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 process by which plants and other organisms (i.e. cyanobacteria and algae) convert light energy from the sun into chemical energy. In the process of photosynthesis, carbon dioxide (CO2) and water (H2O) undergo a series of chemical reactions initiated by light energy to produce glucose (C6H12O6) and oxygen gas (O2). As sunlight shines down on plants, water is absorbed by the root system of the plant.