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Mitochondria and chloroplast are double membrane bound organelles. Mitochondria: Mitochondria are cylindrical or sausage shaped cell organelles and contains two membranes, outer and inner. The inner compartment is called the matrix containing DNA, RNA, ribosomes, enzymes of Krebs cycle etc and outer membrane forms the continuous limiting boundary of the organelle. Inner membrane forms number of infoldings called the cristae which increases the surface area. Oxysomes are present on inner mitochondrial membrane. Mitochondria are semiautonomous organelles, i.e., have their own DNA and ribosomes.
Functions of mitochondria:
Mitochondria are essential for aerobic respiration.
- Mitochondria provide intermediates for synthesis of important biomolecules such as chlorophyll, cytochrome, steroids etc.
- Mitochondria regulate the calcium ion concentration in the cell.
- Mitochondrial matrix contains enzymes for the synthesis of fatty acids.
- Synthesis of many amino acids takes place here
Chloroplast: They are green coloured plastids which are disc shaped. The space limited by inner membrane of chloroplast is called as stroma. Stroma has organised flattened membranous sacs called the thylakoids. Thylakoids are arranged in stacks called grana. Matrix of a chloroplast contains DNA, RNA, ribosomes and enzymes. Chloroplast is also a semiautonomous organelle.
Functions of chloroplast:
- Photosynthesis is performed by chloroplast.
- Chloroplast stores starch grains.
- Maintains balance of C02 concentration in the air.
- Keeps oxygen balance constant in atmosphere by liberating 02 into the atmosphere, used during respiration and combustion.