HardBiologyHigh School (11–12)Diversity of Living Organisms › The Five KingdomsConceptualBoard ExamA-Level
Baker's yeast ( Saccharomyces ) and Candida, a yeast that can cause thrush, are single cells with a…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Baker's yeast (Saccharomyces) and Candida, a yeast that can cause thrush, are single cells with a nucleus and a wall of chitin. They absorb their food. Where does the simplified key put them? Where does biology put them? What does this show about a key?
Need a reminder? The key ideaShow
The two-kingdom system (Plantae and Animalia) did not separate prokaryotes from eukaryotes, single cells from many-celled bodies, or photosynthetic from non-photosynthetic organisms. R. H. Whittaker (1969) proposed five kingdoms: Monera, Protista, Fungi, Plantae and Animalia. He used the cell structure, the body organisation, the mode of nutrition, the reproduction and the evolutionary relationships. The simplified key sends every single cell with a nucleus to Protista.
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 key. A true nucleus, then one cell: the key stops at Protista.
Step 2. Biology. A wall of chitin and food absorbed from outside are the marks of Fungi. Yeasts are single-celled fungi.
Step 3. The lesson. A simplified key works for most organisms, but it has exceptions. It is a tool, not a law.
Answer: the key says Protista, biology says Fungi; a key has exceptions.
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