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Comparing and Contrasting Gas Exchange in Humans, Protozoa and Plants.

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Emily 12JS Comparing and Contrasting Gas Exchange 25/01/02 in Humans, Protozoa and Plants Introduction: This essay aims to compare and contrast gas exchange in the above organisms in terms of complexity, size and efficiency. Note that: Protozoa: Are a group of single-celled organisms, which belong to the kingdom Protoctista e.g. amoeba. Comparing the structure of gas exchange systems in the three organisms: Humans and plants have complex gas exchange systems compared to those in protozoa. The three diagrams below show the basic structure of the three organisms. Comparing the mechanisms of the three organisms' gas exchange systems: The most simple gas exchange system is present in protozoa. Gas exchange occurs across the whole surface of the organisms by diffusion; the movement of molecules from an area of high concentration to an area of low concentration across a semi-permeable membrane. ...read more.


In humans, alveoli are small (100?m in diameter) and surrounded by very narrow capillaries, through which red blood cells are squeezed as they pass along them. This narrow passage reduces the speed at which red blood cells pass through alveoli hence allowing more oxygen gas to be absorbed in a given amount of time. In all of the three organisms, the gas, which enters it is soon dissolved on moist surfaces so that it can be transported more easily. In plants, the carbon dioxide dissolves on the moist surfaces of cells in the spongy mesophyll layer and moist layers of root hair cells. In protozoa diffusion is passive across a plasma membrane. The oxygen dissolves in the cytoplasm of the cell. In humans, oxygen gas dissolves in the moisture of alveolar epithelium and diffuses across this and the endothelium of the capillary into the erythrocyte. ...read more.


The lungs only allow exchange of gasses, whereas in plants the cells used for gas exchange are not. Water is also able to diffuse by osmosis and minerals and water can also diffuse across the root hair cells. In protozoa, ammonia, the waste product also leaves the cell across the plasma membrane. The respiratory system in humans in protected, whereas those in plants and protozoa are not. The lungs protect the delicate lungs from being punctured. Unlike the respiratory systems in plants and protozoa, humans only have two lungs, whereas the other organisms have several million ways of dissolving into them. A high surface area to volume ratio makes gas exchange efficient in protozoa in relation to their size and hence rate at which oxygen is consumed. Humans have, in average of 700 million alveoli, which cover an area of approximately 90m2, this also makes gas exchange efficient. Plants have several million root hair cells and stomata, hence also making gas exchange efficient in relation to their size. ...read more.

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