Life Cycle Of A Plant
An Overview Of The Plant Lifecycles
Plants are very helpful to humans. We eat plants in order to stay healthy and strong, use household products which is mostly made of plants to remain tidy in appearance, for shelter and other usefulness, etc. Nowadays, as a result of increasing number of human population, shortage of food supply and some plants being endangered has become apparent. In other words, plants are important to maintain the balance of nature. We humans need them.
While it is true that plants consist of almost 375,000 varieties of species on earth, plants like humans and other animals are also living organisms. Trees, flowers, bushes, and even green algae are some common terms used to describe plants. Life is a matter of give and take relationship, which means if we give something good to others, expect something good in return.
Just like us, the more we plant trees and help them to increase in number, expect them to give us fresh air that we all need to breathe in and a food to munch. In other words, for without them, life here on earth would be very impossible as the earth is the only planet where it can support various forms of life. Also, they are the only living organisms that are capable of using light from the sun into energy useful for them and for other processes of life here on earth.
Unique to them is their ability to make their own food and this allows them to adapt and survive enough to almost wide range of habitats on earth. Simply say, they adapt in order to help them survive.
This is the story of the life cycle of plants in general. However, in order to have a clear picture of them, plant’s life cycle can be broken down and described into specific sections.
The Seed
Plant begins its life cycle as a seed, which after a certain period of time, germinates and develops into a plant. Seed is actually a sprouting plant and a result of matured ovule of gymnosperm and angiosperm plants that occurs after the process of fertilization and has become necessary in the reproduction and dispersal of plants. In order for a seed to develop and function into a healthy strong plant, sufficient amount of water and sunlight are needed.
Seeds perform various functions for the plants from the nourishment of the embryo to dispersal of the seed from one location to another. Due to plant’s limited ability to disperse from a condition favorable to them for growth, they have developed ways to disperse by their seeds naturally either by wind, water or animals. Some seeds have wings, hair and dust-like structures that helps in transport, some floats in water or the so-called ‘buoyant seeds’ that flows from different bodies of water while some are being eaten by animals that drop off the soil and this allows them to be distributed from one place to another.
Germination and the Seedling
The term simply denotes sprouting of a seedling from a seed of an angiosperm and gymnosperm plants. As a general rule, the process describes something that expands and develop into a greater being from a small existence or germ.
For a successful seed germination to take effect, environmental factors such as water, temperature, light and oxygen must be established in the first place. Seeds need a significant amount of water for proper moisture content. This allows them to swell and break their seed coats and eventually starts to form roots and leaves. Temperature, on the other hand, affects the growth rate and plant metabolism at the cellular level. Some seeds germinate in a temperature range favorable to them. Some germinates above the room temperature, others germinate only after the period of dormancy while the other germinates only in response to varying warm and cold conditions. Plants starved in oxygen gas also affects the success of germination for metabolism and growth. Sufficient supply of oxygen on the other hand, is required in the process called aerobic respiration where oxygen aids energy for seedling until it grows leaves. And lastly, light also has significant effect on germination. Some needs independent to light or darkness but most seeds are light sensitive and largely affect the germination’s success. Many seeds especially in the forests, will never germinate until the canopy openings allows ample amount of light to enter and be absorbed by these seeds for growth and seedling.
The Root
One important organ of a plant for nutrient assimilation and absorption is the structure called root. This structure usually lies below the surface of the soil or ground though some roots can also be aerial thus, capable of growing above the ground. The root performs a number of functions for plant growth and development. First, it allows inorganic nutrients such water to be absorbed by plants and transported to other plant structures. Second, roots function as anchor for the whole plant structure thus, preventing soil erosion. Third, roots are capable of synthesizing a substance called cytokinin that dictates the rate of plant growth. Lastly, and the most important of all, roots serve as storage of food and nutrients as it allows symbiotic relationship with a number of bacteria and fungi where nutrients stored among roots were being assimilated.
