Flashcards in Angiosperms Deck (54)
How many species of angiosperm are there?
What are they important for?
Food source, Commercial products, Influence climate
What is a flower?
A feature specialised for sexual reproduction, a specialised shoot with modified sporpphyll
What are the sporophyte in angiosperms called?
What are the different floral organs?
Sepals, Petals, Stamen and carpel
What are the sepals?
Usually green and enclose the flower before it opens
What are the petals?
Brightly coloured to attract pollinators- not in wind pollinated plants,
Why are the petals and sepal sterile floral organs?
Not directly involved in reproduction
What is the role of the stamens?
Produce microspores that develop into pollen grains containing male gametophytes
How are the stamens structured?
Composed of a filamentous sac and the anther, where the pollen is produced
What is the role of the carpel?
Make megaspores and the female gametophytes, number is analogous, depends on species
How is the carpel structured?
At the tip is a sticky stigma that receives pollen. Style leads from the stigma to the ovary at the base of the carpel
What are the fruits?
Typically is a mature ovary
How does the fruit form?
Develops from ovules after fertilisation as the wall of the ovary thickens
What is the role of the fruit?
protect dormant seeds and aid in their dispersal
Where are the male gametophytes?
In the pollen
Where are the female gametophyte?
In the ovule
How is the pollen grain structured?
Two haploid cells, one is generative and develops into two sperm, the other is the tube cell
What happens when the pollen reached the stigma?
Pollen tube grows down style, sperm travel through micropyle - pore in the integument, and discharge into the female gametophyte
How does fertilisation occur?
One of the sperm will fertilise the egg, forming a diploid zygote, the other fuses with the two nuclei in the large central cell, producing a triploid cell
What is double fertilisation?
One fertilisation event produces a diploid embryo and a triploid cell - unique to angiosperms
What is the function of the triploid cell?
cell divides repeatedly and develops into the endosperm, which is a tissue rich in starch and other reserves that nourish the developing embryo
What is the function of double fertilisation?
Hypothesis is the it wouldn't be beneficial to develop endosperm and waste resources if the egg isn't fertilised, so is a way of conserving resources
What happens once the seed gets to a favourable environment?
Coat ruptures and embryo emerges as a seedling, using food stored in the endosperm and cotyledons
How is the female gametophyte produced?
Occurs in the ovary. meiosis occurs to form four haploid cells, only one survives, splits by mitosis to form 8 cells, 7 within a single embryo sac are accessory and polar cells for formation of the seed and one which is the egg
How is the mate gametophyte produced?
In the pollen, single diploid uncle splits by meiosis into four haploid cells, each become a pollen grain, then split again. Pollen grain consists of generative cell and tube cell
How did Angiosperms evolve?
Named the abominable mystery, not sure
When did the major branches of the clade diverge?
In the late mesozoic
When did they begin to dominate?
By mid cretaceous