Reproduction in Plants Flashcards
What is a dicotyledon?
A plant that produces seeds that contain two cotyledons; they have two primary leaves.
What is an insect-pollinated flower?
A type of flower that relies on an insect transferring pollen grains between flowers.
Name the main components of an insect-pollinated flower.
Anther
Style
Stigma
Pedicel
Receptacle
Ovary
Petal
Filament
Sepal
What is the calyx?
Leafy structures when the plant is first formed in order to protect the flower during it’s development.
What is the corolla?
All the petals of a flower
What is the carpel?
The female part of the plant consisting of a stigma, a style and an ovary
What is the stamen?
Male part of the plant which consists of the anther and the filament which is involved in the production of male gametes in the form of pollen grains.
Describe the adaptations of insect-pollinated plants
Internal anthers and small stigma directly touch insects
Large, bright petals and nectar from glands attract insects
May produce chemicals to the mimic scent of female insects or to intoxicate insects
Grow individually
Large pollen grains, sometimes with projections that attach to insect
What is a wind-pollinated plant?
A type of flower that relies on wind to transfer pollen grains between flowers.
Describe the adaptations of wind-pollinated plants.
External anthers optimise pollen dispersal
Excess pollen compensates for wind wastage Feathery stigma catches pollen from the air
Small, dull petals (no need to attract insects)
Grow densely over large areas
Light pollen grains
How does a pollen grain form in the anther?
- Large numbers of pollen mother cells produced by mitosis
Meiosis of diploid mother cells in the anther forms four haploid microspores - Haploid microspores mature into pollen grains via mitosis
Describe the role of the tapetum in pollen grain development.
- Specialised layer of cells in the anther
- Provides nutrients to developing pollen
grains
Describe the structure of mature pollen grains.
Generative cell (haploid nucleus) produces two male gametes via mitosis
Pollen tube cell (also has its own nucleus) elongates to penetrate ovule
Outer protective coating
Define dehiscence.
The splitting of the anther resulting in the release of pollen grains.
How does the ovule form in the ovary?
Meiosis of megaspore cell produces four haploid megaspores
Growth and development (involving three mitotic divisions) of one of the megaspores
Embryo sac forms containing eight haploid nuclei
Describe the structure of the embryo sac.
Two polar nuclei form endosperm
Ovum forms zygote
Two synergids help generative nucleus of pollen grain to reach ovum
Three antipodal cells
Outer protective coating
Define pollination
The deposition of pollen onto a stigma from an anther
Name the two types of pollination.
Cross-pollination
Self-pollination
What is cross-pollination?
A type of pollination in which pollen is transferred from an anther of one plant to a stigma of a different plant.
What is self-pollination?
A type of pollination in which pollen is transferred from an anther of a plant to a stigma of the same plant.
Compare the genetic diversity produced by cross- and self-pollination.
Cross-pollination results in plants with greater genetic diversity whereas self-pollination produces plants with less diversity.
Outline the adaptations of flowers that promote cross-pollination.
Maturation of pollen and ovary at different times
Physical features prevent self-pollination, e.g. heterostyly, male and female flowers on different parts of the plant
Where does double fertilisation occur?
Embryo sac of ovule.
How do the male nuclei reach the embryo sac?
Pollen grain from one plant lands on the stigma of another
Mitosis of pollen grain to form a pollen tube nucleus and two male gametes
Pollen tube grows from the grain down to the ovule via the digestion of the style
Pollen tube delivers two male gametes
How does the pollen tube enter into the embryo sac?
Via the micropyle
Define micropyle
Pore in the integument of an ovule through which the pollen tube enters the embryo sac
Remains as a pore in the testa (seed coat)
What happens during double fertilisation?
In the embryo sac of ovule:
One sperm cell fertilises an ovum to form a diploid zygote
One sperm cell fuses with two polar nuclei to form a triploid primary endosperm
What happens to the ovule following double fertilisation?
Develops into the seed.
How is the diploid embryo formed following double fertilisation?
Diploid zygote undergoes mitosis to form diploid embryo.
How is the endosperm formed?
Nucleus of triploid endosperm divides by mitosis to form endosperm.
Why is the function of the endosperm?
Acts as a nutrient source for the embryo.
What structure forms the testa?
Integuments develop into the testa.
What happens to the ovary following double fertilisation?
It develops into a fruit wall surrounding the seed.
What is the plumule?
The part of a plant embryo that develops
into the primary shoot.
What is the radicle?
The part of a plant embryo that develops into the root.
What is the hilum?
A scar on the testa as a result of separation from its funicle.
Define germination.
The process by which a plant grows
from a seed.
Give an example of a non-endospermic seed.
Broad bean (Vicia faba)
Describe the stages of germination in a non-endospermic seed.
Seed absorbs water through the micropyle causing swelling of the cotyledon, enzyme activation and the rupture of the seed coat
Food reserves from the cotyledons are hydrolysed
Provides energy for the growth of the plumule and radicle, as well as respiration
Describe the stages of germination in an
endospermic seed.
- Seed absorbs water, activating the embryo to secrete the cell-signalling plant growth factor, gibberellin
- Gibberellins induce the synthesis of amylase
- Amylase diffuses to the endosperm layer and causes the hydrolysis of starch to glucose
State the factors affecting seed germination.
- Water availability (trigger secretions of gibberellin)
- Temperature
- Availability of O, for respiration
- Use of fertiliser provides extra nutrients for growth
