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.
A measure of the number of particles of a substance in a given volume would be concentration. <span>In chemistry, </span>concentration<span> is the abundance of a constituent divided by the total volume of a mixture. There are a number of ways expressing it such as molarity, molality, normality, ppm, percentage and the like.</span>
Answer:
C
Explanation:
Due to the erosion of soils, no trees to protect the ground from drying out.
D, a net transfer of energy
Answer:
False
Explanation:
Phylogenetic analysis is a means of establishing evolutionary relationships.
Synapomorphy is a shared ("syn") character that is different from the form found in an ancestor that distinguishes a clade (monophyletic group)from other organisms
The absence of a trait can be used as a synapomorphy in phylogenetic analysis. For example, the loss of a trait, such as the loss of legs in snakes, can be a valuable synapomorphy for a clade.
