Immune System is the system that consists of proteins and cells.
Answer:
The correct answer will be option-B.
Explanation:
<em>Homo neanderthelensis</em> or Neanderthals are the close relatives of the <em>Homo sapiens</em> or modern humans which became extinct around 10,000 years ago.
The Neanderthals and sapiens are the two related species of the same genus Homo but they showed distinct features like Neanderthals were muscular and shorter in height compared to the <em>Homo sapiens</em>. Recent fossils indicated that Neanderthals and<em> Homo sapiens</em> interbreed in some parts of the world as they were closely related to each other.
Thus, Option-B is the correct answer.
The correct statement about hydrochloric acid and acetic acid is : ( A )
The pH of a solution of hydrochloric acid must be less than the pH of a solution of acetic acid.
Given that pH is the inverse of concentration of H₃O⁺ ions , The stronger acid ( Hydrochloric acid ) dissociates in solution producing a maximum amount of H₃O⁺ ion, while the weak acid ( acetic ) will disassociate partially in a solution producing a lesser amount of H₃O⁺ ion.
Therefore the pH of a solution of hydrochloric acid must be less than the pH of a solution of acetic acid.
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Any condition of unusual deposits of black pigment in different parts of the body is known as melanosis.
This condition is a form of hyperpigmentation that is associated with increased melanin. Hyperpigmentation, which is manifested as darkening on the skin, can be caused by sun damage, inflammation, or skin injuries. <span>There are different types of melanosis such as Melanism, ocular melanosis, smoker's melanosis, oral melanosis, Riehl melanosis.</span>
<u>Answer</u>: The correct statements are-
1. At any stage of mitosis a cell has twice as much as DNA in G1.
2. Metabolically active cells can exit, and sometimes re-enter, the cell cycle.
<u>Explanation</u> :
1.. The cell cycle consists of <em>4</em> distinct phases - M phase which is the mitotic phase and the G1, S and G2 phase which together form the interphase. The interphase is preparatory phase wherein the cell grows in size, replicates the DNA etc. whereas the M phase is the one where events related to cell division takes place.
2. The cell has <em>2C</em> amount of DNA during G1 but since the DNA replication takes place during S phase, the amount of DNA <em>doubles up to 4 C</em> and remains so in G2 and M phase until cytokinesis results in the formation of 2 daughter cells.
3. Sometimes, the metabolically active cells can exit the cell cycle and become <em>quiescent</em> until the conditions are favourable. When these quiescent cells recieve the right stimulus they can re enter the cell cycle.
4. Extracellular conditions such as nutrient availability, presence of certain mitogens, growth factors etc. do regulate the cell cycle progression. <em>If any of these extracellular facotrs are limiting the cell cycle is arrested.</em>
5. Once the cell cycle starts, it can be stopped without leading to cell death. When this happens it is known as <em>cell cycle arrest. </em>During this arrest several factors are assessed and if theire is need for repair of DNA then that also takes place. Once, the limitations are overcome or the repair is done, the cell cycle can then continue.
