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.

Explanation

Two double membrane bound organelle are mitochondria and chloroplasts.
(i) Mitochondria :
For diagram see section-A, Q. No. 20.
Each mitochondrion is a double membrane bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments i.e. the outer compartment and the inner compartment.
The inner compartment is called the matrix. The outer membrane forms the membrane of continuous limiting boundary of organelle. The inner membrane forms a number of infoldings called the cristae towards the matrix. The cristae increase the surface area.
The two membranes have their own specific enzymes associated with the mitochondrial function. Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP.
(ii) Chloroplasts :
For diagram see section-A, Q. No. 22.
Chloroplasts is also a double membrane bound structure like mitochondria. Of the two the inner chloroplast membrane is relatively less permeable. The space limited by the inner membrane of the chloroplast is called the stroma. A number of organised flattened membranous sacs called the thylakoids are present in the stroma.
There are some flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana. The membrane of the thylakoids enclose a space called a lumen.
The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.