Root also follows a pattern or a system of development called the root architecture. This root architecture can be described both by topology variation and biomass distribution within its root system. Having a balanced root architecture means allowing the plant to use the soil and nutrients efficiently thus important to provide support to bigger trees and plants.
The Stems
Another important structures located aboveground portion of the plant that support other structures such as leaves and flowers are called stems. These structures are necessary as the leaves need to be exposed to the sun to receive light for the process of food making called photosynthesis and as the flowers need to be exposed for pollination.
Stem structures provide functions relevant to growth and development. First, structures such as leaves, flowers, and fruits depend largely to stems. Second, stem allows water, nutrients and the products of photosynthesis to be transported from one structure to another. The stem tubes that transport the water and other nutrients up into the plants are the structures called xylem while the stem tubes that carry the food back down to the plant is called the phloem. Lastly, stem has minimal functions in the photosynthetic process of making food except for the cactus wherein the stem plays a chief role in the process of photosynthesis.
Stems can be classified as herbaceous or woody prior to their textures. Banana tree for instance, is a herbaceous plant with no permanent woody tissue and will soon die after flowering due to its short life span. Trees such as shrubs and other trees with permanent woody tissues belong to woody trees. They are very common to have secondary layer of xylem that persist indefinitely. As to the direction of stems, they can be described either erect, if stems are in vertical upward path; ascending, when stems are rising in slanting path; decumbent, when reclining on the ground; prostate, when lying flat on the ground; and twining by coiling the other plant stems.
The leaves and their structures
Leaf is an organ familiar in plant morphology and the term foliage, is used to describe leaves as an attribute for plants. The structure is called the ‘powerhouse of the plant’ as this structure is the main site specialized in the photosynthetic process of making food.
Externally, leaf consists mainly of layers of flat, thin structures capable of maximizing its ability to capture light from the sun by efficiently exposing their surfaces to light necessary in promoting photosynthesis. Similarly, the interior structures of leaf at the cellular level, have developed ways to maximize the ability to capture light from the sun for the chloroplasts and the stomata that were concentrated mostly in the lower epidermis which helps in regulating the carbon dioxide absorption and oxygen release. The waxy substance called the cuticle, functions the same way as to regulate excessive water loss and protects the leaf from insects and other outside conditions. While most of the food manufacture takes place in the palisade mesophyll, gas exchange happens in the spaces in the region called the spongy mesophyll.
Leaves can also be described by a variety of means. First, it can be described according to petiole. Petiolated leaves are those with stalks and this depends from one plant to another. While those leaves that do not have petioles belong to sessile leaves and that the leaf is directly connected to the stem of the plant. Second, leaves can be described according to blade structure either simple, with no divided blades or compound, with divisions reaching the midrib structure of the leaf. Lastly, according to edge of the leaf either Entire leaf with smooth leaf margin; Sinuate with curves/ waves edges; Dentate with teeth- like margin and a lobed with divisions on the leaf margin. Moreover, regardless of physical attributes of each leaf presented, it’s the process of photosynthesis that all these leaves depend on.
Photosynthesis
Animals including humans inhale oxygen gas and exhale carbon dioxide gas in order to survive and stay alive.To do this, sufficient supply of oxygen is needed to support all forms of life. Plants are the only organisms capable of doing this task in the process called photosynthesis. Photosynthesis refers to the ability of green plants to use light energy coming from the sun to chemically combine carbon dioxide and water to produce sugar molecules and oxygen. This happens in the chloroplasts of the leaves which contains chlorophyll pigment that absorbs light energy while the gas exchange of carbon dioxide and oxygen happens in the stomata of the leaves.
The Flower
The flower, also known as bloom, is a plant structure important in the reproduction of flowering plants and in making seeds. This structure functions well as plant’s reproductive organ for the union of sperm and eggs from different plant population in the process called pollination.
