A stem-cell niche is an area of a tissue that provides a specific micro-environment, in which stem cells are present in an undifferentiated and self-renewable state.
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The first theories of matter were put forward by Empedocles in 450 BC, he proposed that all matter was composed of four elements - Earth, air, fire and water. Later, Leucippus and Democritus suggested matter was made up of tiny indestructible particles continuously moving in empty space.
Explanation:
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