Water & Chemical Elements (College Board AP® Biology): Flashcards
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Define polar molecule.
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Define polar molecule.
A polar molecule has an unequal distribution of charge, giving it a partially negative region and a partially positive region.
Why is water a polar molecule?
The electrons in its covalent bonds are shared unequally between oxygen and hydrogen.
The oxygen atom gains a partial negative charge (δ⁻) and the hydrogen atoms gain a partial positive charge (δ⁺).
The weak forces of attraction that form between the partially positive hydrogen of one water molecule and the partially negative oxygen of another are called .
The weak forces of attraction that form between the partially positive hydrogen of one water molecule and the partially negative oxygen of another are called hydrogen bonds.
True or False?
Hydrogen bonds are stronger than the covalent bonds within a water molecule.
False.
Hydrogen bonds are weak forces of attraction between molecules. The covalent bonds joining oxygen and hydrogen within a water molecule are much stronger.
Water has a high , meaning a large amount of energy is needed to raise its temperature.
Water has a high specific heat capacity, meaning a large amount of energy is needed to raise its temperature.
Explain why water has a high specific heat capacity.
Hydrogen bonds restrict the movement of water molecules.
These bonds must be disrupted before the kinetic energy of the molecules can increase, so a lot of energy is needed to raise the temperature.
How does the high specific heat capacity of water benefit living organisms?
Water is thermally stable, so its temperature changes slowly even when environmental temperatures fluctuate.
Aquatic birds and mammals expend less energy on thermoregulation during homeostasis.
Enzyme activity inside cells stays close to optimal despite external temperature change.
Explain why water has a high heat of vaporization.
A large amount of energy is needed to break the hydrogen bonds between water molecules before they can escape into a gaseous state.
How does the high heat of vaporization of water allow organisms to cool down?
As water evaporates it absorbs heat energy from the surface beneath it, producing a cooling effect.
In animals, sweating and panting allow heat loss by evaporation.
In plants, transpiration keeps leaves cooler than the surrounding air.
Define cohesion.
Cohesion is the force of attraction between molecules of the same type.
Define adhesion.
Adhesion is the force of attraction between molecules of different types.
How do cohesion and adhesion move water up the xylem of a plant?
Cohesion means water molecules are drawn upwards behind one another as a continuous column.
Adhesion between water molecules and the xylem walls draws water upwards by capillary action.
Define surface tension.
Surface tension is the effect produced when cohesive forces attract water molecules at the surface to the water molecules below them.
True or False?
Surface tension allows small organisms such as pond skaters to walk on the surface of water.
True.
Cohesion between water molecules creates surface tension, which supports the weight of small insects.
True or False?
Adhesion is the force of attraction between water molecules and the walls of the xylem.
True.
Adhesion acts between molecules of different types, so it describes the attraction between water and the xylem wall.
Cohesion acts between the water molecules themselves.
Name the three properties of water that living systems depend on to sustain life.
Polarity
High specific heat capacity
High heat of vaporization
Which three elements are the most prevalent in biological molecules?
Carbon
Hydrogen
Oxygen
They are the main elements in carbohydrates, proteins, and lipids.
Where do organisms get the atoms and small molecules they use to build biological molecules?
They take them up from their environment, then use them to build new biological molecules.
The element is found in some amino acids and so is present in proteins.
The element sulfur is found in some amino acids and so is present in proteins.
Which two types of biological molecule is phosphorus used to build?
Phospholipids (a type of lipid)
Nucleic acids (DNA and RNA)
The element is needed to build nucleic acids and amino acids.
The element nitrogen is needed to build nucleic acids and amino acids.
True or False?
Carbon, hydrogen, and oxygen are found in carbohydrates, proteins, and lipids.
True.
These three elements are the most prevalent in biological molecules and appear in all three of these macromolecule types.
Which element is present in nucleic acids but not in carbohydrates or lipids?
Nitrogen (nucleic acids also contain phosphorus).
Carbohydrates and lipids are built mainly from carbon, hydrogen, and oxygen.
Define phospholipid.
Phospholipids are a type of lipid, built using phosphorus, that group together to form the lipid bilayers of cell membranes.
True or False?
Phosphorus is one of the elements used to build proteins.
False.
Proteins are built mainly from carbon, hydrogen, oxygen, nitrogen, and sulfur. Phosphorus is used to build phospholipids and nucleic acids.
Why do organisms need to take up nitrogen from their environment?
Nitrogen is needed to build amino acids (and therefore proteins) and nucleic acids.
Carbon, hydrogen and oxygen are the most elements in biological molecules.
Carbon, hydrogen and oxygen are the most prevalent elements in biological molecules.
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