Adenine which is a purine base, always pairs with the pyrimidine Thymine in DNA and Uracil(also a pyrimidine) in RNA. The bond which is present between the two bases is a double hydrogen bond.
Guanine which is also a purine base, always pairs with the pyrimidine Cytosine, in the case of both, DNA and RNA. The bond which is present between the two bases is a triple hydrogen bond and hence, is stronger than the A-G double bond.
Discovery In 1928 it was discovered by Frederick Griffith in an experiment generally known as transformation.
Experiment
In his experiment he considered two strains of <em>streptococus pneumonia,</em> one was R-type which was non-virulent and cause no disease in mice, other was virulent and S-type which cause disease and at last death of mice.
This experiment was comprised of four steps which are as follow:
Step 1: First he injected living strain of S into mice, after sometime mouce died.
Step 2: He injected living strain of R into mice, the mice alive as he did not got any disease.
Step 3: He injected heat killed strain of S into mice and mice remain alive.
Step 4: He mixed living R strain with heat killed S strain and then inject into mice. As a result the mice died.
Conclusion: It was found that genetic material from heat killed S stain were transferred to living R (non-virulent) strain, as a result R become virulent and cause the death of mice.
Ductility is a physical property.
A physical property of a material is a property that can be measured or observed without changing the composition of the material.
In this case ductility is a physical property. It is defined as the property of a material associated with the ability to be drawn or stretched into a wire without breaking. The chemical identity of the material is not affected, that is it does not change.
Example of ductile materials include gold, silver, copper, erbium, terbium and samarium.
Other examples of physical properties are:
1. Solubility
2. Melting point.
3. Boiling point.
4. Color
5. Density.
Here's a graph showing the stages.
Look closely at the second stage-- the death rate is low but the birth rate is high.
It's <span>
D. The death rate begins to fall, but birth rates remain high for a time.</span>
Answer: Nerve cell
Cells of the nervous system, called nerve cells or neurons, are specialized to carry "messages" through an electrochemical process.