Edexcel - B2

Edexcel - B2

1. Topic One - Genes and Enzymes

   • Cells and Microscopy
     • Pant and Animal cells have similarities and differences
       • Similarities:
         • Nucleus - Contains DNA, controls what the cell does
         • Cytoplasm - gel-like substance where most reactions happen
         • Cell Membrane - holds cell together, controls what enters and leaves
         • Mitochondria - where most respiration takes place
       • Differences - only plant cells
         • Rigid Cell Wall - made of cellulose, provides support
         • Large Vacuole - contains cell sap
         • Chloroplasts - where photosynthesis occurs, contain chlorophyll
     • Bacterial Cells
       • They are much smaller than plant or animal cells
         • Chromosomal DNA - one long circular chromosome, controls activities and replication, floats free in cytoplasm
         • Plasmids - small loops of extra DNA, contains genes for things such as drug resistance, passed between bacterial
         • Flagellum - hair like structure that rotates to move the cell
         • Cell Wall - provides support for the cell
     • Cells are studied using microscopes
       • Light microscopes - 1590s, see nuclei, chloroplasts, mitochondria
       • Electron microscopes - 1930s, smaller things in more detail, internal structure of mitochondria and chloroplasts, plasmids
       • Calculate magnification - length of image/length of specimen