Comparison of Transport in Mammals and Plants

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Comparison of Transport in Mammals and Plants

If an organism is small and has a large surface area to volume ratio, all the nutrients and respiratory gases can be taken in by diffusion across the body surface.

Most multicellular plants and animals have too small a surface area to volume ratio so diffusion would be too slow to provide the necessary molecules. Therefore, they require a system to transport nutrients and waste products around the organism.

The needs of a plant and animal are similar in some aspects and very different in others.

Both need to transport food molecules around the organism but plants, for instance, do not use the transport system to fight disease.

The following table lays out some of the basic similarities and differences:

Mammals: Plants:
Specialised tubes - arteries, capillaries and veins. Specialised tubes - xylem vessels and tracheids and phloem sieve tubes.
All tubes are composed of living cells. Some tubes are composed of living cells, e.g. phloem. Others are composed of dead cells, e.g. xylem.
The concentration of substances transported is controlled (see homeostasis). The concentration of the substances being transported is not controlled.
The heart controls the circulatory system. The heart is controlled by the nervous system. There is no such control in plants.
The rate of flow is moderate and is regulated by vasoconstriction and vasodilation. The rate of flow in the xylem and phloem is quite slow. The rate of flow in the xylem is controlled by external factors via the stomata (e.g. temperature, wind, humidity).
Uses water as a medium in which to transport substances (it is a good solvent, it has a high specific heat capacity, has good surface tension but is not viscous, and is unreactive). Uses water as a medium in which to transport substances.
The substances being transported are: respiratory gases, glucose, amino acids, fatty acids, glycerol, vitamins, minerals, hormones. Substances being transported are: sucrose, amino acids, fatty acids, glycerol, vitamins, hormones (in the phloem) and minerals and water (in the xylem). Respiratory gases are not transported by this system but move via a series of inter-connecting air spaces.

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