1. All substances that enter or leave a cell must in some way pass through the cell membrane. Resembling a circulatory system for the individual cell is the endoplasmic reticulum. Granular particles concerned with protein synthesis are the ribosomes. Spaces or cavities that serve functions at the cellular level such as digestion, respiration, excretion, and storage are the vacuoles. A portion of the endoplasmic reticulum that aids in the final preparation of certain proteins and mucus-like substances is the Golgi complex. The "powerhouses" of the cell are the mitochondria. Playing a major role in cell division are the two centrioles.
Each chromosome has a set of specific genes. These determine the physical and chemical characteristics of the body. (para 2-2)
2. Adenosine triphosphate (ATP) provides energy for cellular processes such as active transport of substances across membranes, synthesis of chemical compounds for the body, mechanical work (such as muscle contraction). When an ATP molecule provides energy for such a process, it loses a phosphate radical and becomes ADP. Then, the cycle begins again as ADP is converted into ATP within the mitochondria. (para 2-3b)
3. The major component of living substances is water. The fluid within the cell is called intracellular fluid. Located among the cells is the interstitial fluid. In the circulatory systems, fluids serve as a vehicle. Together, the interstitial and circulating fluids are called extracellular fluid. (paras 2-4 and 2-5)
4. Certain chemicals dissociate into ions when they are dissolved. These chemicals are called electrolytes. For good health, these chemicals must be in balance. In other words, each fluid compartment must have a certain concentration of a given electrolyte. (para 2-6)
5. Water has several important physical characteristics: First, it is a fluid; therefore, it has the capacity of flow. Second, it is able to dissolve many substances within itself; thus, it is an excellent vehicle. Because of its heat-carrying capacity and its ability to remove large numbers of calories during evaporation, water is very useful in controlling the body's temperature. (para 2-7a)
6. The human body obtains water in two primary ways: First, water is the major component of items we drink or eat. Second, as food substances are oxidized within individual cells, water is one of the main by-products. (para 2-7b)
7. Water is lost from the body during perspiration, respiration, urination, vomiting, and diarrhea. (para 2-7c)
8. Substances dissolved in the water of the body include gases, nutrients, wastes, and hormones. (para 2-8)
9. Interstitial fluid originates primarily as the blood's fluid portion that escapes into the tissues from the capillaries. Part of this fluid enters the beginning of the venous vessels. A large portion is picked up by the lymphatic system. (para 2-9)
10. The body's tendency to maintain a steady state is called homeostasis. As a part of this, the body maintains appropriate concentrations of oxygen, carbon dioxide, nutrients, electrolytes, and other substances within the tissue fluid. A system that helps to maintain the appropriate concentrations of oxygen and carbon dioxide is the respiratory system. A system that helps to maintain the appropriate concentration of nutrients is the digestive system. Such organ systems are at least partially controlled by feedback mechanisms. These mechanisms resemble the household thermostat.
11. The body needs a certain amount of water to function properly. Lack of fluid may result in heart failure. Too much fluid tends to result in swelling, known as edema. To maintain water balance, there are feedback mechanisms. (para 2-11)
12. If the concentration of electrolytes is greater in the tissue fluid than in the intracellular fluid, the tissue fluid is hypertonic. If the concentrations of electrolytes is less in the tissue fluid than in the intracellular fluid, the tissue fluid is hypotonic. If the concentration of electrolytes are equal in the tissue fluid and intracellular fluid, the fluids are isotonic. (para 2-12)
13. Assume that a substance is more concentrated on one side of a membrane than the other but that it cannot pass through the membrane. The process in which water passes to the side of greater concentration is called osmosis.
If, however, the substance can easily pass through the membrane, the process in which the substance passes through the membrane to the area where it is less concentrated is called diffusion. If the substance needs assistance to pass through the membrane, we call the process facilitated diffusion.
Since the cell membrane allows only some types of substances to pass through it, the cell membrane is semipermeable.
When energy is used to move a substance across a membrane to an area of higher concentration, the process is called active transport.
14. When the cell is in a resting state, the membrane potential is maintained by the sodium/potassium pump. This membrane potential is called the resting potential. The sodium/potassium pump actively transports three positive sodium ions to the outside of the cell membrane and two potassium ions to the inside of the cell membrane. This results in a negative charge inside the cell and a positive charge outside the cell.
When a neuron or muscle fiber is stimulated, the resulting activity is called the action potential. This involves depolarization and subsequent repolarization. First, sodium ions move into the cell by diffusion. This reverses the polarity. Second, potassium moves out of the cell by diffusion that causes repolarization. (para 2-14)
15. A condition in which tissue mass increases without an increase in the number of cells is called hypertrophy. When tissue mass increases due to an increase in the number of cells, it is hyperplasia. Another word for cell multiplication is mitosis. (paras 2-15 and 2-16)
16. The epithelial tissue lining a serous cavity secretes a serous fluid to act as a lubricant. The secretion of sebaceous glands is formed as portions of the cells are sloughed off. (paras 2-20, 2-22)
17. In FCT, the fibroblast moves up and down the fiber. During this movement, it keeps the fiber in repair and restructures it in response to the stresses applied to the body. The collagen fibers are limited in stretchability, particularly when compared to the elastic fibers. As a collagen fiber lengthens, the tension increases considerably. As an FCT becomes warmer, it becomes more stretchable and more resistant to damage; this is the basis of warm-up exercises before more strenuous activities.
18. Fats, oils, and fatty acids are types of lipids. Such substances are stored mostly as neutral fat, which consists of triglycerides. A molecule of triglyceride is formed from a glycerol and three fatty acids. Within the body, triglycerides are kept in a liquid state by adjusting the length of each fatty acid. Within a 3-week period, there is a complete turnover of the triglycerides. Fats may be taken in as fats or converted from other substances, such as carbohydrates. When the diet contains more fats and carbohydrates than necessary for body activities, the result may be obesity.
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