– Mitochondria are clearly visible only when stained.
– Number, shape and size of mitochondria per cell are variable depending on the physiological activity.
– It is sausage-shaped or cylindrical having a diameter of 0.2-1.0 m (average 0.5 micrometer) and length 1.0-4.1micrometer.
– A mitochondrion is a double membrane-bound structure with the outer membrane and the inner membrane.
It divides lumen into 2 aqueous compartments, i.e., the outer compartment and the inner compartment (matrix).
– Inner membrane forms a number of infoldings (cristae) towards the matrix. They increase the surface area.
– The two membranes have their own specific enzymes associated with the mitochondrial function.
– Matrix possesses a circular DNA, a few RNA molecules, ribosomes (70S) and components for protein synthesis.
– The mitochondria divide by fission.
Mitochondria are the sites of aerobic respiration. They produce energy in the form of ATP. So they are called ‘power house’ of the cell.
– Plastids are found in all plant cells and in euglenoids.
– Large sized. Easily observable under the microscope.
– They contain some pigments. – Based on the type of pigments, plastids are 3 types:
Contain chlorophyll and carotenoid pigments. They trap light energy for photosynthesis.
b. Chromoplasts: Contain fat-soluble carotenoid pigments like carotene, xanthophylls, etc. This gives yellow, orange, or red color.
c. Leucoplasts: These are colorless plastids of varied shapes and sizes with stored nutrients.
1) Amyloplasts: Store starch. E.g. potato.
2)Elaioplasts: Store oils and fats. eg-castor,mustard
3) Aleuroplasts: Store proteins. eg-in maize
– These are double membrane bound organelles mainly found in the mesophyll cells of the leaves.
– These are lens-shaped, oval, spherical, discoid or ribbon-like organelles.
– Length: 5-10micrometer. Width: 2-4 micrometer.
– Their number varies from 1 (e.g. Chlamydomonas) to 20-40 per cell in the mesophyll.
– Inner membrane of chloroplast is less permeable.
– The space limited by the inner membrane of the chloroplast is called stroma. It contains many organized flattened membranous sacs called thylakoids.
– Membrane of thylakoids encloses a space called lumen. – Chlorophyll pigments are present in the thylakoids.
– Thylakoids are arranged in stacks called grana or the intergranal thylakoids.
– There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
– The stroma contains small, double-stranded circular DNA molecules, ribosomes and enzymes for the synthesis of carbohydrates and proteins.
– The ribosomes of the chloroplasts are smaller (70S) than the cytoplasmic ribosomes (80S).
– They are non-membranous granular structures composed of ribonucleic acid (RNA) & proteins.
– It is first observed by George Palade (1953),so called palade’s particle
– Eukaryotic ribosome has 2 subunits- 60S (large subunit) and 40S (small subunit). They together form 80S.
TO BE CONTINUED….NEXT PAGE…..