I believe it's the ovule.
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The cells appear different because they have specialized to carry out a specific task and developed accordingly.
Helicobacter pylori. Causes ulcers or even stomach cancer.
The UV is needed by the skin to make previtamin D3. Previtamin D3 or cholecalciferol made from the skin will be changed in the liver into 25- hydroxyvitamin D3 and then sent to the kidney to be changed into 1,25- dihydroxyvitamin D3. The last change in the kidney will active the vitamin D. Vitamin D has a role in the calcium absorption which was will strengthen the bone tissue.