sexual reproduction in plants Flashcards
what are sepals
cover the flower structure while flower is developing. in some species these are modified to petals
what are petals
surround the male and female flower parts. attract animal pollinators - usually brightly coloured and have a scent. may also produce nectar
what is the carpel
THE FEMALE PART
- stigma
- style
- ovary
stigma = surface on which pollen lands and the pollen tube grows down to the ovary
style = connects the stigma to the ovary
ovary = contains the ovules (single egg nuclei)
what is the stamen
THE MALE PART
- anther
- filament
filament = supports the anthers that produce the pollen grains also contain vascular tissue which transports the food materials required for the formation of pollen grains
anther = made up of 4 pollen sacs arranged in 2 pairs
methods of pollination
pollination = transfer of pollen from anther to stigma
- if the transfer occurs between two plants of the same species it is cross pollination ( 2 plants of different genetic make up)
- transfer takes place between flowers of identical genetic constitution, the process is self-pollination
what is self pollination
1) within the same flower. pollen from the anther is transferred to stigma of the same flower
2) occurs between two flowers. pollen from the anther of one transfers to the stigma of the anther
characteristics of insect pollinated flowers
- bright
- smell nice
- petals large
- marking (nectar guides)
- far away from each other
- anthers within flower
- stigma within flower
- small amounts of sticky, sculptured pollen
- larger pollen grains
characteristics of wind pollinated flowers
- little or no petals
- light seeds
- no scent or nectar
- anthers hang outside flowers
- closer together
- large feathery stigmas hand outside flower
- large amounts of smooth pollen
- produces smaller pollen grains
what is male gamete development
- anther typically consists of 4 pollen sacs in which the pollen develops
- vascular tissue supplies water and nutrients to the anther
- the pollen sac is lined with a layer of cells known as the tapetum which regulates pollen development and supplies nutrients to the developing pollen grains
formation of male gamete
pollen mother cell –> 4 pollen grains –> generative nucleus + tube nucleus (pollen tube) –> male nucleus (2)
steps of formation of male gamete
1) meiosis
2) mitosis
3) mitosis
formation of female gamete
megaspore mother cell –> 4 megaspore (3 disintegrate) –> 2 nuclei –> 4 nuclei –> 8 nuclei –> 2 synergids + 3 antipodals + 2 polar nuclei + 1 oosphere
steps of formation of female gamete
1) meiosis
2) mitosis
3) mitosis
4) mitosis
5) cell wall formation
genetic consequences of self and cross pollination
- self pollination is an advantage to a plant if there are no similar plants nearby, it results in in-breeding. this leads to a reduction in the gene pool and reduces variation in the population
- self pollinated species depend on random assortment and crossing over during meiosis and on mutation to bring about variation in the genomes of male and female gametes. therefore self-fertilised species display less genetic variation than cross fertilised species
mechanisms favouring cross-pollination include –>
1) DIOECIOUS
2) MONOECIOUS
3) anthers and stigmas maturing at different times e.g. bluebell
4) structural adaptations which make self-pollination unlikely e.g anthers and stigmas arranged at different levels so that cross pollination between pin-eyed and thrum-eyed flowers is favourable
5) genetic incompatibility which prevent germination of the pollen grain on a genetically similar plant
what is dioecious
having separate male and female plants
what is monoecious
having separate male and female flowers on one plants
what is in-breeding
while out breeding is of greater evolutionary significance due to the fact that some genomes are more successful than others in the struggle for survival - there are advantages to inbreeding e.g. it preserves good genomes which may be suited to a relatively stable environment
describe the process of double fertilisation
1) pollen hydrates and absorbs sucrose produced by the stigma
2) tube grows from the pollen grain
3) grows towards the egg cell up a chemical gradient
4) produces enzymes to digest the cells in the style using the products for nutrition
5) it nether the micropyle and into the embryo sac. the pollen tub nucleus disintegrates
6) one sperm nucleus fuses within the egg cell nucleus to from the diploid zygote
7) the other haploid sperm cell nucleus fuses with the other two polar nuclei to from the triploid endosperm
what does the diploid zygote become
divides by mitosis
becomes the plumule (shoot) ,radicle (root) and cotyledons (leaves)
what does the triploid endosperm become
food store
what does the outer integument become
seed coat (testa)
what does the ovule become
seed
what does the funicle of the ovule become
funicle of seed
attaches at the hilum
