A student prepares a cell homogenate from spinach leaves. She performs a cell fractionation experiment to determine the shortest amount time of centrifugation at 2000xg that will yield the highest percentage of chloroplasts in the pellet fraction. She splits the spinach homogenate into 5 equal parts and centrifuges the parts at 2000xg for 0, 5, 10, 15 or 20 min. She then determines the proportion of chloroplasts in the supernatant and pellet fractions. The controlled variable(s) in the student's experiment is/are:. a. proportion of chloroplasts in each fraction.
b. use of same plant homogenate throughout.
c. time of centrifugation in minutes.
d. g-force of centrifugation.

b. use of same plant homogenate throughout.

Explanation:

In an experiment, the controlled variable, also called the CONSTANT is the variable that is kept the same throughout the course of the experiment in order not to influence the result or outcome of the experiment.

In this question, a student performs a cell fractionation experiment to determine the shortest amount time of centrifugation (manipulated variable) at 2000xg that will yield the highest percentage of chloroplasts (responding variable) in the pellet fraction. In this experiment, the variable being controlled is same spinach plant homogenate used throughout.

photosynthesis makes the glucose that is used in cellular respiration to make atp. the glucose is then turned back into carbon dioxide, which is used in photosynthesis. while water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water.

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.