Cells are so little, so they can maximize their ratio of surface area to volume. Smaller cells have a higher ratio which allow more molecules and ions move across the cell membrane per unit of cytoplasmic volume. Cells are so small because they need to be able to get the nutrients in and the waste out quickly.
The cornea is the outer clear, round structure that covers the Iris and the pupil. The Iris is the colored part of the eye.
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Yes, it needs oxygen to metabolize sugars that, in the end, produce carbon dioxide (CO2).
