HardBiologyHigh School (11–12)Diversity of Living Organisms › Bryophytes and PteridophytesConceptualBoard Exam
Kabir says: " Selaginella is halfway to being a seed plant." Explain what he means…
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Kabir says: "Selaginella is halfway to being a seed plant." Explain what he means. Give two features of heterosporous pteridophytes that seed plants also have, and one feature that Selaginella still lacks.
Need a reminder? The key ideaShow
Most pteridophytes are homosporous. Selaginella and Salvinia are heterosporous: microspores grow into male gametophytes, megaspores into female gametophytes. A megasporangium has one megaspore mother cell and makes 4 megaspores. The female gametophyte stays on the parent, and the embryo starts to grow inside it: a forerunner of the seed habit. Gametophytes are haploid, sporophytes diploid.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Two kinds of spores. Selaginella makes microspores and megaspores, which grow into male and female gametophytes. Seed plants also make two kinds of spores.
Step 2. The female gametophyte stays. The female gametophyte is kept on the parent sporophyte, and the zygote starts to grow into an embryo inside it. In a seed plant, the female gametophyte never leaves the parent, and the embryo grows inside it.
Step 3. What is missing. Selaginella does not form a seed: there is no protective seed coat and no ovule that ripens and is scattered with a dormant embryo.
Answer: heterospory and an embryo growing inside a retained female gametophyte are the first steps of the seed habit; a true seed with its coat is still missing.
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