Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

C. Adipocytes

Explanation

Adipocytes, also known as fat cells, are specialized connective tissue cells that store lipids. They provide energy reserves, insulation to maintain body temperature, and cushioning to protect organs from mechanical injury. Under the microscope, adipocytes appear as large, clear “white blobs” because lipid droplets displace the nucleus to the side. They are the primary cell type in adipose tissue and are essential for both energy balance and organ protection.

Why Other Options Are Wrong

A. Fibroblasts

Fibroblasts are the main cells in connective tissue proper and are responsible for producing fibers like collagen, elastin, and reticular fibers, as well as ground substance. They do not store lipids or function as fat storage cells.

B. Chondrocytes

Chondrocytes are the cells found in cartilage. Their main function is to produce and maintain the cartilaginous matrix. They provide structural support but are not involved in lipid storage or cushioning organs through fat deposits.

D. Osteocytes

Osteocytes are mature bone cells located within lacunae. They help maintain the mineral content of bone and communicate with other bone cells for remodeling. They do not store fat or provide cushioning through lipid reserves.

Correct Answer:

C. Stratum granulosum

Explanation

The stratum granulosum is composed of keratinocytes that begin producing keratin and lipids, which help create a water-resistant barrier for the skin. As keratinocytes reach this layer, they start to die, losing their nuclei and organelles. This layer provides protection against dehydration and external harm. It is also the second site where immune Langerhans cells can be found, reinforcing the skin’s defense role.

Why Other Options Are Wrong

A. Stratum basale

The stratum basale is the deepest layer of the epidermis and contains mitotically active keratinocytes, melanocytes, and Merkel cells. It is not where keratin and lipids accumulate or where keratinocytes die. Its function is cell regeneration, not water barrier formation.

B. Stratum spinosum

The stratum spinosum is made of living keratinocytes connected by desmosomes, giving it a spiny appearance. While it does contain Langerhans cells, keratin and lipid accumulation does not occur here, and the keratinocytes are not yet dead.

D. Stratum corneum

The stratum corneum is the outermost epidermal layer made of fully dead keratinocytes stacked in multiple layers. While it provides a barrier, this is the result of earlier processes in the stratum granulosum. The corneum does not produce keratin or lipids; it simply contains the end product.

Correct Answer:

B. Sympathetic nervous system

Explanation

The sympathetic nervous system (SNS) controls vasoconstriction and vasodilation through signals from the vasomotor center in the medulla oblongata. Increased SNS activity causes smooth muscle contraction in the tunica media, leading to vasoconstriction and higher resistance. Reduced SNS activity allows relaxation, causing vasodilation and decreased resistance. This system plays a central role in regulating blood pressure and blood flow distribution.

Why Other Options Are Wrong

A. Somatic nervous system

The somatic nervous system controls voluntary skeletal muscle movement, not involuntary smooth muscle activity in blood vessels. It does not regulate vasoconstriction or vasodilation.

C. Parasympathetic nervous system

The parasympathetic system primarily promotes “rest and digest” functions, including slowing the heart rate and stimulating digestion. It has minimal influence on blood vessel diameter compared to the SNS.

D. Central nervous system only

While the vasomotor center is in the CNS, it exerts its effect through the sympathetic branch of the autonomic nervous system. The CNS alone does not directly innervate smooth muscle for vasoconstriction and vasodilation.

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.

Correct Answer:

B. Fibroblasts

Explanation

Fibroblasts are the primary cells of connective tissue proper. Their main function is to produce the protein fibers of the extracellular matrix, including collagen for strength, elastin for flexibility, and reticular fibers for support. They also secrete ground substance, which, together with fibers, forms the connective tissue matrix. Fibroblasts are essential for tissue repair and wound healing because they generate the structural framework of tissues.

Why Other Options Are Wrong

A. Adipocytes

Adipocytes are fat cells that store lipids for energy, insulation, and protection. They do not produce fibers or extracellular matrix. Their role is storage, not structural protein production.

