Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

A. Protons, electrons, neutrons

Explanation

Atoms are the fundamental units of matter, and they are composed of protons, electrons, and neutrons. Protons carry a positive charge and are located in the nucleus, neutrons have no charge and also reside in the nucleus, and electrons carry a negative charge and orbit the nucleus. The number and arrangement of these particles determine the atom’s identity, behavior, and chemical properties.

Why Other Options Are Wrong

B. Protons, neutrons, molecules

Molecules are combinations of atoms, not subatomic particles. Atoms must exist first before molecules can form.

C. Electrons, ions, compounds

Ions and compounds are chemical forms created by atoms, not the subatomic particles that make them up. Electrons are correct, but ions and compounds are not.

D. Protons, nucleic acids, enzymes

Nucleic acids and enzymes are biological macromolecules, not components of atoms. Atoms are far more basic units of matter, consisting only of protons, neutrons, and electrons.

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. Sensation

Explanation

Sensation is a vital function of the integumentary system. Sensory nerves in epithelial tissue detect stimuli such as touch, temperature, pain, and pressure. These receptors allow the body to respond rapidly to environmental changes and prevent injury, as in reflexively pulling away from a hot surface. Without this sensory role, individuals would be unable to perceive harmful conditions and could sustain serious damage.

Why Other Options Are Wrong

A. Protection

Protection refers to the skin’s barrier role against pathogens, chemicals, UV radiation, and physical injury. While important, it does not involve detecting or transmitting stimuli like pain or temperature.

C. Excretion

Excretion is the elimination of small amounts of metabolic waste, such as salts and urea, through sweat. This supports homeostasis but does not relate to sensing or responding to external stimuli.

D. Thermoregulation

Thermoregulation involves maintaining body temperature through sweating, shivering, vasodilation, and vasoconstriction. While essential for homeostasis, it does not explain how the body perceives a hot stove or other sensory input.

Correct Answer:

B. Sectioning

Explanation

Sectioning is the process of cutting tissues into very thin slices so they can be placed on microscope slides for examination. A cryostat or microtome is often used to achieve the required thinness. Sectioning is essential because it allows light to pass through the sample and enables stains to highlight cellular and tissue structures. Without sectioning, tissues would be too thick to study under the microscope.

Why Other Options Are Wrong

A. Fixation

Fixation preserves tissues by stabilizing proteins and preventing decay, but it does not involve cutting them into thin slices. Sectioning is needed after fixation to prepare samples for microscopy.

C. Staining

Staining involves applying dyes to tissues to make structures such as nuclei, cytoplasm, and extracellular fibers visible. It does not involve slicing the tissue into thin sections.

D. Culture

Culture is the process of growing cells or microorganisms under controlled conditions. It is used to detect pathogens or study living cells, not to prepare thin slices for microscopic study.

Correct Answer:

A. Protection

Explanation

Protection is one of the primary functions of epithelial tissue. The tightly packed epithelial cells form a barrier that shields the body from physical abrasion, dehydration, and harmful exposure to chemical and biological agents. Specialized cells like keratinized epithelial cells in the skin provide extra resilience. This protective role is essential for maintaining internal stability and preventing tissue injury or infection from environmental factors.

Why Other Options Are Wrong

B. Sensation

Sensation refers to detecting stimuli such as touch, temperature, pain, and pressure through sensory nerves in epithelial tissue. While important, it does not describe the barrier function against mechanical, chemical, or biological damage.

C. Absorption and secretion

Absorption and secretion involve the movement of substances across epithelial surfaces, such as nutrients in the intestines or fluids in the kidneys. This is different from serving as a barrier to external harm.

D. Excretion

Excretion is the removal of metabolic wastes, such as salts and urea, through sweat or other processes. While the skin contributes to this function, excretion is not the same as the protective role of epithelial tissue.

Correct Answer:

C. Stratum lucidum

Explanation

The stratum lucidum is a thin, translucent layer of dead keratinocytes found only in thick skin, such as the palms and soles. These cells lack nuclei and organelles and provide an additional barrier that enhances protection in areas exposed to friction. It lies between the stratum granulosum and stratum corneum and is not present in thin skin. Its transparency gives it a distinct microscopic appearance.

Why Other Options Are Wrong

A. Stratum basale

The stratum basale is the deepest layer of the epidermis, where mitosis produces new keratinocytes. It contains melanocytes and Merkel cells and is not composed of dead cells. Unlike the lucidum, it is found in both thin and thick skin.

B. Stratum spinosum

The stratum spinosum is composed of living keratinocytes connected by desmosomes, giving it a spiny appearance. It provides flexibility and strength but is not exclusive to thick skin and does not contain dead, organelle-free cells like the lucidum.

D. Stratum corneum

The stratum corneum is the outermost layer of the epidermis, consisting of many layers of dead keratinocytes. While it is composed of dead cells, it is found in both thick and thin skin and is not the translucent layer specific to thick skin like the stratum lucidum.

Correct Answer:

C. Semi-permeable

Explanation

A semi-permeable membrane is one that allows some substances to pass through while preventing others from crossing. The plasma membrane demonstrates this property by permitting small nonpolar molecules, like oxygen and carbon dioxide, to diffuse freely, while restricting larger or charged molecules unless assisted by transport proteins. This selectivity is essential for maintaining homeostasis, regulating nutrient entry, and protecting the cell from harmful substances.

Why Other Options Are Wrong

A. Fully permeable

A fully permeable membrane would allow all substances, regardless of size or charge, to cross freely. This would disrupt homeostasis and expose the cell to harmful compounds. Since the plasma membrane is selective, not everything can pass.

B. Impermeable

An impermeable membrane would prevent any substances from crossing. This would cut the cell off from nutrients, oxygen, and waste removal. Because cells require constant material exchange to survive, the plasma membrane cannot be impermeable.

D. Non-permeable

Non-permeable is similar in meaning to impermeable, describing a barrier that does not allow any substances to cross. This does not fit the function of the plasma membrane, which must allow selective entry and exit of materials for the cell to function properly.

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 Answer:

B. Anaerobic fermentation

Explanation

Erythrocytes lack mitochondria, so they cannot perform aerobic respiration or oxidative phosphorylation. Instead, they generate ATP through anaerobic fermentation (glycolysis). This process produces ATP without consuming oxygen, ensuring that red blood cells deliver oxygen to tissues rather than using it themselves. While less efficient than aerobic pathways, anaerobic fermentation provides enough energy to sustain erythrocyte function.

Why Other Options Are Wrong

A. Aerobic respiration

Aerobic respiration requires mitochondria and oxygen, which erythrocytes lack. This process occurs in most other body cells but not in red blood cells.

C. Oxidative phosphorylation

Oxidative phosphorylation is the mitochondrial process that produces large amounts of ATP from oxygen and glucose. Because red blood cells have no mitochondria, they cannot perform this process.

D. Protein synthesis

Protein synthesis occurs in cells with nuclei and ribosomes. Mature erythrocytes lack both, so they cannot synthesize proteins. This process is unrelated to ATP generation in red blood cells.