Transcript angiosperms
Reproduction in ANGIOSPERMS The flowering plants Overview of Role of flowers Flowers are developed from a series of modified leaves arranged in rings(whorls) They emerge from buds Flowers are reproductive structures They are involved in Sexual reproduction Some parts of a flower produce gametes Fertilization occur within the flower Part of the flower become a fruit in which embryos are stored until they are dispersed Flower structure The calyx, composed of individual sepals, surround and protects the flower bud. Dog rose Rosa canina Most species of flowering plants are hermaphroditic; contain both male and female reproductive parts However, many species have mechanisms to prevent self fertilization inorder to ensure greater genetic variation in offspring Flower consist of female parts Carpel; comprising stigma, style and ovary containing ovules Note: Although it isn’t a big deal, your text book uses the term Pistil incorrectly and this may cause confusion. The pistil is the entire female reproductive organ. Carpel is the term that refers to an ovary, style and stigma. In flowers where there is only one of these then the carpel=the pistil and the two terms and synonymous. However in flowers with more than one carpel the pistil refer to all the carpels together. Flower structure Holds the ovules and after The Stalk topconnecting of the style; the Receives stigma fertilisation develops into a to the thePOLLEN ovary.itHolds generally the sticky stigma =stigma + style + ovary fruit to protect the seed and inora in position order to that trap facilitates pollen aid in dispersal of the seed. pollination grains Stigma Ovule Style Carpel = pistil (in this case) Ovary Petal Anther Sepal Filament Male Parts Stamens; each comprising an anther (containing pollen) and a filament stalk which supports Consists of pollen sacs the anthers and holds them a (typically 4), pollen grainsinare Male part of flower comprising positionhere. to facilitate dispersal formed These grains filament and anther pollen contain theof male gamete which if formed by meiosis. Flower structure Stigma Style Carpel = pistil (in this case) Ovary Petal Anther Sepal Filament Parts that offer Protection or support petals, sepal and receptacle Flower structure Smallmain modified that are While Thickened role arealeaves isatattraction the top of usually green in colour (though of athe pollinator, stem from to a where degree the may be coloured and petalthey flower offer grows. protection It supports to rolethe like(petaloid)) and whose is stamens flower pistil to protectand the young flower bud Stigma Style Carpel = pistil (in this case) Ovary Petal Anther Sepal Filament Receptacle Parts that attract pollinators (if applicable) Petal Nectary Ovary position differs between flowers Not all flowers are so simple Composite head of a daisy So this is actually a group of two different types of flowers Pollination A Pollen grain contains the male gamete (2 nuclei/sperm cells) Pollination is the transfer of pollen from anther to a receptive stigma Pollination ≠ Fertilisation Pollen from a flower could land on the stigma of the same flower = self pollination Pollination Pollen transferred from the anther on one flower to the stigma of another flower on a different plant = cross pollination Types of pollination ANIMAL BASED POLLINATION: an animal picks up pollen and transfer it to stigma of another flower Insect pollination Insect-pollinated flowers may have: • Brightly coloured petals • Strong sweet fragrance • Nectar producing glands • Guidelines to lead insects to Nectar a) Mode of Pollination b) Bird pollination Bird-pollinated flowers may have: • Long tube shaped flowers • Bright red and yellow flowers • No odour c) Mammal pollination Animal -pollinated flowers may have: • White flowers • Strong fruity odour • Flowers opening at night Animal Pollination Plants tend to specialise in pollinators This ensures the pollen is delivered to same species of plant Yellow archangel Lamiastrum galobdolon being pollinated by a bumble bee Bombus hortorum Types of pollination 2. Wind Pollination: wind “picks up” pollen and carries it to stigma of another flowerWindpollinated flowers may have: • Large stigmas outside the flower • Little or no fragrance • Light non-sticky pollen Fertilisation Pollination ≠ Fertilisation The male gamete (the male nucleus) has to get to the egg cell The egg cell lies in an ovule in an ovary at the centre of the plant The pollen grain germinates on the stigma It grows a pollen tube down the style Its male nuclei travel down the pollen tube to the ovule Fertilisation Pollen grain Stigma Style Ovule Embryo sac Ovary © 2008 Paul Billiet ODWS Pollen tube Fertilisation Embryo sac Polar nuclei Egg cell Micropyle © 2008 Paul Billiet ODWS Fertilisation There are two haploid “sperm” cells in the pollen grain. Double fertilization occurs One “sperm” cell fuses with the egg to develop into diploid (2N) embryo plant that becomes the seedling The other fuses with 2 other haploid cells in the ovule to form the endosperm(3N); a tissue that provides nutrition to the embryo whilst waiting for seed germination. The double fertilisation Ovule Nucellus Pollen tube Male nucleus + 2 polar nuclei = endosperm nucleus (3n) Male nucleus + egg cell = zygote (2n) © 2008 Paul Billiet ODWS Pollen tube entering micropyle From flower to fruit Marsh marigold Caltha palustris © 2008 Paul Billiet ODWS Fruits help disperse seeds To increase the chance of survival of a species, seeds need to be spread away from the parent plant to reduce competition for resources such as water, soil minerals and sunlight. Plants invest energy in making fruits Fruits assist with dispersing seeds There are various mechanisms for seed/fruit dispersal Fruits and seed dispersal Animal dispersal Strawberry Fragaria vesca Explosive dispersal Bird’s foot trefoil Lotus corniculatus Animal dispersal Wood avens Geum urbanum Wind dispersal Ragwort Senecio © 2008 Paul Billiet ODWS Dandelion Stages of Strawberry developement