Lessons 25–26 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology Grade 11, 1st edition. Sharq Publishing and Printing Joint-Stock Company, Tashkent, 2018
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Laboratory work 3
Textbook: pp. 131–132
GoalCompare a natural (desert) and an artificial (cotton field) ecosystem by food chains and traits; work with tables.
The third lab compares a natural and an artificial ecosystem. First, lists of species found in both are made and each is sorted as producer, consumer or decomposer. Then a table is filled in: in the natural ecosystem selection is natural, impact is small, species diversity is high and there is self-regulation; in a cotton field humans aim for maximum yield, selection is artificial, extra energy and fertiliser are added, and minerals leave with the harvest. Both ecosystems have producers, consumers and decomposers, the main energy source is the sun, and the ecological pyramid rule applies. Conclusion: they are similar in structure but differ in stability and in how they are managed.
Worked examples
In a desert: saxaul (producer) → gerbil (consumer) → snake (consumer) → bird of prey; bacteria and fungi (decomposers) break down remains. In a cotton field: cotton → sap-sucking aphid → ladybird → sparrow; the number of species is much smaller.
Counting: if 24 species were found in the desert and 6 in the cotton field, the desert has 24 : 6 = 4 times as many. This shows that diversity is higher in the natural ecosystem.
Class activity
Choose two 5 × 5 step plots in the school yard or a nearby garden (one of natural grass, one of planted flowers or crops). Count the species found in 10 minutes and record them in a table. Do not catch or touch insects; keep away from bees and snakes.
Practice
1
Write three traits shared by both ecosystems.
Producers, consumers and decomposers are present; the main energy source is the sun; the ecological pyramid rule applies.
2
A natural ecosystem has 30 species, a cotton field 5. How many times more species does the natural ecosystem have?
6
3
Why do minerals decline in a cotton field but not in a desert?
In a field minerals leave with the harvest, while in a desert decomposers return them to the soil.
4
Build a pond food chain from perch, the alga Chlorella, cormorant, daphnia and dragonfly larva.