CHARACTERISTICS AND LIFE PROCESSES OF FERNS.
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CHARACTERISTICS AND LIFE PROCESSES OF FERNS.
The fern body plan is divided into three main parts:
- frond (leaf),
- rhizome,
- and sporangium.
The fronds are divided into smaller divisions called pinnae.
On the underside of the pinnae are the sori, which are clusters of sporangia that produce spores for reproduction.
The rhizome is the horizontal underground stem that stores nutrients and produces fronds above and roots below.
The roots anchor the plant and absorb nutrients from the soil.
Biological classification.
Division/Phylum Filicinophyta
Reasons:
- Presence of sori
- Sporophyte is dominant.
- The sporophyte is independent of the gametophyte.
- It is a seedless vascular plant.
Class Pteropsida/Nephrolepis
Reasons:
- Presence of sporangia on the lower surface of the leaves.
- Presence of fertile leaves
Habitat:
- Growing in humus on tree trunks as epiphytes, especially on palm trees.
STRUCTURE OF A FERN
- They are vascular plants with true roots, stems, and leaves.
- They do not bear flowers and, therefore, are seedless plants.
- The ferns have large leaves divided into several leaflets called fronds.
- Mostly, the fronds sprout directly from a short prostrate underground stem (rhizome) at ground level.
- Some species have an upright stem
- Fronds bear a cluster of sporangia at the undersides.
- Each cluster of sporangia is called a sorus (plural: sori) from which the spores develop.
- Some sori are protected by a thin flap of tissue called an indusium.
- The fronds have developed vascular tissues with xylem and phloem tissues.
- Stems of ferns are mostly underground stems (rhizomes).
- The stem possesses an adventitious root system that grows from the stem.
- The stems and roots of ferns have a vascular system.
LIFE PROCESS OF FERN
- Ferns obtain food through their roots and photosynthetic fronds.
- They undergo gas exchange by simple diffusion through the leaf stomata.
- Excess salts and other waste materials are removed through the roots.
- They grow throughout their life cycle, from spores to mature plants.
- Ferns perform tropic movements, where they grow towards unilateral sources of stimuli such as water, gravity, and light.
- The sperm also swim through a film of water to fertilise the egg.
- They respond to light, gravity, and water.
The reproductive structure of Fern
- Sori/sporangia
- Rhizome
Reproduction Process in Fern.
- The life cycle is an alternation of generations.
- The sporophyte bears sori at the underside of a fertile frond.
- Each sorus has sporangia. Within a sporangium, diploid cells called sporocytes, or spore mother cells, undergo meiosis and generate haploid spores.
- Matured spores are scattered when the sporangia dry up and rupture through an explosive mechanism.
- When a spore lands on a favourable ground or substrate, it germinates into a small gametophyte.
- The small gametophyte is called a prothallus.
- Prothallus bears antheridia and archegonia on the under surface, which are the male and female sex organs, respectively.
- The antheridia release flagellated sperms.
- Sperm with flagella swim in a film of water to the egg produced by the archegonium for fertilization.
- The fertilized ovum develops into a fern, which is the sporophyte.
- In ferns, the dominant phase of the life cycle is the sporophyte, and the gametophyte is greatly reduced in size.
- It has no structures for protection against water loss; therefore, its habitat should be moist.
Adaptive features of the fern to its habitat
- Rhizome is a perennating organ
- Sori on the lower surface of leaves to be protected against rain and dew
- Cuticle on the upper surface of leaves to reduce excessive transpiration.
- Adventitious roots cling to support and absorb water and mineral salts
Economic Importance of a Fern
- Many fern species are grown and used as ornamental plants for indoor and outdoor decorations.
- Some species of ferns are used for medicinal purposes.
- Some species of ferns are used as food in some parts of the world
- They are useful in eliminating hazardous heavy metals from the soil (e.g., arsenic).
Explain alternation of generations.
- The life cycles of all land plants alternate between two generations of distinct multicellular organisms: gametophytes and sporophytes.
- The alternation of generations is distinguished by the fact that the life cycle includes both multicellular haploid organisms (gametophyte “gamete-producing plant”) and multicellular diploid organisms (sporophyte “spore-producing plant”).
- The process of alternation of generation
- The sporophyte produces mature spores in specialized structures (e.g., sporangia) through meiosis and may be dispersed by wind or a self-explosive mechanism
- When a spore falls on moist soil, it germinates and grows (by mitosis) into a green-leafy gametophyte plant.
- The gametophyte may, in turn, produce gametes (by mitosis) in special sex organs called an archegonium (female organ) and an antheridium (male organ).
- Sperm cells produced by antheridia swim in a film of water on the plant to the egg in the archegonium for fusion or fertilization.
- This fertilization produces a zygote that develops into the sporophyte plant.
- The cycle then repeats itself.
Remember,
- Alternation of generations occurs prominently in bryophytes and ferns than in higher plants.
- In higher plants, the gametophyte is drastically reduced; the flower’s sporophyte is seen as the tree/plant.
- Sporulation: Involves the production of spores that may germinate and develop directly into an adult moss, usually when conditions are favourable.
Review Questions.
- Give the distinctive features identifiable with the fern plant.
- Describe the life processes of the fern.
- Examine the impact of the abundance of ferns in an ecological setting.
