Lessons 3–4 · 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
3
Features of the ecosystem level of life. The biogeocenosis as a biological system
Textbook: pp. 14–17
GoalExplain the concepts of biogeocenosis and ecosystem, their similarities and differences, and the size classes of ecosystems.
New words
biogeocenosis · biogeotsenozecosystem · ekotizim (ekosistema)biocenosis (community) · biotsenozbiotope (habitat of a community) · biotop
Explanation
A biogeocenosis is an open, self-regulating system made of a community of living organisms (biocenosis) linked by exchange of matter and its non-living environment (biotope) in a particular area; the doctrine was created by V. N. Sukachev. It has definite boundaries and is usually named after the dominant plant (a juniper or walnut forest). The term «ecosystem» was introduced in 1935 by A. Tansley: a complex of living organisms and their physical environment of any size, linked by exchange of matter and flow of energy. Every biogeocenosis can be called an ecosystem, but not every ecosystem is a biogeocenosis (for example, an aquarium or a drop of water). By size, ecosystems are micro- (a rotting stump, a puddle), meso- (an orchard, a pond, a lake) and macroecosystems (steppe, desert, ocean); the largest is the global ecosystem, the biosphere. The main processes at the biogeocenosis level are synthesis of organic matter, regulation of species numbers and flows of matter and energy.
Worked examples
A patch of sand desert with saxaul and camel-thorn, where lizards, gerbils and snakes live, is a biogeocenosis: it has boundaries, a biocenosis and a biotope. A puddle formed by rain, with algae and ciliates, is a microecosystem but is not usually called a biogeocenosis.
A one-hectare apple orchard in the Zarafshan valley is a mesoecosystem; the whole Kyzylkum desert is a macroecosystem; all living layers of Earth are the global ecosystem. The larger the system, the harder it is to define its boundary.
Class activity
In three groups list five examples each of 1) micro-, 2) meso-, 3) macroecosystems. Justify which of them can be called a biogeocenosis. Do not go to natural water bodies and puddles without your teacher.
Practice
1
Which two parts make up a biogeocenosis?
The biocenosis (living community) and the biotope (its non-living environment).
2
State the main difference between «ecosystem» and «biogeocenosis».
An ecosystem is a system of any size with vague boundaries; a biogeocenosis is a naturally bounded area named after its dominant plant.
3
Sort into micro-, meso- or macroecosystems: a rotting stump, a lake, the taiga, an aquarium.
Stump and aquarium – micro; lake – meso; taiga – macro.
4
Why is a biogeocenosis called an «open» system?
Because it exchanges matter and energy with its surroundings: it takes in solar energy and gives off heat and substances.