What is the difference between positive and negative reinforcement?

Positive reinforcement means that when someone engages in a behavior, it brings about a desired result. For example, if a little girl is at the grocery store with her family and sees a cereal that she wants but her mother refuses to get it, she may kick and scream and cry. As a result, her mother may decide to cave in and get whatever it is that she wants. In this situation, the little girl will be positively reinforced to kick and scream, because as a result she was able to get the box of cereal that she wanted. Negative reinforcement includes the behavior extinguishing an undesired stimulus. For example, say a college student has finals coming up and is stressed as a result, but decides to go drinking with his friends and suddenly feels better or less stressed. This is negative reinforcement because the act of drinking alcohol takes AWAY his stress and anxiety.

What processes occur in Prophase I of Meiosis?

In Prophase I of Meiosis, homologous chromosomes undergo crossing over. Crossing over includes the overlapping of genetic material at points which are called "chiasmata", which forms a structure called a "tetrad" (think of two replicated chromosomes attached or overlapped). DNA is not replicated in this phase (this happens in Interphase before Meiosis begins). Genetic material is exchanged in this process between chromosomes, which contributes greatly (along with Independent Assortment) to genetic variability between gametes.

What affect does Aldosterone have on the body?

Aldosterone increases the amount of Sodium ions and water reabsorbed within the Distal Convoluted Tubule and the Collecting Duct of the Kidneys. It does this by increasing Na+/K+ channels in these areas. As Na+ is reabsorbed (or pumped out of the renal tubule), K+ is secreted (or taken into the renal tubule). The movement of Na+ increases the osmotic gradient outside of the renal tubule, which in turn pulls water out of the tubule (so that it is also reabsorbed). Prolonged Aldosterone secretion can lead to problems such as hypokalemia (abnormally low blood levels of Potassium).