Lessons 7–8 · 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
7
The cellular level of life and its features
Textbook: pp. 33–37
GoalExplain the main provisions of cell theory and the similarities and differences of prokaryotic and eukaryotic cells.
The cell is the unit of structure, function and development of life. Cell theory was formulated in 1838–1839 by M. Schleiden and T. Schwann and later extended by R. Virchow (a cell arises only from a cell) and K. von Baer (a multicellular organism develops from a single egg cell). The modern provisions: the cell is the unit of life; a new cell arises by division of an existing cell; the cells of all organisms are similar in structure and chemical composition; in multicellular organisms specialised cells form tissues; hereditary information is stored in the cell and passed on to offspring. A bacterial cell is prokaryotic: it has no nuclear membrane, its DNA lies in the nucleoid (and in circular plasmids), and its wall is made of murein. Fungal, plant and animal cells are eukaryotic: they have a membrane-bound nucleus and organelles. The fungal cell wall is made of chitin and the plant wall of cellulose; plants have plastids and a large central vacuole; animal cells have no cell wall or plastids. The reserve substance is glycogen in fungi and animals and starch in plants.
Worked examples
An amoeba and an egg cell differ sharply, yet both have a membrane, cytoplasm, DNA and ribosomes: this shows unity of structure.
A gut bacterium (E. coli) cell has no nucleus, its DNA lies in the nucleoid in the cytoplasm, and there are no mitochondria; ATP synthesis occurs at the cell membrane.
Class activity
“Three cells”. Teams fill a table with columns for bacterial, plant and animal cells: wall, nucleus, plastids, reserve substance, site of ATP synthesis.
Practice
1
State three main provisions of cell theory.
For example: the cell is the unit of life; a new cell arises from cell division; the cells of all organisms are similar in structure.
2
Compare prokaryotic and eukaryotic cells on three features.
Prokaryotes have no nuclear membrane or membrane-bound organelles, and their DNA is circular (nucleoid); eukaryotes have a membrane-bound nucleus, organelles and linear chromosomes.
3
In which cells does the cell wall consist of chitin and in which of cellulose?
Chitin – in fungi; cellulose – in plants.
4
Why does cell theory confirm the unity of the living world?
All organisms consist of cells, cells share the same chemical composition, membranes, DNA and ribosomes, and arise only by division; this points to common origin.