Most flowers vary in structures so a typical flower can be used to describe its parts. These can be of four sets namely; sepals, petals, stamens and pistils. The sepals or sometimes called calyx are the outermost part structure and are usually green in color. These structures resembles that of plant’s leaves and functions as a bud support/ protection as the flower continues to grow within. The petals/ corolla on the other hand, are the showy part of most flowers. This structure comes in a variety of colors which is necessary in attracting pollinators. Another flower parts called the stamens where anther and the filament are located, contain pollens which serve as the male sexual organ of the flower. The pistils on the other hand has reproductive unit called the carpel which consists of stigma, style and ovary. These are the structures where pollens will be placed during the process of pollination. After pollination, the ovary will be developed into a fruit while the ovule into a seed.
Pollination and Reproduction
In fact, flowers are not capable of moving from one location to another thus, it’s a big challenge for them to pollinate though they are capable of self-pollination. That’s why many of them have evolved over generations into an attractive objects to some animals, allowing these animals or the ‘biotic vectors’ to spread out the pollen grains from one place to another. Some factors such as wind and water (abiotic vectors) can be useful enough to transfer the pollens between plants.
Plant death
Annual plants in temperate climates germinate after the last spring frost, undergo vegetative growth, and flower in the late summer and early autumn. The annual plant then dies with the first frosts of late autumn. The seeds of an annual plant remain dormant over the winter until the temperature is warm enough to germinate anew in the following spring. Grain crops such as wheat, rice, and corn are annual plants, as are tomatoes, peppers, marigolds, and lettuce. Farmers will need to re-cultivate these crops from new seeds every year.
Biennial plants are the smallest group. After the last spring frost, biennials germinate and then continue to vegetative growth over the course of the season. Instead of flowering in the same year of germination, however, the plant itself ceases growth and becomes dormant over the late fall and winter months. In the spring of the following year, the plant begins to grow anew and will flower over the course of the season before death. Carrots, parsley, and foxglove are biennials.
Perennial plants live for 3 years or more. After germination, most will grow and flower or set seed over the course of many seasons. Herbaceous perennials, such as orchids, dahlias, ferns, and grasses, have a root system that will lie dormant over the winter while the stalk and other above-ground tissues die. The stem and other parts will then re-grow in the following year. Deciduous perennials are woody shrubs and trees that do not grow over the winter, but have some above-ground tissues that remain intact: The trunk (stem) and branches remain, but the leaves die and fall from the plant and re-grow the following spring. Most trees in temperate climates are deciduous, such as cherry trees, apple trees, oak trees, and pear trees. Evergreen perennials experience year-round vegetative growth, though many in temperate climates will flower or seed only during the spring. Tropical plants with year-round growing seasons are evergreen as well. Temperate evergreens are almost exclusively trees and many are long-lived, such as Redwoods, pine trees, spruces, and fir trees.
The amount of time it takes a plant to germinate, grow, bear seeds, and eventually die is referred to as senescence. The senescence of a tomato is annual, for example. This is determined by genetics, but can be in response to a plant’s environment, as well. In longer-lived plants such as trees, death might only be signaled by a lack of vital nutrients in the environment.
Plant death is an important part of the life cycle. After death, the plant’s body is broken down into its nutrient components by micro-organisms and insects, and by oxidation reactions that break apart the plant structures. As this occurs, the plant’s components enrich the surrounding soil and make it more hospitable for new plants to germinate and grow. This is called succession. In a field of dirt, only grasses, ruderals, and other hearty plants may grow at first. These plants bring nutrients to the soil surface and drop nutrient-covered seeds.
They then die and their own components are given back to the soil. The field is now hospitable to plants with more nutritional requirements for growth, and seeds that are spread there will germinate and begin their life cycle. After many years, the soil will be enriched to the point where long-lived trees, annual flowers, and other plants with more stringent growth requirements will begin to populate the area. This is the reason that a mature forest cannot simply be planted: It takes many successive plant generations to build a suitable environment, and once the suitable environment is in place, long-lived perennial trees that characterize a forest take many more years to grow to maturity.
