Pollination is a very important part of the life cycle of a flowering plant. It is part of the sexual reproduction process of flowering plants, which results in seeds that will grow into new plants. Flowers are the structures of flowering plants that contain all the specialised parts needed for sexual reproduction.
Plants have gametes, which contain half the normal number of chromosomes for that plant species. Male gametes are found inside tiny pollen grains on the anthers of flowers. Female gametes are found in the ovules of a flower. Pollination is the process that brings these male and female gametes together. The wind or animals, especially insects and birds, pick up pollen from the male anthers and carry it to the female stigma. Flowers have different shapes, colours and smells, and often sugary nectar and nutritious pollen, to encourage animals to visit and pollinate them.
Wind-pollinated flowers are shaped to make it easy for the wind to pick up or deposit pollen. Many flowers can be pollinated by their own pollen — a process called self-pollination. However, this does not always result in the genetic variation needed for species to survive. Many plants have ways to make sure they are only pollinated by pollen from a flower on a different plant, which is called cross-pollination.
Bees: Flower nectar provides bees with the sugar to fuel their flights. The proteins and amino acids in pollen are vital nutrients needed by young bee larvae back in the next.
Bees are not picky and frequently visit a large variety of flowers. Less elegant than other pollinators, beetles blunder their way through delicate blossoms searching for food, a mate, or perhaps the bathroom. Beetles frequently visit magnolias and flowers close to the ground. Butterflies: Butterflies often visit round flowers with flared petals that lead to narrow throats that conceal nectar.
Butterflies frequently visit salvias and sunflowers. Flies: Some flies act just like bees, visiting sweet-smelling flowers. Others have more disgusting tastes. They are attracted to flowers with putrid odors, meat-like colors, or fur-like textures that lure them in by pretending to be the fresh dung of dead animals that flies desire. Hummingbirds: The long, thin bill and tongue of a hummingbird allows it to reach the nectar hidden deeply in tubular flowers.
The Ruby-throated hummingbird is the only species that breeds on the East Coast each summer, after traveling up from Mexico and Central America. Hummingbirds frequently visit beebalm and honeysuckle. Moths: Most moths go unnoticed even though they outnumber butterflies 10 to 1. They are often active at night and dull in appearance. Night-blooming flowers have sweet scents and white or cream colored blossoms that reflect the moonlight to attract moths after the sun sets.
Wind: Not all pollination relies on animals. Wind pollinates grains, most nuts, many trees, and the wild grasses that provide forage for livestock. The odds are small that a pollen grain will find its way to a corn silk, but each kernel of corn is a tiny fruit resulting from successful wind pollination. Pollinator populations are at risk.
Decades of stressors including the loss, degradation, and fragmentation of pollinator habitats; the improper use of pesticides and herbicides; and diseases, predation, and parasites have all hurt pollinators. You can help pollination by creating a pollinator-friendly habitat without sacrificing aesthetics. Add diversity to your landscape with a beautiful tapestry of native plants that evolved with local pollinators and thrive under the conditions in your region.
However, many mature seeds enter a period of dormancy marked by inactivity or extremely-low metabolic activity. This period may last for months, years, or even centuries. Dormancy helps keep seeds viable during unfavorable conditions.
Upon a return to optimal conditions, seed germination takes place. These conditions may be as diverse as moisture, light, cold, fire, or chemical treatments. Fruits are categorized based on the part of the flower they developed from and how they release their seeds. After fertilization, the ovary of the flower usually develops into the fruit. Fruits are generally associated with having a sweet taste; however, not all fruits are sweet. In most cases, flowers in which fertilization has taken place will develop into fruits, while unfertilized flowers will not.
The fruit encloses the seeds and the developing embryo, thereby providing it with protection. Fruits are diverse in their origin and texture. The sweet tissue of the blackberry, the red flesh of the tomato, the shell of the peanut, and the hull of corn the tough, thin part that gets stuck in your teeth when you eat popcorn are all fruits.
As the fruit matures, the seeds also mature. Fruits may be classified as simple, aggregate, multiple, or accessory, depending on their origin. If the fruit develops from a single carpel or fused carpels of a single ovary, it is known as a simple fruit, as seen in nuts and beans. An aggregate fruit is one that develops from numerous carpels that are all in the same flower; the mature carpels fuse together to form the entire fruit, as seen in the raspberry.
