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A Handbook of Biology
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.
(NEET 2019)
The mitochondria divide by fission.
Mitochondria are the sites of aerobic respiration or Kreb’s cycle.
They produce energy in the form of ATP. So they are called ‘power
houses’ of the cell.
Function
5.
Plastids
Plastids are found in all plant cells and in euglenoids.
Large sized, easily observable under the microscope.
They contain some pigments.
Contain chlorophyll
and carotenoid
pigments.
a) Chloroplasts:
Contain fat soluble
carotenoid pigments like
carotene, xanthophylls etc.
This gives a yellow, orange or
red colour.
b) Chromoplasts:
c) Leucoplasts:
These are colourless plastids of varied shapes and sizes with
stored nutrients. They include:
-
Amyloplasts: Store starch. E.g. potato.
-
Elaioplasts: Store oils and fats.
-
Aleuroplasts: Store proteins.
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: 5-10 μm. Width: 2-4 μm.
Their number varies from 1 (e.g. Chlamydomonas) to 20-40 per cell in
the mesophyll.
Inner membrane of chloroplast is less permeable.