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.
Carbon dioxide, water, and sunlight are used to produce glucose, oxygen, and water. Photosynthesis occurs in two stages. These stages are known as the light reaction stage and the dark reaction stage. The light reaction stage takes place in the presence of light and occurs within the chloroplast grana.