Development of Pollen Grains and Embryo Sac

6.2

Development of Pollen Grains and Embryo Sac

The Importance of Rough Surface of the Pollen

Helps it to stick easily to the stigma and pollinating agents.

The Structure of Ovule

Ovules are structures of a flower formed inside the carpel.
Ovules develop from a layer of tissues inside the ovary.
A single ovary may contain one or more ovules.
The ovule attaches to the ovary wall through a stalk called the funicle.
The area of attachment of the funicle to the ovary is called the placenta.
The placenta supplies nutrients to the ovule through the funicle.
A mass of tissues inside the ovary develops forming a lump called nucellus.
The nucellus consists of parenchyma tissue.
The nucellus tissue develops into two layers called the integument.
At the end of the integument, there is a little opening, called the micropyle which allows the entry of air and water into the seed during germination.
One of the nucellus cells is the megaspore mother cell or also known as the embryo sac mother cell which will develop to form an embryo sac.

Process of Embryo Sac Formation

Ovule is formed in the ovum.
Each ovule contains one embryo sac (2n).
The embryo sac mother cells (2n) undergoes mitosis to form four haploid megaspore cells (n).
Three megaspores degenerated and remaining one.
The remaining megaspore undergoes mitosis three times to form haploid embryo sac cells with eight nuclei.
- Three cells move to one and near to micropyle, forming two synergid cells and one egg cell.
- Three more cells move to another end to form three antipodal cells.
- One cell with two nuclei located at the center to form polar nuclei.
- The structure formed is known as embryo sac which is protected by integument.

6.2

Development of Pollen Grains and Embryo Sac

The Importance of Rough Surface of the Pollen

Helps it to stick easily to the stigma and pollinating agents.

The Structure of Ovule

Ovules are structures of a flower formed inside the carpel.
Ovules develop from a layer of tissues inside the ovary.
A single ovary may contain one or more ovules.
The ovule attaches to the ovary wall through a stalk called the funicle.
The area of attachment of the funicle to the ovary is called the placenta.
The placenta supplies nutrients to the ovule through the funicle.
A mass of tissues inside the ovary develops forming a lump called nucellus.
The nucellus consists of parenchyma tissue.
The nucellus tissue develops into two layers called the integument.
At the end of the integument, there is a little opening, called the micropyle which allows the entry of air and water into the seed during germination.
One of the nucellus cells is the megaspore mother cell or also known as the embryo sac mother cell which will develop to form an embryo sac.

Process of Embryo Sac Formation

Ovule is formed in the ovum.
Each ovule contains one embryo sac (2n).
The embryo sac mother cells (2n) undergoes mitosis to form four haploid megaspore cells (n).
Three megaspores degenerated and remaining one.
The remaining megaspore undergoes mitosis three times to form haploid embryo sac cells with eight nuclei.
- Three cells move to one and near to micropyle, forming two synergid cells and one egg cell.
- Three more cells move to another end to form three antipodal cells.
- One cell with two nuclei located at the center to form polar nuclei.
- The structure formed is known as embryo sac which is protected by integument.