Reproduction in plants is very Good subject

plants

1. Topic: Reproduction in Plants Subject: Biology (5090) Teacher: Ms Suaad Shabbir

2. O Level Learning outcomes Id entify and draw the sepals, petals, stamens (anthers and filaments) and carpels (stigmas, styles, ovaries and ovules) of an insect-pollinated flower Identify and draw the anthers and stigmas of a wind-pollinated flower Relate the structure of the parts of flowers to their functions, limited to the parts listed in (1) Compare the flower structure and the pollen from insect-pollinated and wind-pollinated flowers Outline the process of pollination and distinguish between self-pollination and cross-pollination Discuss the potential effects of self-pollination and cross-pollination on a population, in terms of variation, capacity to respond to changes in the environment and reliance on pollinators Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (production of endosperm and details of development are not required) Understand that after fertilisation the ovules develop into seeds and the ovary develops into a fruit Investigate and describe the structure of a seed, limited to embryo (radicle, plumule and cotyledons) and testa Understand that seed and fruit dispersal by wind and by animals is a means of colonising new areas and of reducing competition Relate the features of wind-dispersed fruits and animal-dispersed fruits to their functions Investigate and state the environmental conditions that affect germination of seeds, limited to: suitable temperature, water and oxygen Describe the process of germination, including the role of enzymes

3. Reproduction is the production of new living individual or offspring. It is a means to ensure the survival of species. Two basic forms of reproduction: a) Asexual reproduction b) Sexual reproduction 3

4. Asexual Reproduction It involves one parent and results in the production of genetically identical offspring. Main features/Characteristics of asexual reproduction Only one individual is involved. Does not involve production of sex cells thus no fusion of gametes. Offspring are exact copies ( clones ) of the parent. It shows rapid mode of multiplication. 4

5. Vegetative propagation Definition : A type of asexual reproduction employed by plants wherein new independent individuals emerge from the vegetative parts of plants, such as specialized stems, leaves, roots, and not from seeds or spores. It is a form of asexual reproduction of a plant. Only one plant is involved and the offspring is the result of one parent. The new plant is genetically identical to the parent. New plants grow from parts of the parent plant. It is a process by which new organisms arise without production of seeds or spores. It can occur naturally or be induced by horticulturists. Many plants develop underground food storage organs which overwinter & develop into the following year’s plant. Examples are bulbs (onions), tubers (potatoes) and rhizomes (ginger) 5

6. Vegetative propagation 6 Tubers are swollen portions of an underground modified stem that store food so a plant can lie dormant over the winter, for example, potatoes. Potato has several eyes which grows into new plant when planted with a portion of the swollen tuber. It is a common mode of vegetative propagation in the case of potato.

7. Advantages & Disadvantages of Asexual Reproduction ADVANTAGES DISADVANTAGES 1. Youngs are identical to parent so good features will always be passed on 1. There is little variation 2. Only one parent is involved 2. They do not adapt to the changing environment. 3. No gametes are needed - the process is quick 3. If the parent has no resistance to a particular disease, none of the off spring will have resistance. 4. Without dispersal plant grows in the same environment as the parent 4. Lack of dispersal can lead to competition for nutrients, water and light 5. It stores large amounts of food that allows rapid growth when conditions are favourable 7 Note: Asexual reproduction produces clones . It is common among the simplest organisms. It produces offspring without the need of gametes or searching for a mate.

8. Advantages & Disadvantages of Sexual Reproduction ADVANTAGES DISADVANTAGES 1. Variation in the offspring- better chance at surviving diseases & climate changes etc. 1. Two parents are always needed 2. New varieties are produced 2. Growth of a plant from seed (a product of fertilization-sexual repro.) is vegetative propagation (type of asexual repro.) . 3. In plants seeds are produced and dispersed away from the parent plant thus reducing competition. 8 It involves the fusion of nuclei from two different parents to form a zygote & the production of genetically dissimilar offspring . Two individuals, a male and a female are involved. One sex cell (male gamete) fuses with the sex cell of another parent (female gamete) in the process termed fertilization to form a zygote which grows & develops into a multicellular individual. Humans, fish, frogs, cats, dogs reproduce sexually. Most flowering plants reproduce sexually. Sexual Reproduction

9. Comparison of Asexual & Sexual Reproduction In asexual reproduction the offsprings produced are identical . In sexual reproduction , the new individuals differ genetically from their parents. 9 ASEXUAL SEXUAL 1 Cell division, vegetative propagation, spores Sexual reproductive organs in plants and animals 2 One parent Two parents 3 No sex cells Male & female sex cells (haploid gametes) 4 No zygote Fertilization forms a diploid zygote 5 Undergoes mitosis Undergoes meiosis 6 Offspring genetically identical to parent Offspring genetically different from both parents 7 Rate rapid under favourable environments Takes a long time 8 Population increases rapidly Population increases slowly 9 Plants & simple organisms Takes place in plants & more complex organisms

10. Flowers are the organs of sexual reproduction in plants . They vary greatly in size, shape, colour & other attributes. 10

11. Note: If peduncle bears a single pedicle (flower stalk) then these types of flowers are termed as solitary flowers. Peduncle bearing more than one flower stalks the arrangement is known as inflorescences . 11

12. Main parts of a Flower 12 Pistil / Gynoecium (Female reproductive part) Androecium (Male reproductive part) Calyx Epicalyx found in Hibiscus Corolla Collective name for sepals & petals = Perianth

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14. 14 1 st whorl = sepals / calyx 2 nd whorl = petals / corolla 3 rd whorl = stamens / androecium 4 th whorl = carpels / pistil / gynoecium

15. Types of flowers Bisexual/hermaphrodite flower These bear male & female reproductive organs on same flower . Unisexual flower They bear female and male reproductive organs on separate flowers . Shown below is the male flower bearing 10 stamens. 15 Hibiscus Rose

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17. Structure & Function of a Flower FLOWER PART STRUCTURE FUNCTION Calyx (Sepals) Outermost whorl on the receptacle May be completely free or fused. Made of green leaf-like structures called sepals Epicalyx forms an extra whorl outside the calyx in some flowers e.g. Hibiscus Protection from sun or rain Sticky glands ward off pests If green, serves to photosynthesize food If colourful, serves to attract insects for pollination Enclose and protects the floral parts during bud stage. Corolla (Petals) Second whorl On the inner side of calyx Base contains nectary which produces sweet nectar Colourful so a ttracts insects for pollination Protects the stamen & carpel Provides a base for insect landing Directs them towards the nectary through nectar guide . 17 In flowering plants, flowers are the main reproductive organs. Flowers may be bisexual or unisexual.

18. FLOWER PART STRUCTURE FUNCTION Androecium/ Stamen (male organ) Third whorl Many s tamens (number varies) comprising of anther attached to filament. Anther is bilobed each comprising of 2 pollen sacs Pollen sac produces pollen grain which contain male gamete Xylem & phloem continuous throughout filament & anther to provide nourishment to growing pollen grains. Supports anther Produces pollen grains (differ in shape & size depending on plant species) Releases mature pollen grains Gynoecium/ Carpel/Pistil (female organ ) Fourth/ innermost whorl Few or many carpels Maybe free or fused together Consists of a stigma (apical portion- receives pollen) , a style (slender propagation on top of ovary) & an ovary ( contains ovules) Stigma collects pollen grains by excreting a sugary sticky substance Stimulates germination of pollen grains Develop into fruits Contains ovules which develop into seeds 18 Note: The floral parts of a plant come in multiples of 4 or 5. Flowers that are complete consist of calyx, corolla, stamens & carpels. The presence of both male & female organs makes the flower bisexual or perfect.