I believe the answer to be D.
Answer:
A front
Explanation:
A front forms at the boundaries. This is when two air masses collide.
FEEDBACK MECHANISM is a regulatory mechanism in which presence of certain level of substance promotes or inhibits its further formation.
The regulation of secretion of Thyrocalcitonin from thyroid gland is an example of such feedback control mechanism. It occurs in two ways:
a) When calcium levels are too high, the thyroid detects this and releases calcitonin. calcitonin stimulates the kidneys to release more calcium and it causes bones to absorb more calcium and build more matrix. This is called Negative Feedback Control.
b) In response to a decrease in calcium levels, parathyroid hormone is released, which causes the release of calcium from bone and retention of calcium in the body, and the calcium level rises back to normal. This is called Positive Feedback Control.
Answer:
a state in which opposing forces or influences are balanced.
Explanation:
<h2>Cell Cycle
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Explanation:
Eukaryotes grow and divide by cell cycle.
The main parts of a cell cycle are an ordered series of events – Gap 1 or G1 phase, Synthesis or S phase, Gap 2 or G2 phase, and the mitosis or M phases.
Interphase period (G1, S, G2 phases) - cell grows by size, duplicates its content, replicates its DNA, and finally prepares for mitotic cell division
.
Mitosis and cytokinesis - formation of two identical daughter cells
Cell cycle is regulated by regulatory or restrictive checkpoints in the cell cycle which are activated with detection of a defective DNA.
Proliferation of undesired or cells with defective DNA like in case of tumor cells is controlled by the action of suppressing agents like p53 and cyclins.
The tumor suppressor gene protein p53 prohibits division of tumor cells. Cyclins regulate cell cycle by activation of the enzyme cyclin-dependent kinase.
