plant reproduction Flashcards
what are the functions of the petals?
- plural: corolla
- colourful to attract insects
what is the receptacle?
where the petals are attached
what is the function of the sepal?
protects the flower when it’s in the bud
which parts of a flower are considered ‘male’ and what are the parts collectively called?
- anther and filament
- the stamen
what is the function of the anther?
produces and releases pollen grains
what are the functions of the filaments?
carries water and nutrients to anther and positions it where pollen can be picked up
which parts of a flower are considered ‘female’ and what are the parts collectively called?
- stigma, style and ovary
- the carpel
what is the function of the stigma?
selects pollen grains and stimulates growth of pollen tube
what is the function of the style?
positions stigma where it can best receive pollen
what is the function of the ovary?
retains and protects ovule, becomes fruit after fertilisation
what is the function of the ovule?
contains the embryo sac, becomes seed after fertilisation
what are the differences between an insect-pollinated and a wind-pollinated plant?
- i: large & colourful petals, w: small and brown
- i: makes smaller quantities of spiky pollen, w: larger quantities of lighter
- i: anthers and stigma inside petals, w: hang outside petals
- i: small & sticky stigma, w: large & feathery
- i: pleasant scent, w: none
- i: nectar present, w: none
describe how male gametes develop
- pollen mother cell in pollen sacs of anthers divide by meiosis
- this produces a tetrad of 4 haploid, genetically varied cells
- each cell becomes a pollen grain, with a double-layered cell wall (intine & exine) (protects from UV and drying out)
- nucleus divides by mitosis to produce 2 genetically identical nuclei (pollen tube nucleus & generative nucleus)
- when pollen is ripe, is released when pollen sac bursts (dehiscence)
describe the formation of female gametes
- egg mother cell (megospore) nucleus divides by meiosis but cell doesn’t divide
- this produces 4 nuclei in one cell, 3 of which die
- this provides variation and means it is now a haploid cell that can be fertilised to make a diploid zygote
- single nucleus left undergoes 3 rounds of mitosis, producing 8 identical haploid nuclei (3x antipodals, 2x polar nuclei, 1x egg cell with 2x synergids)
- this structure is called a embryo sac
what is the definition of cross- pollination?
when pollen is transferred from the anther of one plant to the stigma of another
what is self-pollination?
when pollen falls from anther onto the stigma of the same flower (or another flower on the same plant)
what are the advantages and disadvantages of cross-pollination?
- AD: prevents inbreeding, results in more genetic variation, reduces chances of producing harmful allele combinations
what are the advantages and disadvantages of self-pollination?
- AD: can preserve good genomes which may be suited to a suitable environment
- DIS: allows less variation (depends only on crossing over/ independent assortment in meiosis)
how do plants ensure cross-pollination?
- stamen and stigma mature at different times (dichogamy)
- irregular flower structure: anther below stigma so pollen can’t fall onto it
- chemical self-incompatibility: pollen cannot germinate on the stigma of the flower which produced it
- plants that are separated into male and female
what is the definition of fertilisation?
fusion of male and female gametes to produce a diploid zygote
describe the stages of double fertilisation
- pollen grains land on stigma and germinate- produces pollen tube
- pollen tube nucleus controls growth of pollen tube: synthesises enzymes which digest a path for the tube, synthesises the tube as it grows and uses the digested tissue as a nutrient source
- pollen tube grows through gap in the integuments (micropyle) whcih allows it to enter the embryo sac
- PTN enters through one of the synergids
- synergid disintegrates, allowing a path for the other nuclei to enter
- generative nucleus divides by mitosis to form 2 male gametes
- one gamete enters egg cell and fuses- zygote, other fuses with 2 polar nuclei- triploid endosperm nucleus
define what a dicotyledon is and give an example of one
- a plant with 2 seed leaves/cotyledons, embryo lies between them
- broad bean: non-endospermic (endosperm (food store) is absorbed into cotyledons)
define what a monocotyledon is and give an example of one
- one cotyledon
- maize: endospermic (endosperm remains as food store)
give an example of a survival strategy that plants can undergo
- seeds can become dormant until suitable conditions are present (testa can also acts as chemical & physical protection)
- when dormant, water content falls below 10%, which metabolic rate
- allows plant to survive dessication
