Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

B. Two

Explanation

The plasma membrane is composed of a phospholipid bilayer, meaning it has two layers of phospholipids. In this arrangement, the hydrophilic phosphate heads face the aqueous environments inside and outside the cell, while the hydrophobic fatty acid tails face inward, away from water. This bilayer structure allows the membrane to function as a barrier while enabling selective transport of molecules. It is the foundational feature of all cell membranes.

Why Other Options Are Wrong

A. One

A single layer of phospholipids would not provide the necessary barrier between the cell’s internal environment and its surroundings. One layer would expose hydrophobic tails to water, which is energetically unfavorable. Thus, one layer is structurally unstable and not found in typical cell membranes.

C. Three

A three-layer structure is not characteristic of biological membranes. Adding an extra layer would disrupt the balance of hydrophilic and hydrophobic interactions and compromise membrane function. The bilayer arrangement is the simplest and most stable design for maintaining selective permeability.

D. Four

Four layers of phospholipids are not found in natural plasma membranes. A quadrilayer would be energetically inefficient and structurally unnecessary. Cells only require a bilayer to create the stable yet flexible membrane that supports life processes, making four layers biologically incorrect.

Correct Answer:

C. Oxygen

Explanation

Oxygen is a small, nonpolar molecule that can diffuse freely across the phospholipid bilayer. Because it is nonpolar, it dissolves easily in the hydrophobic interior of the membrane, and its small size allows it to pass rapidly without the need for carrier or channel proteins. This property is critical for gas exchange in cells, as oxygen must diffuse quickly to support cellular respiration.

Why Other Options Are Wrong

A. Glucose

Glucose is large and polar, meaning it cannot pass directly through the lipid bilayer. Instead, it requires carrier proteins for facilitated diffusion or active transport. Its polarity and size prevent it from being classified as small and nonpolar.

B. Water

Water is small but polar. While it can cross membranes slowly by diffusion, most water movement occurs through specialized channels called aquaporins. Its polarity prevents it from being classified as nonpolar.

D. Benzene

Benzene is nonpolar, but it is larger compared to oxygen and not classified as small. While it can dissolve in the lipid bilayer and diffuse, it does not fit the description of “small and nonpolar” in the same way oxygen does.

Correct Answer:

C. Tunica media

Explanation

The tunica media is the middle layer of a blood vessel and is primarily composed of smooth muscle. It plays the most important role in controlling vessel diameter. When smooth muscle contracts, vasoconstriction occurs, narrowing the lumen and increasing resistance. When smooth muscle relaxes, vasodilation occurs, widening the lumen and decreasing resistance. This regulation is critical for maintaining blood pressure and controlling blood flow.

Why Other Options Are Wrong

A. Tunica interna

The tunica interna, or intima, is the innermost layer made of endothelium. It provides a smooth lining for blood flow and helps prevent platelet adhesion, but it does not regulate vessel diameter.

B. Tunica externa

The tunica externa, or adventitia, is the outer connective tissue layer that provides support and anchors the vessel to surrounding structures. It does not actively control vessel constriction or dilation.

D. Endothelium

The endothelium is the single layer of cells lining the lumen, part of the tunica interna. While important for preventing clotting and controlling permeability, it does not play a role in adjusting vessel diameter.

Correct Answer:

A. Polarity

Explanation

Polarity is a structural property of epithelial tissue that refers to the presence of distinct surfaces. The apical surface faces outward toward the lumen or external environment and may have modifications such as cilia or microvilli. The basal surface anchors epithelial cells to the basement membrane, which connects them to underlying connective tissue. This polarity allows epithelial tissue to carry out directional processes such as absorption, secretion, and transport.

Why Other Options Are Wrong

B. Avascularity

Avascularity refers to the absence of blood vessels in epithelial tissue, requiring nutrients to diffuse from underlying connective tissue. While true for epithelium, it does not describe distinct surfaces like apical and basal.

C. Regeneration

Regeneration describes the ability of epithelial tissue to replace cells rapidly through stem cell division. While important for healing, it is unrelated to the structural polarity of epithelial cells.

D. Sensation

Sensation refers to the presence of nerve endings in epithelial tissue that allow detection of stimuli such as touch, temperature, and pain. This property does not explain the division into apical and basal surfaces.

Correct Answer:

B. Hemopoiesis

Explanation

Hemopoiesis (also called hematopoiesis) is the process by which the formed elements of blood—red blood cells, white blood cells, and platelets—are produced in the bone marrow. Stem cells differentiate into specific blood cell types according to the body’s needs. This process is essential for maintaining oxygen transport, immune defense, and clotting. When hemopoiesis is impaired, conditions such as anemia, leukopenia, or thrombocytopenia may develop.

