B2 Movement into and out of cells

• Diffusion is the net movement of anything generally from a region of higher concentration to a region of lower concentration.
• osmosis is the movement of water molecules from a solution with a high concentration of water molecules to a solution with a lower concentration of water molecules, through a cell's partially permeable membrane.
• The pressure of the water pushing outwards on the cell wall is called turgor pressure.
• the cell becomes soft and floppy. It is said to be flaccid.
• If the cells in a plant become flaccid, the plant loses its firmness and begins to wilt.
• When the cell membrane tears away from the cell wall, the cell is said to be plasmolysed. Plasmolysis can kill a plant cell because the cell membrane is damaged as it tears away from the cell wall.
• cells need to take in substances which are only present in small quantities around them. If the substance has a lower concentration outside the cell than inside, then we would expect the substance to diffuse out of the cell.
• If the cell needs this substance, then it has to do something to make it go into the cell instead of diffusing out of it. Cells can use energy to make substances move across their membranes, up the concentration gradient. This process is called active transport.

  The energy needed to do this is provided by respiration. Aerobic respiration, in mitochondria in the cell, releases energy for the cell to use. Some of this energy is used for active transport, moving substances against their concentration gradients.
• In plants, for example, root hair cells take in nitrate ions from the soil. The concentration of nitrate ions inside the root hair cell is usually higher than the concentration of nitrate ions in the soil. The diffusion gradient for the nitrate ions is out of the root hair, and into the soil. But the root hair cells are still able to take nitrate ions in, using active transport.
• Water diffuses through partially permeable membranes, including cell membranes, by osmosis.
• Animal cells burst in pure water and shrink when placed in a concentrated solution. Plant cells do not burst in pure water because their cell wall stops this
• Protein carriers in cell membranes change shape to move substances across the cell membrane during active transport.
• independent variable is the factors that change

  dependent variable is the change that happens because of independent variables

  
• tight and firm, full of water. It is said to be turgid.