Thursday, December 30, 2010

Research Paper on Plants

Research Paper on Plants

Upon considering nutrition the primary factor to take into consideration is the metabolic strategy of the organism in question. Fungi are heterotrophic, obtaining both carbon and energy from organic compounds; they are chemo-organotrophs.

Plants are autotrophic, they obtain their carbon from atmospheric CO2 and their energy from light; they are photolithotrophs. The nutritional requirement of the organism is thus dictated by its nutritional strategies, this essay will concern itself with the comparison of molecules absorbed, mechanisms, regulation and organs of absorption.

Plants can synthesize their organic molecular compounds out of inorganic nutrients, the processes of energy transduction and carbon fixation occur in the chloroplasts in the reaction of photosynthesis. Plant leaves have many physiological adaptations to ensure maximal rates of photosynthesis, however there are many other nutrients required by plants and it is the acquisition of mineral nutrients via root absorption that will be focused upon.


Fungi entail an organic carbon source, but they also have a requirement for inorganic ions. The essential elements required by plants and fungi are very similar, both plants and fungi need macronutrients, N, P, K, Mg, Ca, S, but plants also require Fe as a macronutrient, whereas fungi require it as a micronutrient. The micronutrients commonly required are Cu, Zn, Mn, Mo, and plants also require B and Ni.

Plants must obtain all of their minerals from the soil, and they are taken up as inorganic ions as they re found in the soil, the plant cannot chemically breakdown molecules. Fungi utilise both organic and inorganic sources to obtain mineral ions. Fungi absorb nutrients through the plasma lemma as low molecular weight compounds, and as bioorganic chemicals usually exist as insoluble macromolecular complexes, the fungi secrete exocellular enzymes to break them down into their soluble monomeric units.

In plants ion uptake occurs in regions of the root younger than the suberization of the exodermis, usually at the root tip. Similarly both enzyme secretion and nutrient uptake in fungi occur at the nascent tip where the wall is thin and deformable. The mechanisms for uptake utilize various transporters in the plasma membrane, in plants cations are driven through uniports by the electrochemical gradient, and anions are taken up by secondary active transport through H+ cotransporters. In fungi both facilitated and passive diffusion and active transport mechanisms are used to take up nutrients, they also have the mechanisms of insoluble sinks, immobile binding sites and metabolic sinks for accumulation of nutrients in hyphae without active transport and siderophores for the uptake of iron.

In plants and fungi when the region local to the organ of uptake is depleted of nutrients, the roots and hyphae respectively extend into a fresh area; this overcomes the limitations of diffusion rates (and bulk flow in soil) to a stationary cell.

Fungi, unlike plants, can regulate their metabolism, via catabolite repression, whereby fungi utilise the nutrient source that is in the greatest abundance and switch off unnecessary metabolism.

Fungi also breakdown older regions and the products are absorbed by the new regions, plants can have senescing regions but it is not a continual process.

The nutrient acquisition of both types of organisms is improved when they are in a symbiotic association and form mycorrhizae, the plants supplying the organic nutrients and the fungi improving the absorption of mineral ions and water.

There are aspects of fungal and plant nutrition that are very similar, when considering mineral ions, however it is the lack of photosynthetic ability in fungi that mean the two organisms are also very different.

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