Cell Structure
Lipi Shorts
Karnataka · KSEEB · Class 9 · Science
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Cell Structure
Central idea
A cell is a tiny factory: the nucleus is the manager with the rule book, mitochondria are the power generators, the membrane is the security gate, and in plants the cell wall is the strong outer fence.
Central idea
Robert Hooke first saw cells in cork in 1665. The cell theory says all organisms are made of cells and every cell comes from an existing cell.
Every living thing is built from one or more cells.
The cell is the unit of life
Bacteria are prokaryotic: their DNA floats free, with no membrane-bound organelles. Plant, animal and fungal cells are eukaryotic and far more organised.
Prokaryotic cells have no true nucleus; eukaryotic cells do.
Prokaryotic vs eukaryotic
Both share a nucleus, cytoplasm, membrane, mitochondria and ribosomes. Plants add a cellulose cell wall, chloroplasts for photosynthesis and a large central vacuole.
Plant cells have everything animal cells have, plus three extras.
Animal vs plant cell
Small molecules like oxygen cross by diffusion and water by osmosis. The cell wall, by contrast, is fully permeable and only gives support.
The membrane is selectively permeable: it chooses what passes.
The membrane controls traffic
See it in a diagram
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Myth vs truth
✕ Myth
The cell wall and the cell membrane are the same thing.
✓ Truth
The membrane is selectively permeable and is in every cell; the cell wall is a rigid cellulose layer outside the membrane, found only in plant (and fungal/bacterial) cells.
Myths vs truth
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Word meanings
organelle
a specialised structure inside a cell that carries out a particular function
nucleus
the organelle that holds the DNA and controls the cell's activities
mitochondrion
the organelle where aerobic respiration releases energy from glucose
ribosome
a tiny structure that builds proteins from amino acids
Word meanings
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Themes & message
•
The cell is the basic unit of structure and function in all living things.
•
Each organelle has a specific job, and the parts work together.
•
Plant and animal cells share a common plan but differ in key features.
Themes & message
Key facts at a glance
Cell theory
All living things are made of cells; the cell is the unit of life; cells come from cells
Two cell types
Prokaryotic (no true nucleus) and eukaryotic (true nucleus)
Control centre
Nucleus: holds DNA, directs the cell
Key facts at a glance
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