Lessons 2–3 · 2 lessons · O‘. Pratov, A. To‘xtayev, F. Azimova, Z. Tillayeva. Biology, Grade 5. Revised and expanded 5th edition. “O‘zbekiston” publishing house, Tashkent, 2020
3
Characteristics of living organisms
Textbook: pp. 9–12
GoalList the eight main characteristics of living organisms and explain each with an example.
New words
metabolism, the exchange of substances · metabolizmautotroph, makes its own food · avtotrofheterotroph, feeds on ready-made food · geterotrofirritability, response to a stimulus · ta’sirlanish
Explanation
Living organisms differ from non-living nature in eight ways. First is metabolism, the exchange of substances: it is the sum of assimilation (building new substances, which uses energy) and dissimilation (breaking substances down, which releases energy). Second is nutrition: autotrophs (green plants, some bacteria) make their own food, while heterotrophs (animals, fungi, most bacteria) feed on ready-made food. Third is respiration: most organisms take in oxygen and give out carbon dioxide. Fourth is excretion: harmful products are removed. Fifth is irritability: responding to an outside influence (the leaves of the sensitive mimosa fold when touched). Sixth is movement: animals move actively, plants slowly (a sunflower head turns toward the sun). Seventh is reproduction, and eighth is growth and development: growth is an increase in quantity, development is a change in quality.
Worked examples
A seedling grown from a seed gets taller and bigger – that is growth. Then its stem thickens, its leaves unfold and it flowers – that is development.
When touched, a hedgehog rolls into a ball. This is irritability: the organism responds to an outside influence.
Class activity
Make an “Alive or not?” table in class: stone, snow, autumn leaf, cat, seed, fire, bacterium. For each, tick which of the eight characteristics it shows, and write a conclusion. Safety: fire is discussed only from pictures or the teacher’s description.
Practice
1
Which two processes together make up metabolism?
Assimilation and dissimilation.
2
Which organisms are autotrophs and which are heterotrophs? Give two examples of each.
Autotrophs: green plants (for example apple, wheat). Heterotrophs: animals and fungi (for example sheep, mushroom).
3
What is excretion and why is it needed?
Removing products harmful to the organism (carbon dioxide, excess salts and others); if they built up, the organism would be harmed.
4
Why are growth and development not the same thing?
Growth is an increase in quantity (getting bigger); development is a change in quality (new organs and forms appear).