C. Chondrocytes

Chondrocytes are the cells found in cartilage. They maintain the cartilaginous matrix and provide structural support, but they do not produce the diverse fibers that fibroblasts create.

D. Osteocytes

Osteocytes are mature bone cells responsible for maintaining bone tissue. They are embedded in lacunae and communicate with other bone cells, but they do not produce the fibers of the connective tissue matrix.

Correct Answer:

B. Epithelial tissue

Explanation

Epithelial tissue is the primary tissue type that covers and lines the body. It forms the surface of the skin (epidermis), lines the respiratory and digestive tracts, and also makes up glands, ducts, and cavities. It functions in protection, absorption, secretion, and filtration. In the case of burns, the epithelial tissue is damaged, which compromises the body’s first line of defense and requires immediate attention to prevent infection and fluid loss.

Why Other Options Are Wrong

A. Connective tissue

Connective tissue’s primary role is to support, bind, and protect body parts. It includes bone, cartilage, adipose tissue, and blood. While it provides strength and structure, it does not function as a lining or covering layer for organs and surfaces. Therefore, it cannot replace epithelial tissue in maintaining barriers and protective coverings.

C. Nervous tissue

Nervous tissue specializes in transmitting signals and processing information through neurons and supporting cells. Its role is to coordinate body activities and maintain communication between different body systems. It does not line surfaces or form protective outer layers. This makes it distinct from epithelial tissue, which has barrier and lining functions.

D. Muscle tissue

Muscle tissue is responsible for producing movement through contraction, whether voluntary (skeletal), involuntary (smooth), or rhythmic (cardiac). While essential for motion and organ function, it does not line or cover body surfaces. It cannot serve as a protective barrier for the skin or internal cavities. This makes it the wrong answer in this context.

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:

B. Collagen

Explanation

Collagen is a fibrous protein that is long and string-like, forming strong fibers within connective tissue. It is the most abundant protein in the human body and provides tensile strength and structural support to tissues such as skin, tendons, ligaments, cartilage, and bone. Collagen fibers resist stretching, making them essential for maintaining tissue integrity under mechanical stress.

Why Other Options Are Wrong

A. Actin

Actin is a globular protein that forms microfilaments in the cytoskeleton and plays a role in cell shape, intracellular transport, and muscle contraction. It is not long, fibrous, or specialized for structural support in connective tissue like collagen.

C. Myosin

Myosin is a motor protein involved in muscle contraction, interacting with actin filaments to generate movement. While important for muscle physiology, it is not a fibrous protein that forms structural support fibers in connective tissues.

D. Keratin

Keratin is a fibrous protein found in epithelial cells, forming hair, nails, and the outer layer of skin. While strong and protective, keratin is specialized for epithelial structures, not for forming long connective tissue fibers like collagen.

Correct Answer:

B. Exocrine gland

Explanation

Exocrine glands use ducts to deliver their secretions directly onto epithelial surfaces or into body cavities. Their effects are local, targeting tissues nearby. Examples include sweat glands, salivary glands, and sebaceous glands. This makes them distinct from endocrine glands, which release hormones into the bloodstream to affect distant targets. The duct system allows exocrine glands to precisely control where secretions are delivered.

Why Other Options Are Wrong

A. Endocrine gland

Endocrine glands are ductless and secrete hormones directly into the bloodstream. Their effects are systemic and target distant organs. This differs from exocrine glands, which use ducts and act locally.

C. Sebaceous gland

Sebaceous glands are a type of exocrine gland that secrete sebum into hair follicles. While they fit within the exocrine category, the question asked for the general type of gland, not a specific example.

D. Thyroid gland

The thyroid gland is an endocrine gland that secretes hormones like thyroxine into the bloodstream. Its effects are widespread and systemic, not local, making it the opposite of an exocrine gland.