Plant Reproduction Flashcards
What does the male part of a flower consist of?
› Male part is called the stamen
› Anther - where pollen grains are formed
› Filament - the stalk of the male sexual organ
What does the female part of a flower consist of?
› Female part is called the carpel
› Stigma - sticky top surface which pollen sticks to
› Style - neck joining the stigma to the ovary
› Ovary - where the ovules are formed
How are the pollen grains formed?
› Happens in the pollen sacs in the anther
› Pollen mother cell divides by meiosis to form pollen grains
› Pollen grains separate and each undergo mitosis
› Forming a tube nucleus and a generative nucleus surrounded by the exine
How is the embyro sac formed?
› Happens inside the ovary
› Megaspore mother cell divides by meiosis, producing four megaspores
› Three degenerate and one develops into the embyro sac, by undergoing mitosis three times, forming eight nuclei
› Two stay in the centre with no membrane, and fuse to form the endosperm nucleus
› Three move to the top, which are the antipodal cells
› Three move to the bottom, one becomes the oosphere, two become the synergid cells
What is pollination?
The transfer of pollen from an anther to a stigma, so that fertilisation is achieved
What are some features of insect pollinated flowers?
› Brightly coloured petals
› Emission of a scent
› Secretion of nectar
What are some features of wind pollinated flowers?
› Small, dry pollen grains
› Stamen outside the flower
› Feathery stigmas
Name some mechanisms that help ensure cross pollination takes place
› Separate male and female plants
› Separate male and female flowers
› Anther below the stigma
What is fertilisation?
The process where a male gamete nucleus fuses with a female gamete nucleus to form a zygote
How does fertilisation happen in plants?
› Pollen grains stick to stigma, absorb water, and germinate
› Contents of the pollen grain push out forming the pollen tube
› Tube nucleus codes for production of hydrolases, which digests through the style tissue
› Generative nucleus divides by mitosis, forming two male gametes
› Tube nucleus degenerates when the tube has penetrated the ovule through the micropyle
› One male gamete fuses with the oosphere to form a diploid zygote
› Other male gamete fuses with the polar nucleus, forming a triploid primary endosperm nucleus, which will divide by mitosis to form the endosperm tissue
What are some changes that take place as the seed develops?
› Zygote divides by mitosis to form the embyro, consisting of a plumule (developing shoot), a radicle (developing root), and one or two cotyledons
› Endosperm tissue is formed as a food storage tissue
› Ovule becomes the seed
› Outer integument dries out and becomes the testa
› Ovary becomes the fruit, ovary wall becomes the pericarp
What are the three main requirements for successful germination?
› A suitable temperature (so enzymes are at their optimum)
› Water (for mobilisation of enzymes, and making cells turgid)
› Oxygen (for aerobic respiration)
