Question

In most species of Paramecium there are how many contractile vacuoles? Is it:
a) one
b) two
c) three
d) four

Answer 1

In most species of Paramecium there are two contractile vacuoles.

So option (B) is correct.

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Answer 2

A diagram of Paramecium caudatum

Species of Paramecium range in size from 50 to 330 micrometres (0.0020 to 0.0130 in) in length. Cells are typically ovoid, elongate, foot- or cigar-shaped. The body of the cell is enclosed by a stiff but elastic membrane (pellicle), uniformly covered with simple cilia, hairlike organelles which act like tiny oars to move the organism in one direction. Nearly all species have closely spaced spindle-shaped trichocysts embedded deeply in the cellular envelope (cortex) that surrounds the organism. Typically, an anal pore (cytoproct) is located on the ventral surface, in the posterior half of the cell. In all species, there is a deep oral groove running from the anterior of the cell to its midpoint. This is lined with inconspicuous cilia which beat continuously, drawing food inside the cell.[8] Paramecia live mainly by heterotrophy, feeding on bacteria and other small organisms. A few species are mixotrophs, deriving some nutrients from endosymbiontic algae (chlorella) carried in the cytoplasm of the cell.[9]

Osmoregulation is carried out by contractile vacuoles, which actively expel water from the cell to compensate for fluid absorbed by osmosis from its surroundings.[10] The number of contractile vacuoles varies from one, to many, depending on species.[8]