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.
Photosynthesis is the plant process where light energy is used to generate the production of ATP. The ATP so formed is used to form the bonds between carbon dioxide molecules and hydrogen atoms released from water by the light energy. The process forms sugar (glucose) molecules and produces oxygen as a waste product. At a glance, the equations: sugar + oxygen --> carbon dioxide + water + ATP energy (cellular respiration) and carbon dioxide + water + sun's energy --> sugar + oxygen (photosynthesis) look to be the reverse of each other.