Answer to Question 1
a
Answer to Question 2
Neural tube defects (NTDs) are a group of birth defects that are caused by incomplete development of the brain, spinal cord, or their protective coverings. Spina bifida is one of the most common types of NTDs. NTDs develop between the third and fourth week after conceptionor before many women even know they are pregnant, and well before prenatal care generally begins. Folate is an essential nutrient required for DNA replication and as a component of enzymatic reactions involved in amino acid synthesis and vitamin metabolism. Knowledge of the folateneural tube defect relationship, and awareness that folate intake was inadequate in many women of childbearing age, prompted public health efforts to increase folate intake. In particular, efforts are focused on encouraging women to consume folic acid, a highly absorbable, synthetic form of this B vitamin. In 1998, the Food and Drug Administration mandated that refined grain products such as white bread, grits, crackers, rice, and pasta be fortified with folic acid. Many countries now fortify refined grain products with folic acid, and rates of NTDs have decreased significantly in these countries.
A closer look at the structure and function of photosystem II
The respiratory system. (a) Sagittal section of the head and neck, revealing the organs of the upper
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Lobes of the brain, with primary receiving and integrating centers of the human cerebral cortex.