Ch 8 introduces the cell as the fundamental unit of life. Students learn about cell structure, differences between plant and animal cells, prokaryotic vs eukaryotic cells, and key organelles.
All living things are made of cells (cell theory). Cells are the basic structural and functional units of life. Unicellular organisms: one cell does everything (Amoeba, bacteria). Multicellular: many specialised cells (humans, plants). Robert Hooke discovered cells in 1665.
Cell membrane: thin, flexible boundary controlling what enters/leaves. Cell wall: rigid outer layer in plants (made of cellulose). Nucleus: contains chromosomes (DNA), directs cell activities. Cytoplasm: jelly-like substance where organelles float. Prokaryotic cells lack a well-defined nucleus (bacteria); eukaryotic cells have one.
Plant cells have: cell wall, chloroplasts, large central vacuole. Animal cells lack these. Both have: cell membrane, nucleus, cytoplasm, mitochondria, ribosomes. Mitochondria produce energy; chloroplasts carry out photosynthesis.
Download: https://ncert.nic.in/textbook/pdf/hesc108.pdf | Complete book: https://ncert.nic.in/textbook/pdf/hesc1ps.zip
Plant cells need a rigid cell wall (made of cellulose) for structural support since plants cannot move. It helps maintain the shape of the plant. Animal cells have only a flexible membrane because animals have an internal skeleton for support and need flexibility for movement.
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