Anatomy and Physiology I with Lab (D312)

Correct Answer

D. 28

Explanation

The electron capacity of the first three principal energy levels follows the 2n² rule, where n is the energy level number:

The first energy level (n = 1) can hold 2 electrons (2 × 1² = 2).

The second energy level (n = 2) can hold 8 electrons (2 × 2² = 8).

The third energy level (n = 3) can hold 18 electrons (2 × 3² = 18).

Adding them together: 2 + 8 + 18 = 28 electrons.

Why other options are wrong

A. 2. This is incorrect because 2 electrons is the maximum capacity of only the first energy level, not the total for the first three levels.

B. 8. This is incorrect because 8 electrons is the maximum number that can fit in the second energy level alone, but not the combined capacity of the first three energy levels.

C. 18. This is incorrect because 18 electrons is the total for the first two levels plus part of the third, but the full capacity of the first three energy levels is 28.

Correct Answer

D. Responsiveness

Explanation

Responsiveness (also known as irritability or sensitivity) is a fundamental characteristic of living organisms. It refers to the ability of an organism to detect and respond to stimuli from the environment. This can include physical changes like temperature or light, or chemical changes in the body. Unlike non-living things, living organisms actively interact with their surroundings to maintain homeostasis and adapt to their environment.

Why other options are wrong

A. Growth

Growth refers to an increase in size or mass of an organism, but it does not directly involve detecting or responding to changes in the environment. While growth is essential to living organisms, it is not the process that distinguishes life based on responsiveness.

B. Differentiation

Differentiation is the process by which cells become specialized for specific functions. While it is crucial in development, it does not directly involve the organism’s ability to respond to external changes in the environment.

C. Movement

Movement is an important characteristic of many living organisms, but not all life forms exhibit visible movement. Movement can occur at the cellular level or at the organismal level, but it is not as central to distinguishing life as responsiveness is.

Correct Answer

A. The movement of molecules across a membrane by means of a protein carrier

Explanation

Mediated transport refers to the assisted movement of molecules across a cell membrane using specific transport proteins. This process is necessary for substances that cannot diffuse freely through the lipid bilayer, such as glucose, ions, and amino acids. Mediated transport can be passive (facilitated diffusion), where molecules move down their concentration gradient, or active (requiring ATP) when molecules are transported against their gradient. Examples include the glucose transporter (GLUT) and sodium-potassium pump (Na+/K+ ATPase).

Why other options are wrong

B. The ability of molecules to pass through the nuclear membrane

While some molecules, like RNA and proteins, pass through the nuclear pore complex, this process is called nuclear transport, not mediated transport. Mediated transport specifically involves membrane transport proteins in the plasma membrane.

C. The process of peptide synthesis on the surface of the ribosome

Peptide synthesis occurs in ribosomes, but it does not involve membrane transport proteins. Instead, ribosomes facilitate the assembly of amino acids into polypeptides using mRNA as a template.

D. The movement of vesicles by intermediate filaments

The movement of vesicles within a cell is facilitated by cytoskeletal components, such as microtubules and motor proteins (kinesin and dynein), not intermediate filaments. Intermediate filaments primarily provide structural support, while vesicle transport is classified under cytoskeletal transport, not mediated transport.

Correct Answer

C. Because the 3D structure necessary for its function is disrupted

Explanation

Protein denaturation occurs when the protein's three-dimensional structure is disrupted, usually due to changes in temperature, pH, or chemical environment. The 3D shape of a protein is crucial for its function, as it determines how the protein interacts with other molecules. When the shape is altered, the protein can no longer perform its specific biological function, leading to a loss of activity.

Why other options are wrong

A. Because it becomes more soluble in water. Denaturation does not primarily affect the solubility of a protein, but rather its structure. A denatured protein may actually become less soluble in water, depending on the environment.

B. Due to the destruction of its amino acids. Denaturation does not destroy the amino acids themselves but changes the protein's structure, which interferes with its ability to function.

D. It leads to a reduction in the number of peptide bonds. Denaturation does not break peptide bonds. The amino acid sequence remains intact; it's the folding of the protein that is disrupted, affecting its function.

Correct Answer

C. Glucagon

Explanation

During fasting, the body needs to increase the availability of glucose for energy. Glucagon is released by the pancreas to stimulate the breakdown of glycogen into glucose in the liver, raising blood glucose levels. This response is a natural mechanism to ensure that the body has enough energy during periods without food intake.

Why other options are wrong

A. Insulin

This is incorrect because insulin is secreted in response to high blood glucose levels, typically after eating. During fasting, insulin levels decrease to prevent further storage of glucose and facilitate the breakdown of energy stores.

