AP biology 2009 free response

Topics: Water, Heat, Surface tension Pages: 10 (1076 words) Published: September 14, 2014
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 ion

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

AP® BIOLOGY
2009 SCORING GUIDELINES (Form B)
Question 3 (continued)
Water’s ability to moderate temperature within living organisms/environments (2 points maximum):
• Specific heat—moderates climates, maintains stable temperature in cells, constant internal environment
• High heat of vaporization—perspiration cooling, evaporative cooling • Ice forming and acting as insulator for lakes, keeping water in liquid state Water from the roots to the leaves of plants (2 points maximum): • Transpiration—moving water away from leaves due to water potential differences/evaporation through stomata

• Capillary action of water due to adhesion and cohesion
• Root pressure—driven by osmosis/movement of water into roots • Negative pressure potential—caused by surface tension of water as it is pulled up xylem

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

© 2009 The College Board. All rights reserved.
Visit the College Board on the Web: www.collegeboard.com.

AP® BIOLOGY
2009 SCORING COMMENTARY (Form B)
Question 3
Sample: 3A
Score: 10
For the most part this response follows the structure of the question. In part (a) the response demonstrates how...
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