Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

B. Blood consists of plasma and formed elements, including cells and platelets.

Explanation

Blood is considered a connective tissue because it has a fluid extracellular matrix (plasma) and cellular components. Plasma is mostly water with dissolved proteins, nutrients, and waste products. The formed elements include red blood cells (carry oxygen), white blood cells (immune defense), and platelets (involved in clotting). Together, plasma and formed elements allow blood to transport substances, defend the body, and maintain homeostasis.

Why Other Options Are Wrong

A. Blood consists only of plasma and proteins.

This ignores the presence of formed elements such as red blood cells, white blood cells, and platelets, which are essential to blood’s function.

C. Blood consists only of red blood cells suspended in plasma.

This is incomplete because it leaves out white blood cells and platelets, which are critical for immunity and clotting.

D. Blood consists of plasma, proteins, and no cellular components.

This is false because blood has both plasma and formed elements. Without cells, blood could not transport oxygen, fight infections, or clot.

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. Hemopoietic stem cells (HSC)

Explanation

Hemopoietic stem cells (HSC) are pluripotent stem cells located in the red bone marrow that generate all of the formed elements of blood. These include red blood cells, white blood cells, and platelets. HSCs continually divide and differentiate to replace aging or damaged blood cells, ensuring proper oxygen transport, immunity, and clotting. Their critical role is the foundation of hematopoiesis, making them essential for survival.

Why Other Options Are Wrong

A. Totipotent stem cells

Totipotent stem cells exist only in early embryonic development and can generate all tissues, including extraembryonic structures like the placenta. They are not present in bone marrow and do not specifically generate blood cells.

C. Multipotent mesenchymal stem cells

Mesenchymal stem cells in bone marrow give rise to bone, cartilage, and fat cells, not to all formed elements of the blood. They support skeletal and connective tissue development rather than hematopoiesis.

D. Unipotent stem cells

Unipotent stem cells produce only one specialized cell type, such as skin stem cells generating keratinocytes. They lack the ability to generate the multiple formed elements of blood.

Correct Answer:

B. Elastic (conducting) arteries

Explanation

During systole, elastic (conducting) arteries such as the aorta expand as blood enters their lumen. Their abundance of elastic fibers allows them to absorb systolic pressure and store potential energy in their walls. This expansion reduces the workload on smaller arteries and helps maintain smooth blood flow. By stretching during systole and recoiling during diastole, these vessels prevent extreme fluctuations in blood pressure.

Why Other Options Are Wrong

A. Muscular (distributing) arteries

Muscular arteries regulate blood flow to specific organs through vasoconstriction and vasodilation. They lack the high concentration of elastic fibers needed to absorb systolic pressure surges.

C. Arterioles

Arterioles are small resistance vessels that control blood flow into capillaries. They do not expand significantly during systole and play little role in absorbing pressure fluctuations.

D. Veins

Veins carry blood back to the heart at low pressure. They do not experience systolic surges or expand in the same way as elastic arteries. Instead, they rely on valves and skeletal muscle pumps to aid venous return.

Correct Answer:

B. Excretion

Explanation

Excretion refers to the elimination of metabolic waste products from the body. The skin assists this process through sweat glands, which release substances such as urea, salts, and ammonia in sweat. While the kidneys are the primary excretory organs, the integumentary system plays a supportive role in waste removal and maintaining homeostasis. This process highlights how the skin contributes to both waste elimination and thermoregulation.

Why Other Options Are Wrong

A. Secretion

Secretion is the release of substances like mucus, hormones, or enzymes that serve a functional role in the body. While glands in the skin also secrete substances such as sebum for lubrication, this is different from the removal of waste, which is excretion.

C. Filtration

Filtration refers to the process of separating substances based on size or charge, such as in the kidneys’ glomeruli. It is not a function of the skin and does not describe the elimination of waste through sweat glands.

D. Absorption

Absorption refers to the uptake of substances into the body, such as nutrients through the intestines or certain medications through the skin. This is the opposite of excretion, which involves releasing substances from the body rather than taking them in.

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. 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. Macrophages

Explanation

Macrophages are immune cells found in connective tissue that play a vital role in the body’s defense system. They engulf and destroy pathogens, cellular debris, and dead cells through phagocytosis. In wounds or infections, macrophages are essential for clearing damaged tissue, preventing the spread of infection, and stimulating repair. They act as the “clean-up crew” of the immune system and are critical for both innate and adaptive immune responses.

Why Other Options Are Wrong

A. Fibroblasts

Fibroblasts are connective tissue cells that produce collagen and other fibers of the extracellular matrix. While important for wound healing, they do not engulf or eliminate pathogens.

C. Adipocytes

Adipocytes are fat cells that store lipids, provide insulation, and cushion organs. They do not participate in the immune response or remove debris from infected or injured tissue.

D. Chondrocytes

Chondrocytes are cartilage cells responsible for maintaining the cartilaginous matrix. They are not immune cells and have no role in fighting infections or clearing debris.

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.