MediumBiologyHigh School (11–12)Diversity of Living Organisms › Gymnosperms and AngiospermsNumerical
A species of Cycas has 22 chromosomes in each leaf cell.
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A species of Cycas has chromosomes in each leaf cell. How many chromosomes are there in a pollen grain, in a cell of the female gametophyte, and in a cell of the embryo?
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. One set. , so .
Step 2. The haploid parts. The pollen grain and the female gametophyte both grow from spores made by meiosis. Each has chromosomes.
Step 3. The embryo. It grows from the zygote, which forms when a male gamete () fuses with the egg (). It has chromosomes.
Answer: pollen grain , female gametophyte , embryo .
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