Lessons 5–6 · 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
5
Eukaryotes: the diversity of plants
Textbook: pp. 17–18
GoalKnow plant diversity (lower and higher plants) and explain their importance in nature and human life.
New words
lower plants · tuban o‘simliklarhigher plants · yuksak o‘simliklarthallus · tallomvegetative organs · vegetativ organlar
Explanation
Eukaryotic plants are divided into lower and higher plants. Lower plants (algae) live in water or damp places; they may be unicellular, colonial or multicellular, and their body is not divided into tissues and organs, so it is called a thallus. Most higher plants have developed vegetative organs such as root, stem and leaf, and tissues; they are younger in evolutionary terms. In a multicellular plant cells are specialised: some carry out photosynthesis, others transport substances or strengthen the body. Through photosynthesis plants release oxygen, turn solar energy into organic matter, protect soil from erosion, affect climate and water balance, and are a source of food, raw materials and medicines for animals and humans. In Uzbekistan rare species are protected and listed in the Red Book of the Republic of Uzbekistan.
Worked examples
Chlorella is a unicellular lower plant and Spirogyra a filamentous multicellular alga: neither has root, stem or leaf.
Cotton and wheat are higher plants: they have root, stem, leaves and tissues, and the root absorbs water and mineral salts from the soil.
Class activity
“Lower or higher?” Cards carry plant names (Chlamydomonas, moss, fern, poplar, Ulothrix, cotton). A group sorts them into two categories and gives one feature for each.
Practice
1
What is a thallus? In which plants is it found?
A body not divided into root, stem and leaf; in lower plants (algae).
2
State two differences between lower and higher plants.
Lower: thallus, aquatic environment, no tissues. Higher: root, stem, leaf and tissues, evolutionarily younger.
3
Why do mudflows and soil erosion increase when a forest on a mountain slope is cut?
Roots hold the soil and slow rainfall; without plants the soil is easily washed away.
4
Why are cells specialised in a multicellular higher plant?
Life functions are shared among groups of cells, so each process (photosynthesis, transport, support) runs more efficiently.