Battling Beetles - TEACHER

observing fruits
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  © Macmillan Publishers Ltd 2008 SCIENCE TEACHER  LP-BIO-INT-0014 Reproduction Reproduction in plants: Observing fruit development Objectives of the lesson To pollinate a flower and observe fruit development over a period of several weeks. Teaching methods Student activity with potential for teacher-led class discussion as a follow-up lesson. Expected outcomes Students understand the process of fertilisation and can explain why some plants produce fruit and seeds. Student pre-knowledge required for this lesson Flowering plants can reproduce sexually. Pollination is the step before fertilisation, and involves a pollen grain landing on a stigma. Materials & resources required Student Worksheet SW-BIO-INT-0014. Time required  40 minutes, with an optional follow-up 10-minute session when fruit has ripened. Equipment list A locally growing fruit-bearing flowering plant such as a mango, pawpaw, Crotalaria , Tecoma ; tweezers. Safety Be careful of sharp points when using tweezers. Teaching the lesson Introduction Explain to the class that fertilisation occurs after pollination. Fertilisation is the formation of a zygote  or seed, which is a pollen grain fused with an ovule. 1  Begin by asking students why some plants produce fruit (to protect seeds and to help their dispersal). Ask them to suggest why seeds might be advantageous to a plant (they can survive harsh environments; they can be dispersed easily by animals, or by wind and water). 2  Take them to a flowering, fruit-bearing plant in the school grounds and allow them to work through worksheet SW-BIO-INT-0014. Depending on the abundance of the plant you choose, students may have to share or work in groups. As students observe the development of their fertilised flower, some flowers may not develop — in these cases, explain to students that this is chance, not their technique, and ensure that each student is in a group observing a successfully fertilised flower. 3  When students have answered all the questions on the worksheet (this will be after the plant has produced fruit), you may like to lead a class discussion using the questions on the worksheet as a basis.  © Macmillan Publishers Ltd 2008 SCIENCE TEACHER  4  Additional exercise for more able students: Discuss the mechanism of fertilisation. When a pollen grain lands on a stigma, it absorbs water and nutrients, causing it to swell up. The wall of the pollen grain ruptures, and a pollen tube grows through the stigma and style towards the ovary. On reaching the ovule, the pollen tube enters the embryo sac and fuses with the ovum. The ovary develops into the fruit, with the ovary wall forming the  pericarp  (fruit wall). The pericarp may become fleshy (as in mango) or dry (as in Tecoma ). StigmaStyleEmbryo sacMicropyleFemale eggnucleusPollen tubePollen grainPollen tubenucleusMale nucleiOvary wall  Ask students to copy the diagram above, and to use it as a basis for describing the fertilisation process in their own words. Conclusions and summary Fruit develops from the ovary and is the ‘packaging’ for seeds, which are fertilised ova. Pollination and fertilisation are different processes: pollination  happens when a pollen grain touches the stigma; fertilisation  is the fusion of the nuclei of a pollen grain and an ovum. Assessment Formal, by marking the answers to questions on the worksheet; or informal, by observing participation in class discussions. Answers to questions 1  Pollination 2  The pollen will enter the ovary and fuse with the ovum; this is fertilisation. 3  The (calyx) corolla, stamens and style have withered and died. The ovary has started to develop into a fruit. (Note: in some plants the calyx remains as the fruit grows.) 4  When it was fertilised by the pollen grain, the ovum became a seed.  © Macmillan Publishers Ltd 2008 SCIENCE TEACHER  5  If the seed is planted, a new plant will grow. 6  Seeds can endure harsh environments such as drought, cold and fire, which a plant could not. They can also be moved easily so that new plants can grow in less harsh conditions. These features enable species to survive environments that they might not be able to survive without seeds. 7  Producing fruit is a selective advantage ; plants and animals that eat the fruit are unable to digest the seeds, which are egested; this helps the dispersal of seeds to new areas so the plant species can spread to new places and/or environments.
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