Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

B. Sensation

Explanation

Sensation is a key function of the integumentary system. The skin contains sensory receptors such as Merkel cells, Meissner’s corpuscles, Pacinian corpuscles, and free nerve endings that detect stimuli including touch, vibration, pressure, pain, and temperature. This sensory input allows the body to react quickly to environmental changes, prevent injury, and maintain homeostasis. Without these receptors, the body would not be able to perceive harmful stimuli, increasing the risk of damage.

Why Other Options Are Wrong

A. Protection

Protection refers to the skin acting as a barrier against pathogens, chemicals, and UV radiation. While critical, it does not involve detecting or transmitting sensory information from the environment.

C. Excretion

Excretion is the removal of metabolic waste such as salts, urea, and ammonia through sweat glands. This is not related to sensory input or perception of external stimuli.

D. Thermoregulation

Thermoregulation involves controlling body temperature through sweating, vasodilation, and vasoconstriction. Although this is a skin function, it is separate from the detection of stimuli, which is specific to sensation.

Correct Answer:

C. Stratum corneum

Explanation

The stratum corneum is the outermost layer of the epidermis, consisting of dead keratinocytes that have lost their nuclei and organelles. These cells are stacked in numerous layers, forming a durable barrier that protects the underlying tissues. This layer continuously sheds and renews, maintaining the integrity of the skin’s surface. Its function is critical for preventing water loss and protecting against environmental damage.

Why Other Options Are Wrong

A. Stratum basale

The stratum basale is the deepest epidermal layer where new keratinocytes are produced by mitosis. It contains melanocytes and is responsible for skin regeneration, but it does not consist of stacked dead cells like the stratum corneum.

B. Stratum granulosum

The stratum granulosum is located below the stratum corneum and contains keratinocytes that are beginning to die and accumulate keratohyalin granules. While it is part of the keratinization process, it is not the outermost layer with fully dead stacked keratinocytes.

D. Stratum spinosum

The stratum spinosum is composed of living keratinocytes connected by desmosomes, giving it a spiny appearance. It provides structural support and flexibility, but it is not the layer where dead cells stack to form the protective barrier of the skin.

Correct Answer:

B. Carrier protein

Explanation

Carrier proteins can mediate active transport, which moves molecules up their concentration gradient from low concentration to high concentration. This process requires ATP or another energy source, since it goes against the natural flow of diffusion. A common example is the sodium-potassium pump, which actively exchanges sodium and potassium ions to maintain proper electrochemical gradients in cells. Carrier proteins are essential for maintaining cellular homeostasis.

Why Other Options Are Wrong

A. Channel protein

Channel proteins allow ions or water to move across membranes, but this occurs through facilitated diffusion down a concentration gradient. They provide a hydrophilic passage without requiring ATP. Therefore, they cannot move substances up a concentration gradient.

C. Receptor protein

Receptor proteins are specialized for signaling and communication. They bind specific ligands, such as hormones or neurotransmitters, to trigger a cellular response. They do not function in moving molecules across a membrane and cannot provide the active transport role performed by carrier proteins.

D. Structural protein

Structural proteins help maintain the shape, stability, and framework of the cell membrane or cytoskeleton. They provide support but do not participate in transport processes. As such, they cannot move molecules across the membrane or influence concentration gradients.

Correct Answers:

A. Polarity; B. Attachment; C. Avascularity; D. Regeneration

Explanation of Each Correct Answer

A. Polarity

Epithelial tissue exhibits polarity, meaning its cells have distinct surfaces. The apical surface faces the external environment or lumen and may have cilia or microvilli, while the basal surface attaches to the basement membrane. This organization allows directional functions like absorption and secretion.

B. Attachment

The basal surface of epithelial cells attaches to a basement membrane, which anchors them to the underlying connective tissue. This attachment provides structural stability and helps maintain the tissue’s integrity.

C. Avascularity

Epithelial tissue is avascular, meaning it contains no blood vessels. Nutrients and oxygen must diffuse from the capillaries in the underlying connective tissue. This property helps maintain thin tissue layers ideal for absorption and protection.

D. Regeneration

Epithelial tissue has a high regenerative capacity. Cells at the basal layer constantly divide and replace worn-out or damaged cells. This rapid turnover, usually every 2–6 days, helps maintain protective barriers and allows wounds to heal quickly.

Why Other Options Are Wrong

E. Vascularity

This is incorrect because epithelial tissue is avascular, not vascular. Blood vessels are present only in the underlying connective tissue.

