Answer:
The correct answer is b. He determined that DNA contains four nitrogenous bases.
Explanation:
Levene was an American biochemist who studied the structure of DNA in the early 1900s and in 1920 he found that DNA consists of four nitrogenous bases that are Adenine, Guanine, Thymine, Cytosine.
He also found deoxyribose sugar and phosphate group and said that nucleotide is the basic unit of DNA which contains a ribose sugar with attached nitrogenous base and phosphate group.
He also concludes that an equal amount of adenine, guanine, thymine, and cytosine makes the DNA which is now known as tetranucleotide hypothesis. So the correct answer is b. He determined that DNA contains four nitrogenous bases.
Answer:
(d). B-cells.
Explanation:
Adaptive immunity can be described as immunity which develops in response to exposure to a pathogen (or foreign molecule). throughout the life. It is divided into two types, humoral immunity and cell-mediated immunity.
Humoral immunity is mediated by B cells that secrete antibodies against particular antigens. These antibodies recognize and neutralize the antigens and activate cell-mediated immunity, which is mediated by T cells.
Thus, the correct answer is option (d).
The correct answer would be A. The number of neutrons present in Krypton-82 would be 46. The atomic number of an atom represents the number of protons present while the mass number is the sum of the neutrons and protons in the atom. The mass number for the given atom is 82. So, 82-36 = 46 neutrons present.
Macrophages
Using the receptors on their surface and through the facilitation by immunoglobulins that attach to the foreign matter, macrophages 'hold' the foreign bodies in the body and 'ingest' them through phagocytosis. Lysozymes in the cells then in 'digest' the foreign matter.
Answer:
directional selection, is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.
