Question

Haplo-diplontic life cycle is observed in how many of the following plants.
Pinus, Sphagnum, Polytrichum, Polysiphonia, Dryopteris, Riccia, Marchantia, Pteris, Selaginella, Ectocarpus, Volvox.
A. 6
B. 7
C. 8
D. 9

Answer 1

A haplo-diplontic life cycle involves the alternation between haploid and diploid generations in an organism. In plants, the diploid sporophyte gives rise to the haploid spores through meiosis.

Complete answer:
- The haplo-diplontic life cycle is observed in bryophytes and pteridophytes.
- Bryophytes are nonvascular plants and are divided into three broad subgroups, hornworts, mosses, and liverworts. They reproduce via spores due to the lack of production of fruits or seeds.
- Pteridophytes are vascular plants that do not produce fruits and seeds and reproduce by dispersing spores. Ferns, horsetails and lycophytes fall under the category of pteridophytes.

Now, let us look at each plant individually
- Pinus is a gymnosperm with a well-developed vasculature but it reproduces via spores.
- Sphagnum is a moss also referred to as the peat moss and falls under the category of bryophytes.
- Polytrichum, also known as haircap moss or hair moss is a genus of mosses categorized under bryophytes.
- Polysiphonia is a filamentous red algae which falls under the category of thallophytes.
- Dryopteris, also known as wood fern falls under the category of pteridophytes.
- Riccia is a genus of liverworts and is categorized as a bryophyte.
- Marchantia is a plant of a group of liverworts of the order Marchantiales and is categorized as a bryophyte.
- Pterus, a fern, is a homosporous pteridophyte.
- Selaginella, commonly called the spike moss is categorized as a bryophyte.
- Ectocarpus is a filamentous brown alga categorized as a thallophyte.
- Volvox is a green alga which can be classified under thallophyta.
From the description above, we see that seven plants mentioned in the question fall under the category of bryophytes or pteridophytes and exhibit a haplo-diplontic life cycle while the other 4 belong to either gymnosperms or thallophytes.

Therefore the correct answer is (B) 7.

Note: Gymnosperms have a diplohaplontic life cycle, i.e. there are two phases - first is the dominant and sporophyte phase and the second is the brief gametophyte phase, whereas algae have a haplontic life cycle i.e. they have only meiosis.