Q: Calculate the average atomic mass of an element with two isotopes: 90% with mass $$10.0$$ and 10% with mass $$11.0. $$Which formula should you use?

$$\text{Average Mass} = (10.0 \times 0.9) + (11.0 \times 0.1)$$

Question 1

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

Accepted Answer

Oxygen is a major component of water, which makes up most of the mass of living organisms.

Question 2

Why do plants have a higher percentage of carbon by mass compared to humans?

Accepted Answer

Plants store large amounts of carbon in cellulose within their cell walls, which humans lack.

Question 3

A patient is injected with a radioactive isotope for medical imaging. Why is it important that this isotope has a short half-life?

Accepted Answer

Short half-lives allow the isotope to provide enough radiation for imaging while minimizing long-term radiation exposure to tissues.

Question 4

Which of the following best describes the difference between Oxygen-16 and Oxygen-18?

Accepted Answer

Oxygen-18 has two more neutrons than Oxygen-16, but both have the same chemical properties.

Question 5

Calculate the average atomic mass of an element with two isotopes: 90% with mass $$10.0$$ and 10% with mass $$11.0. $$Which formula should you use?

Accepted Answer

$$	ext{Average Mass} = (10.0 	imes 0.9) + (11.0 	imes 0.1)$$

Question 6

What does the decimal value of atomic mass on the periodic table represent?

Accepted Answer

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

Question 7

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 8

Why is water such an effective solvent for ions and polar molecules?

Accepted Answer

Water's bent polar geometry creates partial charges that surround and stabilize ions and polar solutes.

Question 9

Methane ($$CH_4) is $$considered nonpolar. Which property of its molecular structure explains this?

Accepted Answer

Methane has a symmetrical tetrahedral shape, resulting in equal sharing of electrons and no net dipole.

Question 10

During cellular respiration, why does glucose yield more usable energy than water?

Accepted Answer

Glucose contains many high-energy nonpolar covalent bonds that can be broken to release energy, while water does not.

Question 11

A new drug is designed to mimic the structure of a natural neurotransmitter. According to the 'lock-and-key' model, what property must the drug have to be effective?

Accepted Answer

It must have a 3D shape that closely matches the active binding region of the receptor.

Question 12

What is a likely consequence of prolonged use of morphine, based on its interaction with opioid receptors?

Accepted Answer

The body downregulates natural endorphin production, leading to tolerance and potential addiction.

Question 13

If a plant is grown in nitrogen-poor soil, what is the most direct effect on its growth?

Accepted Answer

The plant cannot synthesize amino acids and nucleotides, limiting protein and DNA/RNA production.

Question 14

Which of the following best illustrates the principle 'form follows function' in biological molecules?

Accepted Answer

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

Question 15

Which of the following is a correct statement about 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 16

A scientist discovers a new isotope of nitrogen with a mass number of 15. How many neutrons does this isotope have?

Accepted Answer

$$15 - 7 = 8$$ neutrons

Question 17

Which of the following best explains why a molecule with a symmetrical shape and equal sharing of electrons is nonpolar?

Accepted Answer

The molecule's symmetry causes any partial charges to cancel out, resulting in no net dipole moment.

Question 18

If a patient is exposed to a radioactive isotope with a long half-life, what is the primary risk compared to an isotope with a short half-life?

Accepted Answer

The patient will be exposed to radiation for a longer period, increasing the risk of tissue damage.

Question 19

Which of the following scenarios best demonstrates the concept of molecular mimicry in medicine?

Accepted Answer

A drug with a similar 3D structure to a natural hormone binds to the same receptor, producing a similar physiological effect.

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

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