Bio 161: Anatomy and Physiology Final Exam

Correct Answer:

A. Adipose tissue stores fat as white blobs, and areolar tissue contains many fibers for support.

Explanation

Adipose tissue is specialized for fat storage and appears as large white blobs under the microscope because lipids take up most of the cell’s volume, pushing the nucleus to the side. Its primary functions include insulation, cushioning, and energy storage. Areolar tissue, in contrast, contains a loose arrangement of fibers (collagen, elastic, and reticular) that provide support, elasticity, and cushioning. Areolar tissue fills spaces around organs and underlies epithelial tissue, making it the most widely distributed connective tissue in the body.

Why Other Options Are Wrong

B. Areolar tissue stores fat as white blobs, and adipose tissue contains many fibers for support.

This is the reverse of the correct answer. Areolar tissue is fiber-rich, while adipose tissue is specialized for fat storage. Confusing the two would misrepresent their structural and functional roles.

C. Both adipose and areolar tissues primarily contain fibers with little fat storage.

This is incorrect because adipose tissue’s defining feature is fat storage, not fibers. Areolar tissue contains fibers, but adipose does not rely on them for its primary function.

D. Both adipose and areolar tissues primarily store fat and do not contain fibers.

This is incorrect because areolar tissue is fiber-rich and not primarily a fat-storing tissue. Only adipose tissue is specialized for fat storage.

Correct Answer:

B. Pluripotent stem cells (PPSC)

Explanation

Pluripotent stem cells (PPSC) are stem cells that can differentiate into many different types of cells. In the bone marrow, these stem cells give rise to all formed elements of the blood, including red blood cells, various white blood cells, and platelets. This makes them essential for hematopoiesis. Unlike totipotent stem cells, which can form an entire organism, pluripotent stem cells are restricted to forming multiple cell types within a particular category of tissues.

Why Other Options Are Wrong

A. Totipotent stem cells

Totipotent stem cells can form all cell types in the body as well as extraembryonic structures (like the placenta). They are only found in the earliest stages of embryonic development, not in adult bone marrow.

C. Unipotent stem cells

Unipotent stem cells can produce only one type of cell. For example, spermatogonia form sperm, but they lack the flexibility to differentiate into multiple blood cell types.

D. Multipotent stem cells

Multipotent stem cells can differentiate into a limited range of cell types, but they are more restricted than pluripotent stem cells. They cannot give rise to all the diverse blood cells like pluripotent stem cells in the marrow can.

Correct Answer:

A. Glucose

Explanation

Glucose is a large polar molecule and cannot diffuse directly through the hydrophobic core of the phospholipid bilayer. Instead, it requires carrier proteins or transporters, such as the GLUT family, to cross the cell membrane. Its size and polarity make it poorly permeable to lipid environments, so facilitated diffusion or active transport is essential for glucose entry into cells, especially for energy production.

Why Other Options Are Wrong

B. Water

Water is polar but very small, which allows it to cross membranes more easily than glucose. It can move through simple diffusion, but more efficiently through aquaporin channels. Unlike glucose, water is not considered large, and its transport does not require carrier proteins.

C. Oxygen

Oxygen is a small, nonpolar molecule that can easily diffuse through the hydrophobic phospholipid bilayer without assistance. Its nonpolar nature allows it to dissolve in the lipid portion of the membrane. Therefore, it does not need special transport mechanisms like glucose does.

D. Benzene

Benzene is a nonpolar, hydrophobic molecule. Because of its nonpolarity, it readily dissolves in the lipid bilayer and crosses without assistance. It is neither large nor polar, so it does not face the same transport restrictions as glucose.

Correct Answer:

B. Hydrophobic

Explanation

Hydrophobic means “water-fearing” and refers to molecules or molecular regions that do not interact well with water. The fatty acid tails of phospholipids are hydrophobic, so they orient inward, away from the aqueous environments inside and outside the cell. This inward orientation creates the nonpolar interior of the phospholipid bilayer and is essential for forming a stable barrier that regulates what enters and exits the cell.

Why Other Options Are Wrong

A. Hydrophilic

Hydrophilic means “water-loving” and describes molecules that readily interact with water. This property applies to the phosphate heads of phospholipids, which face outward toward aqueous environments, not to the fatty acid tails.

C. Amphipathic

Amphipathic refers to molecules that contain both hydrophilic and hydrophobic regions. While this applies to an entire phospholipid, the question specifically asked about the tails that avoid water, making hydrophobic the correct term.

D. Lipophilic

Lipophilic describes molecules that dissolve in fats or lipid environments. While hydrophobic regions can also be lipophilic, the correct scientific term for avoiding water is hydrophobic. Lipophilic is more descriptive of solubility in fats rather than water avoidance.

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. 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. 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 Answers:

A. Carbohydrates; B. Lipids; C. Proteins; D. Nucleic acids

Explanation of Each Correct Answer

A. Carbohydrates

Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen. They provide quick energy (glucose), store energy (glycogen), and serve structural roles (cellulose in plants).

B. Lipids

Lipids include fats, oils, phospholipids, and steroids. They store long-term energy, provide insulation, form cell membranes, and act as signaling molecules (hormones).

C. Proteins

Proteins are made of amino acids and perform structural, enzymatic, transport, and signaling functions. Examples include collagen, hemoglobin, and enzymes that drive metabolic reactions.

D. Nucleic acids

Nucleic acids, such as DNA and RNA, store and transmit genetic information. DNA provides the instructions for protein synthesis, while RNA helps translate those instructions into functional proteins.

Why Other Options Are Wrong

E. Vitamins

Vitamins are organic compounds required in small amounts for enzyme function and metabolic processes, but they are not considered one of the four macromolecules.

F. Minerals

Minerals are inorganic elements like calcium, potassium, and iron. They play important roles in structure and physiology but are not classified as organic macromolecules.

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.