AP Biology Free-Response Practice Questions

You should immediately realize that this is a question about cellular respiration. You should draw on your knowledge of this topic to answer the question. Use the organism that you used when completing this lab (commonly germinating peas).

(A) Key points to include: the organism you chose, clear identification of the experimental variable, clear explanation for the variables that you must control, an explanation of the apparatus that you will use to measure the cellular respiration

Here is a possible response:

Cellular respiration can most easily be measured by consumption of O2 or by the production of CO2. In this experiment, the volume of O2 consumed by germinating peas will be measured. The experiment will test peas that have been germinating one day vs. peas that have been germinating for three days. Therefore, the number of days the peas have been germinating will be my experimental variable. I will use an apparatus called a respirometer to measure the amount of O2 consumed. This device will be submerged underwater with a pipette attached to the end. I will be able to measure the amount of water drawn into the pipette by comparing where the water mark begins and where it ends. I will eliminate the production of CO2 as a variable by using potassium hydroxide (KOH) to fix CO2 into a solid form: potassium carbonate (K2CO3). KOH will be added to an absorbent cotton ball and placed on the bottom of the respirometer with a non-absorbent cotton ball in between, so the KOH will not interfere with the experiment. Because volume must be controlled, I will use glass beads to control the volume differences between the two germinating pea samples.

I will place each respirometer in the same tub of water to control temperature between the two germinating pea samples.

Hypothesis: Measuring cellular respiration for 30 minutes at intervals of 10 minutes at a time will demonstrate that peas that have been germinating for three days will consume more oxygen through cellular respiration than peas that have been germinating one day.

Procedure: I will place 20 peas that have been germinating for one day in one respirometer and 20 peas that have been germinating for three days in another respirometer. After a 10-minute equilibration period, I will begin to measure the amount of oxygen consumed at 10-minute intervals for 30 minutes. I will record results measured by the graduated intervals on the pipette attached to the respirometer.

(B) Key points to include: labels on each axis, regular intervals on the graph, a specific title on the graph, points plotted on the graph, and a line connecting the appropriate points. If there is more than one plot on the graph, you should use a dotted line for one line and a solid line for the other. Alternatively, you can simply write a short phrase above each line for identification.

Here is a sample graph:

(C) Key points to include: clear explanation of the graph and clear explanation of the significance of the results

Here is a possible response:

The graph shows that peas that have been germinating for three days consume more oxygen during a 30-minute period than peas that have been germinating for one day. The peas that have only been germinating for one day are not as well developed. Therefore, these peas are not undergoing as much cellular respiration as the more developed peas that have been germinating for three days.

Key points to include: genes, base pairs, replication, proteins, diversity

Here is a possible response:

DNA is composed of only four different base pairs, and there is only one different base pair, uracil instead of thymine, in RNA. This has created a very simple system for duplication. When a cell replicates its DNA during mitosis, it simply unzips the double helix and adds nucleic acids along its length until a duplicate set of complementary strands is created. The base pairs bond with hydrogen bonds, with cytosine bonding to guanine and adenine bonding to thymine. DNA molecules are very long, but because the code only involves four different base pairs, it can easily be duplicated. The DNA strands are actually copied in small segments and linked together to form an entire strand.

Although there are only four different base pairs, the longer the strand gets, the more combinations of base pairs can be created. These long series of base pairs code for longer and more complex proteins that can differ in minor or very significant ways. For example, sickle cell anemia is caused by only one base pair difference in the genetic code for hemoglobin, but this base pair causes an incredible difference in the function of the protein. The high number of potential combinations from only four base pairs and the impact of small changes in the sequence of base pairs contributes to the diversity of proteins in an organism. This diversity of proteins contributes to the diversity of organisms that exist because physiological function is essentially protein driven. In essence, long and diverse code leads to diverse proteins, which leads to diverse organisms.