Rate of Contraction (contractions per minute) Osmolarity of Solution (mM) Paramecium caudatum is a single-celled protist that resides in freshwater lakes and ponds. These organisms contain unique organelles called contractile vacuoles that when filled with water will contract to remove excess water from the organism. An experiment was conducted to observe the speed of the contraction of this vacuole at varying degrees of solute concentration in the environment. The rate at which the contractile vacuole contracted and expelled excess water was plotted against the osmolarity of the environment as shown in the graph. Which of the following is the correct explanation for the data? At higher osmolarity, lower rates of contraction are required because more salt diffuses into the paramecia. The contraction rate of the vacuoles increases as the osmolarity decreases because the amount of water entering the paramecia by osmosis increases. The contractile vacuole is less efficient in solutions of high osmolarity because of the reduced amount of ATP produced from cellular respiration. In an isosmotic salt solution, there is no diffusion of water into or out of the paramecia, so the contraction rate is zero.
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As the osmolarity of the solution increases, the rate of contraction of the vacuole also increases. This is because the higher osmolarity outside the cell causes water to move out of the cell through osmosis, leading to an increased need for the contractile Show moreā¦
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