Answer to Question 1
Age-related physical changes seen within each stage of the life cycle affect body size and composition, which in turn impact nutrient and energy requirements. The Dietary Reference Intakes (DRIs) recommend specific nutrient and energy intakes for each life stage group in addition to additional needs seen in pregnancy and lactation so that nutrient and energy requirements can be met throughout life.
Answer to Question 2
The U.S. National Center for Health Statistics (NCHS), part of the Centers for Disease Control and Prevention (CDC), has compiled reference standards into growth charts. The charts indicate expected growth for well-nourished infants, children, and adolescents utilizing percentile curves that represent growth patterns from birth through 20 years of age. Adequacy of growth (i.e., weight) can be plotted in reference to age and sex. Growth is then monitored over time and used as a general indicator of health.
1–12 Elements essential to animal life and health
Willem de Zwart: Still Life with Apples in a Delft Blue Bowl, 1880–1890
The activation energy barrier.
Is there anything in life that is permanent, or is the world constantly changing?
Life cycle of the beef tapeworm (Taenia saginata).
Electromagnetic Spectrum of Radiant Energy