Specialized Eukaryotic Cells and Tissues
Cancer is a disease in which cells begin to divide when they shouldn’t, producing masses of cells called tumors. Cancerous tumors are called “malignant” ones because of their ability to grow aggressively, invade surrounding healthy tissue, and “metastasize”, or spread to different locations in the body as tumor cells break off, travel through the blood or lymph, and establish new tumors.
Cancer is generally caused by environmental agents known as “carcinogens”, which include chemicals (such as those found in cigarette smoke) and radiation (like the UV rays of sunlight) that mutate cells, causing them to become cancerous.
Tumors that originate from epithelial cells are generally known as carcinomas, and it is estimated that about 90% of all human cancers are carcinomas. Tumors that originate from muscle tissue are called “sarcomas”, and tumors can also originate from nervous and connective tissues. Epithelial tissue exists in various locations in the body, including the skin, the mucous membranes lining the lungs and gastrointestinal tract, and the linings surrounding major organs.
The observation that 90% of human cancers are carcinomas implies that:
|A||Most carcinogens, like UV light, penetrate very deeply into underlying tissues.|
|B||Epithelial cells by their very nature are more susceptible to mutation than cells of other tissue types.|
|C||Cigarette smoking causes more tumors in humans than does UV light.|
|D|| Most carcinogens do not penetrate tissues very deeply.|
Since carcinogens, whether chemicals or radiation, are contacting the body from the environment, and we know that epithelium is always the tissue that separates the body from the environment, we would expect the carcinogens to initially contact epithelium. If they penetrated tissue deeply, all types of cancers would be equally prevalent; the fact that carcinomas make up 90% of all cancers implies that after the carcinogen contacts the epithelium, it generally does not penetrate much deeper. There is no reason to believe that choice B is correct, and choice C is irrelevant to the question.