Answer: Possession of Valves
Explanation: Veins possess valves which ensures that blood flows in only one direction. Valves helps blood to flow back to the heart against gravitational force.
Arteries don't have valves because the pressure originating from the heart is capable of causing the blood to flow in one direction.
Answer:
Explanation:
1.) All organisms differ in traits such as size and behavior.
2.) No two individuals are exactly alike.
3.) There was a gradual change in each species.
4.) Fossils were different from the living animals. However, these fossils had many similarities to modern forms of life.
5.) Species on the Galapagos Islands resembled species on the mainland but they were different in certain characteristics.
6.) Some organisms became isolated on many islands.
The energy goes up beacsue warmer air goes up while cold air goes down. This is called convetion.
The heaviest elements settled in the Earth's center.
The Earth on the other hand starts with a core of iron and radioactive materials such as uranium and plutonium, which release energy in the form of heat, through a process known as nuclear fission. It went through a fusion stage - a "liquid-pasty" state - which allowed that, due to gravity, the denser materials sank towards the center, while the lighter ones floated towards the crust, a process called planetary differentiation.