNA of a prokaryotic cell is circular, found free the cytoplasm, and it is notassociated with proteins. Bacteria are prokaryotic cells.
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Viruses
Viruses are acellular (do not contain cells or is not made up of cells) and are non-living microorganisms. The capsidprovides the virus with a protective outer coat and surrounds the viral DNA or RNA.
Magnification
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Optical microscopes
Optical uses glass lenses and light to view both dead and living specimens. Specimens can be viewedin colour. As light is used, light has a longer wavelength than electrons, so the light microscope has alower resolution compared to the electron microscopes.
Transmission electron microscope
Principles:
Electrons pass through / enter (thin) specimen. TEM focuses using magnets. The denser partsabsorb more electrons so appear darker. Electrons have short wavelength so give high resolution,higher than a scanning electron microscope and so smaller organelles can be seen and withgreater detail.
Limitations:
1. Cannot look at living material as the specimen must be in a vacuum;
2. Specimen must be (very) thin;
3. The preparation of specimen could lead to the production of artefacts
4. Complex staining method / complex / long preparation time;
5. Only 2D images produced.
Scanning electron microscope
Thin sections do not need to be prepared. The SEM shows surface of specimen and a 3-D imageis formed.
Preparing a temporary mount:
1. Thin slice/section;
2. Put on slide in water / solution / stain;
3. Add cover slip;
The rules of producing a scientific drawing.
1. No sketching
2. No overhanging or crossed lines
3. No shading
4.. Must look similar;
5. Correctly labelled;
6 Correct scale stated
Cell fractionation and Ultracentrifugation
1. Cell homogenisation to break open cells.
2. Filter to remove (large) debris / whole cells.
3. Use isotonic solution to prevent damage to the organelles.
4. Keep cold to reduce damage by enzymes and use a buffer to prevent protein / enzyme denaturation.
5. Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments / heavy organelles.
6. Re-spin (supernatant / after nuclei / pellet removed) at higher speed to getmitochondria in pellet / at bottom.
