A: Chloroplast: Chloroplast is the cell organelle which contains
chlorophyll pigments in the thylakoid membranes and carries out
photochemical reactions.
It is lens shaped and may be oval, spherical discoid or ribbon like
with a size of 5-10 µm (length) and 2-4 µm (width).
The double membrane of the chloroplast encloses a space called stroma.
A continuous system of tubules extends in the stroma called thylakoid
system. The thylakoids appear as membranous sacs and are stacked like
piles of coils called grana.
Flat membranous tubules called the stroma lamellae connect the
thylakoids of different grana.
The thylakoid membrane encloses a space called lumen. The
photosynthetic pigments chlorophyll a, b, xanthophyll and carotene are
present in the membrane.
The stroma contains enzymes of photosynthesis (carbohydrate synthesis)
and also shows DNA, RNA and 70S ribosomes.
Q: Describe the structure and function of power houses of cell.
A: Mitochondria: The mitochondria are called power houses of cell as
they produce chemical energy in the form of ATP by oxidation of
glucose and
other food molecules.
The mitochondrion is sausage or cylindrical shaped organelle with a
size of 0.2 µm to 1.0 µm diameter and 1.0 µm to 4.1 µm length.
The outer membrane is smooth and the inner membrane is folded into
finger like projections called cristae. The fluid filled portion
inside the double membrane is the matrix.
The matrix contains enzymes of Kreb's cycle, DNA, RNA and 70S
ribosomes. The inner mitochondrial membrane contains protein complexes
and enzymes related to electron transport and ATP synthesis.
Functions: Mitochondria are the sites of aerobic respiration in which
Kreb's cycle and electron transport take place. They produce cellular
energy in the form of ATP.
Mitochondria also take part in photorespiration. As they contain DNA,
RNA and 70S ribosomes they also prepare proteins.
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