F. Contractility

Contractility is a property of muscle tissue, not epithelial tissue. Epithelial tissue specializes in protection, absorption, secretion, and sensation, but not contraction.

Correct Answer:

B. Vitamin D production

Explanation

The skin contributes to Vitamin D production when exposed to ultraviolet (UV) radiation from sunlight. This stimulates the conversion of a cholesterol derivative into Vitamin D precursors, which are further processed in the liver and kidneys into calcitriol, the active form of Vitamin D. Calcitriol is essential for calcium absorption in the intestines, enabling proper calcium uptake into bones for strength and density. Without this process, bones can become weak or brittle, leading to conditions such as rickets or osteoporosis.

Why Other Options Are Wrong

A. Thermoregulation

Thermoregulation refers to maintaining body temperature through mechanisms like sweating, vasodilation, or vasoconstriction. While important, it does not involve Vitamin D synthesis or calcium absorption into bones.

C. Excretion

Excretion refers to the removal of metabolic waste products such as salts, urea, and ammonia via sweat. This is a function of the skin but is unrelated to calcium uptake or Vitamin D synthesis.

D. Sensory reception

Sensory reception is the skin’s ability to detect stimuli such as touch, pressure, pain, and temperature via sensory receptors. While critical for protection and interaction with the environment, it does not influence calcium absorption or Vitamin D production.

Correct Answer:

B. Shape of epithelial cells

Explanation

Epithelial tissue can be classified by cell shape. Squamous cells are thin and flat, ideal for diffusion and filtration (e.g., alveoli, blood vessels). Cuboidal cells are cube-like and often involved in secretion or absorption (e.g., kidney tubules, glands). Columnar cells are tall and rectangular, specialized for absorption and secretion (e.g., intestinal lining). Identifying the shape of cells helps determine the function and location of the epithelium in the body.

Why Other Options Are Wrong

A. Function of epithelial cells

Function refers to what the epithelium does (e.g., absorption, secretion, protection). While related, the classification described here was specifically about shape, not function.

C. Number of layers of cells

Number of layers distinguishes simple (one layer) from stratified (multiple layers) epithelium. The question specifically emphasized shapes such as squamous, cuboidal, and columnar, not layering.

D. Location of epithelial cells

Location refers to where the epithelium is found in the body (e.g., intestines, lungs, kidneys). While location often determines epithelial type, classification here is based strictly on cell shape.

Correct Answer:

C. Number of layers of cells

Explanation

Epithelial tissue is classified based on two main features: the shape of the cells and the number of layers. When classified by the number of layers, there are two categories: simple epithelium, consisting of a single cell layer specialized for absorption, secretion, and filtration; and stratified epithelium, consisting of multiple layers designed for protection against abrasion and stress. This system helps distinguish epithelial types in various parts of the body.

Why Other Options Are Wrong

A. Shape of epithelial cells

Shape refers to classifications such as squamous (flat), cuboidal (cube-shaped), or columnar (tall), not the number of layers. The question specifically focused on layering, not shape.

B. Function of epithelial cells

Function includes absorption, secretion, filtration, or protection, but the classification discussed in the question is based on the number of layers, not what the cells do.

D. Location of epithelial cells

Location refers to where epithelium is found, such as in the lungs, intestines, or skin. While important, it is not the method of classification described here.

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. Glycerol backbone

Explanation

The glycerol backbone is the central part of a phospholipid molecule that connects the hydrophilic phosphate head to the hydrophobic fatty acid tails. This arrangement creates the amphipathic nature of phospholipids, which is essential for forming the bilayer structure of the plasma membrane. Without the glycerol backbone, the phospholipid could not maintain its structural integrity, and the membrane would not be able to organize into a stable bilayer.

Why Other Options Are Wrong

A. Phosphate head

The phosphate head is hydrophilic and interacts with water, but it does not connect the different parts of the phospholipid. Its role is to face the aqueous environments inside and outside the cell, not to serve as the structural link within the molecule.

C. Fatty acid tails

The fatty acid tails are hydrophobic and orient away from water inside the bilayer. While critical for membrane barrier function, they are attached to the glycerol backbone rather than acting as the connecting element. They provide hydrophobic properties but are not the “glue” of the molecule.

D. Cholesterol

Cholesterol is not part of the phospholipid structure itself. Instead, it inserts between phospholipids in the bilayer to regulate fluidity and stability. It does not connect the phosphate head to the fatty acid tails and plays a separate regulatory role in membrane dynamics.