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32.2 Pollination and Fertilization
Animal pollination is more common than windpollinated angiosperms.
Both produce seeds but have different reproductive strategies.
Gymnosperms involve the transfer of pollen from the male to the female cone.
The sperm for the egg can be found in the pollen tube.
Pollination has been studied for a long time.
While studying how characteristics were passed on from one generation to the next, Mendel successfully carried out self- as well as cross-pollination in garden peas.
Artificial selection is used to produce the present-day crops.
Today's corn is a result of years of breeding that started with teosinte.
Today's ears of corn are vastly different from the teosinte that the ancient Mayas began cultivating.
The genetic difference between the two plants is insignificant.
Pollination can be self-pollination and cross-pollination.
Self-pollination occurs in flowers where the stamen and carpel mature at the same time, and are positioned so that the pollen can land on the flower's stigma.
This method of pollination doesn't require an investment from the plant to provide food for the bees.
There is an interactive website to review self-pollination and cross-pollination.
Living species are designed to ensure survival of their offspring.
In changing environmental or stress conditions, genetic diversity is required so that some of the offspring can survive.
The production of plants with less genetic diversity is caused by self-pollination.
Cross-pollination leads to greater genetic diversity because the microgametophyte and megagametophyte are derived from different plants.
Plants have developed many ways to avoid self-pollination because of cross-pollination.
Self-pollination is nearly impossible because of these flowers.
The stigma of this flower is mature and can only be pollinated by pollen from another flower.
Physical features of some flowers prevent self-pollination.
The primrose is a flower.
The pin-eyed flower has anthers positioned at the pollen tube's halfway point, while the thrum-eyed flower's stigma is located at the halfway point.
The insects cross-pollinate while looking for the same substance at the bottom of the tube.
This phenomenon is called Heterostyly.
Cucumber has male and female flowers on different parts of the plant, making self-pollination difficult.
The male and female flowers are different in other species.
Plants depend on pollinators to transfer pollen, so all of these are barriers to self-pollination.
Most of the pollinators are insects such as bees, flies, and butterflies.
Other plant species are pollinated by wind and water.
In recent decades, incompatibility genes have been found in many angiosperm species.
The pollen tube stops growing if plants don't have compatible genes.
Self-incompatibility is controlled by the S. The stigma and style of the ovule make it difficult for pollen tubes to enter.
The type of pollen that the carpel allows to grow inside is what distinguishes it.
The stigma cells interact with the pollen.
In some plants, like cabbage, the pollen is rejected at the surface of the stigma.
In other plants, pollen tube growth is stopped after one-third the length of the style.
The cause of pollen tube death is either programmed cell death or degradation of pollen tubeRNA.
The activity of a ribonuclease is degraded.
The ribonuclease is produced from the cells of the style in the extracellular matrix.
The mechanism that prevents self-fertilization in many flowering plant species is called self-incompatibility.
The production of inbred and hybrid plants is affected by the self-incompatibility mechanism.
The bees are the most important pollinators of fruit trees and garden plants.
Since bees can't see the color red, bee-pollinated flowers usually have shades of blue, yellow, or other colors.
Bee's collect energy-rich pollen for their survival.
They visit flowers that are open during the day, are brightly colored, have a strong smell, and have a tubular shape.
The pollen sticks to the bees' fuzzy hair, and when the bee visits another flower, some of the pollen is transferred to the second flower.
There have been many reports about the decline of honeybees.
If honeybees disappear, many flowers will remain unpollinated.
The impact on fruit growers could be devastating.
Important agents of pollination are insects.
Many flies prefer flowers that have a decaying smell or rotting flesh.
These flowers have dull colors, such as brown or purple.
They are found on the corpse flower, amorphophallus dragon, arum, and carrion flower.
The energy comes from the nectar and the protein comes from the pollen.
Many species of figs are pollinated by insects.
The monarch butterfly pollinates many garden flowers and wildflowers.
These flowers have bright colors, are open during the day, and have guides to help you get to the nectar.
The pollen is carried on the butterfly's limbs.
The flowers are pale or white and allow the moths to land.
