Lessons 1–2 · 2 lessons · A. Zikiryayev, A. To‘xtayev, I. Azimov, N. Sonin. Biology. Basics of Cytology and Genetics, Grade 9, revised and expanded 5th edition. “Yangiyul Poligraph Service”, Tashkent, 2019
1
Characteristic properties of living organisms
Textbook: pp. 5–7
GoalName the general properties of living organisms and tell them apart from non-living bodies.
All living organisms are built of cells, and the cell is the smallest unit that contains all the properties of life. An organism constantly exchanges matter and energy with its surroundings: in assimilation, simple substances are built up into the organism’s own complex substances; in dissimilation, substances are broken down and energy is released. Nutrition, respiration and excretion go with this, and the organism grows and develops. A living being responds to the environment (irritability) and keeps its internal conditions within a normal range, which is called homeostasis. Reproduction, heredity and variation keep life going and create the diversity of species. Non-living bodies (such as a stone or a fire) may seem to share a few of these features, but they do not have all of them together.
Worked examples
An avalanche moves and grows, but it has no cells, no metabolism and no heredity, so it is not alive.
A cactus stores water in its tissues in a desert and uses it in a drought: an example of reserves and homeostasis.
Class activity
“Alive or non-living?” Students sort 10 pictures or words (e.g. mushroom, fire, seed, cloud, microbe, machine) into two groups and justify each choice with at least two properties.
Practice
1
List at least five basic properties of life.
For example: cellular structure, metabolism, nutrition, respiration, excretion, growth and development, irritability, reproduction, heredity and variation.
2
State the difference between assimilation and dissimilation.
In assimilation substances are synthesised and energy is used; in dissimilation substances are broken down and energy is released.
3
Which property of living organisms is shown by leaf fall in autumn and by an animal hibernating in winter?
Responding to environmental change (irritability) and adaptation; it also helps the organism keep its internal conditions.
4
If dissimilation stopped in a cell and only assimilation tried to continue, what would happen? Explain your answer.
Assimilation would stop: the energy for synthesis comes from dissimilation, and the simple substances from breakdown are raw material for synthesis. So the two processes depend on each other.