Microtubules originate on the centre of the cell taking the positive end to the periphery of the cell, while the negative end remains turned to the centre of the cell. The melanosomes move along these microtubules using motor proteins desiganted kinesins and dyneins. The kinesins are responsible for moving the melanosomes to the positive end of the microtubule (periphery of the cell) generating dark-colored cells, whereas dyneins move the melanosomes to the negative end of the microtubule (centre of the cell) generating light-colored cells.
A fossil would from through mineral replacement by replacing the existing material of the animals bones with minerals, to become petrified. The Minerals will keep the fossil preserved longer.
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These are performed by organelles.
<span>Cell is the most basic unit of matter that can carry out all the processes of life however not all cells are alike.The different structures found within the cell is called the organelles and are assigned to perform specific function in the specific cell. It is also said that organelles maintain the life of the cell. The organelles of a single cell like the organs of a multicellular organism is very essential for the survival of the body. The presence of organelles in both unicellular and multi-cellular organisms are very essential in orde to maintain life and carry on with its individual functions.</span>