Plants, Animals, Viruses and Lichens: Quick Revision

A brief note on Plants, Animals, Viruses and Lichens. Try each question at the end before you open its answer.

Plantae and Animalia

Viruses, viroids and prions

• Not cells, so not in the five kingdoms.
• Ivanowsky (1892): the agent of tobacco mosaic passes a bacterial filter. Beijerinck (1898): Contagium vivum fluidum. Stanley (1935): viruses can be crystallised.
• A virus: DNA or RNA, never both, in a protein capsid; an obligate parasite, inert outside a cell. Plant viruses: mostly single-stranded RNA. Bacteriophages: mostly double-stranded DNA.
• Human viral diseases: mumps, smallpox, herpes, influenza, AIDS.
• A viroid (Diener, 1971): free RNA, no coat; potato spindle tuber disease.
• A prion: a misfolded protein; BSE in cattle, CJD in humans.

Lichens

An alga (phycobiont, makes food) and a fungus (mycobiont, shelter, water and minerals) living as one body. Lichens grow slowly and do not grow in polluted air.

A worked example

A city survey looks at $40$ trees at a busy junction, of which $2$ have lichens, and $40$ trees in a park, of which $26$ have lichens.

1. Junction. $\dfrac{2}{40} \times 100\% = 5\%$ of the trees.
2. Park. $\dfrac{26}{40} \times 100\% = 65\%$ of the trees.
3. Judgement. Lichens are missing where the air is polluted, so the junction air is likely much dirtier.

Practice with new numbers

A program to try

The program works out the worked example.

Mistakes to avoid

• Putting viruses in Monera. They are not cells.
• Giving a virus both DNA and RNA. One or the other.
• Calling a lichen one organism. It is two, from two kingdoms.
• Thinking the sporophyte is haploid. Sporophyte $2n$; gametophyte $n$.

Check yourself

1. Name three diseases of humans caused by viruses.

2. What did Stanley show in 1935?

3. Why can a lichen grow on bare rock, where neither partner could live well alone?

4. How does the life cycle of a plant differ from that of an animal?