Presentation on theme: "Reproduction in Flowering Plants. Principle Parts of Flowers Reproductive organs are in structures called Flowers Many Flowers contain male and female."— Presentation transcript:
Pollination Before fertilisation, mature pollen needs to be transferred to the receptive Stigma –That is POLLINATION
Pollen Germination After pollination Stigma secretes sucrose solution stimulating pollen to germinate A pollen tube grows out of a pore in the pollen grain Rapidly penetrates the style tissue Pollen tube growth is controlled by tube nucleus – located at tip of the tube
Pollen Germination Secretes digestive enzymes to allow penetration Pollen tubes are: –Positively hydrotropic –Negatively aerotropic –When approaching ovule it becomes positively chemotropic to a substance produced by the micropyle
Fertilisation The tip of the pollen tube enters the ovule through the micropyle Comes into contact with the embryo sac Male nuclei are released through a pore in the pollen tube tip
Double Fertilisation One male nucleus fuses with egg nucleus to form diploid zygote –Gives rise to the embryo Other male nucleus fuses with the 2 polar nuclei (2n fusion/diploid nucleus) to make a triploid nucleus (3n) –primary endosperm nucleus –Gives rise to the endosperm nutritive tissue
Candidates should be able to draw a diagram of a broad bean (internal and external) and label; micropyle, testa, position of radicle, plumule, cotyledons.
Candidates should be able to describe the germination of the broad bean, including the uptake of water and mobilisation of food reserves.
Mobilisation of food reserves during germination Food reserves in seeds are mainly _____ which is insoluble (why?) The reserves must be broken down to simpler soluble substances They can then be transported to the growing apex of the shoot (plumule) or root (radicle)
Firstly, water is taken up by the seed causing tissues to swell The seed coat (testa) ruptures as the radicle pushes through Amylase hydrolyses starch Proteases hydrolyse proteins During germination, the cotyledons stay underground the plumule is bent over (hook shaped) as it pushes through the soil, protecting the tip