Easy. Answer is oxygen because it says which one was missing before any life was on earth. And in order to have life on earth you need oxygen!
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The answer is: D. all of the above.
When Earth receives energy from the Sun, some energy is reflected back into space, some is absorbed by the atmosphere, and some is absorbed by land and water on Earth's surface.
Answer:
The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.
There are two main types of circulatory systems: 1. open circulatory systems and closed circulatory systems. Open circulatory systems are systems where internal organs and body tissues are surrounded by circulatory fluid. This fluid is called hemolymph, and it's pretty much like blood, except that it doesn't contain oxygen transporting cells.
2. The closed circulatory system of some mollusks and all vertebrates and higher invertebrates is a much more efficient system. Here blood is pumped through a closed system of arteries, veins, and capillaries. Capillaries surround the organs, making sure that all cells have an equal opportunity for nourishment and removal of their waste products. However, even closed circulatory systems differ as we move further up the evolutionary tree.
Answer:
An energy pyramid is a model that shows the flow of energy from one trophic level to the next along a food chain. The pyramid base contains producers—organisms that make their own food from inorganic substances. All other organisms in the pyramid are consumers
Explanation:
Step 1: Copy of one side of DNA strand is made (called mRNA, messenger RNA)
step 2: mRNA moves to cytoplasm, then ribosome
step 3: mRNA goes through ribosome 3 bases at a time
step 4: transfer RNA (tRNA) matches up with the open DNA bases
step 5: tRNA releases the amino acid at the top, which joins the chain of amino acids being produced
