Lessons 13–14 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology, Grade 10, 1st edition. “Sharq” publishing and printing joint-stock company, Tashkent, 2017
13
The organism level of life and its features
Textbook: pp. 60–62
GoalExplain the features of the organism level of life, the difference between unicellular and multicellular organisms, and how organisms are regulated.
An organism is a whole biological system that can live independently, regulate and renew itself; it is unicellular or multicellular. At this level metabolism and energy exchange, irritability, growth, development, reproduction, adaptation, behaviour and the regulation of vital processes are studied. Each organism is an individual and contributes to evolution by leaving offspring and adapting to a changing environment. In a unicellular organism (amoeba, Euglena, Chlamydomonas, bacteria) one cell performs all vital functions and regulation is mainly humoral-chemical. The body of a multicellular organism consists of specialised cells, tissues, organs and organ systems; its cells are somatic (body) or sex cells. Vital processes depend on the coordinated work of organs. In animals regulation works through the neuro-humoral system: the nervous system acts quickly, hormones more slowly but for longer. In plants growth and development are regulated by phytohormones (auxin, gibberellin, cytokinin). All regulation rests on hereditary information.
Worked examples
Euglena photosynthesises in light and absorbs ready organic matter in the dark: one cell performs many functions on its own.
The heart rate speeds up when we are frightened: the nervous system gives a quick signal and the hormone adrenaline keeps the effect going for a while – an example of neuro-humoral regulation.
Class activity
“Which level?” Students assign 10 events (a damaged cell, leaf fall, a fish swimming against the current ...) to the cell or organism level and justify their choices.
Practice
1
List four processes studied at the organism level.
For example: metabolism, irritability, growth and development, reproduction, adaptation.
2
Compare unicellular and multicellular organisms in three respects.
In a unicellular organism one cell does everything, there are no tissues or organs, and regulation is humoral-chemical; in a multicellular organism cells are specialised, tissues and organs exist, and regulation is neuro-humoral.
3
Give three examples of phytohormones and state their general role.
Auxin, gibberellin, cytokinin; they regulate the growth and development of plants.
4
Why does hormonal regulation complement nervous regulation but not replace it?
A nerve signal arrives instantly at an exact target; hormones spread through the blood and act more slowly but for longer and more widely. Quick reactions need the nervous system, long processes need hormones.