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Who Gains, Who Loses?
No living thing lives alone. Every plant and animal interacts with its neighbours, and biology has a simple code for these interactions: a plus for a gain, a minus for a loss and a zero for no effect on that partner. A mutualism is plus-plus, a commensalism is plus-zero, a parasitism is plus-minus, and a competition is minus-minus. Exam questions give you a pair, such as an orchid on a mango tree or a lichen on a rock, and ask you to name the relationship. The same few examples appear year after year, which makes this one of the easiest biology topics to master if you hold the sign code and the standard example for each box. This short also covers insectivorous plants, which are partial feeders, not parasites.
1. A lichen, formed by an alga living with a fungus, is an example of:
2. An orchid growing on the branch of a mango tree without harming it is an example of:
3. Cuscuta (amarbel), which has no chlorophyll and no roots, is a:
4. Which of the following is a partial stem parasite with green leaves?
5. The pitcher plant traps insects mainly to obtain which nutrient?
6. What does a legume plant receive from Rhizobium bacteria living in its root nodules?
7. Which interaction harms both the species involved, as they compete for the same food or space?
8. In a cactus, which part mainly carries out photosynthesis?