Stomata are located on the underside of the leaf and are flanked by guard cells. These guard cells close the stomata by:.

"do a testcross with a homozygous recessive plant."

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.