Answer:
Molecules can be made of one type of element pr a mixture of element.
Molecule is two or more atoms bonded together.
Compound act like a different substance (because have different properties from its constituent elements).
Explanation:
A molecule is the combination of one or more atoms. These atoms may be from different elements are of the same elements. All the compounds are molecule but not all the molecules are compound. For example,
H₂O is a water molecule and also a compound. H₂ is just a molecule not a compound because both atoms are from same element.
The compound have different properties from its constituent elements. e.g water is compound made up of hydrogen and oxygen. Hydrogen is flammable gas and oxygen support combustion, while water doesn't have these properties. However in mixture elements retain their own properties that's why mixture is different from the compound.
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.
The answer is 99.9 percent.
