Q.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.
Mitochondria and chloroplasts are the two organelles that are double-membrane-bound.
Characteristics of Mitochondria are:
→ 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.
→ Each mitochondrion is a double membrane bound structure with the outer membrane and the inner membrane dividing its lumen distinctly into two aqueous compartments,- outer and inner compartments.
→ The outer membrane forms the continuous limiting boundary of the organelle.
→ The inner membrane forms a number of infoldings called the cristae towards the matrix.
→ 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 are:
→ They are the sites for aerobic respiration.
→ They provide energy in the form of ATP for all vital activities of living cells.
→ They have their own DNA and ribosomes. Hence, they are regarded as semi-autonomous organelles.
→ They have several enzymes, intermediately required for the synthesis of various chemicals such as fatty acids, steroids, and amino acids.
→ The Chloroplasts are also double membrane bound organelles.
→ A number of organized flattened membranous sacs called the thylakoids are present in the stroma.
→ Thylakoids are arranged in stacks-like the piles of coins called grana.→ In addition, there are 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.
Functions of Chloroplast are:
→ They trap solar energy and utilise it for manufacturing food for plants. Hence, they are involved in the process of photosynthesis.
→ They contain the enzymes required for the synthesis of carbohydrates and proteins.