A teacher cuts one Planaria into five pieces and keeps them in clean pond water…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A teacher cuts one Planaria into five pieces and keeps them in clean pond water. After two weeks, how many worms will there be? Name the process, and say why it is not the usual way most animals reproduce.
Need a reminder? The key ideaShow
In asexual reproduction one parent makes new individuals without gametes: fission (binary in Amoeba and Leishmania, multiple in Plasmodium), fragmentation (Spirogyra), regeneration (Planaria), budding (Hydra), spores (Rhizopus) and vegetative propagation in plants. In binary fission each round doubles the number of cells.
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 pieces. Each of the pieces grows its missing parts, so there are worms.
Step 2. The process. This is regeneration: special cells divide and make the lost parts.
Step 3. Other animals. Most animals do not have such cells, so they cannot make a whole body from a piece.
Answer: worms, by regeneration, which most animals cannot do.
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