I disagree it should be A
Answer: the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.
Explanation:
Requires energy input from a cell and enables A cell to move a substance against its concentration gradient
A graphic that shows the number of organisms in each trophic level of the ecosystem is called a (c) number pyramid. It is in a form of a pyramid and the bottom indicates the largest number of the organisms. It could also be a source of the quantitative analysis of the ecosystem.
Answer:
Ralph is looking at a vein (likely a muscular vein).
Explanation:
Of all three great types of vessel present in vertebrates (arterial, venous, lymphatic), only veins and lymphatic vessels may normally contain valves. This is an essential feature of vessels which present low pressure flow, since it ensures that such flow is unidirectional.
Since blood cells are not typically found in lymphatic vessels, the vessel in question can be assumed to be a vein.