A multiple fruit develops from an inflorescence or a cluster of flowers. An example is the pineapple where the flowers fuse together to form the fruit. Accessory fruits sometimes called false fruits are not derived from the ovary, but from another part of the flower, such as the receptacle strawberry or the hypanthium apples and pears. Types of fruit : There are four main types of fruits. Simple fruits, such as these nuts, are derived from a single ovary.
Aggregate fruits, like raspberries, form from many carpels that fuse together. Multiple fruits, such as pineapple, form from a cluster of flowers called an inflorescence. Accessory fruits, like apples, are formed from a part of the plant other than the ovary. Fruits generally have three parts: the exocarp the outermost skin or covering , the mesocarp middle part of the fruit , and the endocarp the inner part of the fruit.
Together, all three are known as the pericarp. The mesocarp is usually the fleshy, edible part of the fruit; however, in some fruits, such as the almond, the seed is the edible part the pit in this case is the endocarp.
In many fruits, two, or all three of the layers are fused, and are indistinguishable at maturity. Fruits can be dry or fleshy. Furthermore, fruits can be divided into dehiscent or indehiscent types. Dehiscent fruits, such as peas, readily release their seeds, while indehiscent fruits, like peaches, rely on decay to release their seeds. Some fruits can disperse seeds on their own, while others require assistance from wind, water, or animals.
In addition to protecting the embryo, the fruit plays an important role in seed dispersal. Seeds contained within fruits need to be dispersed far from the mother plant so that they may find favorable and less-competitive conditions in which to germinate and grow. Some fruits have built-in mechanisms that allow them to disperse by themselves, whereas others require the help of agents such as wind, water, and animals.
Modifications in seed structure, composition, and size aid in dispersal. Wind-dispersed fruit are lightweight and may have wing-like appendages that allow them to be carried by the wind.
Some have a parachute-like structure to keep them afloat. Some fruits, such as the dandelion, have hairy, weightless structures that are suited to dispersal by wind. Wind dispersal : Wind is used as a form of dispersal by lightweight seeds, such as those found on dandelions. Seeds dispersed by water are contained in light and buoyant fruit, giving them the ability to float. Coconuts are well known for their ability to float on water to reach land where they can germinate. Similarly, willow and silver birches produce lightweight fruit that can float on water.
Animals and birds eat fruits; seeds that are not digested are excreted in their droppings some distance away. Some animals, such as squirrels, bury seed-containing fruits for later use; if the squirrel does not find its stash of fruit, and if conditions are favorable, the seeds germinate.
Humans also play a major role in dispersing seeds when they carry fruits to new places, throwing away the inedible part that contains the seeds. Seed dormancy allows plants to disperse their progeny through time: something animals cannot do.
Dormant seeds can wait months, years, or even decades for the proper conditions for germination and propagation of the species. Privacy Policy. Skip to main content. Plant Reproduction. Search for:.
Pollination and Fertilization. Pollination and Fertilization Plants can transfer pollen through self-pollination; however, the preferred method is cross-pollination, which maintains genetic diversity. Learning Objectives Determine the differences between self-pollination and cross-pollination, and describe how plants have developed ways to avoid self-pollination. Key Takeaways Key Points Pollination, the transfer of pollen from flower-to-flower in angiosperms or cone -to-cone in gymnosperms, takes place through self-pollination or cross-pollination.
Cross-pollination is the most advantageous of the two types of pollination since it provides species with greater genetic diversity. Maturation of pollen and ovaries at different times and heterostyly are methods plants have developed to avoid self-pollination.
The placement of male and female flowers on separate plants or different parts of the plant are also barriers to self-pollination. Key Terms pollination : the transfer of pollen from an anther to a stigma that is carried out by insects, birds, bats, and the wind heterostyly : the condition of having unequal male anther and female stigma reproductive organs cross-pollination : fertilization by the transfer of pollen from an anther of one plant to a stigma of another self-pollination : pollination of a flower by its own pollen in a flower that has both stamens and a pistil.
Pollination by Insects Plants have developed adaptations to promote symbiotic relationships with insects that ensure their pollination. Learning Objectives Explain how pollination by insects aids plant reproduction. Key Takeaways Key Points Adaptations such as bright colors, strong fragrances, special shapes, and nectar guides are used to attract suitable pollinators.
