In a papaya orchard, the leaves of many trees curl up, turn yellow with a patchy pattern, and the…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a papaya orchard, the leaves of many trees curl up, turn yellow with a patchy pattern, and the trees stay short. A virus is the cause. Name four signs of a virus disease in plants, and three diseases that viruses cause in humans.
Need a reminder? The key ideaShow
Viruses, viroids and prions are not in the five kingdoms. A virus is an obligate parasite: DNA or RNA, never both, inside a protein capsid. Ivanowsky (1892) found that the cause of tobacco mosaic passed through a bacterial filter; Beijerinck (1898) called it Contagium vivum fluidum; Stanley (1935) crystallised the virus. Diener (1971) found the viroid, free RNA with no coat. A prion is an abnormally folded protein (BSE, CJD).
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. Signs in plants. Mosaic patterns, rolling and curling of the leaves, yellowing and clearing of the veins, and dwarfing or stunted growth.
Step 2. Diseases in humans. Mumps, smallpox, herpes, influenza and AIDS (any three).
Answer: mosaic, leaf curling, yellowing and vein clearing, dwarfing; for example mumps, influenza and AIDS.
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