AP Bio Unit Review

What type of bond is found in water molecules?

• Covalent

• Hydrogen

• Ionic

• Van der Waals

Answer explanation

Bonds between hydrogen and oxygen in water are covalent bonds. The two atoms are sharing their valence electrons.

Recall: This is a POLAR covalent bond since it is unequal sharing of the electrons

How does the covalent bond in water create the hydrogen bond between water molecules?

Answer explanation

The covalent bond is a POLAR covalent bond. This leads to an unequal sharing of electrons. This causes a partial positive end (hydrogen) and partial negative end (oxygen). The partially negative oxygen of one water molecule is attracted to the partially positive hydrogen of another water molecule.

Water property responsible for water movement up the stem

• Adhesion and cohesion

• Less dense as solid

• Specific heat

• Surface tension

Answer explanation

Adhesion is the attraction of water molecules to other polar substances. The water is hydrogen bonded to the walls of the capillary tubes (xylem) of the plant.

Cohesion is the attraction of water molecules to other water molecules. The water is hydrogen bonded to another water molecule creating a “string” of like when you connect a barrel of monkeys.

Water property responsible for evaporative cooling

• Adhesion and cohesion

• Less dense as solid

• Specific heat

• Surface tension

Answer explanation

Specific heat involves the amount of heat absorbed or released to increase or decrease the temperature of the substance by 1 degree Celsius.

Water has a high specific heat, and the water (sweat) will absorb the heat to cool off the animal.

Water property responsible for lake life surviving winter

• Adhesion and cohesion

• Less dense as solid

• Specific heat

• Surface tension

Answer explanation

Due to the hydrogen bonds, water molecules are unable to compact tightly which leaves space between the molecules and causes it to expand upon freezing making it less dense. This causes water to float to the surface creating a buffer to inhibit the lake from freezing which preserves life during winter.

Tags

NGSS.MS-PS1-4

What type of bond is found between water molecules?

• Covalent

• Hydrogen

• Ionic

• Van der Waals

Answer explanation

The bond WITHIN water between the oxygen and hydrogen is a covalent bond since the atoms are sharing electrons from their valence shells. This causes a partial positive charge at the hydrogen and a partial negative charge at the oxygen. Those partial charges lead to hydrogen bonds BETWEEN water molecules as the oxygen of one water is attracted to a hydrogen of another water.

What is a hydrogen bond?

Answer explanation

Attractive bond between an electronegative atom (e.g., oxygen or nitrogen) bonded to a hydrogen AND a hydrogen

Recall, the oxygen/nitrogen is partially negative, and the hydrogen is partially positive so the oppositely charged poles are attracted leading to the hydrogen

What property of water is responsible for skipping rocks on a pond?

• Adhesion

• Cohesion

• Evaporative Cooling

• Less Dense as Solid

Answer explanation

Cohesion is due to the water molecules being attracted to other water molecules. These water molecules create a surface to the pond. Due to the large number of hydrogen bonds, the water has a high surface tension which is why the rock skips on the pond. Not enough force to break the bonds.

What property of water is responsible for aquatic life surviving winter?

• Adhesion

• Cohesion

• Evaporative Cooling

• Less Dense as Solid

Answer explanation

Due to the hydrogen bonds, water molecules are unable to compact tightly which leaves space between the molecules and causes it to expand upon freezing making it less dense. This causes water to float to the surface creating a buffer to inhibit the lake from freezing which preserves life during winter.

Tags

NGSS.MS-ESS2-4

What property of water is used by organism during sweating?

• Adhesion

• Cohesion

• Evaporative Cooling

• Less Dense as Solid

Answer explanation

Evaporative cooling is the act of water molecules absorbing the heat from the surface causing the water to evaporate (and taking the heat energy away from the organism).

Tags

NGSS.MS-ESS2-4