Important insect pollinators include bees, flies, wasps, butterflies, and moths. Bees and butterflies are attracted to brightly-colored flowers that have a strong scent and are open during the day, whereas moths are attracted to white flowers that are open at night. Flies are attracted to dull brown and purple flowers that have an odor of decaying meat. Nectar guides, which are only visible to certain insects, facilitate pollination by guiding bees to the pollen at the center of flowers.
Insects and flowers both benefit from their specialized symbiotic relationships; plants are pollinated while insects obtain valuable sources of food. Key Terms nectar guide : markings or patterns seen in flowers of some angiosperm species that guide pollinators to nectar or pollen.
Pollination by Bats, Birds, Wind, and Water Non-insect methods of pollination include pollination by bats, birds, wind, and water. Learning Objectives Differentiate among the non-insect methods of pollination.
Key Takeaways Key Points Flowers that are pollinated by bats bloom at night, tending to be large, wide-mouthed, and pale-colored; they may also give off strong scents.
Flowers that are pollinated by small birds usually have curved, tubular shapes; birds carry the pollen off on their heads and neck to the next flower they visit. Wind-pollinated flowers do not produce scents or nectar; instead, they tend to have small or no petals and to produce large amounts of lightweight pollen.
Some species of flowers release pollen that can float on water; pollination occurs when the pollen reaches another plant of the same species. Some flowers deceive pollinators through food or sexual deception; the pollinators become attracted to the flowers with false promises of food and mating opportunities.
Key Terms food deception : a trickery method employed by some species of orchids in which only bright colors and perfume are offered to their pollinators with no food reward. Double Fertilization in Plants Angiosperms undergo two fertilization events where a zygote and endosperm are both formed.
Learning Objectives Describe the process of double fertilization in plants. Key Takeaways Key Points Double fertilization involves two sperm cells; one fertilizes the egg cell to form the zygote, while the other fuses with the two polar nuclei that form the endosperm. After fertilization, the fertilized ovule forms the seed while the tissues of the ovary become the fruit.
In the first stage of embryonic development, the zygote divides to form two cells; one will develop into a suspensor, while the other gives rise to a proembryo. In the second stage of embryonic development in eudicots , the developing embryo has a heart shape due to the presence of cotyledons. As the embryo grows, it begins to bend as it fills the seed; at this point, the seed is ready for dispersal.
Key Terms double fertilization : a complex fertilization mechanism that has evolved in flowering plants; involves the joining of a female gametophyte with two male gametes sperm suspensor : found in plant zygotes in angiosperms; connects the endosperm to the embryo and provides a route for nutrition from the mother plant to the growing embryo proembryo : a cluster of cells in the ovule of a fertilized flowering plant that has not yet formed into an embryo.
Development of the Seed Monocot and dicot seeds develop in differing ways, but both contain seeds with a seed coat, cotyledons, endosperm, and a single embryo. Learning Objectives Name the three parts of a seed and describe their functions and development. Key Takeaways Key Points In angiosperms, the process of seed production begins with double fertilization while in gymnosperms it does not.
In both monocots and dicots, food reserves are stored in the endosperm; however, in non-endospermic dicots, the cotyledons act as the storage. In a seed, the embryo consists of three main parts: the plumule, the radicle, and the hypocotyl. In dicots, the hypocotyls extend above ground, giving rise to the stem of the plant, while in monocots, they remain below ground.
In dicot seeds, the radicle grows downwards to form the tap root while lateral roots branch off to all sides, producing a dicot tap root system; in contrast, the end of germination in monocot seeds is marked by the production of a fibrous root system where adventitious roots emerge from the stem. Seed germination is dependent on seed size and whether or not favorable conditions are present.
Key Terms testa : the seed coat radicle : the rudimentary shoot of a plant that supports the cotyledons in the seed and from which the root is developed downward; the root of the embryo hypocotyl : in plants with seeds, the portion of the embryo or seedling between the root and cotyledons plumule : consisting of the apical meristem and the first true leaves of the young plant coleoptile : a pointed sheath that protects the emerging shoot in monocotyledons such as oats and grasses.
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