Draw a neat diagram of megasporangium of an angiosperm and label any six parts. [ $\frac{1}{2} \times 6 = 3$ ]

Q: Draw a neat diagram of megasporangium of an angiosperm and label any six parts. [$\frac{1}{2} \times 6 = 3$]

The **megasporangium of an angiosperm is the ovule** — draw its longitudinal section as a rounded body attached to the placenta by a stalk, enclosing the embryo sac. **Diagram description (L.S. of ovule):** - Draw an oval/kidney-shaped body attached by a slender stalk to the placenta. - Show two integuments enclosing the nucellus, leaving a small pore (micropyle) at one end. - Inside the nucellus, show the oval embryo sac with the egg apparatus at the micropylar end and antipodals at the chalazal end. **Any six parts to label:** 1. **Funicle** — stalk that attaches the ovule to the placenta. 2. **Hilum** — region where the funicle joins the body of the ovule. 3. **Integuments** — one or two protective envelopes around the nucellus. 4. **Micropyle** — narrow pore at the tip through which the pollen tube enters. 5. **Nucellus** — nutritive parenchymatous tissue. 6. **Embryo sac / female gametophyte** — 7-celled, 8-nucleate structure (egg apparatus, central cell, antipodals). (**Chalaza**, the basal region, may be labelled as an alternative.)

Sexual Reproduction in Flowering Plants

Megasporangium (Ovule) Structure

Official Answer

The megasporangium of an angiosperm is the ovule — draw its longitudinal section as a rounded body attached to the placenta by a stalk, enclosing the embryo sac.

Diagram description (L.S. of ovule):

Draw an oval/kidney-shaped body attached by a slender stalk to the placenta.
Show two integuments enclosing the nucellus, leaving a small pore (micropyle) at one end.
Inside the nucellus, show the oval embryo sac with the egg apparatus at the micropylar end and antipodals at the chalazal end.

Any six parts to label:

Funicle — stalk that attaches the ovule to the placenta.
Hilum — region where the funicle joins the body of the ovule.
Integuments — one or two protective envelopes around the nucellus.
Micropyle — narrow pore at the tip through which the pollen tube enters.
Nucellus — nutritive parenchymatous tissue.
Embryo sac / female gametophyte — 7-celled, 8-nucleate structure (egg apparatus, central cell, antipodals).

(Chalaza, the basal region, may be labelled as an alternative.)

ovulemegasporangiumfunicleintegumentsmicropylenucellusembryo sacchalaza

Marking Scheme

13 marks total = ½ mark for each correctly labelled part ( $\frac{1}{2} \times 6$ ).
2A neat, correctly oriented longitudinal section of the ovule is expected before labels are credited.
3Acceptable labels (any six): funicle, hilum, integuments, micropyle, nucellus, embryo sac, chalaza, egg apparatus/egg cell, synergids, central cell/polar nuclei, antipodal cells.

Hint

Ovule = megasporangium. Label from outside in: funicle, hilum, integuments, micropyle, nucellus, embryo sac (add chalaza/antipodals if needed).

Quick Oral Answer

The megasporangium of an angiosperm is the ovule; its key labelled parts are the funicle, hilum, integuments, micropyle, nucellus and the 7-celled 8-nucleate embryo sac, with the chalaza at the base.

Analysis & Explanation

Concept:

The ovule is technically the megasporangium because it houses the megaspore mother cell, whose meiosis produces the megaspore that forms the embryo sac.

Key structure:

The ovule develops from the placenta of the ovary.
The nucellus is protected by integuments, which remain open at the micropyle.
The functional megaspore enlarges into the embryo sac, typically 7-celled and 8-nucleate (Polygonum type): one egg + two synergids (egg apparatus), one central cell with two polar nuclei, and three antipodal cells.

Exam trap:

Marks are awarded ½ each per correct label on a neat, proportionate diagram — a messy sketch or unlabelled parts lose marks.
Do not confuse the ovule (megasporangium) with the anther/microsporangium.

Real-world:

After double fertilization, this very megasporangium matures into the seed — the integuments become the seed coat and the embryo sac gives the embryo and endosperm.

Common Mistakes

1Drawing the anther/microsporangium instead of the ovule — the megasporangium of an angiosperm IS the ovule.
2Labelling fewer than six parts or placing the micropyle and chalaza at the wrong ends (micropyle is near the egg apparatus, chalaza is basal).
3Forgetting that the embryo sac is 7-celled and 8-nucleate and mislabelling the egg apparatus and antipodal cells.

Interesting Facts

In most angiosperms (about 80% of species) the ovule is anatropous, i.e. inverted so that the micropyle lies close to the funicle.

The mature embryo sac usually has 8 nuclei but only 7 cells, because the large central cell contains two polar nuclei that later fuse to form the triploid primary endosperm nucleus.

Double fertilization — a feature unique to angiosperms — takes place entirely inside this megasporangium.

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Frequently Asked Questions

Why is the ovule called the megasporangium?

The ovule contains the megaspore mother cell (megasporocyte) in its nucellus. This cell undergoes meiosis to produce megaspores, one of which forms the female gametophyte. Since it is the site that produces and bears the megaspores, the ovule is functionally the megasporangium of the angiosperm.

How many cells and nuclei are there in a typical angiosperm embryo sac?

A typical mature embryo sac is 7-celled and 8-nucleate (Polygonum type). It has an egg apparatus of three cells (one egg + two synergids) at the micropylar end, three antipodal cells at the chalazal end, and one large central cell containing two polar nuclei.