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AS/A2 Biology AQA Specification A Module 1 Rashpal Chana September 2004

AS/A2 Biology AQA Specification A Module 1 Rashpal Chana September 2004. Cell seen by Light Microscope Cell seen by Electron Microscope. Microscopy Three types: Transmission Electron – electrons transmitted through specimen  can see internal organelles

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AS/A2 Biology AQA Specification A Module 1 Rashpal Chana September 2004

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  1. AS/A2 Biology AQA Specification A Module 1 Rashpal Chana September 2004

  2. Cell seen by Light MicroscopeCell seen by Electron Microscope

  3. Microscopy Three types: Transmission Electron – electrons transmitted through specimen  can see internal organelles Scanning Electron – electrons bounce off from surface of specimen  can see external features Light Microscope – Uses photons of white light

  4. Structure & Function Organelles found in Cells (Eukaryotic) • Endoplasmic Reticulum (ER) • An internal transport system made of cavities about  4nm • All cavities interconnect, and interconnect with the Nuclear Membrane • There are two types: • Rough ERSmooth ER • Flattened cavities * Tubular cavities • Encrusted with Ribosomes on the * Not encrusted with cytoplasm side. Ribosomes • Function: • Isolates & Transports Proteins Synthesis & Transport of Lipids & Steroids

  5. Golgi Body • Series of flattened cavities, lying parallel to one another, having vesicles pinching of the ends of the cavities. • Function: • Synthesis of Glycoproteins • Packages Glycoproteins in membrane-bound vesicles • Note: Cells actively involved in Glycoprotein Production (enzymes), or actively involved in secretory function have large prominent Golgi body

  6. Mitochondrion • In Animal Cells Rod Shaped, in Plant Cells, • Round Shaped. • Bound by double membrane • 1µm in , 2.5µm in length. • Inner Membrane highly folded to form a number of projections called CRISTAE. • Function: Sites of Energy (ATP) Production; Site of Respiration. • Cells actively involved in functions requiring large amounts of energy will have many mitochondria. • Ribosomes • 20nm in  • Made in the Nucleolus, migrate to cytoplasm via nuclear pores • Made up of 2 subunits of RNA • May be attached to ER or lie freely in cutoplasm. • May be in small clusters (called Polysomes) • Function: Sites of Protein Synthesis

  7. Nucleus • Usually Largest Organelle • Contains the Genetic Material, DNA which is attached to Proteins called Histones • Surrounded by double membrane, called Nuclear Membrane. • Nuclear Membrane has many Nuclear Pores 50-100nm in  • When the cell is not dividing, genetic material appears as tiny granules called Chromatin. • Function: Contains the Genetic Material responsible for protein synthesis, cell division etc.

  8. Lysosomes • Spherical Organelles 1 - 2.5µm in  • Contain enzymes (Hydrolases) • Function: Involved in Extracellular or Intracellular digestion, • can also cause Autolysis. • Plant Cell Wall • Consists of fibres of cellulose, which lie parallel to one another. • Each fibre consists of repeated  Glucose units • Hydrogen Bonds between the fibres form Cross Bridges • Width of about 10µm • Function: Very Tensile & tough structure, which maintains cell shape, prevents plant cells from bursting or shrinking. • Note Cell Wall in Fungi is NOT cellulose. Instead, Muco-polysaccaride layer

  9. Chloroplasts • Found in Photo-autotrophic organisms only. • Bi-Convex Lens shaped. • 2-3 µm • 4-10µm • Originate from simple organelles called Proplastids. • Inside the Cytoplasm (Stroma), is a system of layers of membranes called Grana. • Grana made up of Thylakoid membranes, which contain light absorbing pigments. • Stroma is an organic matrix of proteins, nucleic acids, DNA and enzymes. • Following a period of illumination, Photosynthesis takes place, and Starch Grains & Lipid Globules appear. • Function: Photosynthesis takes place in these organelles.

  10. Cilia / Flagella • Involved in movement • About 0.1 µm in  • Cilia, up to 1 µm in length, flagella up to 10 µm • Many cilia present, whereas, usually only 1 flagella • Eukaryotic cells have ‘9+2’ microtuble structure • Prokaryotes have ‘9+0’

  11. Cell / Plasma Membrane • Under the light microscope seen as two dark lines separated by a lighter layer. • Middle lighter layer made up of a Phospholipid-Bilayer • Each Phospholipid has hydrophilic head and hydrophobic tails. • Heads point outwards (may have carbohydrates attached, Glycolipid), tails interact with each other in the middle • Tails are long chains of hydrocarbons, and may have single or double bonds, between carbon atoms. • Double bonds (Unsaturated), means tails ‘kink’, causing more gaps between phospholipids,  membrane is ‘fluid’ • Proteins found throughout bilayer. Three types: • Carrier Proteins – span right through bi-layer, involved in transport • Extrinsic Proteins – on outer surface, may have carbohydrates attached (Glycoproteins) • Intrinsic Proteins – on cytoplasm side

  12. Proteins can move in between the phospholipids. • Cholesterol also found in between the bi-layer, causes rigidity. • 7.5nm width

  13. Ultrastructure of a Eukaryotic cell

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