Why Other Options Are Wrong

A. Hemostasis

Hemostasis is the process that stops bleeding, involving vasoconstriction, platelet plug formation, and coagulation. It does not describe the formation of blood cells.

C. Hemolysis

Hemolysis is the breakdown or destruction of red blood cells, releasing hemoglobin. It is the opposite of producing new blood cells.

D. Hematocrit

Hematocrit is a laboratory measurement describing the percentage of red blood cells in whole blood. It is not the process of blood cell formation.

Correct Answer:

B. Spectrin and actin

Explanation

Spectrin and actin are cytoskeletal proteins found just beneath the plasma membrane of red blood cells. They form a lattice that maintains the biconcave shape of erythrocytes while allowing flexibility to squeeze through narrow capillaries. This structural support provides resilience and durability, enabling red blood cells to survive the mechanical stress of circulation for about 120 days.

Why Other Options Are Wrong

A. Collagen and elastin

Collagen and elastin are structural proteins found in connective tissue, not in erythrocytes. They provide strength and elasticity to tissues like skin, ligaments, and blood vessels but do not support red blood cells.

C. Keratin and myosin

Keratin is found in epithelial tissues (hair, nails, skin), and myosin is a motor protein involved in muscle contraction. Neither contributes to the durability of erythrocytes.

D. Tubulin and fibrin

Tubulin is the protein building block of microtubules in the cytoskeleton, and fibrin is a clotting protein involved in blood coagulation. They do not maintain the shape or resilience of red blood cells.

Correct Answers:

A. Digestive tract; B. Blood vessels; C. Respiratory passages; D. Surface of organs; E. Hollow, tubular organs

Explanation of Each Correct Answer

A. Digestive tract

Epithelial tissue lines the digestive tract, such as the stomach and intestines, where it controls absorption of nutrients and secretion of digestive fluids.

B. Blood vessels

The inner lining of blood vessels is composed of simple squamous epithelium, also called endothelium, which allows smooth blood flow and exchange of substances.

C. Respiratory passages

Epithelial tissue lines the respiratory tract, including the trachea and bronchi. It often has cilia and mucus-secreting cells to trap and remove particles.

D. Surface of organs

Epithelial tissue covers the outer surfaces of many organs, serving as a protective barrier and interface between the organ and its environment.

E. Hollow, tubular organs

Epithelial tissue lines hollow organs such as the bladder, intestines, and uterus, regulating absorption, secretion, and protection.

Why Other Options Are Wrong

F. Skeletal muscles

Skeletal muscles are composed of muscle tissue, not epithelial tissue. Their role is contraction and movement, not lining or covering surfaces.

Correct Answer:

C. Regeneration

Explanation

Regeneration is a hallmark property of epithelial tissue. Epithelial cells have a short life span, typically 2–6 days, and are continuously replaced by stem cells located in the basal layer. This rapid turnover allows epithelial tissue to repair itself quickly after injury, such as cuts, abrasions, or burns. The regenerative ability is essential for maintaining protective barriers and ensuring proper tissue function even after damage.

Why Other Options Are Wrong

A. Vascularity

Epithelial tissue is avascular, meaning it has no direct blood supply. Nutrients and oxygen diffuse from the underlying connective tissue. Vascularity does not explain the process of wound healing through stem cell replacement.

B. Sensation

Sensation refers to the presence of sensory nerve endings in epithelial tissue that detect stimuli such as touch, temperature, and pain. While important, it does not account for the replacement of cells after injury.

D. Protection

Protection describes the barrier function of epithelial tissue, which prevents damage from pathogens, chemicals, and physical forces. While protection is enhanced by regeneration, the specific property described is the replacement of damaged cells by stem cells.

Correct Answers:

A. Fixation; B. Sectioning; C. Staining

Explanation of Each Correct Answer

A. Fixation

Fixation preserves tissue immediately after removal from the body. Chemicals like formalin stabilize proteins, prevent decay, and maintain the structural integrity of cells and tissues so they can be examined accurately.

B. Sectioning

Sectioning cuts tissues into thin slices using tools like a microtome or cryostat. These thin sections allow light to pass through the tissue, making cellular structures visible under the microscope.

C. Staining

Staining uses dyes such as hematoxylin and eosin (H&E) to highlight structures like nuclei, cytoplasm, and fibers. This step provides contrast so that cells and tissues can be clearly distinguished under the microscope.

Why Other Options Are Wrong

D. Culturing

Culturing involves growing microorganisms or cells under controlled conditions. It is not part of histological preparation for microscopic slides.

E. Incubation

Incubation refers to maintaining living cells or microbes at specific conditions to encourage growth. It is used in microbiology, not histology slide preparation.