Calyx constitutes the outermost whorl Stamen = male structure
Capel = female structure
STUDY UNIT THEME A.4: PLANT REPRODUCTION (3 LECTURE)
LITERATURE: RAVEN ET AL 12TH ED CHAPTER 40
STUDY OBJECTIVES: After studying this theme, you should be able to:
1. Label the parts of a flower on a diagram, and describe the functions of each
part.
A flower is the reproductive station found in angiosperms It is produced when the leaves have become
modified for reproduction (Lateral shoot with limited growth)
2. Identify where eggs and pollen grains are formed in the flower.
Pollen Formation:
Anthers contain 4 microsporangia, which produce microspore mother cells (x2).
Microspore mother cells produce microspores (x) through meiosis
, The microspores, through mitosis & wall differentiation, become pollen.
Inside each pollen grain is a generative cell – this cell later divides to produce 2
sperm cells
Pollen grain shapes are specialized for specific flower species. Fertilization
requires that the pollen grain grow in a tube that penetrates the style until it
encounters the ovary. Most pollen grains have a furrow/pore from which this
pollen tube emerges – some grains have 3 furrows.
Embryo sac formation
Egg develop in the ovules of the angiosperm flower.
Within each ovule is a megaspore mother cell.
Just as in pollen production, the megaspore mother cell undergoes meiosis to
produce four haploid megaspores.
In most plants, however, only one of these megaspores survives (the rest are
absorbed by the ovule)
The lone remaining megaspore enlarges and undergoes repeated mitotic
divisions to produce eight haploid nuclei that are enclosed within a seven-celled
embryo sac.
Within the embryo sac, the 8 nuclei are arranged in precise positions.
One nucleus in located near the opening of the embryo sac in the egg cell
Two others are located together in a single cell in the middle of the embryo sac
(polar nuclei)
Two more nuclei are contained in individual cells called synergids that flank the
egg cell
The other 3 nuclei reside in cells called the antipodals, located at the end of the
sac, opposite the egg cell.
The first step in uniting the 2 sperm cells in the pollen grain with the egg and
polar nuclei is the germination of pollen on the stigma of the carpel and its
growth toward the embryo sac.
Capel = female structure
STUDY UNIT THEME A.4: PLANT REPRODUCTION (3 LECTURE)
LITERATURE: RAVEN ET AL 12TH ED CHAPTER 40
STUDY OBJECTIVES: After studying this theme, you should be able to:
1. Label the parts of a flower on a diagram, and describe the functions of each
part.
A flower is the reproductive station found in angiosperms It is produced when the leaves have become
modified for reproduction (Lateral shoot with limited growth)
2. Identify where eggs and pollen grains are formed in the flower.
Pollen Formation:
Anthers contain 4 microsporangia, which produce microspore mother cells (x2).
Microspore mother cells produce microspores (x) through meiosis
, The microspores, through mitosis & wall differentiation, become pollen.
Inside each pollen grain is a generative cell – this cell later divides to produce 2
sperm cells
Pollen grain shapes are specialized for specific flower species. Fertilization
requires that the pollen grain grow in a tube that penetrates the style until it
encounters the ovary. Most pollen grains have a furrow/pore from which this
pollen tube emerges – some grains have 3 furrows.
Embryo sac formation
Egg develop in the ovules of the angiosperm flower.
Within each ovule is a megaspore mother cell.
Just as in pollen production, the megaspore mother cell undergoes meiosis to
produce four haploid megaspores.
In most plants, however, only one of these megaspores survives (the rest are
absorbed by the ovule)
The lone remaining megaspore enlarges and undergoes repeated mitotic
divisions to produce eight haploid nuclei that are enclosed within a seven-celled
embryo sac.
Within the embryo sac, the 8 nuclei are arranged in precise positions.
One nucleus in located near the opening of the embryo sac in the egg cell
Two others are located together in a single cell in the middle of the embryo sac
(polar nuclei)
Two more nuclei are contained in individual cells called synergids that flank the
egg cell
The other 3 nuclei reside in cells called the antipodals, located at the end of the
sac, opposite the egg cell.
The first step in uniting the 2 sperm cells in the pollen grain with the egg and
polar nuclei is the germination of pollen on the stigma of the carpel and its
growth toward the embryo sac.
