Question

The male cone of Pinus is composed of microsporophylls. Each microsporophyll has
A. One microsporangium on the abaxial side
B. Two microsporangia on the adaxial side
C. Two microsporangia on the abaxial side
D. One microsporangium on the adaxial side

Answer 1

Hint: The gymnosperms produce haploid microspores and megaspores, hence they are called heterosporous. Pinus is a gymnosperm.

Complete answer: Within sporangia two kinds of spores are produced- one is arranged spirally along an axis to form lax or compact strobili or cones.
1. Microsporangiate or male strobili are the strobili bearing microsporophylls and microsporangia.
These microsporophylls are arranged spirally and each of them has two microsporangia.
These are developed away from the stems or leaves (abaxially).
The microspores develop into a male gametophyte. It is confined to a limited number of cells called a pollen grain. Within the microsporangia the development of pollen grains takes place.
2. Macrosporangiate or female strobili are the cones bearing megasporophylls with ovules or megasporangia. In pinus, the male or female cones or strobili are borne on the same tree.
From one of the cells of the nucleus, the megaspore mother cell is differentiated and the nucellus is protected by envelopes. This composite structure of nucellus is called an ovule.
The ovules are clustered to form the female cones.

3. Now, the megaspore mother cells divide to form four megaspores (meiotically).
One of the ovules enclosed in the megasporangium develops into a multicellular female gametophyte. The female gametophyte has two or more archegonia or female sex organs.
4. The pollen grain is released from the microsporangium and is carried in air currents and comes in contact with the opening of the ovules present on the megasporophylls.
Then the pollen tube carrying the male gametes grows inside the archegonia in the ovules and their contents are discharged near the mouth of the archegonia, this is the process of fertilization.
After fertilization, the zygote develops into an embryo and the ovules develop into seeds.

So, the correct answer is “Option C. Two microsporangia on the abaxial side”.

Note: The male and the female gametophytes do not have an independent free-living existence. The seeds that are developed are not covered.