Question

Name two cell organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.

Answer 1

There are many cell organelles which are membrane-bound, The two organelles which have double membrane are the mitochondria and choloroplast.

Mitochondria

• Are sausage or cylindrical-shaped organelles found in cytoplasm
  
• Are the sites of aerobic respiration (complete breakdown of glucose to release energy)
  
• Number and size varies.
  
• Has 2 membranes; outer membrane and inner membrane
  
• Inner membrane forms a number of infoldings called the cristae
  
• Cristae contains many enzymes required for forming ATP (storage form of energy inside a cell)
  
• Fluid-filled space inside the mitochondria is called the matrix
  
• Matrix contains a circular DNA, few RNA molecules and ribosomes (70S).
  
• Are also called the powerhouses of the cell (because they generate energy required for the cell and store it in the form of ATP)
  
• Are semi-autonomous (They have their own DNA and replicate on their own and can also synthesize most of its proteins)
  

Chloroplast

• They are mainly present in the in leaf epidermal cells.
• They are cylindrical-shaped organelles
• They are the sites of photosynthesis
• They have 2 membranes; outer and inner membrane
• The fluid-filled internal space is called the stroma
• The stroma contains thylakoids which contain the pigments chlorophyll and carotenoids.
• The stroma also contains a circular DNA, few RNA molecules and ribosomes (70S).