The mechanism of cell crawling in protist species is not well defined. Pseudopodia extension involves interactions between actin and myosin (the same molecules that are involved in vertebrate muscle contraction) . However, prior to the study described below, no-one had provided convincing data that actin and myosin were actually involved in cell crawling in protists. Anatomical studies had identified the cytoskeletal protein actin just below the surface of the cell membrane in several species of protist, but physiological studies had failed to show a functional link between actin, myosin, and cell crawling.
In a study by N. Poulsen et al. (Diatom gliding is the result of an actin-myosin motility system, Cell Motility and the Cytoskeleton 44 (1999) :23-22) , researchers tested whether motility in a particular species of diatom involves interactions between actin and myosin. 
-Refer to the study by Poulsen et al. and the figure above. Latrunculin A is a reversible toxin that disrupts the formation of actin fibres. A culture of a particular species of diatom was treated with this toxin diluted in a buffer, while another culture was treated only with the buffer (no toxin; control) . The motility of cells in each culture was assessed by counting the number of cells that were moving during a defined period of time. Which of the following conclusions is reasonable based on the above figure?
Definitions:
Sexual Response Cycle
The sequence of physical and emotional phases that occur during sexual activity, including arousal, plateau, orgasm, and resolution.
Muscle Tension
A physiological condition in which muscles remain semi-contracted for an extended period, which may be caused by stress, anxiety, or physical activity.
Engorged Genitals
An increase in blood flow leading to the swelling of genital tissues, often associated with sexual arousal.
Sunday Stroll
A leisurely, casual walk taken on Sundays, often for relaxation and enjoyment.
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