Organelles

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Nucleus

Structure- 

  • Largest organelle.
  • When stained shows darkened patches-kromatin
  • Surrounded by nuclear envelope
  • Made of two membranes with fluid between them.
  • Holes called nuclear pores- go through envelope.
  • Allow relitively large moilecules to pass through
  • Dense, spherical structure (nucleolous) inside nucleus. 

Function- 

  • Houses nearly all cells genetic information. 
  • Chromatin consists of DNA and proteins- instuctions for making proteins.
  • Some proteins regulate cells acivities. 
  • When cells divide chromatin condenses into visible chromosomes.
  • Nucleolous makes RNA and ribosomes.
  • These pass into cytoplasm and proteins are assembled at them. 


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Endoplasmic reticulum

Structure- 

  • Consists of series of flattened membrane bound sacs called cisternae.
  • Continuous with outer nuclear membrane. 
  • Rough endoplasmic reticulum is studded with ribosomes. 
  • Smooth endoplasmic reticulum is not. 

Function-

  • Rough ER transports proteins that were made on the attatched ribosomes. 
  • Some of these proteins may be secreted from cell. 
  • Some will be placed on cell surface membrane. 
  • Smooth ER is involved in making lipids the cell needs. 
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Golgi apparatus

Structure-

  • Stack of membrane bound flattened sacs. 

Function- 

  • Recieves proteins from ER and modifies them 
  • May add sugar molecules to them.
  • Packages modified proteins into vesticles to be transported. 
  • Some modified proteins may go to the surface of cell to be secreted 
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Mitochondria

Structure-

  • May be spherical or sausage shaped.
  • Two membranes seperated by fluid. 
  • Inner membrane is highly folded to form cristae.
  • Central part of mitochondria is matrix.

Function- 

  • Where ATP is produced during respiration.
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Chloroplasts

Structure- 

  • Found only in plant cells and cells of some protoctists. 
  • Two membranes seperated by fluid filled space. 
  • Inner membrane is continuous with elaborate network of flattened membrane sacs called thylakoids.

Function-

  • Site of photosynthesis in plant cells.
  • Light energy is used to drive the reactions of photosynthesis.
  • From this carbohydrate is made from water and carbon dioxide.
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Lysosomes

Structure- 

  • Spherical sacs surrounded by single membrane.

Functions-

  • Contain powerful digestive enzymes that break down materials. 
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Ribosomes

Structure- 

  • Tiny organelles
  • Some in cytoplasm and some are bound to ER.
  • Each ribosome consists of two subunits. 

Function-

  • Site of protein synthesis in the cell. 
  • Act as assembly line where coded information (mRNA) from nucleus is used to assemble proteins from amino acids. 
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Centrioles

Structure- 

  • Small tubes of protein fibres (microtubules) 
  • pair of them next to nucleus in animal cells and cells of some protocists. 

Function- 

  • Take part in cell division
  • Form fibres known as the spindle 
  • Move chromosomes during nuclear division.  
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