Question

In Cycas, the ovules are attached to megasporophyll
A. Laterally
B. Dorsally
C. Ventrally
D. Apically

Answer 1

Hint: In all cycads apart from the genus Cycas, ovules are abided on megasporophylls in the megastrobili. In Cycas, the ovules grow on individual megasporophylls which look like a leaf that is considered as a primitive arrangement. The microspores of all the cycads grow into microstrobili.

Complete Answer:
- The cycads grow slowly, and are dioecious (that means that cycads are either male or female) gymnosperms, the microsporangia (prospective pollen) and megasporangia (prospective ovules) happening on different individual sporophytes.
- The microspores reach the 3-celled stage of development of the male gametophyte after they are shed in the form of pollen grains from the microsporangia.
- During this, the elongation of the megastrobilus splits the megasporophylls, and the pollen grains in wind have access to the micropyles of ovules.
- During the process of pollination, each ovule gives out a mucilaginous droplet, also known as the pollination droplet, via the micropyle. Few of the pollen grains become immersed in this droplet and are taken-up in the ovule.
- Female cones containing the loosely arranged sporophylls and missing a central axis, describe the cycadaceae. They endure their ovules on the borders of a basal, stalk-like structure.

Hence the correct answer is A.

Additional information: The time gap between pollination and fertilization is more than a few months in cycads. The sperm cells are multi-flagellate and are one of the largest in the plant kingdom.
- Each pollen tube might contain 2 to 22 sperm cells, depending on the genus. The pollen tubes that develop from the pollen grains go through the megasporangium of the ovule to the archegonia of the female gametophyte.
- Fertilization of the eggs of more than a few archegonia occurs before the early growth of many embryos (polyembryony), only one out of which lives in the mature seeds. Cycad embryos form two seed leaves also known as the cotyledons.
- The seeds are coloured brightly and covered by an outer flesh-like layer and a stone-like layer of the integument. The seeds of some cycads can germinate in the megastrobilus without a period of dormancy.

Note: When megasporophyll is young, in the middle part of it, 4 to 6 ovules rise in the form of a hypodermal mass of meristematic cells on the side. These meristematic cells divide twice to make a mass of parenchymatous cells, which is known as nucellus.