Erika Veidis
AP Biology – Period 1
October 30, 2009
AP Cell Energetics Test Free Response Questions
1. In order to determine the effects of light intensity on the rate of photosynthesis,
four vials must first be filled with 10 germinating peas. A fifth vial must be filled
with glass beads of equal volume to 10 germinating peas instead of the peas.
This will be the control. A stopper attached to a pipette must be attached to the
top of each vial, and wrapped so that it is air-tight. Each vial must be placed in a
pan filled with water. This water must be room temperature to eliminate the
variable of temperature from the experiment. Placing the vials in water serves
the purpose of allowing the student to observe and approximate the amount of
oxygen being produced in photosynthesis by counting the bubbles released. The
pans must be placed in areas of differing light intensity. For example, one should
be placed in the dark, one should be placed in the shade, one should be placed
in partial sunlight, and one should be placed in direct sunlight. It does not matter
where the pan containing the vial with beads is placed, as the results won’t be
affected by light intensity, as no photosynthesis is occurring. In photosynthesis,
the plant consumes carbon dioxide and releases oxygen. The number of oxygen
bubbles being released from each vial will show the rate of photosynthesis in the
peas. The bubbles must be counted over the course of 20 minutes for each vial
and then recorded. As the light intensity increases, the rate of photosynthesis
should too. More energy from the sunlight will increase the rate of photolysis, the
initial step in photosynthesis which splits water molecules, which will in turn
increase the rate of the chain of reactions in photosynthesis. As the rate of
photosynthesis increases, the number of bubbles (oxygen) being released should
increase as well.
2. The optimum temperature for respiration in yeast is 30o Celsius. Enzymes work
best at a specific temperature, and since respiration is a series of enzymecatalyzed reactions, temperature affects the rate of respiration. As temperature
increases, the kinetic energy of the molecules increase, which causes the
reactions to speed up. However, too high temperatures may cause some
enzymes to denature, or unravel and lose function, which explains the decrease
in the rate of respiration. At 70o C, the rate of respiration, measured by the
number of bubbles of gas per minute, is 0, which means that respiration is not
occurring at all, due to the denaturing of the enzymes. The enzymes reached
their peak at 30o, the optimum temperature, before the temperature proved to be
unfavorable to their function.
Yeast cells are placed in an apparatus with a solution of sugar. Four of these
apparatuses are made, each with the same amount of yeast cells and sugar
solution. Each is filled with a solution with a different pH. The apparatus detects
bubbles of gas released by yeast cells, which will provide data about how the pH
affects the rate of respiration. These results should be similar to the results of
the experiment concerning the effects of temperature on the rate of respiration, in
that the rate of respiration should increase as the enzymes approach an optimum
pH, and then decrease as the enzymes get denatured by too high of a pH.