Why is a countercurrent system a more efficient system for gas exchange?

A countercurrent system a more efficient system for gas exchange. Because water is viscous, this would require a lot of energy, so the counter-current system is a more efficient way of increasing the amount of oxygen diffusing into the blood. The unidirectional flow of water is another advantage.

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prophase: we can observe the chromosomes to coil up and condense. they become visible. nuclear membrane and envelope disintigrate.s

metaphase: chromosomes align at the center, the metaphase plate. spindle fibers attach to centromeres of the sister chromatids. they meet at kinetochores.

anaphase: sister chromatids are pulled towards each opposing centromere, set on different poles.

telophase: chromosomes are now clustered up only on either sides of the cell. nuclear membranes reform, and a new cell wall forms along the cell plate. this will lead to cytokinesis, the process that divides the cell membrane and forms the cell wall.

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