The beginning of the Cambrian Period is marked by the evolution of hard body parts such as calcium carbonate shells. ... These body parts fossilize more easily than soft tissues, and thus the fossil record becomes much more complete after their appearance.
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Nerve plexuses are composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve plexuses—except in the thoracic region—as well as other forms of autonomic plexuses, many of which are a part of the enteric nervous system. A plexus is a bundle of intersecting nerves, blood vessels, or lymphatic vessels in the human body. These bundles typically originate from the same anatomical area and serve specific areas of the body. Bundles of nerves that form a plexus communicate information to your brain about pain, temperature, and pressure.
Answer:
HIV (human immunodeficiency virus) is a virus that attacks a type of white blood cell called a T-helper cell (also called a CD4 cell). People who have been infected with HIV develop AIDS. People with AIDS often develop diseases caused by organisms that usually do not harm people who are not infected with HIV. Explain why the organisms are more harmful to people with HIV than to people without HIV
<span>If you look at hominids' mouths you can learn a lot. You can compare the teeth to see what they eat. Different foods cause a different amount and type of wear. You can also point out individuals by matching their teeth with what you know about them.</span>
