Answer: By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.
Explanation:
Answer:
Chemotrophs are a class of organisms that obtain their energy through the oxidation of inorganic molecules, such as iron and magnesium
Explanation:
In 1929 the American astronomer Edwin Hubble discovered that the distances to far-away galaxies were proportional to their redshifts. Redshift occurs when a light source moves away from its observer: the light's apparent wavelength is stretched via the Doppler effect towards the red part of the spectrum. Hubble’s observation implied that distant galaxies were moving away from us, as the furthest galaxies had the fastest apparent velocities. If galaxies are moving away from us, reasoned Hubble, then at some time in the past, they must have been clustered close together.
Answer:
The correct answer is B. Tapping the patellar tendon will usually result in a spinal reflex.
Explanation:
The patellar reflex is the involuntary contraction of the quadriceps femoris muscle by flexion of the patellar tendon. It is a reflex of spinal or stretching type. It was discovered, studied and first reported in 1875 by William Erb.
By striking the patellar tendon, the leg is extended as alpha motor neurons direct a nerve impulse to the quadriceps femoris muscle. The femoral nerve, responsible for such reflex, extends throughout the thigh and its synapses are found in the lumbar spinal nerve 2 to 4 of the spinal cord. Therefore, this movement is involuntary and responds to a need for automatic regulation of body muscles.