Tutor profile: Alyssa K.
What is the difference between operant conditioning and classical conditioning. Give an example of both.
Operant conditioning is a form of learning that is based on reward and punishment. For example, if you wanted to teach a rat to press a button, every time that it pressed the button, you would give it a treat. Classical conditioning is a form of learning based on associations. This is done through pairing a neutral stimulus with one that already causes a response. Over time, the neural stimulus becomes conditioned, and it alone will result in the same response. For example, if you presented someone who was arachnophobic (extremely afraid of spiders) with a spider, they would experience fear. Conversely, if you rang a bell in the presence of these same individuals, they would not be afraid. However, if you rang a bell every time you presented the spider to these individuals, over time they would be conditioned to associate the sound of the bell with fear. Therefore, ringing the bell without a spider would induce fear.
Subject: Basic Chemistry
What is ionization energy, and how does it change through the periodic table? Why?
Ionization energy is the amount of energy required to remove an electron from an atom. As you move across the periodic table in a given row, which is known as a "period", the number of electrons increases. At the end of the period, the outer shell, which is called the "valence shell", contains the maximum number of electrons it can hold. In this state, the atom is most happy, or "stable", and the amount of energy required to remove the electron increases. In other words, the ionization energy increases as you move from left to right along a period in the periodic table. As you move down a given column in the periodic table, the elements increase in the number of shells that they contain. As a result, the valence shell's increase in distance from the nucleus. Because the nucleus contains a positive charge, the negatively charged electrons are attracted to the nucleus. As the number of shells increase, the distance of the valence shell to the nucleus increases; and as a result, the attractive force decreases and it is easier to remove an electron from the valence shell. Therefore, the ionization energy decreases as you move down a column in the periodic table.
Explain the solubility differences between peptide hormones and steroid hormones. How are these two groups of hormones transported in the body, and where are their target receptors located?
Peptide hormones are derived from peptides, which have an amino group and a carboxyl group. In the body's environment, peptides exist as zwitterions (contains both a positive and negative charge), with a positive charge on the amino group and a negative charge on the carboxyl group; and as a result, they are polar. Conversely, steroid hormones are composed primarily of carbons and hydrogens, giving them a neutral charge, and resulting in a non-polar character. The polarity/non-polarity of these hormones impact how they travel through the body, and where their target receptors as located. Because of the polar nature of water, peptide hormones are able to travel freely through the blood, whereas steroid hormones must be transported by a protein. Once reaching the target cells, polar hormones bind to receptors on the surface, whereas steroid hormones enter the cell and bind to receptors inside. This is because the inside layers of the cell membrane is non-polar, preventing peptide hormones from bypassing, but enabling steroid hormones to enter freely.