HD is called an autosomal dominant disorder because only one copy of the defective gene, inherited from one parent, is necessary to produce the disease. The genetic defect responsible for HD is a small sequence of DNA on chromosome 4 in which several base pairs are repeated many, many times.
Carbon dioxide cannot pass through the protective waxy layer covering the leaf (cuticle), but it can enter the leaf through an opening (the stoma; plural = stomata; Greek for hole) flanked by two guard cells. Likewise, oxygen produced during photosynthesis can only pass out of the leaf through the opened stomata.
In plant photosynthesis, the energy of light is used to drive the oxidation of water (H 2 O), producing oxygen gas (O 2), hydrogen ions (H +), and electrons. Most of the removed electrons and hydrogen ions ultimately are transferred to carbon dioxide (CO 2), which is reduced to organic products.