Today we will see how to make project on 'project on pollination for class 12' this project is only for class 12th student and this project is belongs to 'sexual reproduction in flowering plants' in this project we will cover following steps
1. Introduction 4
2. What is pollination? 5
3. Parts of flower 6-8
ᬏWhorl#1
Whorl#2
Whorl#3
Whorl#4
4. Types of pollination 9-14
Cross Pollination
Self-Pollination
5. Agents of pollination 15-20
Biotic agents: Ornithophily, Entomophily
Abiotic agents: Anemophily, Hydrophily
6. Methods for cross pollination 21-23
7. Artificial hybridization 24-25
8. Advantages & Disadvantages Of cross pollination
INTRODUCTION
All living organisms have one major goal in common, which is to pass along their genetic information to the next generation by creating offspring. Flowering plants create seeds, which carry the genetic information of the parents and develop into a new plant.
There are two critical stages in the life cycle of a flowering plant:
1) The transfer of pollen from anther to stigma. As we will saw in the lecture on "Breeding Systems", most flowering plants have different types of mechanisms to promote the transfer of pollen from an anther in one flower to a stigma in a different flower, and hopefully this flower will be on a different plant.
2) The dispersal of seeds away from the parent plant. Plants often solicit the aid of animals, as well as abiotic forces such as wind, to accomplish both of these.
Much of the flower diversity that you have observed thus far this semester is because of adaptations for pollination by different mechanisms. In this lecture, we will discuss the main types of pollination mechanisms. However, please keep in mind that there are always exceptions; plants and animals that visit flowers have minds of their own!
The vast majority of flowering plant species are pollinated by insects; in fact, it seems that flowering plants and many major groups of insects co-evolved together. Animals other than insects can also be important pollinators: bats, birds (especially hummingbirds), and even a few mammals.
WHAT IS POLLINATION?
POLLINATION’ is the process of transfer of pollen grains from anther of a flower to the stigma of the flower.
Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma. The goal of every living organism, including plants, is to create offspring for the next generation. One of the ways that plants can produce offspring is by making seeds.
Abiotic pollination refers to situations where pollination is mediated without the involvement of other organisms. Only 10% of flowering plants are pollinated without animal assistance. The most common form of abiotic pollination, anemophily, is pollination by wind. This form of pollination is early dominant in grasses, most conifers, and many deciduous trees.
The process of pollination requires pollinators: organisms that carry or move the pollen grains from the anther to the receptive part of the carpel or pistil (stigma). This is biotic pollination.
FLOWER: It is the reproductive part of the plant (angiosperms).
PARTS OF FLOWER
There are four whorls of a flower which are as follows:-
Whorl #1: The Calyx
The calyx, which is the outermost whorl of a flower, protects the inner whorls, especially when the flower is in its bud state. The calyx is made up of sepals, which are two small green structures at the flower's base that look like tiny leaves.
Whorl #2: The Corolla
The second whorl of the flower is the corolla, which is composed of the flower's petals. The petals serve two purposes: to protect the reproductive organs of the flower and to attract pollinators. Because of this second purpose, they are usually brightly colored and scented so that animals and insects will come close to them and move around the flower's pollen.
⇨ The first two whorls of the flower -- the calyx and the corolla -- are collectively called the Perianth.
Whorl #3: The Stamens
The third whorl of a flower is the stamen, the male reproductive part. The stamen is made of a thin vertical thread-like structure called a filament and circular or
oblong structure called an anther. The anther produces pollen, which is the male contribution to the reproduction process in plants. It consists of microsporangium which may be monothecous or dithecous.
Whorl #4: The Carpels
At the center of the flower is the fourth whorl -- the carpels, which contain the pistil of the flower. The pistil is the plant's female reproductive organ, which is composed of three parts: the ovary, the style, and the stigma.
The ovary contains the eggs, or ovules, of the plant, and when the ovules are fertilized, the ovary sometimes turns into a fruit to house the seed.
