Answer: Layer a is 500 million years old.
Explanation:
Trilobite is a member of the group of extinct arthropods found as fossils and they can be identified by the three-lobed as well as three segmented forms. These were the marine animals. These were appeared initially in the Cambrian Period. They used to live 542 million years ago so the fossils can be estimated to be aged of 500 above years old. These animals used to dominate in the sea area.
Pro cells have cell wall but eukar don’t
Autonomic nervous system innervates the entirety of the gastrointestinal tract
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
Plants make seeds that can grow into new plants, but if the seeds just fall to the ground under the parent plant, they might not get enough sun, water or nutrients from the soil. Because plants cannot walk around and take their seeds to other places, they have developed other methods to disperse (move) their seeds. The most common methods are wind, water, animals, explosion and fire.
