The nucleus of an atom contain protons and neutrons, which make up most of the mass of an atom.
The answer would be 2 and 3 ( 2nd answer choice)
1. The correct answer is; are body cells is going to shrink. <span>Salty seawater is a hyperosmotic solution, meaning that it has more solutes than the cell inside. The water will move (from the cell) via osmosis in order for the solutions to reach equilibrium. Also, salty solution exerts more pressure on the of the cell, so the cell will shrink.</span>
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2. The correct answer cells in the fish will stay the same size. This will occur because both solutions, freshwater lake and river have similar (or equal) solute concentrations. Those solutions are called isosmotic. There is no movement of water or the solutes, so the cell stays the same.</span>
3. The correct answer is to swell. <span>This will happen because sea star egg has the same solute concentration as its first environment-ocean meaning that this solution is hyperosmotic comparing to the lake (ocean is saltier than the lake, it has more solutes). When you put the sea star egg in the lake, the water from the lake will move (via osmosis) into the egg, to reach equilibrium. Water will cause the cell to swell.</span>
<span>There are numerous proteins in muscle. The main two are thin actin filaments and thick myosin filaments. Thin filaments form a scaffold that thick filaments crawl up. There are many regulatory proteins such as troponin I, troponin C, and tropomyosin. There are also proteins that stabilize the cells and anchor the filaments to other cellular structures. A prime example of this is dystrophin. This protein is thought to stabilize the cell membrane during contraction and prevent it from breaking. Those who lack completely lack dystrophin have a disorder known as Duchene muscular dystrophy. This disease is characterized by muscle wasting begininng in at a young age and usually results in death by the mid 20s. The sarcomere is the repeating unit of skeletal muscle.
Muscle cells contract by interactions of myosin heads on thick filament with actin monomers on thin filament. The myosin heads bind tightly to actin monomers until ATP binds to the myosin. This causes the release of the myosin head, which subsequently swings foward and associates with an actin monomer further up the thin filament. Hydrolysis and of ATP and the release of ADP and a phosphate allows the mysosin head to pull the thick filament up the thin filament. There are roughly 500 myosin heads on each thick filament and when they repeatedly move up the thin filament, the muscle contracts. There are many regulatory proteins of this contraction. For example, troponin I, troponin C, and tropomyosin form a regulatory switch that blocks myosin heads from binding to actin monomers until a nerve impulse stimulates an influx of calcium. This causes the switch to allow the myosin to bind to the actin and allows the muscle to contract. </span><span>
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