Q.A longitudinal section of a mature, inverted (anatropous) ovule is described, with several leader lines each pointing to a different part that must be named. The ovule hangs from a short stalk that attaches it to the placenta and runs back alongside the ovule's body; the ovule is wrapped in protective covering layer(s) that enclose a central nutritive tissue; embedded within that tissue is a large oval sac holding the egg apparatus and other cells; a narrow pore lies at the tip of the ovule close to where the stalk joins it, and directly opposite this pore, at the base, the covering layer(s) and stalk merge into a common region. Name the part indicated at each position:

Structure of the Ovule

The ovule (megasporangium) is the structure inside the ovary that develops into a seed after fertilisation. Learning to label a longitudinal section of a mature, inverted (anatropous) ovule is a standard part of the chapter on sexual reproduction in flowering plants.

The main parts are:

• Funicle — the stalk by which the ovule is attached to the placenta of the ovary.
• Hilum — the region where the body of the ovule fuses with the funicle.
• Integuments — one or two protective covering layers that enclose the ovule, leaving a small opening at one end.
• Micropyle — the narrow pore at the tip of the ovule, formed by the integuments; it is the point through which the pollen tube usually enters.
• Nucellus — the central mass of nutritive parenchymatous tissue enclosed by the integuments.
• Embryo sac (female gametophyte) — the large oval sac embedded in the nucellus, containing the egg apparatus, central cell and antipodal cells.
• Chalaza — the basal region, lying opposite the micropyle, where the integuments and funicle merge and the nucellus joins the stalk. …