AP Biology : 1.1 Structure of Water and Hydrogen Bonding – Exam Style questions with Answer- MCQ

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Question

The figure presents a lake covered by a layer of ice. The air above the ice is negative 5 degrees Celsius. Immediately below the ice, the temperature of the lake water is 0 degrees Celsius. The water deeper in the lake is 4 degrees Celsius. There is a fish in this deeper water.

 

As shown in the diagram, when environmental temperatures drop below freezing, a layer of ice typically forms on the surface of bodies of freshwater such as lakes and rivers.
Which of the following best describes how the structure of ice benefits the organisms that live in the water below?

A. The water molecules in ice are closer together than those in liquid water, so the ice prevents the passage of air to the water, maintaining a constant gas mixture in the water.

B. The water molecules in ice are closer together than those in liquid water, so the ice forms a barrier that protects the organisms in the water from the freezing air temperatures.

C. The water molecules in ice are farther apart than those in liquid water, so the ice floats, maintaining the warmer, denser water at the lake bottom.

D. The water molecules in ice are farther apart than those in liquid water, so the ice floats, preventing the escape of gases from the liquid water.

▶️Answer/Explanation

Ans: C
The water molecules in ice are farther from each other than are water molecules in liquid water, so ice is less dense than liquid water and floats on its surface, while the denser water at 4 degrees Celsius sinks to the bottom, maintaining a steady temperature all winter.

Question

Water molecules are polar covalent molecules. There is a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms due to the uneven distribution of electrons between the atoms, which results in the formation of hydrogen bonds between water molecules. The polarity of water molecules contributes to many properties of water that are important for biological processes.

Which of the following models best demonstrates the arrangement of hydrogen bonds between adjacent water molecules?

A.    The figure presents two water molecules. Each water molecule consists of an oxygen atom bonded to two hydrogen atoms. The molecules are shaped like a wide letter V. In this figure, the two molecules are side by side, with all four hydrogen atoms aligned horizontally below, and both oxygen atoms aligned horizontally above. Hydrogen bonds are shown between the right hydrogen atom of the left water molecule, and the left hydrogen atom of the right water molecule.

B.

The figure presents two water molecules. Each water molecule consists of an oxygen atom bonded to two hydrogen atoms. The molecules are shaped like a wide letter V. In this figure, the two molecules are oriented such that the oxygen atoms of each are close together and the hydrogen atoms point away. Hydrogen bonds are shown between the two oxygen atoms.

C.

The figure presents two water molecules. Each water molecule consists of an oxygen atom bonded to two hydrogen atoms. The molecules are shaped like a wide letter V. The two molecules are oriented with the oxygen atoms below and the hydrogen atoms above. One water molecule is placed below and slightly to the right of the other water molecule. Hydrogen bonds are shown between the two hydrogen atoms on the right side of each water molecule and between the oxygen atom of the upper water molecule and the left hydrogen atom of the lower water molecule.

 

D.

The figure presents two water molecules. Each water molecule consists of an oxygen atom bonded to two hydrogen atoms. The molecules are shaped like a wide letter V. The water molecules are side by side but in different orientations. The molecule on the left is oriented with the hydrogen atoms below and the oxygen atom above. The water molecule on the right is rotated a quarter turn such that the oxygen atom is to the left and the two hydrogen atoms stick out to the right. A hydrogen bond is shown between the right side hydrogen atom of the water molecule on the left and the oxygen atom of the water molecule on the right.

▶️Answer/Explanation

Ans: D
The hydrogen bonds between these water molecules correctly show the attractive force between the hydrogen atom of one water molecule and the oxygen atom of the adjacent water molecule.

Question

In vascular plants, water flows from root to leaf via specialized cells called xylem. Xylem cells are hollow cells stacked together like a straw. A student explains that evaporation of water from the leaf pulls water up from the roots through the xylem, as shown in Figure 1.

The figure presents a diagram of water flow through a plant. Arrows labeled Xylem Tissues Carry Water point from the roots into and up through the stem of the plant. Some of the arrows also point into a leaf. The leaf is shaded and labeled Water from the Soil. Arrows point out from the leaf into the air and are labeled Evaporation of Water from Leaves. A zoomed in portion of the stem shows the xylem in the stem, with dots representing water molecules and arrows pointing up through the xylem. A zoomed in portion of the leaf shows a cross section of the leaf with leaf cells on each side of a row of xylem-like cells that contain the dots that represent water. More dots are shown moving from the leaf into the air through an opening between the leaf cells.

Figure 1. Model of water movement through the xylem, with magnified models of water movement in the stem and leaf.

Which statement describes how water is pulled up through the xylem to the leaves of the plant?

A. As water exits the leaf, hydrogen bonding between water molecules pulls more water up from below.

B. As water exits the leaf, signals are sent to the roots to pump more water up to the leaves through the xylem by adhesion.

C. Evaporation from the leaf decreases the hydrogen bonds that form between the water molecules in the xylem, which helps the water molecules to be pulled up the xylem.

D. Evaporation of water from the leaf increases the hydrogen bonds that form between water molecules in the air, providing the energy for transport.

▶️Answer/Explanation

Ans: A
As water exits the leaf, hydrogen bonding pulls more water molecules up through the leaf and xylem by cohesion.

Question

In a water molecule, hydrogen atoms are attached to oxygen atoms
through which type of bond?
(A) hydrogen bond
(B) nonpolar covalent bond
(C) polar covalent bond
(D) ionic bond

▶️Answer/Explanation

Ans:

(C) Oxygen atoms and hydrogen atoms are joined in covalent bonds
within a water molecule. Because oxygen has a higher electronegativity
than hydrogen does, the electrons in this bond are unequally shared,
and this results in a polar covalent bond. Choice (A) is incorrect
because hydrogen bonds occur between different water molecules, not
within a given water molecule. Choice (B) is incorrect because
nonpolar covalent bonds form between atoms with similar
electronegativities. Choice (D) is incorrect because the electrons in the
bonds within a water molecule are shared; they are not transferred as is
the case in an ionic bond.

Question

The attraction between the partially positive charge on a hydrogen atom
on one water molecule and the partially negative charge on an oxygen
atom on another water molecule is called a(n)
(A) hydrogen bond.
(B) nonpolar covalent bond.
(C) polar covalent bond.
(D) ionic bond.

▶️Answer/Explanation

Ans:

(A) Hydrogen bonds occur between the hydrogen atom of one water
molecule and the oxygen atom of another water molecule. Choices (B)
and (C) are incorrect because both describe intramolecular bonds, not
intermolecular bonds between different molecules. Choice (D) is
incorrect because there is no transfer of electrons between water
molecules.

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