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.
(diagrams) Labelled diagrams should show: For Mitochondria—outer membrane, inner membrane, cristae, matrix, outer compartment, inner compartment. For Chloroplast—outer membrane, inner membrane, grana, stroma.
(mitochondria_characteristics) Mitochondria are bound by a double membrane. The outer membrane is smooth and forms the continuous limiting boundary. The inner membrane divides the lumen into two aqueous compartments—the outer compartment and the inner compartment. The inner membrane forms infoldings called cristae towards the matrix, which increase the surface area. The inner compartment contains a dense homogeneous substance called the matrix. The matrix possesses a single circular DNA molecule, a few RNA molecules, ribosomes (70S), and components required for protein synthesis.
(mitochondria_functions) Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called 'power houses' of the cell. The two membranes have their own specific enzymes associated with mitochondrial function. Mitochondria divide by fission.
(organelles) The two double membrane bound cell-organelles are Mitochondria and Plastids (Chloroplasts).
(plastids_characteristics) Plastids are pigment-containing organelles found in plant cells only. Chloroplasts are a type of plastid. They contain grana, which is the site of light reactions, and stroma, which is the site of dark reactions. Like mitochondria, they contain their own DNA and ribosomes.
(plastids_functions) Chloroplasts are responsible for trapping light energy essential for photosynthesis in plant cells.
Explanation
This question tests the student's understanding of membrane-bound organelles. Mitochondria and plastids are the only two double membrane-bound organelles mentioned in the NCERT context. The answer covers their structural characteristics (double membrane, cristae, matrix, grana, stroma) and their functions (ATP production and photosynthesis). Both organelles have their own DNA and ribosomes, indicating their semi-autonomous nature.
Solution Steps
Step 1: Identify the two double membrane-bound organelles from the context—Mitochondria and Plastids.
Step 2: Describe the structural characteristics of mitochondria including outer membrane, inner membrane, cristae, and matrix.
Step 3: State the functions of mitochondria—aerobic respiration and ATP production.
Step 4: Describe the characteristics of plastids/chloroplasts including grana and stroma.
Step 5: State the functions of chloroplasts—trapping light energy for photosynthesis.
Step 6: Mention the labelled diagrams showing key structures of both organelles.