Answer:
Scientists believe that the different types we know emerged as early humans adapted to infectious diseases.
Explanation:
Different human blood types probably emerged to ward off infectious diseases. The incompatibility of some blood types, however, is only an "accident" of evolution. But this is a relatively recent problem, since blood transfusion has been around for only a few hundred years.
There are four main blood types. The oldest is B, which must have originated about 3.5 million years ago - it existed even before the human species evolved from its hominid ancestors, from a genetic mutation that modified one of the sugars in the surface of red blood cells.
Approximately 2.5 million years ago, mutations inactivated sugar, resulting in type O blood, which has neither type A nor B. sugar. AB blood, as it is easy to suppose, is covered by both sugar A and sugar by B.
Nitrogen fixation is the process by which nitrogen is taken from its relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds useful for other chemical processes (such as, notably, ammonia, nitrate and nitrogen dioxide).
Nitrogen fixation is performed naturally by certain types of anaerobic bacteria. Legumes such as clover contain symbiotic bacteria of this type within nodules in their root systems, producing nitrogen compounds that help to fertilize the soil. See George Washington Carver.
Nitrogen can also be artificially fixed for use as fertilizer or in other industrial processes. The most popular method is by the Haber process. Artificial fertilizer production has achieved such scale that it is now the largest source of fixed nitrogen in the Earth's ecosystem.
(This is the definition from the http://encyclopedia.kids.net.au/page/ni/Nitrogen_fixation website)
Options for the question have not been given. They are as follows:
blood vessel length
blood viscosity
blood vessel diameter
blood colloid osmotic pressure
Answer:
blood colloid osmotic pressure
Explanation:
- Peripheral resistance is the resistance to blood flow by blood vessels.
- It is directly proportional to blood vessel length as more the distance to travel, more will be the resistance.
- It is also directly proportional to blood viscosity as more energy is required to push viscous material.
- It is indirectly proportional to blood vessel diameter. More the diameter of the vessel, easier it is for the blood to pass.
- However, it does not depend on blood colloid osmotic pressure. Colloid osmotic pressure is created by the protein components of blood and they do not have any direct impact on blood flow.