The yucca plant is an example of a plant that is pollinated.
The shape of the flower has changed in a way that allows successful pollination.
The sticky stigma is deposited by the moths for fertilization.
Eggs are deposited into the ovary.
Eggs get food from the flower and develop seeds as they grow.
There is a relationship between the corn earworm moth and the Gaura plant.
Bats are the primary pollinators of flowers in the tropics and deserts.
The flowers are large and white and can be seen at night.
The flowers have a strong scent and produce a lot of saliva.
They are large and widemouthed to fit the head of the bat.
The bats have their faces and heads covered with pollen as they look for the next flower.
The hummingbird and sun birds are small birds that pollinate plants.
The flowers visited by birds are usually sturdy and oriented in such a way as to allow the birds to stay near the flower without getting their wings entangled in the nearby flowers.
The flower's shape allows access to the bird's beak.
Birds pollinate flowers that are open during the day.
The bird's head and neck are where the pollen is deposited and transferred to the next flower.
The range of extinct plants has been determined by collecting and identifying pollen from 200 year old bird specimen from the same site.
Hummingbirds can reach the nectar of certain flowers with their adaptations.
Most species of conifers and angiosperms are pollinated by wind.
Pine cones are brown and odorless, while the flowers of wind-pollinated angiosperm species are usually green, small, and produce large amounts of pollen.
Unlike insect-pollinated flowers, flowers adapted to pollination by wind do not produce scent or nectar.
In wind-pollinated species, the microsporangia hang out of the flower, and as the wind blows, the lightweight pollen is carried with it.
The flowers emerge early in the spring so that the leaves don't block the movement of the wind.
The flower has a feathery stigma.
A person is near a tree.
The male and female catkins are from the goat willow tree.
Both structures are light and feathery to better catch the wind-blown pollen.
Australian sea grass and pond weeds are pollinated by water.
The pollen floats on water and when it comes into contact with the flower, it is deposited inside the flower.
Orchids are highly valued flowers, with many rare varieties.
In the tropics of Asia, South America, and Central America, they grow.
There are at least 25,000 species of orchids.
Food or sexual deception is used by certain orchids.
There is a bee orchid in this picture.
Some orchid species have evolved different ways to attract the desired pollinators, which is an exception to this standard.
They use a method called food deception, in which bright colors and perfumes are offered, but no food.
The green-winged orchid bears bright purple flowers and emits a strong scent.
The bumblebee is attracted to the flower because of the strong scent, which usually indicates food for a bee, and in the process picks up the pollen to be transported to another flower.
Orchids use sexual deception.
Chiloglottis trapeziformis emits a compound that smells like a female wasp's scent.
The male wasp is attracted to the scent and lands on the orchid flower.
Some orchids, like the Australian hammer orchid, use scent as well as visual tricks in order to get the attention of the wasp.
The flower of this orchid emits a scent similar to that of a female wasp.
The male wasp tries to mate with a female wasp, and in the process picks up pollen, which it then transfers to the next counterfeit mate.
It must grow through the style to reach the ovule after it is deposited on the stigma.
The generative cell and the pollen tube cell are contained in the microspores.
The generative cell travels through a pollen tube.
Water, oxygen, and certain chemical signals are required for the growth of the pollen tube.
The growth of the pollen tube is supported by the tissues of the style.
If the generative cell has not already split into two cells, it will now form two sperm cells.
The synergids present in the embryo sac help guide the pollen tube through the ovule sac.
No other sperm can enter after fertilization is complete.
The fertilized ovule forms the seed, whereas the tissues of the ovary become the fruit.
One spermfertilizes the egg to form the 2n zygote and the other spermfertilizes the central cell to form the 3n endosperm in angiosperms.
This is called a double fertilization.
The upper cell and the lower cell are formed after fertilization.
Nutrition can be transported from the mother plant to the embryo through the suspensor.
The terminal cell gives rise to a proembryo.
The food reserves are moved into the two cotyledons in non-endospermic dicots.
The embryo and cotyledons are forced to bend when they run out of room inside the developing seed.
The seed is ready for dispersal once the embryo and cotyledons fill it.
