Page 105 - Algae Anatomy, Biochemistry, and Biotechnology

88 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 2.60 A desmokont dinoflagellate (Prorocentrum sp.) and its swimming pattern.

In isokont biflagellate algae such as Chlamydomonas or Dunaliella (Chlorophyta), during the
effective stroke the flagella bend only at the base, push more water backwards than adhereing to
them during the forward recovery stroke, thus bringing about net forward movement. While swim-
ming these cells also rotate. Speed ranging from 100 to 200 mm sec 21 can be reached by these cells
during forward swimming. Backward swimming is also possible, during which the flagella perform
undulatory movement (Figure 2.64).
An interesting question is why the algae swim. All algae in an aquatic environment have a need
to exchange molecules such as O 2 ,CO 2 , and NH 3 with environment. As all solid boundaries in a
liquid medium have associated with them a boundary layer in which water movement is reduced
(due to the no-slip boundary), this layer will impede the nutrient uptake of the organisms by creat-
ing a small depleted layer around them. Turbulence is very ineffective in transporting nutrients
towards such small organisms as the smallest length scale of turbulent eddies are of the order of
several millimeters. Therefore, algae must rely on molecular diffusion to overcome the nutrient gra-
dient across the boundary layer. Diffusion, that is the slow mixing caused by the random motion of
molecules, is important in the world of low Reynolds number, because here stirring is not any good.
The alga’s problem is not its energy supply; its problem is its environment. At low Reynolds
number you cannot shake off your environment. If you move, you take it along; it only gradually
falls behind.

FIGURE 2.61 A dinokont dinoflagellate (Peridinium sp.) and its swimming pattern.