CONTRACTILE RINGS are a contractile ring of actin micro filaments that eventually results in the division of the cytoplasm.
The contractile ring are usually formed during the early anaphase phase of the cell division cycle. During the cellular cleavage, the contractile rings tighten around the cytoplasm of the cell until it is pinched into two daughter cells.
        
             
        
        
        
I believe the correct answer is: HIV is spread during unprotected sex or through contact with infected blood; it cannot be cured, but early treatment can minimize the long-term consequences.
<h2>Explanation:</h2>
Human Immunodeficiency Virus is a type of virus which causes an impairment of the immune system of the person making them susceptible to diseases such as tuberculosis, influenza and any other disease that can exploit this opportunity. It is spread by a person coming into direct contact with infected bodily fluids such as saliva during deep kissing, semen during intercourse, blood after an accident or even fluids when sharing needles and syringes for drug addicts. There is no cure but the current form of treatment slows down the virus to prevent some consequences.
<h2>Further Explanation:</h2>
The virus is enters the body through open wounds or surfaces such as the vagina or mouth where the skin is very thin and can tear. After penetrating the skin, it attaches to specific immune cells called CD8+ T-cells on points called receptors. It then enters the cell and replicates itself in the nucleus of the cell and as it goes out, it kills these immune cells making the person to have a weak immune system. The current drugs used called AntiRetroVirals (ARVs) such as the drug Zidovudin stops the virus from replicating thus reducing the total amount of virus in the body called the Viral Load. Some drugs target enzymes called proteases and reverse transcriptase that help the virus to replicate. This viral load is what is counted to estimate the total volume of HIV someone has in their body. Infected persons should use protection while having sex and also avoid sharing sharp objects to prevent transmission. They also need to take their medication to make them much more healthier in addition to taking proper balanced diets. 
Level: High School
Subject: Biology
Topic: The Immune System
 
        
                    
             
        
        
        
At the end of the prophase each daughter cell will have eight chromosomes
        
             
        
        
        
Answer:
B.  Semitendinosus
Explanation:
The medial edge of the popliteal fossa is created by  Semitendinosus muscles.
 
        
                    
             
        
        
        
Answer:
Patent ductus arteriosus (PDA) is an extra blood vessel found in babies before birth and just after birth.
Explanation:
The ductus arteriosus is a normal blood vessel that connects two major arteries — the aorta and the pulmonary artery — that carry blood away from the heart.
The lungs are not used while a fetus is in the womb because the baby gets oxygen directly from the mother's placenta. The ductus arteriosus carries blood away from the lungs and sends it directly to the body. When a newborn breathes and begins to use the lungs, the ductus is no longer needed and usually closes by itself during the first 2 days after birth.
If the ductus doesn't close, the result is a patent (meaning "open") ductus arteriosus. The PDA lets oxygen-rich blood (blood high in oxygen) from the aorta mix with oxygen-poor blood (blood low in oxygen) in the pulmonary artery. As a result, too much blood flows into the lungs, which puts a strain on the heart and increases blood pressure in the pulmonary arteries.