Reproduction in plants Flowering

Understandings Flowering involves a change in gene expression in the shoot apex. The switch to flowering is a response to the length of light and dark periods in many plants. Most flowering plants use mutualistic relationship with pollinators in sexual reproduction Success in plant reproduction depends on pollination, fertilization and seed dispersal.

Flowering and gene expression When a seed germinates, a young plant is formed that grows roots, stems and leaves and these are called vegetative structures, which indicates that it is currently in vegetative phase. Flowers can only be produced when something stimulates the plant to change from the vegetative phase into reproductive phase Stimulus is a change in the length of light and dark periods.

Short day plants and Long day plants Chrysanthemums: Irises: Flower in autumn when the nights have become long enough Flower in summer when the nights have become short enough

Flowering controlled by phytochrome

Read page 430 and annotate the diagram

Sunlight contains red wavelength light Pr is converted to Pfr Much less in sun light Pfr is unstable and is converted back into Pr in the dark

Gene Expression and Flowering Pfr has been found to be the active form of phytochrome Receptor proteins are present in the cytoplasm of leaf cells to which Pfr (not Pr) binds These proteins will then cause transcription of genes needed for flowering Long day plants Large amounts of Pfr remain to bind to the proteins and promote transcription Short day plants The receptor protein inhibits the transcription of the flowering genes when bound to Pfr. At the end of a long night there is very little Pfr so there is no inhibition and the gene is transcribed Short day plants – Pfr inhibits flowing Long day plants – Pfr promotes flowing

The mRNA... …was transcribed from a flowering time gene (FT gene). FT mRNA is transported to the shoot apical meristem (via the phloem). ...here it is translated into a FT protein. This binds to a transcription factor and may flowering genes are activated. The meristematic cells differentiate (gene expression) and the reproductive phase begins. mRNA mRNA Phytochrome

Complete question on page 430 Exam Q

How could plants be manipulated to flower out of season? Exam Q

Flower Structure Draw a picture of an animal pollinated flower

Flower Structure Draw a picture of an insect pollinated flower

Flower Dissection

Pollination Pollination and evolution Pollination is the transfer of male gametes of to the female part of the flower (Stigma). Pollinators such as bees are attracted because they can gain food (nectar) and the pollen will be able to attach itself onto the bees and potentially land on a stigma. This double-beneficial relationship is called Mutualism. Symbiotic relationship. Also attracted by scent and colours

Fertilization Fertilization occurs once a pollen has landed on the stigma and a reaction called the enzymatic reaction will create a tube (Pollen tube) within the stigma that allows the gamete from the pollen to travel to the ovary. Two male nuclei enter the olule. Here the male and female gametes fuse. One male nuclei fuses with the egg and the other fuse with the polar nuclei to produce and triploid endosperm Ovule becomes the seed and ovary becomes the fruit Tube nucleus

Seed dispersal FIND SOME INTERESTING WAYS THAT SEEDS ARE DISPERSED

Structure of Seeds Draw the internal and external structure of a seed

Exam Q

Planning a germination experiment

Keywords Vegetative phase - The phase before reproductive phase and can be stimulated into the reproductive phase when the stimulus is present (Light). This can be spotted when there are vegetative structures present. Pollinators - Animals that help transfer the pollen. Examples are honey bees and hummingbirds. Mutualism - Both organisms receive benefits. Example is when the honey bees or hummingbirds obtain nectar from the flower and help spread the pollen. Enzymatic Reaction - A reaction that only occurs once a pollen lands on top of the stigma and it creates a tube called the pollen tube. The pollen tube allows the sperm from the pollen to swim towards the ovary.