A portal of entry<span> is the site through which micro-organisms enter the susceptible host and cause disease/infection. Infectious agents enter the body through various </span>portals<span>, including the mucous membranes, the skin, the respiratory and the gastrointestinal tracts.</span>
Answer:The world population increased from 1 billion in 1800 to 7.7 billion today. The world population growth rate declined from 2.2% per year 50 years ago to 1.05% per year. Other relevant research: ... We show how the world population grew over the last several thousand years and we explain what has been driving this change.
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This process is called Denitrification. The process is undertaken by the denitrifying bacteria, whose action is converting nitrates in the soil to free atmospheric nitrogen and therefore, depleting soil fertility and reducing agricultural productivity. Examples of denitrifying bacteria are thiobacillus denitrificans, micrococcus denitrificans among others.
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The return of blood to the heart is assisted by the action of the skeletal- muscle pump. As muscles move, they squeeze the veins running through them. Veins contain a series of one-way valves, and they are squeezed, blood is pushed through the valves, which then close to prevent backflow.
