AP BIOLOGY 2012 SCORING GUIDELINES

AP? BIOLOGY 2012 SCORING GUIDELINES

Question 4

Note: At least 1 point must be earned from each of parts (a), (b), and (c) in order to earn a maximum score of 10.

The element carbon is contained in all organic compounds.

(a) Discuss the role of photosynthesis and cellular respiration in carbon cycling in the biosphere. (2 points maximum)

Photosynthesis Cellular respiration

Discussion (1 point per box) x Removes CO2 from the atmosphere. x Reduces (or uses) CO2. x Fixes carbon into organic molecules (sugars). x Metabolizes (oxidizes, catabolizes) organic molecules (sugars). x Returns CO2 to the atmosphere. x Releases CO2.

(b) For THREE of the following, predict and explain the effect on the carbon cycle if: x decomposers were absent x deforestation occurred x volcanic dust accumulated in the atmosphere x the average ocean temperature increased (6 points maximum)

Decomposers absent Deforestation

Volcanic dust in atmosphere

Average ocean temperature increased

Prediction (1 point per box; 3 points maximum) x Less CO2 in atmosphere. x More carbon stored in dead

organisms. x More CO2 in atmosphere. x Fewer carbon compounds in

organisms. x More CO2 in atmosphere. x Fewer carbon compounds in

organisms. x More CO2 in atmosphere. x Less CO2 in ocean.

x Less CO2 in atmosphere.

x No net change in CO2 reservoirs.

Explanation (1 point per box; 3 points maximum) x CO2 is not released. x Organic material is not degraded.

x Decreased photosynthesis.

x Less solar radiation causes less photosynthesis.

x Increased decomposition/rate of respiration.

x Decreased CO2 solubility (less photosynthesis).

x Increased photosynthesis (e.g., algae blooms).

x Decreased O2 solubility, resulting in decreased respiration.

x Increased photosynthesis AND respiration.

? 2012 The College Board. Visit the College Board on the Web: .

AP? BIOLOGY 2012 SCORING GUIDELINES

Question 4 (continued)

(c) Explain how increased CO2 in the atmosphere results in greater acidification of oceans and describe the effect on marine organisms. Include in your discussion TWO examples of how human activity can increase atmospheric CO2. (4 points maximum)

Explanation (1 point)

Effect (1 point)

Examples (1 point each; 2 points maximum)

x CO2 dissolves, forming an acid (carbonic acid); the release of H+ ions

decreases pH.

( CO2 + H2O R H2CO3 R H+ + HCO3 )

x Decreases ability to make corals/shells/exoskeletons.

x Decreases availability of CO32 for formation of CaCO3 because more H+

combines with CO32 .

x Decreases efficiency of enzymes in suboptimal pH.

x Combustion of gasoline/diesel.

x Combustion of coal.

OR Combustion of fossil fuels.

x Combustion of natural gas.

x Combustion of wood.

x Combustion/decomposition of wastes.

x Deforestation reduces photosynthesis.

? 2012 The College Board. Visit the College Board on the Web: .

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