Respiration
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The molecule known as ATP, short for adenosine triphosphate, it the key for cellular work. The cell taps this energy source, ATP, by using enzymes to transfer phosphate groups from ATP to other compounds, which is the process of phosphorylation. The price of most cellular work is the conversion of ATP to ADP and inorganic phosphate. To keep working, the cell must regenerate its supply of ATP from ADP and inorganic phosphate. Three processes which involve the usage or formation of ATP are cellular movement, active transport, and chemiosmosis.
All cell movements are a manifestation of mechanical work; they require a fuel (ATP) and proteins that convert the energy stored in ATP into motion through ATP hydrolysis. The cytoskeleton, a cytoplasmic system of fibers, is critical to cell motility. The cytoskeleton, which consists of three parts: microfilaments, intermediate filaments, and microtubules, plays a structural role by supporting the cell membrane and by forming tracks along which organelles and other elements move in the cytosol. Cells have evolved two basic mechanisms for generating movement. One mechanism involves a special class of enzymes called motor proteins. These proteins use energy from ATP to walk or slide along a microfilament or a microtubule. Some motor proteins carry membrane-bound organelles and vesicles along the cytoskeletal fiber tracks; other motor proteins cause the fibers to slide past each other. The other mechanism responsible for many of the changes in the shape of a cell implies assembly and disassembly of microfilaments and microtubules. A few movements involve both the action of motor proteins and cytoskeleton rearrangements.
The process of active transport also requires energy in the form of ATP. Active transport is the pumping of molecules or ions through a membrane against their concentration gradient. Active transport is limited by the number of protein transporters present. There are two types of active transports, primary and secondary. Primary active transport involves using energy (usually through ATP hydrolysis) at the membrane protein itself to cause a conformational change that results in the transport of the molecule through the protein. The most well-known example of this is the sodium/potassium pump. The sodium/potassium pump is an antiport, it transports potassium into the cell and sodium out of the cell at the same time, with the expenditure of ATP. Secondary active transport involves using energy to establish a gradient across the cell membrane, and then utilizing that gradient to transport a molecule up its concentration gradient.
Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work. A protein complex called ATP synthase, which is the enzyme that makes ATP from ADP and inorganic phosphate, uses the energy of the existing H+ to power ATP synthesis. To form an H+ gradient across a membrane, certain members of the electron transport chain accept and release protons (H+) along with electrons. At certain steps along the chain, electron transfers cause H+ to be taken up and released back into the surrounding solution. In mitochondria, the energy for gradient formation comes from exergonic redox reactions, and ATP synthesis is the work performed.
To determine which of the flasks contains each of the four unknown solutions an experiment can be designed using the principles of diffusion and osmosis. The materials needed will be four semi-permeable dialysis bags, each filled with a different unknown solution, four 250 mL beakers or cups each labeled with A, B, C, or D with its respective flask, distilled water and a scale. To begin mass each dialysis bag and record it. Put each bag into its respective beaker of distilled water. Let it stand for half an hour. After 30 minutes remove each bag, dry it of excess water on the sides, and determine and record its mass. Next calculate