AP biology 2009 free response
AP® BIOLOGY
2009 SCORING GUIDELINES (Form B)
Question 3
Water is essential to all living things.
(a) Discuss THREE properties of water.
(b) Explain each of the following in terms of the properties of water. You are not limited to the three properties discussed in part (a):
•
•
•
the role of water as a medium for the metabolic processes of cells the ability of water to moderate temperature within living organisms and in organisms’ environments the movement of water from the roots to the leaves of plants
(a) Discuss THREE properties of water (6 points maximum):
Name of property and correct description (2 points). Points MUST provide both property and description. Property
Polarity of water
Specific heat/high heat capacity High heat of vaporization
Adhesion
Cohesion
Three states of matter
Repels hydrophobic material
and
Description (2 points jointly)
Polar covalent bonds created by unequal sharing of electrons between O and H within the molecule
Heat absorption without temperature change
Water molecules absorb energy as it changes state/breaking of bonds by absorbing energy
Attraction to other molecules that are polar or have charge
Attraction to other water molecules due to polar nature of water/ surface tension
Ice–liquid–gas (vapor)
Kinetic energy differences
Expands at 4°C to become less dense
Moves aside nonpolar substances
(b) Explain each of the following in terms of water properties (6 points maximum; 2 points for each part). To earn 10 points, students must get at least 1 application point for each area.
Water’s role as a medium for the metabolic processes of cells (2 points maximum):
• Diffusion—allows for movement of materials through an aqueous solution down the concentration gradient • Osmosis—movement of water across membranes due to water potential differences (down the gradient) • Solvent—dissociation/ionization of materials
• Buffer—explanation of role water plays in formation of bicarbonate
2009 SCORING GUIDELINES (Form B)
Question 3
Water is essential to all living things.
(a) Discuss THREE properties of water.
(b) Explain each of the following in terms of the properties of water. You are not limited to the three properties discussed in part (a):
•
•
•
the role of water as a medium for the metabolic processes of cells the ability of water to moderate temperature within living organisms and in organisms’ environments the movement of water from the roots to the leaves of plants
(a) Discuss THREE properties of water (6 points maximum):
Name of property and correct description (2 points). Points MUST provide both property and description. Property
Polarity of water
Specific heat/high heat capacity High heat of vaporization
Adhesion
Cohesion
Three states of matter
Repels hydrophobic material
and
Description (2 points jointly)
Polar covalent bonds created by unequal sharing of electrons between O and H within the molecule
Heat absorption without temperature change
Water molecules absorb energy as it changes state/breaking of bonds by absorbing energy
Attraction to other molecules that are polar or have charge
Attraction to other water molecules due to polar nature of water/ surface tension
Ice–liquid–gas (vapor)
Kinetic energy differences
Expands at 4°C to become less dense
Moves aside nonpolar substances
(b) Explain each of the following in terms of water properties (6 points maximum; 2 points for each part). To earn 10 points, students must get at least 1 application point for each area.
Water’s role as a medium for the metabolic processes of cells (2 points maximum):
• Diffusion—allows for movement of materials through an aqueous solution down the concentration gradient • Osmosis—movement of water across membranes due to water potential differences (down the gradient) • Solvent—dissociation/ionization of materials
• Buffer—explanation of role water plays in formation of bicarbonate