There are different organ systems, such as the cardiovascular system, also known as the circulatory system (the system that gets blood around the body), the muscular system (the system that contains muscles), the nervous system (the system that controls the nerves,and the brain) and the skeleton (the bones).
Anatomy, physiology and biochemistry are similar basic medical sciences.
Asteroid
An asteroid is a space rock. It is a small object in the Solar System that travels around the Sun. It is like a planet but smaller. They range from very small (smaller than a car) to 600 miles (1000 km) across. A few asteroids have asteroid moon.
The name "asteroid" means "like a star" in the ancient Greek language. Asteroids may look like small stars in the sky, but they really do move around the Sun, while stars only seem to move because the Earth spins. Like planets, asteroids do not make their own light. Because of this, some people think "asteroids" is not a good name, and think that the name "planetoid" ("like a planet") would be a better name.
Giuseppe Piazzi found the first asteroid, in 1801. He called it Ceres, and it is the biggest object in the asteroid belt. Others, like Juno, Pallas, and Vesta were found later. In the 1850s so many had been found, that they were numbered by a Minor planet designation starting with 1 Ceres. Today, astronomers using computerized telescopes find thousands of asteroids every month. Asteroid impact prediction is one of the purposes.
Asteroids are the leftover rock and other material from the formation of the Solar System. These rocks were too small to come together to make a planet. Some are made of carbon or metal. Depending on what's on the surface, they are classified into various asteroid spectral types including Type M (metal), Type S (stone), and Type C (carbon).
Most asteroids in our Solar System are in the asteroid belt between Mars and Jupiter. Many are not in the main asteroid belt. The ones that come close to Earth are called Near-Earth asteroids. Many scientists think asteroids striking the Earth killed off all the dinosaurs and caused some of the other extinction events.
Afghanistan
Afghanistan (, also pronounced //; Pashto/Dari: , Pashto: , Dari: ), officially the Islamic Republic of Afghanistan, is a country located in Central Asia and South Asia. It has borders with Pakistan in the south and east, Iran in the west, Turkmenistan, Uzbekistan and Tajikistan in the north, and China in the far northeast.
In early times people passed through it with animals and other goods as it connected China and India with Central Asia and the Middle East. More recently, Afghanistan has been damaged by many years of war. This has resulted in there not being enough jobs.
The country is around in size or area. There are 30 million people in Afghanistan. There are about 3 million Afghan refugees (people who had to leave the country) who are in Pakistan and Iran for some time. In 2011, its capital, Kabul, had about 3,691,400 people living in it.
Afghanistan has many mountains. The mountains are called the Hindu Kush and Himalayas. The big mountain in Afghanistan is Mount Nowshak. There are plains (which have soil that is good for growing plants) and foothills. Part is also dry and called the Registan Desert.
Afghanistan has snow and glaciers in the mountains. Amu Darya is the big water stream, or river.
The country has a lot of a valuable stone called lapis lazuli, which was used to decorate the tomb of the Egyptian king Tutankhamun.
Afghanistan has a continental climate with hot summers and cold winters. Having no water sometimes causes problems for farmers. Sandstorms happen a lot in the desert.
Southern Afghanistan has not many plants because it is dry. There are more plants where there is more water. Mountains have forests of pine and fir, cedar, oak, walnut, alder, and ash trees.
Afghanistan's wild animals live in the mountains. There are wolves, foxes, jackals, bears, and wild goats, gazelles, wild dogs, camels, and wild cats such as the snow leopard in the country. The birds are falcons, eagles and vultures. The Rhesus Macaque and the red flying squirrel are also in Afghanistan.
Many years of war, hunting, and years of no water have killed animals in Afghanistan. There used to be tigers in Afghanistan, but now there aren't any. Bears and wolves are almost gone.
Many people have moved through or invaded the land of Afghanistan. Today's people of Afghanistan are known as "Afghans". They have many traits passed down from these previous peoples.
The largest group of people are the Pashtuns. These make up about half the population. Tajiks are the second-largest ethnic group, making up about one-fifth of the population. Before the 20th century, Tajiks were called Sarts and some come from the Iranian peoples. Most Pashtuns are also related to the Iranian peoples. Some Pashtuns and Tajiks marry each other but at the same time they are rivals. The third-largest group are the Hazaras. They are native to the Hazaristan area in central Afghanistan. The country's other groups include the Uzbek, Aimaq, Turkmen, Nuristani, Baloch, Pashayi and a few others.
Dari-Persian and Pashto are the official languages of Afghanistan. Many people speak both languages. Both are Indo-European languages from the Iranian languages sub-family. They are usually written with the Arabic alphabet. Uzbek and Turkmen are widely spoken in the north and Nuristani and Pashai are spoken in the east. Almost all Afghans follow the religion of Islam.
Afghanistan is a largely rural country. This means there are only a few major cities. About one fifth of the population live in cities. Kabul, the capital, is the largest city. It is south of the Hindu Kush range and alongside the Kabul River. Other cities in Afghanistan include Kandahar, Herat, Mazar-e Sharif, and Jalalabad. The rural population is made up of farmers and nomads. The farmers live mainly in small villages along the rivers. The nomads live in tents while moving from place to place with their animals and belongings. Some people live in the high central mountains. Some live in the deserts in the south and southwest. Millions of people left Afghanistan to get away from the wars that happened in the late 20th and early 21st centuries. Most of them lived in neighboring Pakistan and Iran.
Afghanistan is in the path of important trade routes that connect southern and eastern Asia to Europe and the Middle East. Because of this, many empire builders have decided to rule over the area. Signs that these emperors were near Afghanistan still exist in many parts of the country. Afghanistan is near what used to be the Silk Road, so it has many cultures. From up to 8,000 years ago, the peoples of Afghanistan helped develop (create) major world religions, traded and exchanged many products, and sometimes controlled politics and culture in Asia.
Archaeologists digging a cave in what is now northeastern Afghanistan (in Badakhshan), discovered that people lived in the country as early as 100,000 years ago. They found the skull of a Neanderthal, or early human, as well as tools from about 30,000 years ago. In other parts of Afghanistan, archaeologists uncovered pottery and tools that are 4,000 to 11,000 years old—evidence that Afghans were among the first people in the world to grow crops and raise animals.