Question

Draw a labelled diagram of an ovule including embryo-sac in a flowering plant.

Hint:

Ovule + embryo sac = female gametophyte of flowering plants. It ensures double fertilization, a unique feature of angiosperms.

Answer 1

The ovule is the female reproductive structure in flowering plants. It develops into the seed after fertilization. Inside the ovule lies the embryo sac (female gametophyte), which plays a key role in double fertilization.

Step 1: Main parts of the ovule. \[\begin{array}{rl} 1. & \text{Funicle: Stalk that attaches ovule to placenta.} \\ 2. & \text{Hilum: Junction between ovule and funicle.} \\ 3. & \text{Integuments: Protective layers covering the nucellus.} \\ 4. & \text{Micropyle: Small opening through which pollen tube enters.} \\ 5. & \text{Nucellus: Nutrition tissue for the embryo sac.} \\ 6. & \text{Embryo sac: Female gametophyte with 7 cells (1 egg cell, 2 synergids, 3 antipodals, and 1 central cell with 2 polar nuclei).} \\ \end{array}\]

Step 3: Significance.
The embryo sac is the site of double fertilization: \[\begin{array}{rl} \bullet & \text{One male gamete fertilizes the egg $\rightarrow$ zygote.} \\ \bullet & \text{Other male gamete fuses with two polar nuclei $\rightarrow$ triploid endosperm.} \\ \end{array}\]