Lessons 6 · 1 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
6
The ground-air environment, soil and living organisms as habitats
Textbook: pp. 30–38
GoalExplain the properties of the ground-air, soil and living-organism habitats and the adaptations to them (wind, humus, edaphobionts, parasitism).
In the ground-air environment air density is low, so organisms develop supporting tissues and skeletons (external in arthropods, internal in chordates) and body size is limited; light is abundant, while temperature and moisture change sharply. Air is now about 78 % nitrogen, 21 % oxygen, 0.9 % argon and 0.04 % carbon dioxide (over 400 ppm) – the textbook’s 0.03 % is outdated. Wind acts indirectly: it increases evaporation and takes part in pollination (anemophily) and seed dispersal (anemochory). Soil is the fertile surface layer of the crust; it has no light, stable temperature, little oxygen and much carbon dioxide; edaphobionts (earthworm, mole, mole cricket) are compact, with poorly developed eyes and digging limbs. Organic remains are turned into humus by microorganisms and fungi; the more humus, the more fertile the soil, and mycorrhiza widens the absorbing surface of roots. The body of an organism is a habitat for parasites and symbionts: ectoparasites (louse, tick) live outside, endoparasites (Ascaris, the malaria plasmodium) in internal organs; they have simplified digestive and sense organs, a strong reproductive system and often change hosts.
Worked examples
Farmers replace cotton with alfalfa on a field every few years. Bacteria living in nodules on alfalfa roots turn atmospheric nitrogen into compounds plants can use, and after the alfalfa is ploughed in, the field is richer in nitrogen. For the bacteria, the alfalfa root is a living-organism habitat, and their relationship is symbiosis.
Ascaris lives in the intestine, has no eyes or locomotor organs and lays thousands of eggs daily – an endoparasite. Its eggs spread through dirty hands and unwashed vegetables, so washing hands, fruit and vegetables is necessary.
Class activity
In pairs, make an «advantage – difficulty» table for three habitats (ground-air, soil, living organism). Do not collect soil samples or animals without your teacher’s permission; wash hands after working with soil.
Practice
1
Why are land animals’ body masses smaller than those of water animals?
Air does not buoy as water does; the skeleton and legs must carry the weight, which limits body size.
2
What is humus and how does it affect soil fertility?
The end product of organic decomposition; it improves soil structure and stores nutrients – raising fertility.
3
Why can parasites have simplified digestive organs?
They absorb ready, already digested food from the host, so a complex digestive system is not needed.
4
Classify as ectoparasite or endoparasite: tick, pinworm, flea, malaria plasmodium.