1 Importance of Reproduction ♣produce new generation of individuals to replace those members that die ♣ensure continuation of the species Basic types of Reproduction ∗Asexual Reproduction ∗Sexual Reproduction Asexual Reproduction produce offspring from a single parent without fusion of gametes produce offspring by mitosis new organism exactly like its parent Binary Fission (e.g. Amoeba) Process: 1. Pseudopodia withdrawn 2. Nucleus divided into two 3. Two daughter Amoebas formed Budding (e.g. Yeast) Process: 1. Parent cell produces small outgrowth 2. Outgrowth detaches from parent cell 3. A new cell formed Size: Daughter cell < Parent cell Sporulation (e.g. Mucor) Process: 1. Hyphae develop swellings (sporangium) at the tips 2. Hundreds of spores are formed in sporangium 3. Sporangium bursts open 4. Liberates spores 5. Spores carried by wind 6. Germinates under suitable conditions Vegetative Propagation Principle: 1. A new bud is developed on parent plant 2. Adventitious roots formed & absorbed water and mineral salts for young plant 3. Parent plant develops green leaves for photosynthesis 4. Food stored in a specialized underground storage organ (not transport to parent plant) Vegetative Propagation Principle: 5. Bud formed for growth in next growing season 6. Aerial shoot dies down in dry season 7. Underground storage organ remains dormant till next year Name of storage organs: Perennating Organs Tubers lateral bud scale leaf developing tuber adventitious root decaying parent tuber Corms axillary apical bud aerial shoot bud contractile root adventitious root new corm old corm Rhizomes green leaves node direction of rhizome growth new rhizome growing from axillary bud adventitious root Bulb green leaf carries out photosynthesis fleshly scale leaf provides food for the growth of bud adventitious root axillary bud will give rise to daughter bulb bud will give rise to new shoot Summary of Vegetative Propagation in Angiosperms Name of Perennating Organ Bulb Corm Origin of Organ Short, condenced stem Short, vertical stem Region of Food Storage Examples Fleshly scale leaves surrounding the vertical stem Onion, daffodil Swollen stem base Rhizome Horizontal stem The entire length of horizontal stem Tuber Side branch of stem At the tip of the side branch of stem Gladiolus, Crocus Ginger, lotus, iris Potato, arrowhead Vegetative Propagation Advantages: rapid rate of reproduction can retain desirable characters as offspring are genetically identical to parent large food reserves are provided for daughter plants does not involve external agents or another plants Vegetative Propagation Disadvantages: overcrowding may occur which leads to competition for water, space & light no genetic variation occurs which decreases the ability to adapt to changes in the surroundings diseases of the parent plant are rapidly transmitted to the offspring Artificial Propagation E.g. Cutting: a process by which a piece of branch, stem, root or leaf when planted grows into a new individual Other methods: Grafting & Layering Plants which can use cutting: Bryophyllum… Coleus, African Violet, Artificial Propagation Procedures: Select a healthy leaf Use a razor blade / sharp knife to cut it off Insert the leaf stalk into a small pot containing some suitable soil Tiny new plant will be formed within 6 - 8 weeks Propagation of Coleus by Stem Cutting test tube water What is the purpose of removing some of the leaves ? Ans: In order to prevent water loss by transpiration. test tube water Do any roots grow out of the branch ? Ans: Roots grow out from the cut end after a few days. Sexual Reproduction ♠ provides a mean of survival of the species under unfavourable conditions ♠ have a different genetic make-up from their parents ♠ a good chance for some of the offspring to adapt to the new environment Sexual Reproduction ♠ sex cells & gametes are produced by meiosis ♠ sometimes an organism can produce both male & female gametes (hermaphrodite) ♠ fertilization (male gamete + female gamete) takes place which produce a zygote Sexual Reproduction in Angiosperm Reproductive organ: Flower usually bisexual or hermaphrodite sometimes unisexual Structure of a Flower Anther Stamen (stamens = androecium) Filament Stigma Style Ovary/ Carpels Pistil (carpels = gynoecium) Ovule Petal (petals = corolla) Sepal (sepals = calyx) Receptacle Structure of a Flower Sepal (sepals = calyx) protect flower bud can carry out photosynthesis