In humans, the yolk sac is the
site of origin for blood cells and primordial germ cells. The human yolk sac is
a membrane located outside the embryo and it is connected by a tube through the
umbilical opening to the embryo's midgut. The yolk sac serves as an early site
for the formation of blood and in time, is incorporated into the primitive gut
of the embryo.
<span>The answer to the question of "what kind of relationship would a hummingbird an a daffodil have?" is that they have a mutually beneficial relationship, also called a mutualistic relationship - the hummingbird gets food from the flower and the flower can "use" the bird for polination, so they both benefit from each other's behaviour</span>
Since, the options are not given the question is incomplete. The complete question is as follows:
The laboratory analysis conducted on a child with chronic nasal drainage reveals an elevated number of eosinophils on a white blood cell differential. Based on this finding, which is most likely the cause of the nasal drainage?
a. Bacterial infection
b. Viral infection
c. Chronic inflammation
d. Allergies
Answer: d. Allergies
Explanation:
During the allergy the eosinophils are recruited at the site and these are produced in large number by the bone marrow cells. The allergic conditions may developed during the sinus infections where chronic nasal drainage occurs in order to expel out the pathogen from the body. The parasitic diseases and allergic reactions will result in the excess production of the eosinophils.
The given situation is a result of the allergic reaction which brought about large increase in the number of eosinophils.
Photosynthesis is a process by which plants use sunlight, water, and carbon dioxide to produce carbohydrates, and other biological compounds, which reduces the amount of carbon dioxide in the air. This is the difference between plants and animals. The carbon dioxide is stored in the plants until they decompose or are burned. So, for example, each fall when the trees lose their leaves and the plants die the level of carbon in the atmosphere goes up. The rest of the tree, bark etc., does not continue to absorb carbon. Plants only take in carbon so long as they are growing and not after they have reached their natural height. Planting trees and other plants is one component of the solution to global warming, but the number of plants we have now cannot consume more carbon than they already do, and there is some evidence that warmer temperatures make photosynthesis more difficult.
The answer is RESPIRATION
People who had this mutation back in the 14th century had better chance of survival (better fitness) then people who did not have this mutation. They were majority of people who survived the Black Death because of natural selection. Their offspring inherited this mutation too, and their offspring after.
There was no natural selection for this mutation in some other parts of the world because they were not hit by the Black Death.
Since the same mutation is responsible for immunity to HIV and the Black Death, offspring of the people who have survived the Black Death are immune to HIV too. Part of the world that was hit by the Black Death, now have more people with this mutation.