The vital life processes of plants, such as photosynthesis, respiration, nutrient transfer and gas exchange, all take place within individual cells. All cells are made up of the same structural components and it is variation in these that creates different cells for different purposes.
Although some plants lack of central stem, and plants such as mosses and fern do not produce flowers, the anatomy of most plants can be split into four basic zones; the roots, stem, leaves and flowers. All these parts play a vital role in the plant’s basic functions, including growth, reproduction, nutrient-collection and storage.
Types of root
The roots of most of the plants are a combination of a number of central roots, up to 1.5mm(0.016in) in diameter, with many smaller roots trailing off. Terrestrial roots have fine hairs for trapping moisture, but these are not present in aquatic plants, although they may develop on some bog plants when grown out of water.
The function of stem
A stem in most aquatic plants and performs two basic functions: support and transport. The stem’s function is aided by supporting gas – or air – filled cells that provide buoyancy and help to keep the plant upright. Since the surrounding water provides much of a plant’s support, aquatic stems are often much thinner and more flexible than the terrestrial stems. Flexible stems allow the plant to move with the water, rather than try to hold steady to hold against it, risking damage.
The leaves of a plant are essential tools for collecting sunlight to use in a process of photosynthesis. Gas exchange and some collection of nutrients are also carried out by the leaves. The leaves of terrestrial plants have a think, waxy outer layer called cuticle, which protects the plant from drying out. In aquatic plants this layer is much thinner and liquid is able to pass through much more easily, which helps the plant to take up nutrients. Aquatic plants that produce aerial leaves often show two different leaf shapes below and above the water. This is due to different environments and a change in the cuticle layer.
Although not all aquatic plants are likely to produce flowers in the aquarium, the majorities are flowering plants and will produce seeds and reproduce by flowering in nature. The flowers are usually produced above water, where they can be pollinated by insects, just as terrestrial ones are. Some aquatic plants produce flower beneath the water surface. In these instances, the seeds are capable of floating downstream and a few species do not produce flowers at all, preferring to reproduce by purely asexual means.
(Contents are taken from the book of MiniEncyclopedia Aquarium Plants)