This is a step by step walkthrough of how to solve FRQ (free response question) #2 from the 2014 AP exam. As you are reading through, comment below if you have any questions and I can answer them.
First, read the question and understand the following:
What is the purpose of the table provided in the question?
What information does it tell us?
What is the question asking for?
The table shows the presence/absence of 4 different proteins in 5 different species.
Part (a)
Recall that a cladogram is a diagram showing how closely different organisms are related. Next, interpret the information presented in the table to use it for the cladogram. Can the presence of certain proteins in the organisms tell us which are most closely related, and which are most distantly related? This will help construct the cladogram.
Remember to explain why you constructed the cladogram as such:
Humans and cats are placed in a separate branch from the other animals because they both lack casein and protein B. Also, note that it does not matter if cat or human goes first on that branch, as long as they are on the same branch. The same logic goes for the cow, pig, and horse.
Each protein most likely arose before the branch(es) containing the species with that protein. For instance, lactose is placed at the largest branching point because all the species have it.
Part (b)
What is considered a distinct "step" in the immune response is subjective, but focus on the major steps. There can also be multiple correct answers here since steps may vary. This is an information recall question. Recall what the typical immune response involves. One potential correct answer would be:
1. There are mast cells, which release histamine and recruit other immune cells to the place of infection.
2. The other immune cells, including interleukins, helper T cells, and killer T cells destroy the invading pathogens and any infected host cells. These are all non-specific immunity.
3. The memory B cells are cloned and produce many antibodies specific to this pathogen. This is specific immunity.
4. The antibodies bind to the antigens on the pathogens and neutralize them. This allows killer T cells to then destroy them.
Remember to answer the second question in part (b):
The second time a mother gets infected by this pathogen, her immune system will be able to react much more quickly to combat the infection because the specific antibodies will already be present in her body.
Part (c)
This is another information recall question. Recall what you learned about antibodies being passed from mother to baby, and apply it to this hypothetical situation. A good answer would be:
Since the mother was exposed to it before the baby was born, she will have the antibodies and pass it on to the baby. The baby’s immune system should be able to fight off the bacteria quickly.
Hope this AP Biology FRQ walkthrough helped, and I will be posting more each week leading up to the exam. If you have any requests for specific FRQ walkthroughs, please comment below with the exam year and question number.
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