Did you know that a living tree never stops growing?
Like animals, plants also acquired its ability to adapt as their surrounding environment changes from time to time. Since the first types of plants in our world were traced by scientists to begin their life in an aquatic environment, land-based plants have overcome numerous obstacles associated with life on land. A few includes the absence of aquatic environment for reproduction, an environment to support the plant body, and possible dehydration of the plant.
Out of The Water
The absence of an aquatic environment allows angiosperm to reproduce by attracting insects by utilizing its petals beauty. During the spring time, flowers would allow their pollen to dissipate through their air causing the transport of male gametes to other female flowers. The nectar a flower produces attracts insects such as bees to transport pollen from one flower to another. Another adaptation that allows angiosperm to reproduce outside of an aquatic environment is seed dormancy. This allows flower to prevent germination during an unsuitable weather conditions. This safeguards the seeds from encountering damage from a period of harsh weather as well as herbivores. Another similar mechanism similar to this is delayed germination which allows a prolonged time for the dispersal of all the seeds at the same time. Seed germination rely on multiple environmental stimuli and signals including: water which activates enzymes that initiate cellular respiration, oxygen for aerobic cellular respiration, temperature for signals of season change, fire as other plants are eradicated, more sunlight are obtained, and gibberellins which binds to DNA that will eventually produce enzymes necessary for germination. A seed contains an embryo and stored food with very little water. The absence of water halts metabolic activity and maintains the inactive dormant condition. The tough seed coat protects the embryo from microbes and other organisms. As discussed, the absence of an aquatic environment seems to generate a favorable environment for angiosperm where as an aquatic environment could not possibly provide.
Numerous angiosperm structures such as stem, root, cell wall, and turgor pressure also aid the angiosperm to support them outside of an aquatic environment. The stem of an angiosperm aids support on land by providing a stronghold structure for the flower to grow above ground. The stem internal structure is filled with a system of tissues that allows materials to move up and down from the roots to the shoots in the xylem and phloem. The next adaptation to prevent dehydration is the xylem. The xylem’s tubes supply water for photosynthesis by transporting water and minerals from the roots into the leaf. Along with phloem which move chemicals produced by photosynthesis, both are vital to the adaptation of an angiosperm without a watery environment. As leaves grow on a stem, they provide a safe place for the angiosperm to keep its flowers and fruits as well as a platform for the angiosperm to obtain light energy. The most important organ of the angiosperm is the root. The major functions of roots are absorption of water and nutrients from underground, anchorage of the plant body to the ground, and storage of food and nutrients. The next adaptation that is universal across all organisms that is significant for the structure of angiosperms is the large surface area to volume. When the surface area of the plant is large, the cell can efficiently react with the outside environment such as an adequate amount of oxygen for respiration can diffuse into the cell, and transpiration can be carried out rapidly.
Another flowering plants structure that aids support outside of watery environment is the cell wall. Located outside the cell membrane of the flowering plant, the cell wall provides a strong, yet flexible structural support as well as protection that act as a filtering mechanism to the environment outside of the plant. Since water is vital to the life of a plant, the cell wall acts as vessel to maintain the amount of water inside the cell. Without the cell wall, plants living outside of an aqueous environment could not maintain water level and storage within their system. This leads us to the last adaptation that aids the structure of angiosperms without an aquatic environment which is turgor pressure. Turgor pressure is caused by the flow of water from a site of low solute concentration outside of the cell into area of higher solute concentration, which is inside the cell’s vacuole. This pressure also known as turgidity causes the plasma membrane to be pushed against the cell wall, maintaining the flower’s rigidity and structure.
The last adaptation to be discussed is the adaptation of flower plants to prevent dehydration. The first adaptation of an angiosperm is the functioning of the leaf and stem. Under the leaf contains a set of cells called stomata. Although these pores are known to control gas exchange, they are also vital in the transpiration of the plant by releasing water vapor into the atmosphere. Transpiration, in turn, cools the plants and enables the flow of mineral nutrients and water from the roots to the shoots. Since plants are anchored by their roots, water needs to be obtained another way. With apical meristem being the production center of the hormone auxin in the tip of the shoot, the auxin can move down through active transport and stimulate the movement of hydrogen ions into the cell wall. These results in the decrease in pH that activates an enzyme that breaks down cellulose fibers, allowing the movement of water into the cell, and the cell elongates as cell turgor increases. Leaves hold the most recognizable adaptation during the winter when the weather is harsh to the fragile leaf. In order for plants to conserve water during winter and survive the environment, they shed their leaves which they hope to regrow in the next season. In this way, the plant itself has more water retention within their trunk and branches instead of the leaves. Another amazing property of the leaf is the cuticle; a wax covering that reduces transpiration. Plants that grow in hot and dry habitats would have thicker cuticles in order to reduce transpiration and store more water.