PLANTS IN ECOLOGY
The life cycle of a plant varies depending on the individual species. There are, however, certain requirements for life that most plants need. The growth of a plant is dependent upon light, water, oxygen, carbon dioxide, minerals in the soil, temperature and microbes in the soil. Light, water, and carbon dioxide are needed for photosynthesis which produces food for the plant. Oxygen is needed when it is dark, because the plant then needs oxygen to maintain itself. The correct temperature, soil, and minerals are all needed when the plant first germinates and subsequently grows. Soil helps bind the roots so the plant can anchor itself. Microbes in the soil include a number that are beneficial to plants. Microbial activity helps bring about the decay of organic material (dead plant material and animals) necessary for the production of soil. Temperature or light intensity varies for each type of plant, and this helps explain global plant distribution; light intensity or temperature also effects the rate of photosynthesis in plants; the time at which a plant flowers and the rate at which water loss occurs in a plant (transpiration.)
When these requirements are static for a seed, it will begin to grow or germinate. Sufficient food and minerals are stored in almost all seeds, so that these factors do not limit germination. As water is absorbed by a seed, the inner tissue swells more rapidly than the seed coat. The penetration of water allows the tissues to become hydrated and enzyme activity increases. The food that is stored in the cotyledons or the endosperms are now digested and used.
ll plants need light, water, air, moderate temperatures and most need soil. Some plants, such as mistletoe and duckweed, do not require soil for growth and life but they do not constitute the majority of plants. There are wide variations in the amount of light and water that plants require. A mature Joshua tree, for example can store enough water to last three years or until another rainy season.
Many plants can reproduce either sexually (seeds) or vegetatively (asexual), utilizing other plant parts. Whole plants can be grown from stems, leaves or roots, if the right plant is chosen. The following are some suggestions that can be used to illustrate vegetative reproduction.
Vascular plants are plants that have specialized conducting tissue and are usually grouped as tracheophytes and include the ferns, horsetails, angiosperms (flowering plants) and gymnosperms (pine-like trees). Thallophytes (water type plants) and bryophytes (mosses) do not have true roots, stems, and leaves and possess no specialized system for the conduction of food and water from one part of the plant to another. Plants that have a vascular system are larger and able to cope with a "land situation." There are no plants with a vascular system in a total water environment because the water provides the nutrients the plants require, so they do not have to "conduct" these substances.
Cell walls are made primarily of cellulose but there are also other substances like hemicelluloses, minerals, tannins, resins, pigments, proteins, mucilages, and gums that can be found in plant cell walls. Cell walls are porous, allowing an exchange with substances outside the cell wall. Cellulose has a straight chain structure, forming strong fibers that are ideal cell-wall structural materials and useful in making products.
Plants form the basic food staple for all life forms. They are the major source of food and oxygen on earth, since no animal can supply these necessary components without plants. The cattle we eat as beef, feed on grasses and the fish we eat, consume algae and are therefore dependent on plants for well being. Other important uses of plants include, providing shelter for animals, providing materials for clothing (cotton fibers), paper products, medicines and other chemicals, producing coal from once living plant material, reducing wind speed and noise levels, and reducing soil erosion and water runoff.