Natural levels of nitrate in Minnesota groundwater are usually quite low (less than 1 milligram per liter [mg/L] of nitrate-nitrogen). However, where sources of nitrate such as fertilizers, animal wastes, or human sewage are concentrated near the ground surface, nitrate may seep down and contaminate the groundwater. Elevated nitrate levels in groundwater are often caused by run-off from barnyards or feedlots, excessive use of fertilizers, or septic systems.
Wells most vulnerable to nitrate contamination include shallow wells, dug wells with casing which is not watertight, and wells with damaged, leaking casing or fittings.
Nitrate contamination of a well is often regarded as a first sign of deteriorating groundwater quality.
In immunology two types of immune response are described depending on whether there is prior contact with the antigen.
• At this first contact, only lymphocytes with receptors specific to the antigen in question are stimulated and lead to the production of antibodies capable of neutralizing it. The lymphocytes capable of recognizing a specific antigen are very few and the production of antibodies - of low intensity and limited duration - is detectable only after a period of latency of several days. This is called the primary response. The specificity of the resulting seropositivity, however, makes it possible to detect contamination (seroconversion).
• Upon re-contact with an antigen that has already triggered a primary response, specific antibody production is found to increase rapidly after a short latency period. The secretion of IgG then reaches levels much higher than those observed during the primary response, while that of IgM is of the same order. This early and intense response, called secondary response, most often results in the destruction of infectious agents before any clinical sign.
• Many centuries before the discovery of microbes, it was noted that people who developed a contagious disease without death were then specifically immunized against the disease, without being protected against others.
• The ability to react appropriately to an already received stimulus supposes the existence of a memory. The immune memory is based on the existence of memory B and T lymphocytes, resulting from the clonal expansion due to the first contact with the antigen. Their lifespan is significantly higher than that of other lymphocytes and their high reactivity gives its rapid and intense character to the secondary response.
<span>The fluid flows through the interventricular foramen into the third ventricle, is augmented by fluid formed by the choroid plexus of this ventricle, and passes through the cerebral aqueduct to the fourth ventricle, which also possesses a choroid plexus. The CSF from all theses sources , as well as any formed in the central canal of the spinal cord, escapes from the fourth ventricle into the subarachnoid space through the median aperture and lateral aperture.</span>
An animal cell lacking carbohydrates on the external surface of its plasma membrane would likely be impaired in CELL TO CELL RECOGNITION.
Carbohydrates have diverse functions, one of their functions is that they serve as a recognition signal at the surface of cells.
Carbohydrates located on the surface of cells enable cells to recognize and communicate with one another.
The arrows usually point to the organisms that are doing the eating.
Explanation:
For that reason, we can say that the arrows represent the flow or transfer of energy in an ecosystem. It also specifies the direction of the flow of energy.
