The Fundamental Unit of Life 9 Science — Revision Notes
The cell is the smallest unit of life capable of independent existence and reproduction. All organisms are composed of one or more cells, and understanding
TL;DR: The cell is the smallest unit of life capable of independent existence and reproduction. All organisms are composed of one or more cells, and understa…
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The cell is the smallest unit of life capable of independent existence and reproduction. All organisms are composed of one or more cells, and understanding
Cell Theory
- All living organisms are composed of cells
- Cell is the basic unit of life
- All cells arise from pre-existing cells through division
Prokaryotic vs Eukaryotic Cells
- Prokaryotic: no true nucleus, DNA in nucleoid region, found in bacteria and archaea
- Eukaryotic: true nucleus containing DNA, membrane-bound organelles, found in animals and plants
Cell Membrane and Nucleus
- Cell membrane: semi-permeable, controls entry and exit of substances, selective permeability
- Nucleus: contains DNA, controls cell activities, surrounded by nuclear envelope with pores
- Nucleolus: produces ribosomes within nucleus
Cytoplasm and Organelles
- Cytoplasm: gel-like substance containing organelles, site of metabolic reactions
- Mitochondria: powerhouse of cell, produces ATP through aerobic respiration
- Endoplasmic reticulum: rough (with ribosomes) for protein synthesis, smooth for lipid synthesis
- Golgi apparatus: modifies and packages proteins
- Lysosomes: contain digestive enzymes, break down waste materials
Plant Cell-Specific Organelles
- Chloroplast: site of photosynthesis, contains chlorophyll
- Cell wall: rigid, outside cell membrane, provides structure and support
- Vacuole: large central vacuole stores water and maintains turgor pressure
Key Terms
- Cell: Smallest unit of life, basic structural and functional unit of all organisms
- Organelle: Membrane-bound structure within cell performing specific functions
- Mitochondria: Organelle producing energy in form of ATP
- Chloroplast: Organelle in plant cells containing chlorophyll for photosynthesis
- Ribosome: Site of protein synthesis in cytoplasm
Frequently Asked Questions
Why is the cell membrane called semi-permeable?
The cell membrane selectively allows some substances to pass while blocking others, maintaining cell composition.
What is the main function of mitochondria?
Mitochondria produce ATP through aerobic respiration, providing energy for cellular activities.
Why do plant cells have chloroplasts but animal cells do not?
Plant cells are autotrophic and need chloroplasts for photosynthesis, while animal cells are heterotrophic.
More 9 Science Revision Notes
- Matter in Our Surroundings
- Is Matter Around Us Pure
- Atoms and Molecules
- Structure of the Atom
- Force and Laws of Motion
- Work and Energy
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