BIOLOGY Volume 1 - A Guide to General Biology - 2004

7. AUTOTROPHIC NUTRITION

7.10. Mineral Nutrition in Plants and Animals

7.10.2. Special Adaptations for Obtaining Essential Elements

Insectivorous Plants

Insectivorous, or carnivorous, plants are green plants specially adapted for catching and digesting small animals, particularly insects. In this way, they Supplement their normal autotrophic Nutrition (Photosynthesis) with a form of heterotrophic nutrition. Typically, such plants inhabit nitrogen-deficient environments and use animals as an additional source of nitrogen. By attracting insects through coloration, scent, or sweet secretions, these plants trap them using various mechanisms and then release Enzymes into the trap to digest the captured prey. The resulting products of this extracellular Digestion, mainly Amino Acids, are then absorbed and assimilated.

Some plants feature highly complex trapping mechanisms. Examples include the Venus flytrap (Dionaea muscipula), pitcher plants (Nepenthes), and sundews (Drosera). The sundew is one of the few representatives of such plants native to Britain, as the majority inhabit tropical or subtropical regions. They are typically found in wet heaths and bogs, mostly on mineral-deficient, acidic soils. Examining the detailed anatomy of various traps is beyond The Scope of this book.

Mycorrhiza

A mycorrhiza is a mutualistic (symbiotic) association between a fungus and the roots of a plant. Evidently, the vast majority of terrestrial plants enter into such relationships with soil Fungi, which is of great significance as it supplies plant roots with numerous mineral elements and energy. The fungi receive organic nutrients, primarily CARBOHYDRATES and Vitamins, from the plant, while in return, the plant obtains mineral salts (mostly phosphates, nitrates, ammonium salts, and potassium) and Water through its roots. As a rule, only young roots are infected, whereupon ROOT Hair growth either ceases or is severely inhibited. The network of fungal hyphae extending into the surrounding soil covers a significantly larger surface area than a root system with even well-developed root hairs. It has been suggested that plants of the same or even different species may be interconnected via mycorrhizal networks. This concept has the potential to fundamentally alter our understanding of natural ecosystems.

There are two MAIN TYPES OF mycorrhizae: ectotrophic and endotrophic. Ectomycorrhizae form a sheath around the root and penetrate the intercellular spaces of the epidermis, without, however, entering the Cells themselves. This forms an extensive intercellular network. They are formed by higher fungi, including many edible mushrooms, and are predominantly found in forest plants such as conifers, beech, oak, and many others. The fruiting bodies—the mushrooms we actually harvest—can often be seen growing near these trees.

Endomycorrhizae are found in virtually all other plants. Much like ectomycorrhizae, they form an intercellular network that also extends into the soil; however, in this case, the fungi penetrate inside the root cells (although Cell/30.html">The Plasma Membrane of the host cells remains structurally intact).

Further research into the Structure and function of mycorrhizae will enable the Practical Application of this knowledge in agriculture, forestry, and land reclamation.

Root Nodules

Nitrogen Fixation by root nodules in legumes is discussed in Chapter 13. These nodules harbor Bacteria that stimulate the growth and division of root parenchyma cells, resulting in The formation of swellings, or nodules, on the roots.