Answer:
A pheochromocytoma is a tumor in the adrenal gland. It causes the gland to make too much of the hormones epinephrine and norepinephrine.
Explanation:
Answer:
C. facilitates the absorption of vitamin B12.
Explanation:
The Intrinsic factor is a substance that is produced by the stomach and it has the important function of producing vitamin B12 which is necessary for life. Vitamin B12 is used in the production of mature red blood cells. It also improves the function of the nervous system. The production of this intrinsic factor is a very vital role of the stomach because, in the absence of a stomach, for example, in the case of a gastrectomy, a person can only survive if he is given injections of Vitamin B12.
The stomach also serves as a holding center for food and eventually delivers the food to the small intestine and the duodenum.
Light initially enters the eye through the cornea, it protects the eye and helps to focus light rays into the retina at the back of the eye. The passage of light continues through the pupil which looks like a black circle in the centre of the eye. The pupil is not a structure itself but helps to control the amount of light entering the eye. The iris surrounds the pupil, is the coloured part of the eye. It is a ring of muscles which expand or contract to change the size of the pupil and control the amount of light. The optic nerve carries the visual information from the retina to the primary visual cortex. The optic nerve exits the eye at the back of the retina, the same point where blood vessels enter and exit the eye.
Operons are gene regulatory mechanisms that involve promoting and repressing genes that are involved in the metabolism of organic substances (i.e. sugars). Living organisms have the innate ability to metabolize glucose as the main source of energy. Although, in the absence of glucose, the organism must "learn" to use sugars other than glucose (such as lactose) in order to survive.
For instance, in the <em>lac </em>operon:
In the absence of glucose, various regulatory proteins promote the transcription of the gene related to the metabolism of lactose. This will ultimately lead to the production of the enzyme beta lactosidase which will enable the organism to use lactose as energy in the absence of glucose. This will therefore increase the chances of the organism for survival and will be naturally selected for evolution.
