question_answer 7)

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:

Chloroplasts and mitochondria are double membrane bound organelles. Characteristics of Mitochondria (i) The mitochondria are sausage-shaped or cylindrical having a diameter of 0.2-1.0 µm and average 0.5 µm and length 1.0-4.1 µm. (ii) Each mitochondrion is a double membrane bound structure. (iii) The inner compartment is called the matrix. The outer membrane of mitochondria forms the continuous limiting boundary of the organelle. (iv) The inner membrane forms a number of infoldings called the cristae (single crista) towards the matrix. The cristae increase the surface area. (v) The two membranes have their own specific enzymes associated with the mitochondrial function. The matrix of mitochonrdria also possess single circular DMA molecule, a few RNA molecules, ribosomes (70 S) and the components required for the synthesis of proteins. Functions of Mitochondria Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are known as, 'power house of the cell.'     Characteristics of Chloroplasts (i) The Chloroplasts are also double membrane bound organelles. (ii) The space limited by the inner membrane of the chloroplast is called the stroma.             (iii) A number of organized flattened membranous sacs called the thylakoids are present in the stroma. (iv) Thylakoids are arranged in stacks-like the piles of coins called grana. (v)  In addition, there are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana. (vi) The stroma of the thylakoids enclose a space called a lumen.