Q.With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

A typical angiosperm ovule is the structure that develops into a seed after fertilisation. It is attached to the placenta inside the ovary by a stalk called the funicle. The body of the ovule is covered by one or two protective layers called integuments, which enclose the nucellus (the central mass of cells). At the tip of the ovule, the integuments leave a small opening called the micropyle. Inside the nucellus, a large cell called the embryo sac (the female gametophyte) develops. The region where the funicle, integuments, and nucellus meet is called the chalaza.

Here is a neat, labelled diagram of a typical anatropous ovule (the most common type):

                    Funicle
                       |
                       |
        ---------------+---------------
       |                               |
       |         Integuments           |
       |           (outer)             |
       |           (inner)             |
       |                               |
       |    -----------------------    |
       |   |                       |   |
       |   |       Nucellus        |   |
       |   |                       |   |
       |   |   [Embryo Sac]        |   |
       |   |                       |   | …

The ovule is the structure that, after fertilisation, develops into the seed. In angiosperms, it is found enclosed within the ovary of the flower. Think of the ovary as a chamber, and each ovule as a potential seed waiting to be fertilised. The ovule is not just a simple sac; it has several distinct parts, each with a specific role in protecting and nourishing the female gametophyte.

Let us look at a typical, well-developed ovule. It is attached to the inner wall of the ovary by a small stalk called the funicle. The point where the funicle meets the body of the ovule is known as the hilum — it is the scar that remains on the seed after it detaches. The main body of the ovule is composed of a mass of cells called the nucellus. This is the most important part because it contains the embryo sac, which is the female gametophyte. The nucellus provides nutrition to the developing embryo sac.

Surrounding the nucellus are one or two protective layers called integuments. In most angiosperms, there are two integuments — an outer and an inner one. These integuments cover the entire nucellus except at one end, where they leave a small opening. This opening is the micropyle. The micropyle is crucial: it is the passage through which the pollen tube enters the ovule to deliver the male gametes for fertilisation.

The part of the ovule opposite the micropyle is called the chalaza. This is the basal region where the integuments and the nucellus merge. The chalaza is also the point where the vascular supply from the funicle enters the ovule.

Now, here is a neat, labelled diagram to help you visualise these parts:

                    _________________________
                   /                         \
                  |       INTEGUMENTS         |
                  |   (Outer and Inner)       |
                  |                           |
                  |    +-----------------+    |
                  |    |                 |    |
                  |    |    NUCELUS      |    |
                  |    |                 |    |
                  |    |  (Embryo Sac)   |    |
                  |    |                 |    |
                  |    +-----------------+    |
                  |          |                | …