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Plant and Animal Structure Essay

Duckweeds belong to a family of hydrophytic (aquatic) plants called Lemnaceae and are considered the smallest flowering plants. These plants lack the recognizable stems and leaves and they are instead characterized by several small flattened floating structures, which are believed to be modified leaves, often called as thalloids, with simple or no roots. Duckweed roots do not exhibit secondary growth, branching, presence of root hairs and are not even responsible for the absorption of water needed for survival.

Instead, these roots serve as anchors of the plant in order to keep the orientation of the duckweed right side up besides water turbulence. Roots of the duckweed are also very sticky, which in aid in its dispersal whenever mobile organisms come in contact with it. The stomata on the underside of the thalloids account for the needed water by the organism. Although these plants produce seeds, fruits and flowers, they primarily reproduce asexually.

Buds, called fronds, grow on the thalloids and remain attached to it until maturity and then separate as a new organism from the plant. The simplicity of the structure enables the duckweeds to be light enough to be buoyant above water. However, duckweeds still have a specialized structure called aerenchyma, which contain air pockets, resembling hulls of ships. The preference of natural selection and evolution having water as their habitat, shying away from soil, decreases competition for nutrients from the earth and especially sunshine against larger terrestrial plants.

Since duckweeds grow well in water with high nitrogen and phosphate levels they can be used to facilitate bioremediation of eutrophic waters and unlike algae, they are readily edible with respect to herbivorous fishes. Prickly pear cacti belong to the genus Optunia of the family Cactaceae, the family of cactuses. These cacti are found in abundance in the Western part of the United States and throughout Mexico. Prickly pear cacti have flat, rounded and fleshy modified stems called platyclades.

The cacti platyclades primarily function as storage of water absorbed by cacti, photosynthesis and provide for the conception of flowers. Just as other cacti, prickly pears have spines. However, these species of cacti have two kinds of spines, which are modified leaves, one type of which are large, smooth and fixed, and the other type, termed as glochids, are small, hairlike and unfastens easily from the plant. These modified leaves not only reduce the amount of water lost through plant transpiration, but also provides protection from potential predators.

Prickly pear cactuses characteristically have thigmotactic anthers, the pollen producing part of the plant which can respond to a touch stimulus. Both of these plants have evolved to live on unusual regions, almost inhabitable to most organisms. Their adaptations and modification of essential plant parts, unique to each of their species, have enabled them to survive in these unfavorable circumstances. Even though in soaking or in scorched conditions, Mother Nature does always find a way to nurture and cultivate life.


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