After some time, embryo development is suspended and growth is only resumed when the seed is germinating.
The food reserves in the cotyledons will be used until the first set of leaves start to grow.
There are stages of embryo development in the ovule of a shepherd's purse.
The upper and lower terminal cells are formed after fertilization.
The cell that divides is the basal cell.
The seed develops from the mature ovule.
A typical seed has a seed coat, cotyledons, endosperm, and a single embryo.
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Corn has one cotyledon, called the scutellum, which channels nutrition to the embryo.
There is a radicle that forms the root of the embryo, a plumule that forms the leaves, and a hypocotyl that forms the stem.
The plumule and radicle are not included in the embryonic axis.
Both monocots and dicots have an endosperm.
The radicle grows into the root.
Food is kept in the large endosperm.
The scutellum absorbs the products of the stored products and transports them to the developing embryo.
The scutellum is not a storage organ.
The two cotyledons have connections to the embryo.
The two cotyledons act as absorptive organs to take up the released food reserves, just like in monocots.
Tobacco, tomato, and pepper are examples of endospermic dicots.
The split peas are loaded with food reserves and the peanut seed is loaded with food reserves.
A seed coat is formed from the integuments of the ovule sac.
The plumule, radicle, and hypocotyl are part of the embryonic axis.
The hypocotyls give rise to the stem of the plant.
The hypocotyl does not show above ground in monocots.
The epicotyl is shaped like a hook with the plumule pointing downwards.
The plumule hook is a shape that can persist as long as there is light.
The plumule is protected from damage as the epicotyl pushes through the tough soil.
The young foliage leaves face the sun, and the epicotyl continues to grow after exposure to light.
The typical dicot tap root system is formed by the roots branching off to all sides as it grows downward.
The testa and tegmen of the seed coat are fused.
When the plumule leaves the soil and the protective coleoptile is no longer needed, the leaves expand and unfold.
The primary root dies at the other end of the axis, while other roots emerge from the base of the stem.
The monocot has a root system.
The primary root, or radicle, emerges first, followed by the primary shoot, or coleoptile, and the adventitious roots.
During unfavorable conditions, dormancy helps keep seeds viable.
Seed germination takes place when favorable conditions return.
Favorable conditions could be any of the following.
The emergence of new plants is a result of forest fires.
The seeds produced by plants in warm climates will not grow until the spring.
Plants growing in hot climates may have seeds that need a heat treatment in order to survive in the hot, dry summers.
The ability to grow is hampered by the presence of a thick seed coat.
Presoaking in hot water or passing through an acid environment may be used.
The time taken for a seedling to emerge depends on the seed size.
Large seeds have enough food reserves to grow deep below ground, and still extend their epicotyl all the way to the soil surface.
Light is usually used as a cue for seeds to grow.
This ensures the seeds don't get damaged by the light at the soil surface.
If they were to grow too far beneath the surface, they wouldn't have enough food to survive.
The ovary of the flower develops into fruit after fertilization.
Some fruits have a sweeter taste than others.
The term fruit is used for a ripened ovary.
In most cases, flowers in which fertilization has taken place will develop into fruits, and flowers in which fertilization has not taken place will not.
Some fruits develop from the ovary and are known as true fruits, while others develop from other parts of the female gametophyte and are known as accessory fruits.
The fruit protects the developing embryo by enclosing it.
There are many types of fruits.
The seeds mature as the fruit matures.
Fruits can be classified as simple, aggregate, multiple, or accessory.
The pineapple is an example of this.
There are four main types of fruit.
These nuts are derived from a single ovary.
Fruits form from many carpels.
Pineapple forms from a cluster of flowers called an inflorescence.
The apple is formed from a part of the plant other than the ovary.
The endocarp is the part of the fruit that is eaten, while the mesocarp is the part that is not.
Two or all three of the layers are fused in many fruits.
Fruits can be wet or dry.
Fruits can be divided into dehiscent or indehiscent types.
Peas and peaches rely on decay to release their seeds, while dehiscent fruits, such as peas, are easy to release.
Seed dispersal is the purpose of the fruit.
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