Tutor profile: Christine S.
Subject: Basic Chemistry
What is the difference between ionic and covalent bonding?
Ionic bonding can be defined as an electrostatic attraction between ions of opposite charge. This is usually between a metal (+) and a nonmetal (-). Species that have whole number charges (such as +1, +2, -1, etc.) have a stronger attraction towards one another. It is important to remember that an ionic bond does not mean electrons are being transferred, if electrons were being transferred it would be redox, which leads to the formation of ions, not ionic bonds. Covalent bonds form when electrons are shared between atoms. This is usually between a nonmetal and a nonmetal. Most of the bonds in organic chemistry are covalent. There can be single bond- which is one sigma bond, a double bond- which is one sigma bond and one pi bond = 2 covalent bonds, or a triple bond- which is one sigma and two pi bonds = 3 covalent bonds total. Remember that sigma bonds are the overlapping of atomic orbitals, the strongest type of covalent chemical bond. The first, single bond is always a sigma bond. If there is a double bond, or triple bond, anything after the first sigma bond is a pi bond. A pi bond is the co-planar overlap of P orbitals, which means that the atoms involved must have a P orbital available in order to be formed (would have to be sp or sp2 hybridized since sp3 hybridized atoms have only 4 sp3 orbitals available and no P orbitals).
What are two types of adaptive antigen specific responses?
Two types of adaptive, antigen specific responses are cell mediated and humoral immune. In order to understand and remember these responses, I like to break it down into the types of cells involved, the target, and what causes the immune effects seen with each. The cell mediated response involves helper T cells (which make cytokines), Tc cells (which make cytotoxins), and memory T cells. The targets of this pathway are large microbes and intracellular microbes and the immune effects are from secretes cytokines/cytotoxins. The humoral immune response involves antigen specific B cells- plasma and B memory cells. It targets extracellular microbes and toxins, and the immune effects are due to immunoglobulins (also known as antibodies).
What are the major structures of the gastrointestinal system?
The gastrointestinal system can be broken down into four parts-upper, middle, lower, and accessory portions, which will help you remember the order, location, and basic function of each component. The upper portion: mouth, esophagus, stomach. This is where it all begins, these structures act as an intake source and receptacle through which food passes and initial digestion processes take place. The middle portion: the small intestine- which is further broken down into three parts. The small intestine is where most digestive and absorptive processes occur, and it includes DJI- duodenum, jejunum, and ileum- in that order. So after the upper portion and the food has gotten to your stomach, think DJI. The lower portion: The large intestine, which is a storage channel allowing efficient elimination of wastes. This is the area anatomically ending the gastrointestinal tract. This can be broken down into seven different structures. First- the cecum, this is the start of the large intestine and the appendix sticks off of it. Next, the colon which goes up (ascending colon; ascending = going up), over and across the abdomen (transverse colon; transverse = across), and then down (descending colon; descending = going down), followed by the sigmoid colon. The sigmoid colon leads into the rectum, then anus, and then out. The fourth part: accessory organs! This includes the salivary glands, liver, and pancreas. While these do not carry the food we take in, they do help out in digestion- which is why they are accessories. Kind of like accessories to your outfit, not the main items of clothing you wear (such as a shirt and pants), but they pull the outfit together and make work flawlessly. These organs produce digestive secretions which help dismantle foods and regulate the usage and storage of nutrients. They are important from the start, when you are chewing your food.
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