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Topic 9 Plant Biology - 9.4 Reproduction in Plants Nature of science: Paradigm shifts; more than 85% of the world’s 250,000 species of flowering plants depend on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species. UNDERSTANDING STATEMENTS Flowering involves a change in gene expression in the shoot apex. o Vegetative Structures = o Plant stays in vegetative phase for weeks, months, or years until a trigger causes the plant to change into the reproductive phase and produce flowers. o This happens when meristems in the __________________________________________ _____________________________________________________________________________. o Flowers are structures that allow for ___________________________________. They are produced by the shoot apical meristem and are a reproductive shoot. o ______________________________________ can play a role in changing a leafproducing shoot into a flower-producing shoot, but ___________________________ is the main trigger (__________________________________________) o Light plays a role in the production of either inhibitors or activators of genes that control flowering. Ex: In long day plants, the active form of the pigment phytochrome leads to the transcription of a flowering time (FT gene). The FT mRNA is then transported in the phloem to the shoot apical meristem where it is translated into FT protein. The FT protein binds to a transcription factor. This interaction leads to the activation of many flowering genes which transform the leaf-producing apical meristem into a reproductive meristem. The switch to flowering is a response to the length of light and dark periods in many plants. o Long-day plants flower in the summer when the nights have become short enough. o Short-day plants flower in the autumn, when the nights have become long enough. o Experiments have shown that it is the length of ________________________________ that matters (not daylight) o Plants us a pigment in leaves to measure the length of dark periods. It is called phytochrome and is unusual as it can switch between two forms PR and PFR o When PR absorbs red light of wavelength 660 nm, it is converted into PFR o PR is more stable than PFR, so in darkness PFR very gradually changes into PR o PFR is the active form of phytochrome and that the receptor proteins are present in the cytoplasm to which PFR binds, but not PR o Long day plants o Short day plants SKILL: Drawing of half-views of animal-pollinated flowers. Sepals – Anthers – Filaments – Pollen – Carpel – Stigma – Style – Ovary – Ovule – Most flowering plants use mutualistic relationships with pollinators in sexual reproduction. o Sexual reproduction in flowering plants depends on the transfer of pollen from the stamen to the stigma of another plant. o Pollen is transferred between plants via a number of strategies including wind, and by animals called pollinators. o Examples of pollinators: ______________________________________________________ o Mutualism - _____________________________________________________________________ Success in plant reproduction depends on pollination, fertilization, and seed dispersal. Pollination = ________________________________________________________________ Fertilization = ________________________________________________________________ Seed dispersal = _____________________________________________________________ SKILL: Drawing the internal structure of seeds. Embryo root – Embryo shoot – Cotyledons – Testa – Micropyle – SKILL: Design of experiments to test hypotheses about factors affecting germination.