OCR AS Biology unit 1 summarised

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AS Biology: OCR Syllabus Module 1.1.1
3.1 AS Unit: Cells, Exchange and Transport
Module 1: Cells
1.1.1 Cell Structure
Candidates should be able to:
(a) state the resolution and magnification that can be achieved by a light microscope, a transmission
electron microscope and a scanning electron microscope;
Transmission Electron Scanning Electron
Light Microscope
Microscope Microscope
Resolution 0.2 (200nm) 0.2nm 0.2nm
Magnification ×1500 / 2000 Over 500 000 250 000
(b) explain the difference between magnification and resolution;
Resolution "the ability of an optical system to distinguish between two adjacent
objects"
Magnification increases the apparent size of an object"
Resolving power "the degree of detail that can be seen with a microscope"
The resolving power is inversely proportional to the wavelength of the
radiation used (i.e. the shorter the wavelength, the greater the
resolution).
(c) explain the need for staining samples for use in light microscopy and electron microscopy;
Stains: - most biological structures are transparent
- the stain gives a contrast between different structures
- the stain combines with certain chemicals in the structure
- Iodine solution: Starch blue-black
- Eosin solution: cytoplasm pink
- Feulgens agent
- Aceto-orcein agent DNA dark red / purple
(d) calculate the linear magnification of an image (HSW3);
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AS Biology: OCR Syllabus Module 1.1.1
5. Chloroplast Yes No photosynthesis
6. Rough endoplasmic
Yes Yes protein synthesis
reticulum
7. Smooth endoplasmic
Yes Yes synthesis of lipids
reticulum
modification and packaging of
8. Golgi apparatus Yes Yes
proteins
9. Centriole Yes Yes organises spindle during mitosis
10. Flagella Yes Yes locomotion
chemical sensation, signal
11.…read more

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AS Biology: OCR Syllabus Module 1.1.1
(i) compare and contrast, with the aid of diagrams and electron micrographs, the structure of
prokaryotic cells and eukaryotic cells;
Prokaryotic Cell
There may also be lipid or
glycogen granules within
the cell, so look out for
those!
(for Eukaryotic cell, see part (e))
(j) compare and contrast, with the aid of diagrams and electron micrographs, the structure and
ultrastructure of plant cells and animal cells
See part (f) for the difference between plant and animal cells.…read more

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AS Biology: OCR Syllabus Module 1.1.1
Cytoplasm
- subdivided
- the protoplasm is the name for all of the materials inside the cell membrane
- the cytoplasm is the name for all the material inside the membrane but not the
nucleus
- i.e. all the ground materials including organelles are in the cytoplasm
- the cytoplasm forms a cytoskeleton
o 90% water and inorganic salts and organic molecules
o organelles are absent in prokaryotic cells
Mitochondria
- size: 1 wide, 2.…read more

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AS Biology: OCR Syllabus Module 1.1.1
Golgi apparatus (a.k.a. Golgi body)
- series of complex tubules
- flattened cisternae
- present in cells which actively produce enzymes
- modify and package proteins produced by ribosomes
- e.g. carbohydrates are added to proteins in the golgi body ­ to become
glycoproteins, which are released into the cytoplasm and are fused with the surface
membrane to be released outside.…read more

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AS Biology: OCR Syllabus Module 1.1.1
ribosomal
Ribosomes
- composed of RNA (rRNA)
- each consists of 3 sub-units ­ one slightly larger
than the other ("cottage loaf" shape)
- assembles amino acids into proteins
- operates in conjunction with mRNA
- bound to endoplasmic reticulum
- often several ribosomes collectively (polysome)
- N.B. not all ribosomes are associated with the
endoplasmic reticulum. In growing cells or cells
that are making proteins for internal use, large numbers of ribosomes are found
free in the cytoplasm.…read more

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