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Plant reproduction
Plant reproduction can occur through asexual and sexual means. Asexual reproduction involves only one parent and produces genetically identical offspring through processes like budding, fragmentation, and spore formation. Sexual reproduction involves male and female gametes from two parents, producing offspring with new combinations of genes. In flowering plants, sexual reproduction takes place through flowers, which contain stamens that produce pollen and carpels containing ovaries and eggs. Pollination leads to fertilization and seed formation, and seeds are then dispersed and can germinate to form new plants.
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Plant reproduction
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- 2. What is PlantReproduction Reproduction is one of the most important characteristic of all living beings. It is the production of ones own kind. It is necessary for the continuation of the species on earth and also to replace the dead members of the species. The process by which living organisms produce their offspring's for the continuity of the species is called reproduction. The modes of reproduction vary according to individual species and available conditions. It may be simply by division of the parent cell as in unicellular organisms, by fragmentation of the parent body, by formation of buds and spores, or it may be very elaborate involving development of male and female reproductive organs (stamens and pistils). Irrespective of the mode of reproduction, all organisms pass on their hereditary material to their offspring during the process of reproduction (Reproduction and Heredity, Biology Module Chapter 18)
- 3. Plant Reproduction Asexual Reproduction NoGametes Only one parent needed New organism genetically identical to parent Plants and bacteria reproduce this way
- 4. Asexual Reproduction Fission: As in unicellular organisms like bacteria where the content of the parent cell divides into 2, 4 or 8 daughter cells and accordingly the fission is known as binary or multiple fission. Each newly formed daughter cell grows into a new organism. Budding : A bud like outgrowth is formed on one side of the parent cell and soon it separates and grows into a new individual e.g. in yeast. Fragmentation : In filamentous algae, an accidental breaking of the filament into many fragments, each fragment may give rise to a new filament of the algae by cell division e.g. Spirogyra, green algae. Spore formation : In lower plants like bryophytes reproductive units develop asexually on the parent body. These are called spores. They are microscopic and covered by protective wall. When they reach the suitable environment they develop into a new plant body e.g. in bread moulds, moss, fern.
- 5. Plant Reproduction Sexual Reproduction Maleand Female Gametes involved Two parents are needed New organism will not be genetically identical to either of the parent
- 6. Reproduction in LowerPlants Chlamydomonas (A Unicellular Alga) Asexual-with the help of zoospores Chlamydomonas loses flagella and becomes non-motile. Its protoplasm (cytoplasm and nucleus) divides mitotically and forms 4-8 zoospores. The parent cell wall is ruptured and zoospores are released. Each zoospore develops a cell wall and grows into an adult cell. The parent cell does not exist, any more.
- 7. Reproduction in LowerPlants Sexual Reproduction The cell becomes non-motile by losing its flagella. The protoplasm divides mitotically into 2, 4, 8, 16, 32 daughter cells. Each daughter cell develops flagella and is released in water by the rupture of mother cell wall. It acts as a gamete. The gamete is morphologically identical in structure but all identical (Isogamous). Gametes released from two different mother cells fuse together. The contents of the gametes fuse and form a zygote (diploid). This is the only diploid stage in the life cycle of Chlamydomonas. The zygote develops a thick wall around itself to tide over unfavourable conditions (zygospores) On the return of favourable conditions (temperature, food and water) the diploid nucleus divides by meiosis and forms four haploid zoospores. Each zoospore grows into a new adult Chlamydomonas
- 9. Vegetative Reproduction involvesformation of new plantlets from vegetative (somatic) cell, buds or organs of the plant. It is similar to a sexual reproduciton in that it also requires only mitotic division, no gametic fusion and daughter plants are genetic clones of the parent plant.
- 10. Spirogyra (A MulticellularAlga) Vegetative Reproduction by fragmentation The filament breaks into small fragments. Each fragment grows into a new filament by cell division Sexual Reproduction Two filaments come to lie very close to each other. Cells of the two filaments form a contact with the help of a tube called the conjugation tube. Cytoplasmic contents of each cell round off to act as a gamete. Gamete from one cell (male) passes to the other cell (female) through the conjugation tube. Each filament acts either as male or female. The contents of two gametes fuse in the female cell and form a diploid zygote
- 11. The zygotedevelops a thick wall around itself and tides over the unfavourable period. On the return of favourable conditions the diploid nucleus divides by meiosis into four haploid nuclei. Three of these nuclei degenerate. On germination, wall of the zygote ruptures and a small tube like structure, containing one haploid nucleus comes out. The small tube develops into 1 filament by repeated mitotic divisions.
