MediumBiologyHigh School (11–12)Diversity of Living Organisms › Gymnosperms and AngiospermsConceptualBoard Exam
In one park, Nisha finds pines with both small, soft cones and large, woody cones on the same tree…
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In one park, Nisha finds pines with both small, soft cones and large, woody cones on the same tree. Nearby, some cycads carry only cones full of pollen, while others carry only leaf-like structures with ovules. Explain what she sees, and which trees can set seed on their own.
Need a reminder? The key ideaShow
Gymnosperms have naked ovules on megasporophylls, so their seeds have no fruit. They are heterosporous: male cones make pollen grains (male gametophytes), and each ovule holds a many-celled haploid female gametophyte with archegonia. The wind carries pollen; a pollen tube brings the male gametes. The food store of the seed is the haploid female gametophyte.
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. The pines. The small soft cones are male cones, with microsporophylls that make pollen. The woody cones are female cones, with megasporophylls that carry the ovules. Pinus bears both on the same tree.
Step 2. The cycads. Cycas bears its male cones and its megasporophylls on different trees. The pollen trees are male, and the trees with ovules are female.
Step 3. Setting seed. A pine can be pollinated by its own pollen, carried by the wind. A female cycad needs pollen from a male tree nearby.
Answer: pines carry both kinds of cone on one tree; cycads are separately male and female. Each pine can set seed alone, but a female cycad needs a male tree nearby.
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