SEXUAL REPRODUCTION IN PLANTS Flashcards
(39 cards)
What occurs during subsequent development? (4)
- zygote develops a embryo plant, embryonic root (radical) and embryonic shoot (plumule)
-primary endosperm cell forms a mass of food tissue (endosperm)
-embryo sac develops into a seed
-wall of ovary develops into a fruit
what happens when the pollen tube reaches the ovule? (2)
the pollen tube grows through the micropyle and into the embryo sac; the pollen tube then breaks down and the tube nucleus degenerates, male gametes move into embryo sac and double fertilisation occurs.
what is the function of the pollen tube nucleus? (1)
controls growth of the tube (this is possible because it digests the recipients plant tissue as it moves through the style)
what is the function of the generative nucleus? (1)
follows the pollen tube nucleus down the pollen tube, it divides by mitosis to produce 2 haploid nuclei (male gametes)
what is the nucellus? (1)
a central mass of tissue containing the diploid megaspore mother cell surrounded by two layers of cells called the integuments.
where are the reproductive organs in plants? (1)
in their flowers or inflorescences.
what are the male reproductive structures known as? (1)
known as stamens each stamen consists of an anther and a filament.
what is meant by hermaphrodite? (1)
a multicellular organism that possess both male and female reproductive structures.
what is a stigma? (1)
a platform on which pollen grains may land, a style that supports the stigma and an ovary.
where are the female gametes contained? (1)
inside the ovary contains the ovule contains female gametes.
what are the female reproductive structures known as? (1)
known as carpels which consists of a stigma.
where are the male gametes contained? (1)
the anther produces pollen grains that contain the male gametes.
what happens during double fertilisation? (2)
-one male nucleus fuses with the female gamete forming a diploid zygote.
-the other male nucleus fuse with the polar nuclei to form a triploid primary endosperm cell.
what are the stages of the formation of female gametes? (2)
-megasporogenesis
-megagametogenesis
what happens in megasporogenesis? (3)
-a cell in the ovule differentiates into a megaspore mother cell (diploid)
-this megaspore mother cell undergoes meiosis to form 4 (haploid) megaspores
-3 of the 4 megaspores degenerate and only one megaspore is left in each ovule.
what happens in megagametogenesis? (4)
-megaspore nucleus mow begins to divide mitotically to form 8 nuclei
-6 of the 8 migrate to opposing poles while two nuclei remain at the centre (known as polar nuclei)
-these polar nuclei fuse to form the secondary nucleus
-megaspore matures into an embryo sac
what are the stages of the formation of male gametes? (2)
-microsporogenesis
-microgametogenesis
what does pollen grain in germinate depend on? (2)
pollen grains have shapes and surface protrusions that are unique to each plant species, a plant must have a stigma with complimentary patterns to allow a pollen grain to germinate.
what happens in microgametogenesis? (4)
-pollen grain (haploid) has 2 layers the outer exine layer which is derived from the tapetum and the inner layer (intine). exine is present everywhere apart from the pollen tube (Pollination).
-pollen grain divides in 2 (small generative nucleus and larger vegetative nucleus)
-generative nucleus gives rise to 2 male nuclei; whereas the vegetative nucleus gives rise to the pollen tube.
what is cross pollination? (1)
occurs when pollen is transferred from the anther of one plant to the stigma of another plant.
how pollen carried in cross pollination? (2)
-by insects or other animals
-the wind
what happens in microsporogenesis? (4)
-the anther is automatically divided into lobes which further divide into chambers (microsporgonia) (pollen presents there)
-the archesporial cell (pollen development cell) divides into outer and inner layers (inner layer forms sporogenous tissue or cell that forms pollen cell)
-sporogenious tissue provides nourishment to pollen cell present in sporogenous tissue.
-mother cell divides mitotically to form haploid pollen.
what is the micropyle? (1)
as the integuments grow they almost enclose the nucellus leaving only a tiny hole (the micropyle)
how is fertilisation achieved? (1)
the male gamete within the pollen grain must fuse with the female gamete in the embryo sac.
