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  • Living things are made of cells
  • 1 celled organisms are unicellular
  • 2 or more celled organisms are multi cellular
  • All multi cellular organisms are made of eukaryotic cells



  •  2 types of microscope
  • Light microscope and electron microscope
  • Microscopes work by refracting the light that has passed through an object
  • The light microscope refracts the light rays passing through an object. It has an eyepiece and objective lenses. The light microscope can see individual cells but not structural detail.


  • Found in both plant and animal cells
  • Surrounded by a nuclear envelope. This consists of 2 unit membranes that are perforated by nuclear pores. This allows the exchange of substances between the nucleus and cytoplasm. 
  • Contains chromatin which is composed of coils of DNA bound to proteins called histones.
  • Contains a nucleoplasm which contains a variety of chemical substances such as ions, proteins and nucleotides.
  • Contains a nucleolus which produces rRNA from which ribosomes are assembled.

Endoplasmic Reticulum

  • A complex network of membrane bound cavities called cisternae.
  • May have vesicles, tubules, sacs and layers.
  • Rough ER is covered with ribosomes. These are the sites of protein synthesis. The rough ER temporarily stores and transports the proteins that are made by the ribosomes
  • Smooth ER has no ribosomes attached. They are tubular and they synthesise lipids including steroids. 


  • Small, dense granules scattered through the cytoplasm and on the rough ER's surface.
  • Consist of 2 sub-units each containing RNA and protein
  • The two sub-units combine with each other in the presence of mRNA.
  • The ribosome moves alone the mRNA in translation during which a polypeptide chain is formed
  • Free ribosomes produce proteins for use in the cytoplasm whereas ribosomes bound to the rough ER synthesise proteins which are exported out of the cell


  • Small, hollow cylinders
  • Found in animal cells and in lower plant cells
  • Occur in pairs and the two units lie at right angles to each other
  • They are found in the centrosome in the cytoplasm.
  • Each centriole is made up of 9 groups of microtubules arranged in triplets.
  • They play a part in cells division and are involved in the formation of the nuclear…


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