Question 1

Which of the following statements best explains why oxygen, carbon, hydrogen, and nitrogen make up about 96% of the human body’s mass?

Accepted Answer

They are essential elements that participate in the majority of biochemical reactions necessary for life.

Question 2

A sunflower species has adapted to grow in soils contaminated with lead, zinc, and heavy metals. What biological concept does this adaptation illustrate?

Accepted Answer

Evolution of tolerance to toxic elements

Question 3

Which subatomic particle has a mass approximately $1.7 	imes 10^{-24}$ grams and a neutral charge?

Accepted Answer

Neutron

Question 4

If an atom has an atomic number of 8 and a mass number of 18, how many neutrons does it have?

Accepted Answer

$10$

Question 5

Radioactive isotopes are useful in medical imaging, such as PET scans, because:

Accepted Answer

They decay spontaneously, releasing energy and particles that can be traced in biological systems.

Question 6

Which statement correctly describes the relationship between electron energy levels and their distance from the nucleus?

Accepted Answer

Electrons farther from the nucleus have higher potential energy.

Question 7

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed when two atoms share valence electrons.

Question 8

In a water molecule ($\mathrm{H_2O}$), the electrons are shared unequally between oxygen and hydrogen. What type of bond is this?

Accepted Answer

Polar covalent bond

Question 9

Sodium ($\mathrm{Na}$) has 11 electrons. When it reacts with chlorine ($\mathrm{Cl}$), what happens to sodium’s valence electron?

Accepted Answer

It is transferred to chlorine, forming a positive sodium ion and a negative chloride ion.

Question 10

Which of the following is a weak chemical interaction that helps stabilize the structure of biological molecules?

Accepted Answer

Hydrogen bond

Question 11

What is the main reason water has a high surface tension?

Accepted Answer

Water molecules are held together by hydrogen bonds.

Question 12

Which property of water allows it to moderate temperature in living organisms?

Accepted Answer

High specific heat

Question 13

Why does ice float on liquid water?

Accepted Answer

Ice has a lower density than liquid water due to its expanded structure.

Question 14

A solution is made by dissolving table salt ($\mathrm{NaCl}$) in water. What is the solute in this solution?

Accepted Answer

Sodium chloride ($\mathrm{NaCl}$)

Question 15

Which of the following substances is hydrophobic?

Accepted Answer

Oil

Question 16

How many molecules are present in one mole of any substance?

Accepted Answer

$6.02 	imes 10^{23}$

Question 17

If the concentration of hydrogen ions $[\mathrm{H^+}]$ in a solution is $1 	imes 10^{-7}$ M, what is the pH of the solution?

Accepted Answer

$7$

Question 18

Which process describes the transformation of water from liquid to gas, requiring the absorption of heat?

Accepted Answer

Evaporation (vaporization)

Question 19

Which of the following best explains why water is called the 'solvent of life'?

Accepted Answer

Water can dissolve many ionic and polar substances due to its polarity.

Question 20

A chemical reaction in which the forward and reverse reactions occur at the same rate is said to be at:

Accepted Answer

Chemical equilibrium

Study Guide: Chemical Elements, Atomic Structure, Chemical Bonds, and Water Properties in Biology

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