Plant reproduction facts for kids
Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.
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Asexual reproduction
Asexual reproduction does not involve the production and fusion of male and female gametes. Asexual reproduction may occur through budding, fragmentation, spore formation, regeneration and vegetative propagation.
Asexual reproduction is a type of reproduction where the offspring comes from one parent only, thus inheriting the characteristics of the parent.
Structures
A rhizome is a modified underground stem serving as an organ of vegetative reproduction; the growing tips of the rhizome can separate as new plants, e.g., polypody, iris, couch grass and nettles.
Prostrate aerial stems, called runners or stolons, are important vegetative reproduction organs in some species, such as the strawberry, numerous grasses, and some ferns.
Adventitious buds form on roots near the ground surface, on damaged stems (as on the stumps of cut trees), or on old roots. These develop into above-ground stems and leaves. A form of budding called suckering is the reproduction or regeneration of a plant by shoots that arise from an existing root system. Species that characteristically produce suckers include elm (Ulmus) and many members of the rose family such as Rosa, Kerria and Rubus.
Bulbous plants such as onion (Allium cepa), hyacinths, narcissi and tulips reproduce vegetatively by dividing their underground bulbs into more bulbs. Other plants like potatoes (Solanum tuberosum) and dahlias reproduce vegetatively from underground tubers. Gladioli and crocuses reproduce vegetatively in a similar way with corms.
Gemmae are single cells or masses of cells that detach from plants to form new clonal individuals. These are common in Liverworts and mosses and in the gametophyte generation of some filmy fern. They are also present in some Club mosses such as Huperzia lucidula . They are also found in some higher plants such as species of Drosera.
Usage
The most common form of plant reproduction used by people is seeds, but a number of asexual methods are used which are usually enhancements of natural processes, including: cutting, grafting, budding, layering, division, sectioning of rhizomes, roots, tubers, bulbs, stolons, tillers, etc., and artificial propagation by laboratory tissue cloning. Asexual methods are most often used to propagate cultivars with individual desirable characteristics that do not come true from seed. Fruit tree propagation is frequently performed by budding or grafting desirable cultivars (clones), onto rootstocks that are also clones, propagated by stooling.
In horticulture, a cutting is a branch that has been cut off from a mother plant below an internode and then rooted, often with the help of a rooting liquid or powder containing hormones. When a full root has formed and leaves begin to sprout anew, the clone is a self-sufficient plant, genetically identical.
Examples include cuttings from the stems of blackberries (Rubus occidentalis), African violets (Saintpaulia), verbenas (Verbena) to produce new plants. A related use of cuttings is grafting, where a stem or bud is joined onto a different stem. Nurseries offer for sale trees with grafted stems that can produce four or more varieties of related fruits, including apples. The most common usage of grafting is the propagation of cultivars onto already rooted plants, sometimes the rootstock is used to dwarf the plants or protect them from root damaging pathogens.
Since vegetatively propagated plants are clones, they are important tools in plant research. When a clone is grown in various conditions, differences in growth can be ascribed to environmental effects instead of genetic differences.
Sexual reproduction
In plants, sexual reproduction involves the fusion of gametes from two parent plants, resulting in offspring that are genetically different from either parent. Flowering plants, the dominant plant group, reproduce both by sexual and asexual means. The bryophytes, which include liverworts, hornworts and mosses, reproduce both sexually and vegetatively. Ferns typically reproduce sexually, but some species of ferns can also reproduce vegetatively.
Flowering plants
Flowering plants are the most common type of plants that reproduce sexually. They have specialized reproductive structures called flowers. Flowers contain male sex organs called stamens, which produce pollen. Pollen grains contain the male gametes. Flowers also have female sex organs called pistils or carpels, which include the stigma, style, and ovary. The ovary contains the ovules, which house the female gametes.
Process
- Pollination
Pollination is the transfer of pollen from the anther (part of the stamen) to the stigma (part of the pistil). This can occur through various mechanisms, including wind, water, insects, birds, or other animals. Pollen must reach the stigma for reproduction to take place.
- Fertilization
Once pollen lands on the stigma, it germinates and grows a pollen tube that extends down to the ovary. The male gametes travel through the pollen tube to reach the ovule. Fertilization occurs when the male gametes fuse with the female gametes inside the ovule, resulting in the formation of a zygote.
- Seed development
After fertilization, the zygote develops into an embryo inside the ovule. The ovule matures into a seed, which contains the embryo, along with a protective seed coat. The seed is dispersed from the parent plant and can germinate under favorable conditions to grow into a new plant.
Dispersal and offspring care
One of the outcomes of plant reproduction is the generation of seeds, spores, gemmae and other vegetative organs that allow plants to move to new locations or new habitats.
Plants do not have nervous systems or any will for their actions. Even so, scientists are able to observe mechanisms that help their "children" thrive as they grow. All organisms have mechanisms to increase survival in offspring.
Offspring care is observed in the Mammillaria hernandezii, a small cactus found in Mexico. A cactus is a type of succulent, meaning it retains water when it is available for future droughts. M. hernandezii also stores a portion of its seeds in its stem, and releases the rest to grow. This can be advantageous for many reasons. By delaying the release of some of its seeds, the cactus can protect these from potential threats from insects, herbivores, or mold caused by micro-organisms. A study found that the presence of adequate water in the environment causes M. Hernandezii to release more seeds to allow for germination. The plant was able to perceive a water potential gradient in the surroundings, and act by giving its seeds a better chance in this preferable environment. This evolutionary strategy gives a better potential outcome for seed germination
There are similar reproductive strategies found in both mammals and plants. A divergence between the two is that in harsh environmental conditions, mammals produce fewer and larger offspring, whereas plants produce more seeds.
See also
In Spanish: Reproducción vegetal para niños
