Cell: The Unit of Life

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Vacuoles

Tonoplast facilitates the transport of a number of ions and other

materials against concentration gradients into the vacuole. Hence

their concentration is higher in the vacuole than in the cytoplasm.

In plant cells, the vacuoles can occupy up to 90% of the volume

of the cell.

In Amoeba, the contractile vacuole helps for osmoregulation

& excretion.

Vacuole is bound by a single membrane called

tonoplast.

In many cells (e.g. protists), food vacuoles are formed by

engulfing the food particles.

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5

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These are the membrane-bound space found in the cytoplasm.

It contains water, sap, excretory product and other materials

not useful for the cell.

4.

Mitochondria

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Absent in mammalian

RBCs and prokaryotes.

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Mitochondria

are

clearly visible under the

microscope only when

stained.

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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 μm

(average 0.5 μm) and length 1.0-4.1 μm.

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).

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Inner membrane forms a number of infoldings (cristae) towards the

matrix. They increase the surface area.