The top of the ovary leads to a vertical structure called a style, which supports the stigma.
The stigma catches grains of pollen that the wind or pollinators disperse, and the pollen grains travel down the style to the ovary.
Types of Pollination
It is of two types:
•Natural Pollination which occurs naturally in plants.
•Induced Pollination which is done by artificial means.
👉 Natural pollination is of two types :-
• Self-Pollination
• Cross pollination
SELF POLLINATION
The pollination of a flower by pollen from the same flower (autogamy) or from another flower on the same plant (geitonogamy).
Ex: pea plant, groundnut, barley
Self-pollination is promoted by certain floral adaptation. Accordingly self pollination is of two types i.e., autogamy & geitonogamy.
Autogamy:
It is a type of self-pollination in which an intersexual or perfect flower is pollinated by its own pollen.
Autogamy occurs by two methods:
Homogamy: The anthers and stigmas of chasmogamous or open flowers are brought together by growth, bending or folding. Ex: peas, beans, hibiscus
Cleistogamy: In cleistogamous flowers, the anther dehisce inside closed flowers. Growth of style brings the pollen grains in contact with stigma. Pollination and seed set are assured. Pollinators are not required.
Ex: oxalis, viola
Geitonogamy:
It is a type of pollination in which pollen grains of one flower are transferred to the stigma of another flower belonging to either the same plant or genetically similar plant. In geitonogamy flowers often show modifications.
Advantages of Self Pollination:
1. It maintains the parental characters or purity of the race indefinitely.
2. Self-pollination is used to maintain pure lines for hybridization experiments.
3. The plant does not need to produce large number of pollen grains.
4. Flowers do not develop devices for attracting insect pollinators.
5. It ensures seed production. Rather it is used as fail safe device for crosspollinated
flowers.
6. Self-pollination eliminates some bad recessive characters
Disadvantages of Self Pollination:
1. New useful characters are seldom introduced.
2. Vigor and vitality of the race decreases with prolonged self-pollination.
3. Immunity to diseases decreases.
4. Variability and hence adaptability to changed environment are reduced.
CROSS POLLINATION
(xenogamy /allogamy)
Cross pollination is the transfer of pollen grains from the anther of one flower to the stigma of a genetically different flower. It is also called xenogamy (Gk. xenos - strange, gamos- marriage). The term allogamy (Gk. alios- other, gamos- marriage) includes both geitonogamy and xenogamy. Cross pollination is performed with the help of an external agency.
Agents of Pollination
In angiosperms, pollen are immotile and thus have to be carried to the stigma by external pollinating agents.
Depending upon their nature the agents may be –
1. Biotic agents: Insects, Birds, Snails etc.
2. Abiotic agents: Wind, Water.
BIOTIC AGENTS
I. Entomophily :
It refers to the transfer of pollen grains through the agency of insects like moths,butterflies, wasps, bees, beetles, etc.
Ex: Salvia, Yucca, Ficus
Characters:
They are showy or brightly colored.
Most insect pollinated flowers have a landing platform.
The pollen grains are spiny, heavy and surrounded by a yellow oily sticky
substance called pollen kit.
Stigmas are often inserted and sticky.
Some flowers provide safe place to insects for laying eggs, e.g., Yucca.
II. Ornithophily
It refers to the pollination brought about by birds.
III. Psychophily
Pollination by butterfly, example the Indian paintbrush (Castilleja sp.) by swallowtail butterfly.
ABIOTIC AGENTS
I. Anemophily
It is a mode of cross pollination or transfer of pollen grains through the agency of wind.
Ex: Coconut palm, Date palm, Maize, many grasses, Cannabis.
Characteristics:
◼️ The flowers are colorless, odorless and nectarless.
◼️ Pollen grains are light, small and winged or dusty, dry, smooth, non-sticky and
non wettable.
◼️ Stigma is hairy, feathery or branched to catch the wind-borne pollen grains.