- 13. Reproduction in Angiosperms (Floweringplants) Angiosperms reproduce both vegetative and sexual methods Angiosperms reproduction occurs by fusion of male and female gametes present in the flower. Angiosperms can be classified depending the time they take to complete life cycle and flowering Annuals – Live for one year , produce flowers and seeds within one season Biennials - two seasons, first year vegetative state, second year produce flowers, fruits and seeds Perennials – plants which live for several years , one to few years vegetative stage then after that flowers, fruits and seeds every year Monocarpic - plants are those that flower, set seeds and then die
- 14. Plant Reproduction The Flower: Theflower is the part of a plant that is involved in sexual reproduction
- 15. Plant Reproduction Initiationof flowering The young plant grows vigorously and continue to grow till it attains a definite shape and size with its vegetative parts (roots, stem, leaves) well developed Young or the Juvenile phase Reproductive phase or adult phase Vegetative shoot apex transforms into a reproductive or floral apex and starts bearing flowers
- 16. Plant Reproduction The Partsof the Flower Sepals Petals Carpel Stamen
- 17. Plant Reproduction Sepal: Green leaveswhich protect the flower when it is a bud Petals: Attract insects to the flower
- 18. Plant Reproduction TheStamen: Male Part of the flower Filament – stalk part of stamen Anther – Small bag on top of the filament contains pollen
- 19. Plant Reproduction Structureof the Carpel: Stigma – Pollen grains land here Style – Connects stigma to the ovary Ovary – Contains ovules Ovules – Contain female gametes – eggs Pistil - The ovule producing part of a flower
- 20. Plant Reproduction Stages inSexual Reproduction in Plants: Pollination Fertilisation and Seed Formation Seed Dispersal Germination
- 21. Plant Reproduction Pollination: Happenswhen pollen from one flower is transferred to another flower of the same species Insect Pollination(Entomophily) or Wind Pollination (Anemophily)
- 22. Plant Reproduction TWO TYPESOF POLLINATION Self pollination – transfer of pollen grains to stigma of same or another flower of same plant Cross pollination – transfer of pollen grains to stigma of a flower of another plant of the same species
- 23. Importance of Pollination It results in fertilization and ovule is converted into seed. New varieties of plants are formed through new combination of genes in case of cross pollination. During pollination pollen tube produces growth hormones which convert ovary into fruit. Cross pollination is brought about by various external agencies such as, wind, insects, water, birds and other animals.
- 24. Plant Reproduction InsectPollination: Petals are bright and perfumed. Insect rub against Anther and pollen gets stuck to them Insect move to another plant of same species and pollen sticks to sticky stigma
- 25. Plant Reproduction WindPollination: The flowers have long anthers which hang outside the flower. Pollen is blown out of the anthers by the wind The stigma of a wind-pollinated flower is very large and feathery – able to catch pollen
- 26. Plant Reproduction Fertilisationand Seed Formation: After pollination, pollen tube develops out of the pollen grain and into the style, It then enters the ovule and male gamete travels down to join with the egg – zygote The zygote then becomes the seed. The ovary will turn into the fruit
- 27. Plant Reproduction Dispersal OfThe Seed: The major function of the fruit is to scatter the seed of the plant Animal Dispersal Wind Dispersal Water Dispersal Self Dispersal
- 28. Plant Reproduction AnimalDispersal: Edible Fruits: Animal eats fruit and eventually passes the seed in its droppings, if seed falls in right place it will grow into new plant Hooked Fruits: Fruits have tiny hooks on their surface, sticks to the animals.
