<span> d/ They create small currents in their microenvironment that help to circulate and clean water locally for other organisms.</span>
Contractile vacuoles are organelles that are responsible for excretion function. They perform osmoregulation which manages wastes, water and other needed materials in the cell. They are found in some prokaryoric organisms like the algae, protists, amoeba and other unicellular organisms.
Answer: They compare the number of mutations to determine how long ago species separated and evolved.
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The vacuole usually acts as storage for materials needed by the cell.
The energy produced from flow of water or "Hydro-power" is different to energy produced from iron, petroleum and coal as it is a clean and renewable form of energy. Hydro-power is derived from the kinetic energy of the natural flow of water like in the case of a water mill whereas the other forms listed require combustion of the fuel source that produces harmful gases leaving a negative impact on the environment. Also, hydro-power is one of the cheapest forms of energy production.
However, it should be noted that large-scale production of electrical energy from flowing water known as "Hydroelectric Power" uses man-made dams to store water in lakes as a source of potential energy. These dams can also have a negative impact on the environment as the natural flow of water is restricted. Some scientists also suggest that the construction of a dam leads to an increase in the number of earthquakes in and around the area of construction.