The Fundamental Unit of Life — Question 1
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How do substances like CO2 and water move in and out of the cell? Discuss.
The cell membrane, is selectively permeable i.e., it allows some substance to pass through it while prevents other substances from crossing.
Movement of CO2 — CO2 moves in and out of the cell by diffusion. It accumulates in high concentrations inside the cell. In the cell's external environment, the concentration of CO2 is low as compared to that inside the cell. Therefore, CO2 moves out of the cell, from a region of high concentration, to a region of low concentration by the process of diffusion.
Movement of Water — Water also moves in and out of the cell according to the concentration gradient by the process of osmosis. The movement of water across the plasma membrane is also affected by the amount of substance dissolved in water. Thus, osmosis is the net diffusion of water across a selectively permeable membrane toward a higher solute concentration.
Chapter 5: The Fundamental Unit of Life — Quick Reference
Quick Revision Points
- Cell theory: all organisms made of cells; cell = basic unit; cells from pre-existing cells
- Prokaryotic (no nuclear membrane, bacteria) vs Eukaryotic (true nucleus, plants/animals)
- Plasma membrane: selectively permeable, lipid bilayer
- Osmosis: water from dilute → concentrated through semipermeable membrane
- Organelles: Nucleus (control), Mitochondria (powerhouse), ER (transport), Golgi (packaging), Lysosomes (suicide bags), Plastids (photosynthesis), Vacuoles (storage)
- Plant cell: cell wall, large vacuole, plastids present. Animal cell: no cell wall, centrioles present
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