- 29. Plant Reproduction WindDispersal: The wind provides a very effective method of carrying fruit away from the parent plant Dandelion uses parachute Sycamore tree uses winged fruits
- 30. Plant Reproduction WaterDispersal: The water lily is an example of a plant with fruits that can float. Water currents carry the fruit away, with the seeds inside
- 31. Plant Reproduction SelfDispersal: The gorse plant can scatter its own seed. In summer the plant dries out and suddenly bursts. The seeds shoot out from the fruit, and may land some distance from the parent plant
- 32. Plant Reproduction Germination: Plumule – Will form shoot of plant Radicle – Will become the root of the plant Testa – Protects the seed Food Store – Provides nourishment for the young plan
- 33. Plant Reproduction ConditionsNecessary For Germination: Water Oxygen Warmth
- 34. Vegetative Reproduction in Angiosperms Reproduction of new plants from the portion of the vegetative parts of a plant is very common and is called vegetative reproduction. Stems, roots, leaves and even buds are variously modified to suit this requirement. This is called natural vegetative reproduction. Natural Method : In natural methods, a portion of the plant gets detached from the body of the mother plant and grows into an independent plant. The parts may be stem, root, leaf or even flower
- 35. The undergroundmodification of stem, like rhizome, (in ginger), tuber (potato), bulb (onion) are provided with buds which develop into a new plant and therefore used to carry out vegetative propagation of the plant in the field. Plants with subaerial modification such as Pistia (offset) and Chrysanthemum (sucker) are also used for vegetative propagation. Similarly, tuberous roots (Asparagus and sweet potato) can also be used for propagation as these roots have adventitious (form accidentally) buds which ground into a new plant. Sometimes even leaves contribute to propagation of plants leaves of Bryophyllum that have buds on the margin and these buds grow into small plantlets. When detached from the mother plant they grow into independent plants. In plants like Agave and Oxalis multicellular bodies called bulbils develop near the flower. These are called bulbils which when fall on the ground grow into new plant
- 36. Vegetative Reproduction in Angiosperms Humans have taken advantage of this natural phenomenon and have artificially propagated plants vegetatively by using the specialized parts as by cutting, grafting and layering. Cuttings: Many plants like rose, Bougainvillea, Croton, Coleus, money plants, sugarcane etc. are grown through their stem cuttings. Cuttings of these plants can be grown even in water where they strike roots and develop adventitious buds Layering: In this method, a lower branch of a plant is bent down and covered with moist soil leaving the growing tip above the soil. A ring of bark is removed from the stem before it is bent down. In a few weeks time when enough roots have developed on the underground portion above the ringed part, it. is cut off from the parent plant and grown separately as an independent plant.
- 37. Vegetative Reproduction in Angiosperms Aerial layering or Goatee : In this method a ring of bark is removed from a selected branch, and it is covered with moist moss and enclosed in a polythene sheet when roots appear, the stem is cut below the roots and planted to form a new plant
- 38. Vegetative Reproduction in Angiosperms Grafting – The purpose of grafting is to combine one plant's qualities of flowering or fruiting with the roots of another that offers vigour and resilience. This is a difficult task and requires lots of skill and practice. In most cases, trees and shrubs are available to buy already grafted onto a rootstock. In this stock a branch is inserted which is known as scion or graft. This scion or graft is the stem cutting from the desired plant. Usually the grafted end of stock and scion fit well with each other and are bound firmly with tape or rubber-band until their tissues unite and vascular continuity is established. Grafting is mostly. practised in dicot plants
- 39. Advantages and Disadvantagesof Vegetative Reproduction Advantages (a) Rapid means of reproduction and spread. (b) Offsprings identical to parent. The desired varieties can thus be preserved genetically for use. (c) Food storage organs allow perennation or survival in adverse condition (d) Improved varieties of ornamental plants and fruit trees can be multiplied easily. (e) Vegetative propagation is a quicker, easier and a less expensive method of multiplying plants
- 40. Disadvantages (a)Overcrowding and competition for space unless separated artificially. (b) New varieties cannot be produced by this method except by mutation. (c) Diseases typical of the species are rapidly transmitted and can decimate a crop
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Editor's Notes
- #9 Chlamydomonas loses flagella and becomes non-motile. Its protoplasm (cytoplasm and nucleus) divides mitotically and forms 4-8 zoospores. The parent cell wall is ruptured and zoospores are released. Each zoospore develops a cell wall and grows into an adult cell. The parent cell does not exist, any more The cell becomes non-motile by losing its flagella. The protoplasm divides mitotically into 2, 4, 8, 16, 32 daughter cells. Each daughter cell develops flagella and is released in water by the rupture of mother cell wall. It acts as a gamete. The gamete is morphologically identical in structure but all identical (Isogamous). Gametes released from two different mother cells fuse together. The contents of the gametes fuse and form a zygote (diploid). This is the only diploid stage in the life cycle of Chlamydomonas. The zygote develops a thick wall around itself to tide over unfavourable conditions (zygospores) On the return of favourable conditions (temperature, food and water) the diploid nucleus divides by meiosis and forms four haploid zoospores. Each zoospore grows into a new adult Chlamydomonas
- #37 When, we use the vegetative parts for propagating crops or ornamental plants it is termed as artificial vegetative propagation. Cuttings : rose Layering : strawberry