D. The small intestine has finger-like projections called villi covering the internal surface. See Lesson: Gastrointestinal System.
13. C. Malignant
... [Show More] melanoma is the most dangerous type of skin cancer. It occurs when melanocytes experience uncontrolled cell growth and causes dark patches or lesions to form on the skin’s surface. See Lesson: Integumentary System.
14. B. Basal cell carcinoma affects basal cells in the epidermis, while squamous cell carcinoma affects keratinocytes in the epidermis. Malignant melanoma affects melanocytes in the epidermis. See Lesson: Integumentary System.
15. D. HIV can be transmitted through infected intravenous syringes, semen, vaginal secretions, and blood. See Lesson: The Lymphatic System.
16. D. Because semen and vaginal secretions are rich in macrophages, a person can become infected with HIV through sexual intercourse with an
infected person. See Lesson: The Lymphatic System.
17. B. The inflammatory response begins when mast cells release histamines and other chemicals that cause capillaries to swell. See Lesson: The Lymphatic System.
18. D. There are three types of joints in the human body: synovial, immovable, and partly movable. Partly moveable joints are also called cartilaginous joints. They hold bones together by cartilage and are found in the vertebral discs of the spine. See Lesson: Muscular System.
19. D. All muscles have the ability to contract and extend. To work together, all muscles contract (or shorten) and extend (or lengthen) in pairs following stimulation from the nervous system. See Lesson: Muscular System.
20. D. Either the nervous system or circulating hormones stimulate smooth muscle. This muscle is under involuntary control through both forms of stimulation. See Lesson: Muscular System.
21. D. A neurotransmitter is a type of substance that is released from the presynaptic membrane of one neuron and binds to the receptor on the postsynaptic membrane of a different neuron. By binding, this substance stimulates excitation of the neuron causing a neural impulse to be transmitted. See Lesson: The Nervous System.
22. A. Nodes of Ranvier are the gaps in myelin sheaths that increase the speed of an electrical neural signal down the axon of a neuron. See Lesson:
The Nervous System.
23. B. Pregnancy typically lasts for about 40 weeks, which are traditionally divided into three periods of about 13 weeks each called trimesters. See Lesson: Reproductive System.
24. C. Females generally begin puberty at 10–11 years old; males generally begin puberty about a year later, at 11–12 years old. See Lesson: Reproductive System.
25. C. The nervous and cardiovascular systems work with the respiratory system to regulate blood pH levels. See Lesson: The Respiratory System.
26. A. After gas exchange occurs between blood and cells in body tissues, oxygen-poor blood travels in systemic circulation back to the heart and lungs. This blood has less oxygen and more carbon dioxide. Because oxygen diffuses into the tissues to the cells, oxygen concentration is higher in the tissues than in blood that returns to the heart via the veins. See Lesson: The Respiratory System.
27. A. The heart belongs to the cardiovascular system. It pumps oxygenated blood through systemic circulation and transports deoxygenated blood back to the lungs. See Lesson: The Respiratory System.
28. B. Osteoclasts are bone cells that play a role in bone remodeling. They are found on the surface of bone and aid in bone breakdown by dissolving worn-out bone tissue. See Lesson: Skeletal System.
29. A. Bone resorption is a process that dissolves old bone tissue so that it
can undergo remodeling to produce new bone tissue. When bones dissolve during the resorption process, minerals stored in reservoirs of bone are released and pushed through circulation for use. See Lesson: Skeletal System.
30. D. Sesamoid bone consists of small bones like the patella. These bones provide mechanical support and protection. See Lesson: Skeletal System.
31. D. The posterior pituitary gland at the base of the brain secretes the hormone ADH. This hormone alters how much water is excreted from urine by the kidneys. Thus, it controls the concentration and volume of urine in the body. See Lesson: The Urinary System.
32. D. After filtered fluid leaves Bowman’s capsule, which encloses the glomerulus, it travels to the proximal convoluted tubule before ending up in the loop of Henle. See Lesson: The Urinary System.
33. C. There are seven classification systems in the classical Linnaean system: kingdom, phylum, class, order, family, genus, and species. See Lesson: An Introduction to Biology.
34. D. Water is an excellent solvent that has the ability to dissolve many different substances and participate in a wide range of biochemical reactions. See Lesson: An Introduction to Biology.
35. C. Nucleic acids such as DNA and RNA are a class of biomolecules that
play a role in the transmission of genetic information. See Lesson [Show Less]