<span>The two major forces that shape/reshape the earth are internal forces, i.e.volcanoes and earthquakes and external forces, i.e. weather and the ocean, both of which cause erosion. Volcanoes can add landmass but also can destroy land or cause a winter-like state caused by ash in the atmosphere which can block out the sun and possible killing vast amounts of plant and animal life. Earthquakes can change the land by process of subduction where one plate (land surface or ocean bottom) is forced under another. Erosion wears down geologic formations by the actions of wind and water. Over time water can carve valleys or canyons. Ocean water can erode coastlines by the constant beating of waves on the shore. Wind can carry away particles of land and deposit them elsewhere. Wind and weather combined can be a powerful force for reshaping the earth.</span>
Meristematic tissue have the ability to
divide themselves. It is the primary site for cell division and cell
differentiation. It produces the new cells and are called growing tissue in
plants. The new cells may or may not divide. It is the source of the regenerative
potential of the plant.
<span>
Cancerous cells can originate anywhere in the
body and can spread into or invade adjoining tissues. It keeps growing and dividing
relentlessly to form lumps. It can also break off and travel to distant
tissues. Cancer cells rejects signals from other cells.</span>
Primary spermatocytes, spermatids
