Answer to Question 1
As mentioned, vitamin A also supports reproduction and regulates growth. In men, retinol participates in sperm development, and in women, vitamin A supports normal fetal development during pregnancy. Children lacking vitamin A fail to grow; given vitamin A supplements, these children gain weight and grow taller.
The growth of bones illustrates that growth is a complex phenomenon of remodeling. To convert a small bone into a large bone, some bone cells must undo parts of the bone before other cells can build new bone, and vitamin A participates in the dismantling. The cells that break down bone contain acid and enzymes that dissolve the minerals and digest the matrix. With the help of vitamin A, these bone-dismantling cells destroy selected sites in the bone, removing the parts that are not needed. After completing their work, the bone-dismantling cells die, leaving their excavation site to be rebuilt by the bone-building cells.
Answer to Question 2
phylloquinone (K1); menaquinone (K2)
Radial pattern of shoot growth in plants
The cranium of a young infant changes dramatically in shape with age. Initially the child has severa
Physiological and pharmacologic effects of growth hormone.
World Population Growth
Poverty and population growth
The Distribution of Growth Rates, 1975–2009