Structure of a Flower Petal (petals = corolla) attract insects by scent, colour, insect guide, nectary (produce nectar) Structure of a Flower Stamen: Anther produce pollen grains Filament support anther Structure of a Flower Carpels : Stigma receive pollen grains Style support stigma Ovary/Carpels protect ovule Ovule becomes seed after fertilization Pollination Pollen Grain: carrier of Male gametes Ovule: carrier of Female gametes Pollination: the transfer of pollen grains from anther to stigma Anther Ovule pollen grain ovule pollen sac ovum integuments funicle micropyle Insect Pollinated Flower VS Wind Pollinated Flower Insect-Pollinated Flower generally larger & conspicuous brightly coloured, often with insect-guide nectaries often present at the base of flower which produces nectar often strongly scented Insect-Pollinated Flower anthers found inside the flower stigma found inside the flower having small number of pollen grains which are rougher & heavier with spikes flowers appear in warmer season Wind-Pollinated Flower generally small & inconspicuous green or dull colourd, or no petals at all no nectarties no scent anthers hanging out of the flower Wind-Pollinated Flower stigma is large & feathery, exposed for catching pollen grains having large number of pollen grains which are lighter & with smooth surface flowers sometimes appear in colder & drier season Prevent Self-pollination Different level of stigma & anther Male & female parts mature at different times Unisexual flower Pollen tubes cannot germinate in the same Plant Fertilization fusion of male gamete & female gamete to form a zygote Process pollen grain lands on a stigma and then secretes sugary solution stimulates the development of pollen tube which grows down the style & ovary secretes enzyme to digest a pathway through style liberates male gamete in ovary & fuse with egg cell Fertilization Fate of Flower Parts after fertilization Φ Sepals, petals & stamens : wither & fall off Φ Ovary : becomes fruit Φ Ovary wall: becomes fruit wall Φ Ovule : becomes seed Φ Integument : becomes seed coat Φ Fertilized egg: becomes embryo surrounded by endosperm which supplies food to it Fruits Functions: ◦protect seeds ◦help disperse seeds Fruits Different types of dispersal: ◦ by animal possess spines & hooks which cling to animals’ fur protected by hard seed coat which resists the action of animals’ digestive juice after eaten ◦ by wind some fruits are light & have large surface area to catch wind - others: by explosion, by water Seeds • Seed coat – a tough protective covering – protect embryo from damage – prevent bacteria & fungi from entering seed – micropyle admits water to the embryo before germination Seeds Embryo : – cotyledon • contains starch & protein which nourish the embryo during germination • contains enzymes – plumule • forms leafy shoot – radicle • forms root Structure of Seed plumule radicle micropyle cotyledon seed coat Different forms of seeds Water Conditions necessary for Seed Germination activates enzyme to break down starch to sugars & proteins to amino acids for growth Warm temperature enables enzymes to work properly Oxygen enables seeds to respire aerobically to supply energy for growth Investigation of the conditions necessary for Seed Germination Cotton wool soaked in alkaline pyragallol solution A B C refrigerator D mung bean seeds moist cotton wool dry cotton wool moist cotton wool Which tube acts as the control in this experiment ? Ans: Tube A. Cotton wool soaked in alkaline pyragallol solution A B refrigerator C D mung bean seeds moist cotton wool dry cotton wool moist cotton wool What is the function of the alkaline pyrogallol solution ? Ans: To absorb oxygen in air. Cotton wool soaked in alkaline pyragallol solution A B refrigerator C D mung bean seeds moist cotton wool dry cotton wool moist cotton wool What conditions are favourable for the germination of mung bean seeds ? Ans: Water, oxygen and warm temperature. Cotton wool soaked in alkaline pyragallol solution A B C refrigerator D mung bean seeds moist cotton wool dry cotton wool moist cotton wool Tabulate your results. Fill in the table to show the conditions in each and state whether germination has occurred. Results Condition Tube A B C D Water √ X √ √ Oxygen √ √ X √ Warm temperature √ √ √ X Did seeds germinate? √ X X X AVOID PLASTICS AS FOR AS POSSIBLE As a responsible citizen remember the 4R principle Reduce Reuse Recycle Recover
