Shoots target the above-ground business of the plant. Very young plants may possess only simple, undeveloped shoots. As a plant grows, however, these tender shoots develop into stems and leaves. So, stems and leaves are really part of the shoot system. Stems and leaves are so different and specialized that it is worth considering them separately. Overall, the shoot system enables a plant to grow taller to gain access to energy-giving light, and allows the plant to convert that light energy into the chemical energy of sugar. Like roots, shoots develop from ground, dermal, and vascular tissues. Shoot system is above ground and includes organs such as leaves, buds, stems, flowers, and fruits. The functions of the shoot system include photosynthesis, reproduction, storage, transport, and hormone production.
Organs in Plant Shoot System
Stems are sturdy structures that grow in order to give a plant a fighting chance to spread its leaves in the sun. Stem growth can add to the plant’s height, broaden the area covered by the leaves, or even direct growth from a dark area toward one with more light. To provide mechanical support for a growing plant, stems need to be strong. To help move water and nutrients to the furthest reaches of the plant, stems are stuffed with little transport pipes in the form of xylem and phloem.
Functions of the Stem
In plant growth and development, the plant stem performs the following functions:
- It supports the leaves, flowers and fruits and connects them with the roots. In trees and shrubs, the main stem or trunk provides a strong columnar structure from which branches are attached, raising the leaves upward to be exposed more fully to the sun.
- It conducts water, nutrients and the products of photosynthesis to and from roots and leaves. It accommodates the transport system which is necessary for the vertical and lateral movement of water and sap within the plant body.
- It helps store water, as in cacti, and the products of photosynthesis, as in the trunk of sago palm and sweet palm which store large stock of starch.
- Young green stem also performs a minor role in the production of food through the process of photosynthesis, but in some species (e.g. cactus) the stem is the chief photosynthesizing organ.
- The plant stem serves as a means of asexual reproduction in many plant species.
Leaves are the original solar panels, capturing energy from sunlight in a biochemical process called photosynthesis. The cells within leaf tissues are hectic with biochemistry, importing water and nutrients to support their frantic work, and exporting sugar to provide energy to the remainder of the plant. The import/export business conducted by the leaves is supported by xylem and phloem pipelines, which explains why leaves are so richly veined.
The leaves are the sites of food production for the flowering plant. It is here that the plant acquires light energy and carbon dioxide for photosynthesis and releases oxygen into the air.
Leaves can have various shapes and forms, but they all basically consist of a blade, veins, and a petiole. The blade is the flat extended part of the leaf. The veins run throughout the blade and provide a transport system for water and nutrients. The petiole is a short stalk that attaches the leaf to the stem.
Functions of the Leaf:
The process of producing food, known as photosynthesis, mainly occurs in the leaves of most angiosperms. This process essentially involves the absorption of light mainly by the chlorophyll pigments and the absorption of carbon dioxide via the stomatal pores in the leaves. As a result of the cleavage of the water molecule during photosynthesis, oxygen is generated and released to the atmosphere
Plants lose a large volume of water through the leaves in the form of vapor. The exit of water is through the stomata and the cuticle, but stomatal transpiration is largely more dominant than cuticular transpiration. It is estimated that the loss of water via stomata through the process of transpiration exceeds 90 percent of the water absorbed by the roots.
3. Floral Induction:
The plant leaves synthesize and trans-locate the flower-inducing hormone called florigen to the buds.
4. Food Storage:
The leaves serve as food storage organ of the plant both temporarily and on long-term basis. Under favorable conditions, the rate of photosynthesis may exceed that of translocation of photosynthates towards other organs. During the daytime, sugars accumulate in the leaves and starch is synthesized and stored in the chloroplasts. At night time, the starch is hydrolyzed to glucose and respired or converted to transportable forms like sucrose.
Roots are branched, underground structures that serve two major functions. First, somewhat obviously, roots firmly anchor the plant to a fixed spot. Once a plant takes root and begins to grow in an area with good access to moisture, soil nutrients, and light, it pays to stay. Second, roots serve as transport systems, allowing the plant to suck up water and dissolved nutrients from the soil to support the plant’s growth. Roots have specialized parts that develop from the three major types of plant tissue: ground, dermal, and vascular. The roots of a flowering plant are very important. They keep the plant anchored in the ground and obtain nutrients and water from the soil. The roots also store food. Nutrients and water are absorbed through tiny root hairs that extend from the root system. All roots however, do not originate underground. Some plants have roots that originate above ground from stems or leaves. These roots provide support for the stems.
Functions of Plant Root System:
- Anchorage and support:
The plant root system anchors the plant in the soil and provides physical support. Redwood trees (a gymnosperm) about 100 meters tall have stood erect for thousand years only because millions of individual fibrous roots dig into the ground, even though the depth of penetration is only up to about 5 meters. In general, however, taproot system provides more effective anchorage such that they are more resistant to toppling during storms.
2. Absorption and conduction:
The plant root system absorbs water, oxygen and nutrients from the soil in mineral solution, mainly through the root hairs. They are capable of absorbing inorganic nutrients in solution even against concentration gradient. From the root, these are moved upward. Plants with a fibrous root system are more efficient in absorption from shallow sources.
The root serves as storage organ for water and carbohydrates as in the modified, swollen roots of carrot, sweet potato and yam bean. Fibrous roots generally store less starch than taproots. Some roots are capable of storing large amounts of water; the taproots of some desert plants store more than 70 kg of water.
Some roots are capable of performing photosynthesis, as in the epiphytic orchids and aerial roots of mangrove.
Plants that grow in stagnant water or other watery places have modified roots called pneumatophores to which oxygen from the air diffuses.
In many bulb- and corm-forming plants, contractile roots pull the plant downward into the soil where the environment is more stable.
The plant root system also serves as a natural means of perpetuating a species. In mature agoho or horsetail tree and certain plants, clonal seedlings or offshoots are commonly seen growing profusely around the trunk from horizontally growing roots. Likewise, new plants emerge from left-over tuberous roots after harvest in fields grown to sweet potato and yam bean. As a rule, plants with a fibrous root system are easier to transplant than those with tap roots.
Another component of the shoot system of a flowering plant is the flower. The flower is responsible for seed development and reproduction. There are four main flower parts in angiosperms: sepals, petals, stamens, and carpels. The stamen is considered the male portion of a plant and the carpel is considered the female portion.
Sepal: green, leaf-like structure that protects the budding flower.
Petal: colorful and often scented part of the flower that attracts insects.
Stamen : the part of the flower that produces pollen.
Carpel: consists of the stigma, style, and ovary.