Cell: The Building Block of Life

Most scientists agree that life first appeared in water, though not necessarily the wide open ocean.

Hold a piece of paper with two dots drawn close together at arm's length, and slowly bring the dots closer, and there is a precise point at which your eyes stop being able to tell them apart and see only one blurred point instead.

Cut a potato into two equal pieces, weigh each one, then drop one piece into a beaker of plain water and the other into a strong salt solution, and leave them for an hour. The piece sitting in plain water gets noticeably heavier and firmer.

A tree cannot walk away from a strong wind, and a blade of grass cannot duck out of the way of a grazing goat, so plants have evolved something animal cells never bothered with: a rigid cell wall, sitting just outside the cell membrane, built mainly from a tough carbohydrate called cellulose.

Every eukaryotic cell, meaning every cell with a properly enclosed nucleus, keeps its most important information locked inside that nucleus, wrapped in its own double-layered membrane, studded with pores that let specific material pass between the nucleus and the rest of the cell.