Question 1

Which of the following best explains why oxygen is the most abundant element by mass in most living organisms?

Accepted Answer

Oxygen is a major component of water, which makes up a large portion of living organisms, and is essential for cellular respiration.

Question 2

Plants have a higher percentage of carbon by mass compared to humans primarily because:

Accepted Answer

Plants store large amounts of carbon in their cell walls as cellulose, which is synthesized from atmospheric carbon dioxide.

Question 3

Which of the following best describes the role of calcium and phosphorus in humans compared to plants?

Accepted Answer

Humans use calcium and phosphorus for bone and teeth mineralization, while plants lack mineralized skeletal systems.

Question 4

A farmer notices that his crops are stunted and yellowing. Soil tests reveal a lack of accessible nitrogen. Which of the following best explains the effect of nitrogen deficiency on plant growth?

Accepted Answer

Without nitrogen, plants cannot synthesize amino acids and nucleotides, restricting protein and DNA/RNA production and thus growth.

Question 5

How many neutrons are present in an atom of Oxygen-18?

Accepted Answer

10

Question 6

Why are isotopes with short half-lives preferred for medical imaging procedures?

Accepted Answer

They decay quickly, delivering sufficient imaging radiation while minimizing long-term tissue damage.

Question 7

Given the following isotope abundances for carbon: $$^{12}\mathrm{C} (98.90$$%, mass = 12.000000) and $$^{13}\mathrm{C} (1.10$$%, mass = 13.003355), calculate the average atomic mass of carbon. Use the formula: $$	ext{Average Mass} = (	ext{mass}_1 	imes 	ext{abundance}_1) + (	ext{mass}_2 	imes 	ext{abundance}_2).$$

Accepted Answer

$$12.011$$

Question 8

What does the decimal value of atomic mass (e.g., 12.011 for carbon) on the periodic table represent?

Accepted Answer

The average mass of all naturally occurring isotopes, weighted by their percent abundance.

Question 9

Which of the following statements best explains why water is an excellent solvent for biological molecules?

Accepted Answer

Water's bent polar geometry creates partial charges that allow it to surround and dissolve charged ions and polar solutes.

Question 10

Methane ($$\mathrm{CH}_4) is $$considered nonpolar because:

Accepted Answer

Its tetrahedral shape distributes charge symmetrically, resulting in equal sharing of electrons and no net dipole.

Question 11

Why does glucose contain more usable chemical energy than water?

Accepted Answer

Glucose contains many nonpolar high-energy covalent bonds that release energy when broken during cellular respiration.

Question 12

Which of the following best illustrates the principle of 'form follows function' in molecular biology?

Accepted Answer

The 3D structure of a molecule determines how it interacts with other molecules, such as binding to receptors or storing energy.

Question 13

Which element forms exactly three covalent bonds in most biological molecules, and why?

Accepted Answer

Nitrogen, because it has five valence electrons and typically forms three bonds to complete its octet.

Question 14

A new drug is designed to relieve pain by binding to opioid receptors. Which property would most likely make it more effective than natural endorphins?

Accepted Answer

It has a higher binding affinity for the opioid receptor, allowing it to trigger a stronger pain relief response.

Question 15

Morphine is able to relieve pain because:

Accepted Answer

Its 3D shape mimics the active binding region of natural endorphins, fitting the opioid receptor like a key in a lock.

Question 16

What is a major risk of prolonged morphine use in patients?

Accepted Answer

Chronic morphine binding causes the body to downregulate natural endorphin production, leading to tolerance and addiction.

Question 17

A patient is injected with a radioactive isotope for a PET scan. Which property of the isotope is most important for patient safety?

Accepted Answer

It has a short half-life, so it decays quickly and minimizes radiation exposure.

Question 18

Which of the following best describes the relationship between atomic number, mass number, and isotopes?

Accepted Answer

Isotopes of an element have the same atomic number but different mass numbers due to varying numbers of neutrons.

General Biology: Elements, Atomic Structure, and Molecular Biology Study Guide

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