◼️ Pollen grains are produced in very large number.
II. Hydrophily
It is the mode of pollination or transfer of pollen grains through the agency of water.
Ex: Zostera, Vallisneria
Characters:
◼️Flowers are small and inconspicuous.
◼️Nectar and odor are absent.
◼️Pollen grains are light and non-wettable due to presence of mucilage cover.
◼️ Stigma is long, sticky but wettable.
It is further divided into two parts:
👉 Epihydrophily: Pollination occurring on the water surface
Ex: Elodes, Hydrilla, Vallisneria.
Hypohydrophily: pollination occurring beneath the water surface.
Ex: Najas, Ceratophylum, Zostera.
Methods to Ensure Cross pollination
Dichogamy:
The maturation of the stamens and pistils of a bisexual flower at different times, so that self-pollination is prevented.
-Protoandry
Anthers mature earlier than the stigma of the same flower. There pollen grains become available to stigmas of the older flowers. , ex: Sunflower, Salvia
-Protogyny
Stigmas mature earlier so that they get pollinated before the anthers of the same flower develop pollen grains, e.g., Mirabilis jalapa (4 O’clock). Herkogamy It is a common strategy employed by hermaphroditic angiosperms to reduce sexual interference between male (anthers) and female (stigma) function.
Self-incompatibility (SI)
It is a general name for several genetic mechanisms in angiosperms, which prevent self-fertilization and thus encourage outcrossing and allogamy.
Heterostyly
The condition (e.g. in primroses) of having styles of different lengths relative to the stamens in the flowers of different individual plants, to reduce self-fertilization.
Prepotency
Pollen grains of another flower germinate more rapidly over the stigma than the pollen grains of the same flower, e.g., Apple, Grape.
Dicliny (Uni-sexuality)
Flowers are unisexual so that self-pollination is not possible. The plants may be monoecious (bearing both male and female flowers, e.g., Maize) or dioecious (bearing male and female flowers on different plants, e.g., Mulberry, Papaya).
Artificial Hybridization
Artificial hybridization refers to instances in which these crosses occur under controlled conditions, often under the direction of plant or animal breeders.
PROCEDURE:
1. Emasculation:
The removal of the anthers of a flower in order to prevent self-pollination or the undesirable pollination of neighboring plants.
2.Bagging
The emasculated flowers are immediately covered by paper, plastic or polythene bags. The process is called bagging. It prevents unwanted pollen to come in contact with emasculated flowers. This prevents contamination from foreign pollen grains
3. Rebagging
When the flower is bagged flower attains receptivity, mature pollen grains collected from anthers are dusted on the stigma and the flower is rebagged.
Advantages Of cross Pollination
◼️ Cross pollination introduces genetic re-combinations and hence variations
in the progeny.
◼️ Cross pollination increases the adaptability of the offspring towards changes
in the environment.
◼️ It makes the organisms better fitted in the struggle for existence.
◼️ The plants produced through cross pollination are more resistant to diseases.
◼️ The seeds produced are usually larger and the offspring have characters better
than the parents due to the phenomenon of hybrid vigour.
◼️ New and more useful varieties can be produced through cross pollination.
◼️ The defective characters of the race are eliminated and replaced by better
characters.
◼️ Yield never falls below an average minimum.
Disadvantages of Cross Pollination
It is highly wasteful because plants have to produce a larger number of pollen
grains and other accessory structures in order to suit the various pollinating
agencies.
◼️ A factor of chance is always involved in cross pollination.
◼️ It is less economical.
◼️ Some undesirable characters may creep in the race.
◼️ The very good characters of the race are likely to be spoiled.
BIBLIOGRAPHY
👉 www.google.co.in
👉 www.wikipedia.org
👉 www.slideshare.net
👉 www.biology.lifeeasy.org
👉 www.yourarticlelibrary.com
👉 www.biologyreference.com
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