Respiratory system helps in breathing and it leads to exhalation of the gas carbon dioxide which is not required by the body. The integumentary system is the first line of defense and protects the body from invadig microbes, dust, and other harmful substances. The digestive system protects the body by enabling digestio of food and providing energy to sustain, further the toxic waste materials are also released during the process.
The electrons in the outermost shell of the covalent compounds are shared by nearby atoms. As there are no free electrons for conducting electricity, the covalent compounds are perfect insulators at absolute zero. As the temperature increases, some electrons move from valence band to conduction band. This gives rise to conductivity. But as the numbers of charge carriers are very low, covalent compounds are poor conductors. On the other hand metals are good conductors cause of their bonding. Metallic bonding consists of a sea of electrons rather than discreet bonds. The free electrons are able to move freely. Since electricity and heat need electrons to move, the bonding promotes conductivity.
Answer:
By action potential nerve contract the muscle
Explanation:
The muscle contract when the nervous system sends action potential to the muscle. So the nervous system delivers signal to muscle, the first signal reaches the neuromuscular junction. The signals are passed by a chemical messenger called neurotransmitter release by motor neurons, the chemicals bring reaction and shorten the muscle fibre. When neurotransmitter are absent or reduce in concentration the process reverse and muscle relax again.
You're on K12 haha :0
I think it's the second answer choice but not sure. Sorry if I'm wrong
The right answer is Scientists should conduct long-term studies of DNA technology to determine the consequences.
DDT is a potent insecticide: it kills by opening the sodium channels of insect neurons, destroying them instantly, leading to spasms and then death. Some genetic mutations acting on the sodium channels can make some insects resistant to DDT and other insecticides working on the same principle.
The US Environmental Protection Agency has categorized DDT into the B2 class, that is, potential carcinogen for humans. This supports the fact that the insecticide acts on human DNA.
