"(1) Human population growth reached 6.8 billion in 2010 and it continues to increase" is what led to the other <span>three, since all of these happen from human activity. </span>
Answer:
A. increase the speed of nerve impulses
Explanation:
Schwann cells speed up nerve impulses by secreting a fatty substance called myelin around the axon of peripheral nerves. (Myelin can greatly increase the speed of impulses in neurons because it insulates the axon and assembles voltage-gated sodium channel clusters at discrete nodes along its length.)
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The tadpoles take their food from the yolk of an egg. The egg yolk is equivalent to the placenta. The placenta attaches itself to the uterus to provide the developing fetus with blood and oxygen.
Answer:
Scientists from the UCLA AIDS Institute and the Institute for Stem Cell Biology and Medicine have derived T-cells from human embryonic stem cells, raising hopes for a gene therapy to combat AIDS. The Proceedings of the National Academy of Sciences reported the findings in its July 14, 2006, online edition.
“We may be able to use human embryonic stem cells to treat T-cell and other blood diseases,” says lead author Zoran Galic, assistant research biologist. “This could be a very important weapon in the fight against AIDS.”
The researchers cultured human embryonic stem cells and incubated them on mouse bone-marrow cells, which in turn converted them into blood-forming cells. Those cells were injected into a human thymus that had been implanted in a mouse. The thymus transformed the bloodforming cells into the T-cells that HIV targets for destruction.
“Our results indicate that it’s possible to decipher the signals that control embryonic stem cells’ development into mature T-cells,” says Jerome Zack, associate director of the UCLA AIDS Institute and professor of microbiology, immunology and molecular genetics. “This way we can eventually repopulate the immune system of patients needing T-cells.”
One of the body’s main defenses against disease, Tcells are manufactured in the thymus. The organ shrinks as we age, weakening the immune system. The scientists anticipate that their findings could give rise to gene-therapy approaches for other diseases related to T-cells such as severe combined immunodeficiency, or “bubble-boy disease.”
Explanation:
It sends an electrical impulse to make your heart beat. The job of a pacemaker is to artificially take over the role of your sinus node if it isn't working properly. Electrical impulses are sent by the pacemaker to stimulate your heart to contract and produce a heartbeat