MediumBiologyHigh School (11–12)Diversity of Living Organisms › Bryophytes and PteridophytesConceptual
On a trek, Ira finds many ferns in a cool, shady ravine with a stream, but almost none on the dry…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On a trek, Ira finds many ferns in a cool, shady ravine with a stream, but almost none on the dry, sunny slope above it. Both places get the same rain. Using what you know about the fern's gametophyte and its fertilisation, explain the difference.
Need a reminder? The key ideaShow
Pteridophytes are the first land plants with xylem and phloem. The main plant body is the diploid sporophyte, with true roots, stems and leaves. Sporangia on sporophylls make spores by meiosis (in many ferns, 16 spore mother cells give 64 spores in a sporangium); some form strobili. A spore grows into a free-living prothallus with antheridia and archegonia, and fertilisation needs water. Classes: Psilopsida, Lycopsida, Sphenopsida, Pteropsida.
The worked solution
Have you tried it?
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. The prothallus. A fern spore grows into a small, thin prothallus with no vascular tissue. It dries out easily, so it grows only in cool, damp, shady places.
Step 2. Fertilisation. The antherozoids must swim through water to the archegonium. The damp ravine gives the film of water that they need.
Step 3. The slope. On the dry, sunny slope, prothalli dry out and fertilisation fails, so few new fern plants start there.
Answer: the prothallus needs cool, damp shade, and fertilisation needs water, so new ferns start in the ravine but rarely on the dry slope.
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