Mpf Ap Biology Essays
AP Biology Exam Terms
A major focus of the AP Biology exam is how homeostasis is maintained at every level (organism, population and so on). Homeostasis is the ability to maintain a constant environment, even when faced with a changing external environment. When we are talking at the organism level, we are talking about how the internal environment stays constant even in a changing external environment. When we are talking at the population level, we will talk more about how these populations stabilize around a carrying capacity. In this AP Biology crash course review, we will focus on one of the ways in which the body regulates itself to maintain homeostasis: negative feedback. First, we will investigate what negative feedback is. We will go over the definition and a generic example. Then, once you have an idea of what negative feedback is we can look at some real examples of negative feedback. Finally, we will go over a question that you might see on your AP Biology exam and what your graders will be looking for in a response that earns full points. As always, if you have any questions or comments about this article leave me a comment below.
What is Negative Feedback?
First, let us pick apart what negative feedback means. During the AP Biology exam, you may see words that you cannot remember. The exam is long, and there is a lot of material. Fear not, if you can master picking apart words for meaning instead of memorizing, it may help you out in the long run. So first we will start by going over feedback. We use feedback all of the time in our everyday language. For example, you get feedback from your teachers on exams. Their feedback tells you what should change, and if you’re a good student, you will make changes so that your work will improve. A similar system takes place inside of an organism. An organism will receive feedback in their body about what changes need to happen in order for the body to keep functioning. The body’s goal is to remain at “homeostasis” but environmental changes make that impossible. Feedback can also occur at the level of the population which we will discuss a little bit later in this AP Biology crash course review.
Now that you understand feedback, we will talk specifically about what negative feedback is. There are two types of feedback; you guessed it, negative and positive feedback. The negative and positive have to do with how the body is responding. Negative feedback is when the body is responding to a stimulus by slowing down or stopping the creation of something else. Negative feedback can be a tricky subject to explain in words so see the figure below for more explanation.
In the picture, the final product “G” is inhibiting the bonding of “C”. By inhibiting the interaction of C, there will be less G made. Think about it like this: there is so much “G” being made that it is letting the body know- don’t waste the energy creating me, save it, we have enough!
Real Examples of Negative Feedback:
Now that you have an idea of what negative feedback is we are going to explore two commonly used examples. The first picture that looked at was a generic representation of a molecular level negative feedback. In order to continue your understanding of negative feedback at the molecular level, we will study the mechanism of thyroxine.
Thyroxine is a hormone that has the function of raising body temperature. If the external environment temperature drops, the internal environment temperature will drop as well. If the internal body temperature drops significantly enough, the organism could die. In order to safeguard against that, as temperature drops, the hypothalamus is activated. The hypothalamus will then activate the anterior pituitary gland which is where TSH (thyroid stimulating hormone) is produced. When the thyroid is stimulated, thyroxine will be produced, which will raise the internal temperature.
What if the organism overheats? To safeguard against overheating thyroxine is involved in a negative feedback loop. As thyroxine is produced, it feeds back to the anterior pituitary gland which makes TSH. When thyroxine gets to the anterior pituitary, it’s a signal that there has been enough stimulation of the thyroid, and we need to stop this process. If this is confusing, go back to the first example. Think about that first drawing. In the first drawing, G is thyroxine, and it is inhibiting the pituitary gland from making D.
Though we usually think of negative feedback at the level of the organism, it is also possible to have negative feedback at the population level. This example might clarify any lingering questions that you had about negative feedback because sometimes it is just easier to understand at the “bigger” level. We are going to talk about populations of mice and hawks. The hawk population is increasing and eating more and more mice than before. As the hawks are eating more mice, there are fewer mice running around. The lower number of mice will lead to some hawks to starve and die; this establishes homeostasis of populations. You might remember this being called “carrying capacity”.
The negative feedback comes from fewer mice. As the mice population is depleting, the hawk population will be forced to get smaller as well. This type of feedback is easy to see, and you can apply the understanding of this subject to the thyroxine example and negative feedback in general!
AP Biology Exam
Finally, we should talk about what kind of question you might get on the AP Biology exam. Here is a question from 2008 for us to look at:
Regulation is an important aspect of all biological processes. Choose two processes and describe the specific role of the regulator and discuss how the process will be altered if the regulation is disrupted.
We have already talked about two types of regulation, and you can certainly use those examples for this question. The raters have also included cell cycle regulation and the ovarian cycle as acceptable answers. We will go over one of the processes that are listed, and the other should be completed for studying purposes.
The cell cycle has regulators that allow the cell to proceed with growth and mitosis or to stop growing and wait for mitosis. The regulators of the cell cycle include Cdk, concentration differences, MPF, and S-phase. (If you can’t remember any of these go back and look them up- you will need to know them for the exam) If this cycle were disrupted, you would have a decrease in cell growth like in some muscular dystrophies. It is also possible that if this system was no longer regulated you would have uncontrolled cell growth (cancer).
Wrapping Up Negative Feedback and AP Biology
Homeostasis is important both at the organism level and the population level. In order to maintain homeostasis, we need to have feedback, that tells us how to proceed. There are many molecular negative feedback examples, and the general graphic can help you understand those. We covered thyroxin and predator-prey populations in detail after that in order to help you understand the concept of negative feedback better. Finally, we wrapped up with an example from the AP Biology exam.
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