4. Fast breeder reactors are seldom used anymore because of safety concerns, as they have a higher potential for explosions. But this explosion hazard does not come from the nuclear fission reaction.
o What does it come from? Explain your answer in just one or two sentences.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

explanation:

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.

the tricuspid valve is present between right atrium and right ventricle