Tadpoles have gills allowing them to breathe underwater while frogs have lungs. Tadpoles have tails and fins to help them swim while frogs have arms and legs.
Answer:
Glucose
Explanation:
The brain is an energy-hungry organ. Despite comprising only 2 percent of the body’s weight, the brain gobbles up more than 20 percent of daily energy intake. Because the brain demands such high amounts of energy, the foods we consume greatly affect brain function, including everything from learning and memory to emotions.
Just like other cells in the body, brain cells use a form of sugar called glucose to fuel cellular activities. This energy comes from the foods we consume daily and is regularly delivered to brain cells (called neurons) through the blood.
Studies suggest the quality of the foods consumed over a lifetime affects the structure and function of the brain. For instance, the consumption of omega-3 fatty acids found in fish provides structural material to maintain neurons. Studies also suggest omega-3 fatty acids are essential for the transmission of information between brain cells. In contrast, foods that are rich in sugars and saturated fats have been found to promote oxidative stress, which leads to damage to cell membranes.
The food you eat also affects molecules in the brain that support cognition. Some foods, such as those with turmeric, support cognition by helping to maintain molecular events related to energy metabolism.
Recent studies suggest lifestyle choices that affect the metabolism of nerve cells, such as diet and exercise, may in some cases provide a non-invasive and effective strategy to counteract neurological and cognitive disorders.
Answer:
The preceding section reviewed the major metabolic reactions by which the cell obtains and stores energy in the form of ATP. This metabolic energy is then used to accomplish various tasks, including the synthesis of macromolecules and other cell constituents. Thus, energy derived from the breakdown of organic molecules (catabolism) is used to drive the synthesis of other required components of the cell. Most catabolic pathways involve the oxidation of organic molecules coupled to the generation of both energy (ATP) and reducing power (NADH). In contrast, biosynthetic (anabolic) pathways generally involve the use of both ATP and reducing power (usually in the form of NADPH) for the production of new organic compounds. One major biosynthetic pathway, the synthesis of carbohydrates from CO2 and H2O during the dark reactions of photosynthesis, was discussed in the preceding section. Additional pathways leading to the biosynthesis of major cellular constituents (carbohydrates, lipids, proteins, and nucleic acids) are reviewed in the sections that follow.
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Carbohydrates
In addition to being obtained directly from food or generated by photosynthesis, glucose can be synthesized from other organic molecules. In animal cells, glucose synthesis (gluconeogenesis) usually starts with lactate (produced by anaerobic glycolysis), amino acids (derived from the breakdown of proteins), or glycerol (produced by the breakdown of lipids). Plants (but not animals) are also able to synthesize glucose from fatty acids—a process that is particularly important during the germination of seeds, when energy stored as fats must be converted to carbohydrates to support growth of the plant. In both animal and plant cells, simple sugars are polymerized and stored as polysaccharides.
Gluconeogenesis involves the conversion of pyruvate to glucose—essentially the reverse of glycolysis. However, as discussed earlier, the glycolytic conversion of glucose to pyruvate is an energy-yielding pathway, generating two molecules each of ATP and NADH. Although some reactions of glycolysis are readily reversible, others will proceed only in the direction of glucose breakdown, because they are associated with a large decrease in free energy. These energetically favorable reactions of glycolysis are bypassed during gluconeogenesis by other reactions (catalyzed by different enzymes) that are coupled to the expenditure of ATP and NADH in order to drive them in the direction of glucose synthesis. Overall, the generation of glucose from two molecules of pyruvate requires four molecules of ATP, two of GTP, and two of NADH. This process is considerably more costly than the simple reversal of glycolysis (which would require two molecules of ATP and two of NADH), illustrating the additional energy required to drive the pathway in the direction of biosynthesis.
Conservation of Energy:
As a projectile is launched into the air KE is at its maximum. As the projectile gains altitude PE becomes greater than KE. At the top of its arc, PE is at its maximum. The whole cycle reverses itself on the way down.
Hormone Signaling. The glands of the endocrine system secrete hormones directly into the extracellular environment. The hormones then diffuse to the bloodstream via capillaries and are transported to the target cells through the circulatory system.