B. Prolactin

This is incorrect because prolactin is involved in milk production and is not directly related to energy regulation during fasting. Its levels are typically elevated in lactating individuals.

D. Melatonin

This is incorrect because melatonin is primarily involved in regulating sleep-wake cycles and does not have a significant role in blood glucose regulation during fasting.

Correct Answer

B. A passive form of transport to move large, water-soluble compounds into the cell

Explanation

Facilitated diffusion is a passive transport process where substances like glucose or ions move across the plasma membrane with the help of carrier proteins or channels, but without the need for energy. These substances move from an area of higher concentration to lower concentration, following the concentration gradient. This process does not require energy (ATP), which differentiates it from active transport. It helps larger or water-soluble molecules, which cannot easily pass through the lipid bilayer, to enter or exit the cell.

Why other options are wrong

A. An active process to get needed substances such as glucose into the cell

This is incorrect because facilitated diffusion is a passive process, not active. Active transport requires energy to move substances against their concentration gradient, but facilitated diffusion relies on the concentration gradient and does not use energy.

C. A passive form of transport that moves substances up their concentration gradient

This is incorrect because facilitated diffusion moves substances down their concentration gradient (from high to low concentration), not up. Moving substances against their concentration gradient requires active transport, not facilitated diffusion.

D. An active transport process which moves substances down their concentration gradient

This is incorrect because facilitated diffusion is passive, not active. Active transport would require energy (ATP) to move substances, while facilitated diffusion relies on the concentration gradient and does not require energy.

Correct Answer

A. It reinforces changes in controlled conditions.

Explanation

Positive feedback systems enhance or amplify a change rather than counteracting it. Instead of maintaining stability, positive feedback loops push a process further away from its normal state. These systems are typically used when a rapid or extreme response is required, such as during childbirth (oxytocin release intensifying contractions) or blood clotting (platelets activating more platelets to stop bleeding). Unlike negative feedback, which seeks to restore balance, positive feedback drives the body towards a more intense response.

Why other options are wrong

B. It maintains a constant internal environment.

This describes negative feedback, not positive feedback. Negative feedback regulates internal conditions by reversing deviations from a set point to restore balance, such as temperature regulation or blood sugar control.

C. It produces corrective responses to disruptions.

Positive feedback does not produce corrective responses; instead, it amplifies changes. Negative feedback corrects disruptions by counteracting changes to maintain homeostasis, like shivering to generate heat when cold.

D. It is less common in the body's regulatory mechanisms.

While positive feedback systems are less common than negative feedback, this answer does not fully explain how they differ. The defining feature of positive feedback is its ability to reinforce changes rather than correct them.

Correct Answer

C. Cells will shrink as water moves out to balance solute concentration.

Explanation

In a hypertonic solution, the solute concentration outside the cell is higher than that inside the cell. As a result, water moves out of the cell through osmosis to balance the concentration gradient, causing the cell to shrink. This is a characteristic response of cells in hypertonic environments.

Why other options are wrong

A. Cells will swell and potentially burst due to excess water intake. This is incorrect. Swelling and bursting typically occur in hypotonic solutions where water enters the cell, not in hypertonic solutions where water leaves the cell.

B. Cells will remain unchanged as the solute concentration is balanced. This is incorrect. In hypertonic solutions, the solute concentration is not balanced, and water moves out of the cell, causing it to shrink.

D. Cells will absorb solutes from the surrounding solution to maintain volume. This is incorrect. While cells can take up solutes in certain cases, in a hypertonic solution, the primary process that occurs is the movement of water out of the cell, not the absorption of solutes.

Correct Answer

C. Potassium has a higher reactivity because the valence electron on potassium is farther from the nucleus.

Explanation

Potassium (K) has a higher reactivity than sodium (Na) because its valence electron is farther from the nucleus. This makes the valence electron more easily lost because it is less tightly held by the nucleus due to the increased distance. The atomic radius of potassium is larger than that of sodium, so its outermost electron is more shielded from the attractive force of the nucleus, making it easier to remove.

Why other options are wrong

A. This cannot be determined from the information given.

This is incorrect because the trend in reactivity of alkali metals (like sodium and potassium) is well-known: the reactivity increases as you move down the group in the periodic table, due to the increasing distance of the valence electron from the nucleus.

B. Potassium has a lower reactivity because potassium has more protons than sodium.

This is incorrect because while potassium has more protons, it also has more electron shells, which results in greater shielding and a larger atomic radius, making it more reactive, not less.

D. Both metals have the same reactivity because the potassium and sodium valence electrons experience the same effective nuclear charge.

This is incorrect because the effective nuclear charge felt by the valence electrons decreases as you move down the group, not staying the same. Potassium’s valence electron is less tightly bound to the nucleus compared to sodium’s, making potassium more reactive.